Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02713606 2010-08-20
System and Method For Calibration Of Phased Array Antenna Having Integral
Calibration Network In Presence Of An Interfering Body
Field Of Invention
The present invention relates to phased array antennas, generally and in
particular, to calibration thereof.
Background Of Invention
The antenna of an active phased array system must be able to steer its beam so
that the system can obtain information about the surroundings in different
directions.
It is also desirable that the antenna suppress signals from other directions
than the
direction in which the system is currently transmitting and receiving. A
phased array
antenna comprises a number of transmitting/receiving elements, usually
arranged in a
planar configuration. Each element, or group of elements, is driven by a
transmit/-
receive (T/R) module which controls the phase and the amplitude of the
corresponding antenna element.
On transmission of a signal from a phased array antenna, the signal is divided
into a number of sub-signals, and each sub-signal is fed to one of the
modules. The
modules comprise signal channels guiding the sub-signals to the antenna
elements.
Each signal channel comprises controllable attenuators or amplifiers and
controllable
phase-shifting devices for controlling the amplification and the phase shift
of the
modules. The signals transmitted through the antenna elements interfere with
each
other. By selecting suitable values of the relative amplification and the
relative phase-
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shifting between the modules and by utilizing the interference of the
transmitted
signals, the directional sensitivity of the antenna can be controlled.
During reception in a phased array antenna, the opposite procedure takes place
compared to transmission. Each antenna element receives a sub-signal. The
modules
comprise signal channels for reception and through these signal channels the
sub-
signals are collected in a single point in which all sub-signals are added to
form a
single composite signal. The signal channels for reception also comprise
amplifiers
and phase shifters, and the directional sensitivity of the antenna for
reception can be
controlled in a corresponding way as for transmission, by varying the
amplification
and phase-shifting of the modules.
In order to obtain the desired directional properties of the antenna, it is
desired
to minimize the side lobe levels of the antenna. To enable low side lobe
levels with an
electrically controlled phased array antenna, high accuracy of the
amplification and
the phase shift in the modules is required. In practice, this is achieved by
introducing a
calibration function in the antenna system. Central to the calibration concept
is the
compensation of the various contributions of cables, attenuators, phase
shifters,
regulators and other parts in the transmit/receive channels which respond
differently
at different temperatures, for each antenna element and at each radio
frequency. The
calibration procedure is required to determine what controls should be applied
to the
transmit/receive modules in order to obtain the desired current distribution
on the
antenna aperture.
Phased array antenna architectures typically include a calibration network,
whose purpose is to provide injection of a predetermined calibration signal to
each
antenna element and to the T/R module connected to it. An example of this type
of
calibration network is described in US Patent 7,068,218 to Gottl et al. Goal
et al's
calibration procedure utilizes, in addition to the operational
transmit/receive channels,
also an auxiliary injection network, whose contribution must be known in
advance.
This is determined using the concept of the calibration ratio, which measures
the ratio
between signals injected externally (in principle from infinity) to those
injected
internally.
Much prior art relates to phased antenna calibration and the determination of
calibration ratio. Of the many different approaches that are known in the art,
all
presently fall into one of two categories. Some methods use an external
calibration
signal that is disposed at infinity so that the respective amplitudes and
phases of the
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external calibration signals injected into each antenna element are the same.
This, of
course, greatly simplifies the determination of calibration ratio, but is not
feasible
when there is insufficient space between the external calibration source and
the
phased array antenna, such as when a phased array antenna is recalibrated in
the field.
The other approach disposes the external calibration source proximate to each
antenna element in turn, while ensuring that the distance from the external
calibration
source to each antenna element is the same and that the external calibration
source is
exactly aligned to the optical center of each antenna element. This also
ensures that
the respective amplitudes and phases of the external calibration signals
injected into
each antenna element are the same, but requires critical and consequently
complex
alignment and is both time-consuming and expensive.
When the calibration reference signal is derived from a distant source such as
a satellite, the signal emanates from infinity so that its wavefront is
effectively
equidistant from all the antenna elements. It therefore arrives in the same
phase at all
the antenna elements. But it is not always practical to use a distant source
for the
calibration source, particularly when space is at a premium as is often the
case in field
calibration. In satellite applications, for example, the required band of
frequencies is
not guaranteed and even if the required band of frequencies is provided -- the
signal
may not reach the desired intensity. Prior art approaches that employ so-
called near
zone calibration are known to feed a planar calibration signal successively to
the
antenna elements.
For example, US Pat. No. 6,084,545 (Lier et al.) discloses a near-zone
calibration arrangement for a phased-array antenna that determines the phase
shifts or
attenuation of the elemental control elements of the array. The calibration
system
includes a probe located in the near zone, and a calibration tone generator.
According
to the concept of reciprocity, the near zone calibration procedure can be
applied to
transmit or receive modes as well. In case of receive calibration mode, a
probe
sequentially moves from one antenna element to another, keeping the same
electro-
magnetic coupling conditions (distance from antenna plane, polarization,
orientation
etc.) and transmitting the same test signal. A receive antenna array has a
switching
arrangement, providing appropriate RF-module/antenna element connection to the
measurement unit via controllable phase shifter/attenuator. The near-zone
calibration
goal achieves the same signal parameters (phase and amplitude) coming from
each
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RF-module (and appropriate probe locations) by applying control signals to the
appropriate phase shifters and attenuators.
Regardless of whether near zone or far field calibration is performed, when a
calibration network is factory-calibrated, sets of calibration values must be
pre-
assigned to each antenna. These values cannot be determined in the field and
are apt
to be inapplicable to a replacement antenna element, so that if an antenna
element is
replaced in the field, such an approach is fraught with difficulty.
In summary, far zone calibration allows the calibration signal to be fed
simultaneously to all the antenna elements from a common source and ensures
that it
will arrive at the same phase at all the antenna elements; but is not suitable
for use in
confined spaces, such as when re-calibrating antenna elements in the field. On
the
other hand, near zone calibration requires that in order for the external
calibration
signal to arrive at the same phase at all the antenna elements, it must be fed
to each
antenna element sequentially and this requires precise alignment which is time-
consuming and expensive.
The methods for calibration ratio acquisition described above, are costly and
inaccurate in those cases where the antenna cannot be assumed to be bare i.e.
where
the antenna is electromagnetically coupled to an interfering structure. The
accurate
calibration ratio should take into account electro-magnetic coupling to all
near-by
interfering structures. Even if an interfering structure is absent at some
point in time,
this may be no longer true when the antenna is deployed later in some other
place
where the assumption of a bare antenna no longer holds. One example is a
phased
array cellular antenna located in some urban environment where some physical
obstacles interfere with the antenna. Even worse, these obstacles might not
have been
present at the time of antenna installation. Another example is an antenna
mounted on
aircraft, or on a tank or ship. In this case an aircraft wing may interfere
with an
antenna mounted on the fuselage of the aircraft. By the same token masts on a
marine
vessel may also interfere with antennas installed on it. There is a plethora
of examples
where such interference might be significant.
United States Patent 7,119,739 to Struckman describes a method for near field
to far field DF antenna array calibration.
The disclosures of all publications and patent documents mentioned in the
specification, and of the publications and patent documents cited therein
directly or
indirectly, are hereby incorporated by reference.
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Summary Of Invention
Certain embodiments of the present invention seek to provide calibration of
phased array antennas, electro-magnetically coupled, to some external
structure which
distorts the electromagnetic properties of the bare antenna.
Certain embodiments of the present invention seek to provide computation of
calibration ratio of an antenna in the presence of an interfering body.
Certain embodiments of the present invention seek to provide computation of
calibration ratio in the presence of the combined effect of the interfering
body and the
correction for the spherical wave front from the point RF source.
Certain embodiments of the present invention seek to provide computation of
corrections for calibration ratio measured using external measurement without
an
interfering body for the presence of an interfering body.
Certain embodiments of the present invention seek to provide correction of
calibration ratio obtained by measurements performed under the conditions of
near/intermediate electromagnetic field using RF simulation methods.
Certain embodiments of the present invention seek to provide using simulation
to estimate the electro-magnetic coupling between antenna of interest and an
interfering body located in a close vicinity to that antenna under various
conditions of
antenna illumination by an external point RF source.
Certain embodiments of the present invention seek to provide use of
simulation to estimate the range dependence of magnitude and phase of this
electro-
magnetic coupling as a function of difference in contribution of electro-
magnetic
coupling of an interfering body to the externally injected signals at various
distances
of the external point RF source.
Certain embodiments of the present invention seek to provide computation of
calibration ratio of an antenna using RF source, which is not necessarily a
point
source or a source with a well defined phase center.
Certain embodiments of the present invention seek to provide computation of
calibration ratio of an antenna in presence of an interfering body using RF
source,
which is not necessarily a point source or a source with a well defined phase
center.
The system shown and described herein uses a modified calibration ratio
which takes into account the existence of the interfering structure in the
vicinity of the
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antenna itself. The modified calibration ratio is defined as a ratio of a
signal injected
from infinity in the presence of the interfering structure (aircraft for
example) and an
internally injected signal also in presence of that interfering structure. The
boundary
between the two regions is defined as a function of the application, and
depends on
the dominant wavelength emitted by the source.
"Infinity" is taken to mean that the far zone conditions - regarding the point
source and the combined structure of the antenna and the interfering body -
are met,
namely that:
r> (2-3)D2 (1)
A
Where: r is the distance from the external RF-source to the combined structure
of the
antenna and the interfering body,
D is the maximum of:
1. The combined structure of the antenna and the interfering body size;
and
2. The size of external RF-source aperture,
k is the wavelength of the RF-radiation.
It is appreciated that in aircraft-mounted antenna applications, e.g. as
illustrated in Fig. 5, the far zone condition of the antenna electro-
magnetically
coupled to the wing structure may result in a distance r which exceeds 10
kilometers.
Certain embodiments of the present invention seek to provide calibration ratio
acquisition in field conditions using an inexpensive facility where the
anechoic
chamber as a means of a near zone range is no longer an option and at the same
time a
satellite as a means of a far zone range is also impossible.
Certain embodiments of the present invention seek to provide a method for
estimation of the calibration ratio utilizing a system including an RF point
source
located close to the antenna and synchronized with the transceiver connected
to the
antenna. A signal transmitted from this point source is received by the
antenna and
corrected by a simulation as if it were transmitted by this point source at
infinity. An
additional signal is injected using the auxiliary network. The ratio between
the two
signals, for each antenna element, is the required calibration ratio.
Certain embodiments of the present invention seek to provide calibration ratio
determination and calibration which occurs on the ground, followed by an
operational
stage which is airborne. The calibration ratio takes into account
electromagnetic
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coupling between at least one physical object fixed to the ground and the RF
source;
the physical object may in fact be the ground itself.
There is thus provided, in accordance with at least one embodiment of the
present invention, a system for calibration of a phased array antenna having a
network
of auxiliary channels internally injecting internal signals to the antenna, to
be used in
an environment including at least one interfering member affecting a
calibration ratio
of the antenna, the antenna comprising a plurality of mutually electro-
magnetically
coupled antenna elements, the system comprising an RF source external to the
antenna, disposed a near-by distance therefrom and operative to project
external
signals toward the antenna from the nearby distance, an RF simulation unit
operative
to generate simulated first electro-magnetic coupling -zero far-zone external
fields
projected toward the antenna from an RF source located at a far-zone distance
from
the antenna, assuming that first electro-magnetic coupling between the
mutually
electro-magnetically coupled antenna elements to be zero, and also operative
to
generate simulated first electro-magnetic coupling -zero near zone external
fields
projected toward the antenna from an RF source located at the nearby distance
from
the antenna were the first electro-magnetic coupling between the mutually
electro-
magnetically coupled antenna elements to be zero; and an electro-magnetically
coupled structure-accommodating calibration ratio computer operative to
compute a
Modified Calibration ratio by combining an indication of the internal signals
and the
external signals as received by the antenna, with a correction factor based on
an
output of the RF simulation unit.
Further in accordance with at least one embodiment of the present invention,
the RF source comprises an RF point source.
Still further in accordance with at least one embodiment of the present
invention, the RF source may be spherical or may alternatively be non-
spherical.
Further in accordance with at least one embodiment of the present invention,
the antenna calibrator is operative to combine the calibration ratio and the
correction
factor by adding the phases of the calibration ratio and the correction factor
to obtain a
phase value of the Modified Calibration ratio and adding decibel
representations of
the amplitudes of the calibration ratio and the correction factor to obtain a
decibel
representation of an amplitude of the Modified Calibration ratio.
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Additionally in accordance with at least one embodiment of the present
invention, the RF simulation tool computes the correction factor by computing
electromagnetic fields generated in and propagating within a non-continuous
medium.
Further in accordance with at least one embodiment of the present invention,
the antenna comprises a cellular antenna.
Still further in accordance with at least one embodiment of the present
invention, the system also comprises a platform upon which the antenna is
mounted
and wherein the interfering member is part of the platform.
Further in accordance with at least one embodiment of the present invention,
the signal measurement and recording device measures amplitude and phase of
the
samples of the internal and external signals.
Also provided, in accordance with at least one embodiment of the present
invention, is a method for calibrating an antenna comprising a phased array of
antenna
elements connected to plurality of transceivers, the method comprising
providing an
RF source of externally injected signals located close to the antenna and
synchronized
with the transceivers; determining, per antenna element, a calibration ratio
adapted to
accommodate for presence of at least one interfering structure
electromagnetically
interfering with a signal transmitted from the RF source and received by the
antenna;
and calibrating the antenna using the per-antenna element calibration ratios
adapted to
accommodate for presence of at least one interfering structure.
Further in accordance with at least one embodiment of the present invention,
the determining includes generating simulated far field and near field signals
so as to
simulate a signal transmitted by an RF source located at infinity and located
near the
RF source respectively; internally injecting an internal signal into the
antenna via an
internal injection network synchronized with the transceivers, wherein the
interfering
structure interferes with the internal signal; using the RF source to
externally inject
an external signal into the antenna; and, for each individual antenna element,
Computing the calibration ratio by combining information characterizing the
internal
and external signals as received by the individual antenna element with a
correction
factor characterizing the simulated far field and near field signals and
representing,
per antenna element, the ratio of the simulated far field and near field
signals.
Still further in accordance with at least one embodiment of the present
invention, at least one physical object which is electromagnetically coupled
to
radiation emitted by the RF source thereby to define unwanted radiation in
context of
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the calibration, is present in the course of the determining and calibrating
and is
absent in a subsequent operational stage, the method also comprising screening
the
unwanted radiation.
Further in accordance with at least one embodiment of the present invention,
the screening comprises covering the at least one physical object with RF-
radiation
absorbing material.
Still further in accordance with at least one embodiment of the present
invention, the determining and calibrating occurs on the ground, the
operational stage
is airborne and the physical object is fixed to the ground.
Still further in accordance with at least one embodiment of the present
invention, the determining comprises determining the calibration ratio a
plurality of
times thereby to obtain a plurality of interim calibration ratio results and
averaging the
plurality of interim calibration ratio results to obtain the calibration ratio
adapted to
accommodate for presence of at least one interfering structure.
Additionally in accordance with at least one embodiment of the present
invention, the determining the calibration ratio a plurality of times includes
re-
positioning the RF source a plurality of times, thereby to compensate for
artifactual
noise generated by the at least one interfering structure during calibration
ratio
measurement.
Further in accordance with at least one embodiment of the present invention,
the calibration ratio is determined a plurality of times for a single position
of the RF
source, thereby to compensate for white noise during calibration ratio
measurement.
Additionally in accordance with at least one embodiment of the present
invention, the correction factor includes a phase and an amplitude and wherein
the at
least one interfering structure comprises a plurality of interfering
structures and
wherein generating at least one simulated signal comprises performing the
following
operations for a near field configuration and for a far field configuration:
a.
computing a plurality of simulated first electromagnetic fields generated at
the
plurality of interfering structures respectively due to radiation emitted by
the RF
source; b. computing a plurality of simulated induced currents generated at
the
plurality of interfering structures respectively due to radiation emitted by
the RF
source; c. for each antenna element in the phased array of antenna elements:
1.
simulating a second electromagnetic field generated at the antenna element due
to
radiation emitted by the RF source; 2. computing a plurality of simulated
third
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electromagnetic fields generated at the antenna element due to the plurality
of
simulated induced currents respectively; and 3. generating a total field by
summing
the plurality of simulated third electromagnetic fields and the second
electromagnetic
field; d. for each antenna element in the phased array of antenna elements: 1.
computing a correction factor by computing a ratio of the total field as
computed for
the far field configuration divided by the total field as computed for the
near field
configuration; and 2. computing the phase and amplitude of the calibration
ratio by
measuring phase and amplitude for each of the internal and external signals as
received by each of the antenna elements; and e. for each individual antenna
element,
computing the calibration ratio adapted to accommodate for presence of at
least one
interfering structure by computing a difference between the phases of the
external and
internal signals as received by the individual antenna element, and adding the
phase of
the correction factor.
Further in accordance with at least one embodiment of the present invention,
the antenna is installed on an aircraft and the plurality of interfering
structures include
a fuselage, a first wing, a second wing, an engine, a stabilizer and a rudder.
Still further in accordance with at least one embodiment of the present
invention, the antenna is installed on a ship and the plurality of interfering
structures
include a hull, at least one mast and a bridge.
Additionally in accordance with at least one embodiment of the present
invention, the antenna is installed on a tank and the plurality of interfering
structures
include a hull, a turret and a cannon.
Also provided, in accordance with at least one embodiment of the present
invention, is a computer program product, comprising a computer usable medium
having a computer readable program code embodied therein, the computer
readable
program code adapted to be executed to implement a method for calibrating an
antenna comprising a phased array of antenna elements connected to plurality
of
transceivers, the method comprising providing an RF source located close to
the
antenna and synchronized with the transceivers; determining, per antenna
element, a
calibration ratio adapted to accommodate for presence of at least one
interfering
structure electromagnetically interfering with a signal transmitted from an RF
source,
which is located close to the antenna and synchronized with the transceivers,
the
signal being received by the antenna, wherein the determining includes
generating
simulated far field and near field signals so as to simulate a signal
transmitted by an
CA 02713606 2010-08-20
RF source located at infinity and located near the RF source respectively;
internally
injecting an internal signal into the antenna via an internal injection
network; using
the RF source to externally inject an external signal into the antenna; and
for each
individual antenna element, computing the calibration ratio by combining
information
characterizing the internal and external signals as received by the individual
antenna
element with a correction factor characterizing the simulated far field and
near field
signals; and calibrating the antenna using the per-antenna element calibration
ratios
adapted to accommodate for presence of at least one interfering structure.
Further in accordance with at least one embodiment of the present invention,
the method is carried out in field conditions in which no anechoic chamber is
available.
Still further in accordance with at least one embodiment of the present
invention, the external signals are affected by first electro-magnetic
coupling between
the plurality of mutually electro-magnetically coupled antenna elements and by
second electro-magnetic coupling between the source and the interfering
member, the
system also comprising a signal measuring and recording device measuring and
recording samples of the internal signals and the external signals; and a
correction
factor computation unit operative to compute a correction factor for the
calibration
ratio which factor corrects for presence of the interfering member and has a
phase and
an amplitude, by comparing the simulated first electro-magnetic coupling -zero
far-
zone external electromagnetic fields and the simulated first electro-magnetic
coupling
-zero near zone external electromagnetic fields, and the electro-magnetically
coupled
structure-accommodating calibration ratio computer is operative to compute the
modified Calibration ratio by combining the ratio of the internal and external
signals
as received by the antenna with the correction factor.
Further in accordance with at least one embodiment of the present invention,
the method also comprises computing (in dB) a difference between the
amplitudes of
the external and internal signals as received by the individual antenna
element, and
adding the amplitude (in DB) of the correction factor.
Also provided is a computer program product, comprising a computer usable
medium or computer readable storage medium, typically tangible, having a
computer
readable program code embodied therein, the computer readable program code
adapted to be executed to implement any or all of the methods shown and
described
herein. It is appreciated that any or all of the computational steps shown and
described
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herein may be computer-implemented. The operations in accordance with the
teachings herein may be performed by a computer specially constructed for the
desired purposes or by a general purpose computer specially configured for the
desired purpose by a computer program stored in a computer readable storage
medium.
Any suitable processor, display and input means may be used to process,
display e.g. on a computer screen or other computer output device, store, and
accept
information such as information used by or generated by any of the methods and
apparatus shown and described herein; the above processor, display and input
means
including computer programs, in accordance with some or all of the embodiments
of
the present invention. Any or all functionalities of the invention shown and
described
herein may be performed by a conventional personal computer processor,
workstation
or other programmable device or computer or electronic computing device,
either
general-purpose or specifically constructed, used for processing; a computer
display
screen and/or printer and/or speaker for displaying; machine-readable memory
such as
optical disks, CDROMs, magnetic-optical discs or other discs; RAMs, ROMs,
EPROMs, EEPROMs, magnetic or optical or other cards, for storing, and keyboard
or
mouse for accepting. The term "process" as used above is intended to include
any type
of computation or manipulation or transformation of data represented as
physical, e.g.
electronic, phenomena which may occur or reside e.g. within registers and /or
memories of a computer.
The above devices may communicate via any conventional wired or wireless
digital communication means, e.g. via a wired or cellular telephone network or
a
computer network such as the Internet.
The apparatus of the present invention may include, according to certain
embodiments of the invention, machine readable memory containing or otherwise
storing a program of instructions which, when executed by the machine,
implements
some or all of the apparatus, methods, features and functionalities of the
invention
shown and described herein. Alternatively or in addition, the apparatus of the
present
invention may include, according to certain embodiments of the invention, a
program
as above which may be written in any conventional programming language, and
optionally a machine for executing the program such as but not limited to a
general
purpose computer which may optionally be configured or activated in accordance
with the teachings of the present invention. Any of the teachings incorporated
herein
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may, wherever suitable, operate on signals representative of physical objects
or
substances.
The embodiments referred to above, and other embodiments, are described in
detail in the next section.
Any trademark occurring in the text or drawings is the property of its owner
and occurs herein merely to explain or illustrate one example of how an
embodiment
of the invention may be implemented.
Unless specifically stated otherwise, as apparent from the following
discussions, it is appreciated that throughout the specification discussions,
utilizing
terms such as, "processing", "computing", "estimating", "selecting",
"ranking",
"grading", "calculating", "determining", "generating", "reassessing",
"classifying",
"generating", "producing", "registering", "detecting", "associating",
"superimposing",
"obtaining" or the like, refer to the action and/or processes of a computer or
computing system, or processor or similar electronic computing device, that
manipulate and/or transform data represented as physical, such as electronic,
quantities within the computing system's registers and/or memories, into other
data
similarly represented as physical quantities within the computing system's
memories,
registers or other such information storage, transmission or display devices.
The term
"computer" should be broadly construed to cover any kind of electronic device
with
data processing capabilities, including, by way of non-limiting example,
personal
computers, servers, computing system, communication devices, processors (e.g.
digital signal processor (DSP), microcontrollers, field programmable gate
array
(FPGA), application specific integrated circuit (ASIC), etc.) and other
electronic
computing devices.
The present invention may be described, merely for clarity, in terms of
terminology specific to particular programming languages, operating systems,
browsers, system versions, individual products, and the like. It will be
appreciated
that this terminology is intended to convey general principles of operation
clearly and
briefly, by way of example, and is not intended to limit the scope of the
invention to
any particular programming language, operating system, browser, system
version, or
individual product.
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Brief Description Of The Drawings
Certain embodiments of the present invention are illustrated in the following
drawings:
Fig. I is a simplified functional block diagram illustration of a phased array
antenna calibration system using a point RF-source for computing a calibration
ratio
according to an embodiment of the invention.
Fig. 2 is a pictorial diagram of the measurement setup without an interfering
body (bare antenna), showing the spatial arrangement of the point RF source
and the
antenna elements plane.
Fig. 3 is a simplified electronic schematic diagram of a calibration signal
injection network which may serve as the injection unit of Fig. I according to
one
embodiment of the present invention.
Figs. 4A - 4C, taken together, form a simplified flowchart illustration of an
antenna calibration method operative according to certain embodiments of the
present
invention and including computing a calibration ratio in accordance with the
system
of Fig. 1.
Fig. 5 is a simplified pictorial illustration of conformal antenna, installed
on a
platform comprising an aircraft, only the main electro-magnetically coupled
structures
of which are shown, which antenna is to be calibrated according to an
embodiment of
the invention.
Fig. 6 is a simplified pictorial illustration of array of antennas, installed
on a
platform comprising a boat, only the main electro-magnetically coupled
structures of
which are shown, which array is to be calibrated according to an embodiment of
the
invention
Fig. 7 is a simplified pictorial illustration of an antenna, installed on a
platform
comprising a tank, only the main electro-magnetically coupled structures of
which are
shown, which antenna is to be calibrated according to an embodiment of the
invention.
Fig. 8 is a simplified flowchart illustration of an antenna calibration method
which is similar to the method of Figs. 4A - 4C but is particularly suited for
reducing
white noise effects.
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Fig. 9 is a simplified flowchart illustration of an antenna calibration method
which is similar to the method of Figs. 4A - 4C but is particularly suited for
reducing
artifactual noise effects due to interfering physical objects which may
continue to
provide a certain degree of residual interference even if covered.
Fig. 10 is a simplified flowchart illustration of an antenna calibration
method
which is similar to the method of Figs. 4A - 4C but is particularly suited for
reducing
white noise effects and for reducing artifactual noise effects due to
interfering
physical objects which may continue to provide a certain degree of residual
interference even if covered.
Detailed Description Of The Embodiments
Certain embodiments of the present invention are suited for applications in
which the same electromagnetic environment exists during the phase of
measuring the
calibration ratio as also during the calibration phase itself and likewise
during the
operational phase such that any deviation from this assumption may be assumed
to be
negligible or otherwise reduced until negligible. According to certain
embodiments of
the invention, a modified calibration ratio is employed which represents
effects of the
interfering bodies which are near to the antenna of interest, since simply
measuring
the calibration ratio of a bare antenna knowing that its operational
environment
includes obstacles such as parts of a ship, plane or tank, is not sufficient.
The
calibration ratio is determined by a ratio of two measurements: an internal
injected
signal IN via the injection unit 33 and an external injected signal using a
point RF
source. For the external injection, a RF source is deployed close to the
antenna,
correction is made for large distances including simulating the difference in
electromagnetic coupling between these distances. This simulation computes the
propagation of electromagnetic radiation through a discontinuous dielectric
medium.
The discontinuity involved here represents an interfering body 41 located at
close
proximity to the antenna. Other discontinuities which are present during
calibration
ratio acquisition but absent in the operational stage, such as ground causing
multi-path
effects, may be overcome e.g. by covering the relevant interfering elements
with RF-
radiation absorbing material or by other methods.
The modified calibration ratio is used for antenna calibration as is known in
the art. An example use of a calibration ratio as computed herein, to
calibrate an
CA 02713606 2010-08-20
antenna is described in United States Patent US 6,480,153 to Jung. Jung terms
the
calibration ratio "transfer function".
Fig. I shows a phase array antenna arrangement that includes a bare array 25
of antenna elements 31 to be calibrated which are respectively connected to a
plurality of transceivers 32 operative to control signals transmitted or
received
through the antenna, an internal injection unit 33, (also termed herein
"auxiliary
channel network 33") for injecting calibrating signals into the antenna
elements 31, an
RF source 35 such as a point RF-source, and an amplitude and phase measurement
unit 36, also termed herein "signal measuring and recording device 36".
Signals received by the transceivers 32 are measured by the amplitude and
phase
measurement unit 36. This process includes down conversion, filtering and
generation
of in phase and quadrature sampled signals which are converted to phases and
amplitudes in a fashion known to any person skilled in this field. The
corresponding
phases and amplitudes are stored in a suitable memory device and processed, as
described below with reference to steps 230 and 250 in Fig. 4A, by a electro-
magnetically coupled structure-accommodating calibration ratio computer 38.
Distance measurement unit 37 is operative to measure the physical distance of
the
RF point source from the antenna using, e.g. a laser gun or any other suitable
means.
The distance between point RF source 35 and the antenna 31 as measured by the
distance measuring unit 37 is used by an RF simulation tool 42, as described
below
with reference to Fig. 4A, step 250, to generate a simulated signal which
simulates an
externally injected signal. Electro-magnetically coupled structure-
accommodating
calibration ratio computer 38 is a calibration ratio computer which
accommodates for
interfering structure 41. Unit 38 computes the accommodating calibration ratio
by
combining the measurements of the internal and external injections generated
by
distance measuring unit 37, with the correction factor computed by unit 43,
all as
described herein.
An interfering body 41 is typically disposed in close proximity to the antenna
31
and to the RF source used for external injections 35. An RF simulation tool 42
is also
provided which solves Maxwell equations to compute the electromagnetic fields
which propagate through discontinuous media, obeying specific boundary
conditions.
The RF simulation tool 42 may for example comprise a general purpose computer
running RF simulation software such as but not limited to FEKO Suite software,
a
product of EM Software & systems-S.A. Ltd.; Computer Simulation Technology
16
CA 02713606 2010-08-20
Studio Suite software, a product of CST GmbH; GRASP software, a product of
TICRA Engineering Consultants; WIPL-D Pro software tool, a product of WIPL-D
d.o.o.; or COMSOL MultiPhysics, a product of Comsol Group. A correction factor
computation unit 43 computes a correction factor as described below, e.g.
using
formulae 8 - 14 described below, and may comprise a suitably programmed
computer.
It is appreciated that interfering body 41 as referred to herein is typically
one
which is present both when the calibration ratio is being established and
during
operation of the antenna. Members which interfere, but are not present during
operation of the antenna are typically covered by RF-radiation-absorbing
materials
selected to match the operating frequency of the antenna, as described below
with
reference to step 215 in Fig. 4A, hence can almost be assumed not to exist or
not to be
present, for practical purposes, although the methods of Figs. 9 - 10 below
are
particularly suited to applications in which it is desired to overcome even
minor
residual effects caused by covered interfering members despite their being
covered.
Commercially available RF absorption materials are distributed for example by
ORBIT/FR Inc. as described at their website orbitfr.com, and by TDK RF
Solutions
Inc. as described at their website TDKRFSolutions.com.
Thus the apparatus of Fig. 1 includes two sources of RF-signals: the first is
the internal injection unit 33 that is electro-magnetically coupled to antenna
elements
31 and to the transceivers 32, while the second is the point (typically) RF-
source 35
from which a spherical wave 40 emanates toward the plurality of the antenna
elements
3 1. Comparison of measurement results of these two signals enables derivation
(Fig.
4C, step 370) of what is termed the "phase component" of the calibration ratio
attributed to the plurality of antenna elements, with the effect of
interfering body 41
suitably neutralized according to certain embodiments of the present
invention.
The system of Fig. 1 generates an interfering-structure accommodating
calibration ratio which can be used to calibrate phased array antenna 31. The
RF
source 35 external to the antenna, is disposed a near-by distance therefrom
and is
operative to project external signals toward the antenna 31 from the near-by
distance,
the external signals being affected by first electro-magnetic coupling between
the
plurality of mutually electro-magnetically coupled antenna elements 31 and by
second
electro-magnetic coupling between the point source 35 and the interfering
member
17
CA 02713606 2010-08-20
31. Signal measuring and recording device 36 is operative for measuring and
recording samples of the internal signals and the external signals.
RF simulation unit 42 is operative to generate simulated first electro-
magnetic
coupling -zero far-zone external fields projected toward the antenna from an
RF point
source located at a far-zone distance from the antenna, assuming that first
electro-
magnetic coupling between the mutually electro-magnetically coupled antenna
elements to be zero, and is also operative to generate simulated first electro-
magnetic
coupling -zero near zone external fields projected toward the antenna from an
RF
point source located at the near-by distance from the antenna were the first
electro-
magnetic coupling between the mutually electro-magnetically coupled antenna
elements to be zero. Specifically, RF simulation tool 42 may be used for
computations
of the total effect of the interfering body 41 and the correction for the
spherical wave
front 40 from the point RF source 35 due to electro-magnetic coupling between
the
point RF source 35 and the platform supporting the antenna, e.g. as shown in
Figs. 5 -
7, and due to correction for the spherical wave front 40 from the point RF
source.
Tool 42 may be in use for the computations of corrections for the calibration
ratio to
fulfill far zone conditions of the combined structure of antenna together with
the
interfering body 41.
Correction factor computation unit 43 computes a correction factor, having a
phase and an amplitude, for the calibration ratio due to presence of the
interfering
member by comparing the simulated first electro-magnetic coupling -zero far-
zone
external electromagnetic fields and the simulated first electro-magnetic
coupling -zero
near zone external electromagnetic fields. Electro-magnetically coupled
structure-
accommodating calibration ratio computer 38 is operative to compute a Modified
Calibration ratio by combining the ratio of the external measurement and the
internal
measurement and correction factor.
Fig. 2 shows a suitable spatial arrangement of the point RF source 35 and the
bare antenna, i.e. the phased array antenna of Fig. 1, comprised of the
antenna
elements 31, without an interfering body e.g. structure 41 of Fig. 1 (bare
antenna).
The origin of the antenna array is marked as 0.
Fig. 3 is a simplified electronic schematic diagram of a calibration signal
injection network 110 which may serve as the injection unit of Fig. 1
according to one
embodiment of the present invention. As shown, calibration signal injection
network
110 includes a triad of dividers 111, 112 and 113 interconnected so that a
common
18
CA 02713606 2010-08-20
junction of the dividers 1 11 and 112 serves as a corporate feed point 114 for
injecting
an input signal into the network. Respective junctions between opposite ends
of the
divider 113 and respective ends of the dividers 111 and 112 are connected to
similar
divider triads comprising dividers 115, 116, 117 and 118, 119, 120. Thus, the
dividers
115 and 116 are commonly connected at a first end to one end of the divider
113
whose other end is commonly connected to a first end of the dividers 118 and
119.
The second ends of the dividers 115, 116, 118 and 119 are connected to
respective
couplers 121 each of which is terminated by a respective termination 126. The
input
signal is split initially at the junction between the dividers 111 and 112 and
is again
split at each of the respective junctions between dividers 115, 116 and 118,
119.
Depending on the values of the dividers, different currents will flow through
each of
the couplers 121.
The calibration signal injection network 110 is interposed between the array
of antenna elements 31 to be calibrated, such that when a single input signal
is fed to
the corporate feed point 114 of the calibration network 110, respective
steering signals
are fed to each of the antenna elements 3 1 via respective conventional phase
shifters
and amplifiers (not shown) that are inductively coupled to the current loops
121. The
values of the steering signals fed to each antenna element 31 are
predetermined by the
values of the dividers in the calibration network 110 and are thus known in
advance.
When an antenna array is calibrated using the calibration signal injection
network 110, an input signal is fed to the corporate feed point 114 and the
output
signals flowing through each antenna element 31 are measured. Any offset in
amplitude or phase from a respective desired value is measured and the
corresponding
amplitude and phase offsets are determined.
In conventional use of such a calibration signal injection network, precise
adjustment is required to ensure that the signals fed via the couplers 121 to
the
antenna element are identical in amplitude and phase. Not only does this
require
precise calibration. It also means that if values of the components of the
calibration
signal injection network change for any reason, e.g. owing to changes in
ambient
temperature that may induce changes to the lengths of connectors, such changes
must
be compensated for in prior art systems. This, conventional systems
necessitate
provision of costly circuitry operative to ensure that the calibration signal
injection
network shown therein may be functional according to conventional calibration
procedures. Such circuitry is not required, according to certain embodiments
of the
19
CA 02713606 2010-08-20
present invention, and this greatly reduces the complexity of a phased array
antenna
arrangement having such an integral calibration signal injection network.
Figs. 4A - 4C, taken together, form a simplified flowchart illustration of an
antenna calibration method operative according to certain embodiments of the
present
invention and including computing a calibration ratio in accordance with the
system
of Fig. 1.
In Step 220, an internal signal is injected via injection unit 33 to each
antenna
element. This signal is redirected to the transceivers 32 where it is sampled,
processed
and finally stored (step 230). This step is repeated for all frequencies
needed in the
operational phase. The next step is to inject an external signal to the
antenna elements
(step 240). This is done via the point RF source 35 which is connected by a
cable 34
to the injection unit 33 as the antenna array 25 itself. This allows for a
perfect
synchronization of the signal in its transmit and receive paths. This signal
is also
sampled, processed and stored (step 250). Due to the high level of
synchronization a
pulse signal is integrated later on so as to achieve higher SNR in the
measurement.
A suitable method for computing a calibration ratio under the assumption that
there is no electromagnetic coupling of the antenna to the platform, is now
described:
The calibration ratio is determined by the ratio of the following two measured
signals:
1) Signal injected by the external point RF source 35 and
2) Internal injected signal IN by the auxiliary channels 33.
By definition the calibration ratio (CR ) is given by the following
expression:
0
CR = NO CFO (2)
Where EX is the signal injected by the external point RF source 35 measured
at the input to the electro-magnetically coupled structure-accommodating
calibration
ratio computer 38,
IN is the internal signal as injected via the injection unit 33 measured at
the
input to the electro-magnetically coupled structure-accommodating calibration
ratio
computer 38, and
CF is the correction factor representing the correction for the spherical
wave
front 40 from the point RF source 35.
CA 02713606 2010-08-20
The superscript 0 indicates the assumed absence of the interfering body 41.
The phase of the calibration ratio for antenna element n, (CRn , is found by
the following formula:
0 0 0 + 0 (3)
gCR,n = (PEX,n - (P/N,,, ~CF,n
Where ok,, is the phase of the signal injected by the point RF source 35, as
measured by the electro-magnetically coupled structure-accommodating
calibration
ratio computer 38 for antenna element n,
P/N,n is the phase of the internal injected signal IN , as measured by the
electro-magnetically coupled structure-accommodating calibration ratio
computer 38
for antenna element n,
cp ,: is the phase of the correction factor CF for the spherical wave front
40
from the point RF source 35, for each antenna element which is given as:
(PCE,n C xy + yy + Zy - (xõ - x9 + Y, Y + Zn - Zy ] (4)
The expression in (4) is given in the coordinate system of the antennae array
25 whose origin is marked by 0 and whose unit vectors (x, y, 2) are shown in
Fig. 2.
(Xq, yy, Zq) denotes the position of the point RF source 35 relatively to the
center of the antenna array 25,
(x,,, yn,zn) is the position of antenna element n in antenna array 25,
relative to
the origin 0 and
A is the wavelength of the radiation.
The amplitude of the calibration ratio for antenna element n, may be
computed by the following formula, (note: all the amplitudes are measured in
dB).
"CR,n = AFX,n - N,n + ACF',n (5)
Where Awn is the measured amplitude of the signal injected by the point RF
source 35 for antenna element n,
A,N, is the measured amplitude of the internal injected signal IN for antenna
element n, and
21
CA 02713606 2010-08-20
A~ ., õ is the amplitude of the correction factor CF for the spherical wave
front 40 from the point RF source 35. This produces a small contribution to
the
amplitude at each antenna element, given as:
x' + 2 +zz
20 -lo 9 Yy (6)
(xn-x4/ +ln-yqf +\Zn-Zy/
It is appreciated, as described below with reference to Formulae 17 - 20, that
the correction of the calibration ratio shown and described herein to
accommodate for
electro-magnetic coupling to platform elements and other interfering elements
can be
regarded as an extension of a similar situation, described here, in which
there is no
electromagnetic coupling.
In steps 260 and 270, external signal measurement is simulated; first under
the near zone conditions (step 260) and second under the far zone conditions
(step 270).
This is done using RF simulation tools having a Maxwell's equation solving
functionality. In step 260, the distance between the point RF source 35 and
the antenna
31 is the same as was used for the external signal measurement step 250 e.g.
as
illustrated in Fig. 1 (near-zone configuration). This is done again (step 270)
at a large
distance - the latter representing the far zone conditions of the point RF
source 35 and
the antenna 31 together with the interfering body 41.
The simulation performed in step 260 and 270 typically relies upon detailed
information characterizing the structure and shape of the interfering body 41.
Simulation of the injection from a point RF source 35 to the antenna is
carried out in
both configurations. A difference between these two computations is performed
and
this difference is added phase wise and amplitude wise (steps 370 & 380) to
the
measurement done with point RF source 35 at the nearby distance. It is assumed
that
in simulating the signals at two different distances, only the electro-
magnetic coupling
to the interfering body 41 is modified. On the other hand, the simulation is
not aware
of the variation in the antenna element pattern and it assumes the same
pattern for all
of them. These variations originate in the electro-magnetic coupling between
elements and this is the reason why it is not possible to use simulation only.
The
measurement effected at the nearby distance contains precisely this
information and
therefore it complements the information that is missing in the simulation.
Having the
internal injection results and the modified external injection results, the
ratio between
22
CA 02713606 2010-08-20
them as computed in step 360 of Fig. 4C is used to define the phase and
amplitude of
the modified calibration ratio.
The formula used for calibration ratio computation, e.g. formula 2 above, may
be generalized to include the total effects of the interfering body 41 and the
correction
for the spherical wave front 40 from the point RF source 35 as follows:
CR = N . CF (7)
Where EX is the signal injected by the external point RF source 35 measured
at the input to the electro-magnetically coupled structure-accommodating
calibration
ratio computer 38 (including the interfering body effect),
IN is the internal signal as injected via the injection unit 33 measured at
the
input to the electro-magnetically coupled structure-accommodating calibration
ratio
computer 38 (including the interfering body effect), and
CF is the correction factor, computed by unit 43 in Fig. I and including
corrections due to the effects, on the electro-magnetic coupling ratio, of
interfering
body 41 and the correction for the spherical wave front 40 from the point RF
source
effect.
Steps 280 and 290: The induced currents on the interfering body 41, resulting
from the point RF source 35, are computed:
Fs F. - INF (8)
Fs I'
FF Fb (9)
Where the fields generated on the interfering body 41, FN,,_ and FFF ,
represent
the electromagnetic fields emitted from the point RF source 35 at the near by
distance
and the far zone configuration respectively, and
Ih.1, I~;F represent the induced currents resulting form the point RF source
35
field at the nearby distance and the far zone configuration, respectively.
The superscript i is the index for the i-th element of the interfering body 41
i.e.
a wing, an engine, and so forth.
Induced currents are computed both for the setup at the near by distance (in
step 280 - e.g. using formula 8) and (in step 290 - e.g. using formula 9)
using the
setup that fulfills the far zone requirement for the combined structure of the
antenna
together with the interfering body 41. These computations are carried out
separately
23
CA 02713606 2010-08-20
for each significantly electro-magnetically coupled portion of the interfering
body 41
For example, in the case illustrated in Fig. 5, the significant portions may
be a
fuselage 543, a wing 544, an engine 545, a stabilizer 546 and a rudder 547.
Optionally, higher order effects in the induced currents computations can be
included to account for multiple bouncing of the radiation between the
interfering
parts and the antenna elements and among the different interfering parts
themselves.
Steps 300 and 310: The resulting electromagnetic fields, due to the induced
currents, are computed for each element of the interfering body 41.
IN7; -~ FN7; (10)
Where the fields FNF and FFF, represent the electromagnetic fields, resulting
from the induced currents, for point RF source 35 at the nearby distance and
the far
zone configuration, respectively, for the i-th element of the interfering body
41.
The above computation of fields is effected both for the setup at the near-
zone
configuration (step 300 - formula 10) and for the far-zone configuration (step
310 -
formula 11).
Steps 320 and 330: The total field is computed by summing all the induced
fields, for all the elements of the interfering body 41 and the fields emitted
from the
point RF source 35. This is done once for the setup at the near-zone
configuration, in
step 320. The second computation is made at the far-zone configuration (step
330).
T _ S
FNF FNF +FNF (12)
7'
F F F - FFF +F S
FF (13)
Here, the fields include:
FNF and FFF represent the source electromagnetic fields at the near by
distance and the far zone configuration respectively,
F~,F and FFF represent the induced electromagnetic fields at the
nearbydistance and the far zone configuration respectively and
F,~and FFF represent the total electromagnetic fields at the nearby distance
and the far zone configuration respectively.
24
CA 02713606 2010-08-20
Steps 340 and 350: The resulting electromagnetic total fields are then sampled
at the spatial position of each antenna element. This is done for the near-
zone
configurations (step 340) and for the far-zone configuration (step 350).
Finally (step 360), the correction factor CF for each antenna element 31 is
computed (formula 14) as the ratio of the total fields computed at the near by
distance
and the far zone configuration, sampled at the spatial position of each
antenna element
31 in antenna array 25:
CF,, = ~FtF 1, /[FNF 1, (14)
Where CFõ is the correction factor for the calibration ratio for antenna
element
n, and the square brackets [=]õ stands for the sampled fields at the spatial
position of
antenna element n.
Step 370: The phase of the calibration ratio for antenna element n, (PCR n ,
is
then computed e.g. using the following formula:
(PCR,n = ~9EX,n ~01N,n +(OCF,n (15)
Where cp,.X, is the phase of the signal injected by the point RF source 35, as
measured by the electro-magnetically coupled structure-accommodating
calibration
ratio computer 38 for antenna element n in array 31,
is the phase of the internal injected signal IN , as measured by the
electro-magnetically coupled structure-accommodating calibration ratio
computer 38
for antenna element n, and
lp~.,,. n is the phase of the correction factor CF as computed in step 360,
using formula 14.
Step 380: The amplitude, A(.R,,,of the calibration ratio for antenna element n
is
computed by the following formula:
ACR,n = AEX,n - A/N,,, + ACF,n (16)
Where A,.Xõ is the amplitude of the signal injected by the point RF source 35
as measured by the electro-magnetically coupled structure-accommodating
calibration
ratio computer 38 for antenna element n,
A/Nn is the amplitude of the internal injected signal IN as measured by the
coupled structure-accommodating calibration ratio computer 38 for antenna
element
CA 02713606 2010-08-20
n, and
is the amplitude of the correction for the calibration-ratio as computed
using formula 14.
It is appreciated that, in the absence of any interfering body 41, the
correction
for the calibration ratio computed in step 360 using formula 14, takes the
form of
[F,,: Jn /[F.v,. Jn . This is equal to the differences in the calibration
ratio resulting from
the correction for the spherical wave front 40 from the point RF source 35
only,
namely CF .
As described below with reference to formula 17 - 20, it is possible to
compute a calibration ratio as a result of the electro-magnetic coupling
between the
antenna and its platform, by decomposing the correction factor into two
contributions
one of them being the non electro-magnetically coupled component and the other
one
being the correction component due to the electro-magnetic coupling.
Writing CF as a product CF = CF - CF', formula 7, yields:
CR = N = CFO , CF' (17)
Where CF' is the transfer function of all corrections due to the interfering
body effects without the effects of correction for the spherical wave front 40
from the
point RF source 35.
The correction for the calibration-ratio in this case, for the effects, on the
electro-magnetic coupling ratio, of interfering body 41 only, may be computed
as a
ratio:
[F~ _ 1 1 (1 8 )
F! F FF'F 1
This yields the following formula for the phase of the calibration ratio:
(PCR,n = PCR,n + coCF,n (19)
Where cp'',: n is the phase of the correction for the calibration-ratio, for
the
interfering body effects only, as computed from formula 18.
26
CA 02713606 2010-08-20
The formula for the amplitude of the calibration ratio may be determined by
the
following:
A
AC[,-, ` CR,n - `ee-R,n + n (20)
Where 4F ,n is the amplitude of the correction for the calibration-ratio, for
the
effects, on the electro-magnetic coupling ratio, of interfering body 41 only,
as
computed from formula 18.
Figs. 5 - 7 illustrate three examples of the main structural elements of
certain
platforms supporting certain antenna installations which may be calibrated in
accordance with certain embodiments of the present invention.
Fig. 5 is an illustration of a conformal antenna 542 installed on an aircraft,
with external point RF source 541. The interfering portions (steps 280 and 290
being
performed separately for each) for this case are: the fuselage 543, the wing
544, the
engine 545, the stabilizer 546 and the rudder 547. Fig. 6 is an illustration
of an array
of four antennas 552 installed on a boat, with external point RF source 551.
The
interfering portions (steps 280 and 290 being performed separately for each)
for this
case are: the hull 553, the two masts 554 and 555 and the bridge 556. Fig. 7
is an
illustration of an antenna installed on a tank 562, with external point RF
source 561.
The interfering portions (steps 280 and 290 being performed separately for
each) for
this case are: the hull 563, the turret 564 and the cannon 565.
RF source 35 need not necessarily comprise a point source or source with a
well defined phase center. In this case the measured pattern of this source
replaces the
pattern of the point RF source in the RF simulation tools, for all the
computations
shown and described herein. The calibration ratio is then determined according
to
formula 7 as opposed to formula 17 which is specific for spherical sources.
The
resulting correction factor (CF ) compensates the effects, on the electro-
magnetic
coupling ratio, of interfering body 41 and the effects added due to the
pattern of the
RF source 35.
Fig. 8 is a simplified flowchart illustration of an antenna calibration method
which is similar to the method of Figs. 4A - 4C but is particularly suited for
reducing
white noise effects. The method of Fig. 8 typically includes some or all of
the
following steps, suitably ordered e.g. as shown:
27
CA 02713606 2010-08-20
Step 410: perform steps 210 - 230 of Fig. 4A
Step 420: perform steps 240 and 250 of Fig. I a plurality of times e.g. 3 - 10
times.
Step 430: perform steps 260 - 360 of Figs. 4A - 4C
Step 440: perform steps 370 and 380 a plurality of times such as but not
limited to 3 - 10 times based on step 250 as performed a respective plurality
of times
in step 420
Step 450: average the plurality of results obtained by repeating steps 370 and
380 in step 440 to obtain final phase and amplitude values respectively
Step 460: calibrate the antenna using the final phase and amplitude values
found in step 450
Fig. 9 is a simplified flowchart illustration of an antenna calibration method
which is similar to the method of Figs. 4A - 4C but is particularly suited for
reducing
artifactual noise effects due to interfering physical objects which may
continue to
provide a certain degree of residual interference even if covered. The method
of Fig. 9
typically includes some or all of the following steps, suitably ordered e.g.
as shown:
Step 500: perform steps 210 - 380 of the method of Figs. 4A - 4C including
performing each of steps 240 - 260, 280, 300, 320, 340, 360 - 380 a plurality
of times
such as but not limited to 2- 4 times using a corresponding plurality of
different
positions for RF source 35 which may be a few meters apart
Step 510: average the plurality of phase results obtained by repeating step
370
in step 500, to obtain final phase values
Step 515: average the plurality of amplitude results obtained by repeating
step
380 in step 510, to obtain final amplitude values
Step 520: calibrate the antenna using the final phase and amplitude values
found in steps 510 and 515 respectively
28
CA 02713606 2010-08-20
Fig. 10 is a simplified flowchart illustration of an antenna calibration
method
which is similar to the method of Fig. 4A - 4C but is particularly suited for
reducing
white noise effects and for reducing artifactual noise effects due to
interfering
physical objects which may continue to provide a certain degree of residual
interference even if covered. Typically, plural calibration ratios may be
computed as
per any of the embodiments of the present invention respective plural times
for a first
position of source 35 relative to the antenna, then the source 35 may be moved
and
again, plural calibration ratios may be computed as per any of the embodiments
of
the present invention respective plural times, whereas the final calibration
ratio is
obtained by averaging each of phase and amplitude as obtained over the various
positions and over the plural computations.
The method of Fig. 10 typically includes some or all of the following steps,
suitably ordered e.g. as shown:
Step 600: perform steps 410 - 450 of fig. 8 for each of several positions of
source 35 relative to the antenna
Step 610: average over several final phase values obtained in the several
respective renditions of step 450 of fig. 8 to obtain an output phase value
Step 620: average over several final amplitude values obtained in the several
respective renditions of step 450 of fig. 8 to obtain an output amplitude
value
Step 630: calibrate the antenna using the output phase and amplitude values
found in steps 610 and 620 respectively.
It is appreciated that software components of the present invention including
programs and data may, if desired, be implemented in ROM (read only memory)
form
including CD-ROMs, EPROMs and EEPROMs, or may be stored in any other
suitable computer-readable medium such as but not limited to disks of various
kinds,
cards of various kinds and RAMs. Components described herein as software may,
alternatively, be implemented wholly or partly in hardware, if desired, using
conventional techniques.
Included in the scope of the present invention, inter alia, are
electromagnetic
signals carrying computer-readable instructions for performing any or all of
the steps
of any of the methods shown and described herein, in any suitable order;
machine-
readable instructions for performing any or all of the steps of any of the
methods
shown and described herein, in any suitable order; program storage devices
readable
by machine, tangibly embodying a program of instructions executable by the
machine
29
CA 02713606 2010-08-20
to perform any or all of the steps of any of the methods shown and described
herein,
in any suitable order; a computer program product comprising a computer
useable
medium having computer readable program code having embodied therein, and/or
including computer readable program code for performing, any or all of the
steps of
any of the methods shown and described herein, in any suitable order; any
technical
effects brought about by any or all of the steps of any of the methods shown
and
described herein, when performed in any suitable order; any suitable apparatus
or
device or combination of such, programmed to perform, alone or in combination,
any
or all of the steps of any of the methods shown and described herein, in any
suitable
order; information storage devices or physical records, such as disks or hard
drives,
causing a computer or other device to be configured so as to carry out any or
all of the
steps of any of the methods shown and described herein, in any suitable order;
a
program pre-stored e.g. in memory or on an information network such as the
Internet,
before or after being downloaded, which embodies any or all of the steps of
any of the
methods shown and described herein, in any suitable order, and the method of
uploading or downloading such, and a system including server/s and/or client/s
for
using such; and hardware which performs any or all of the steps of any of the
methods shown and described herein, in any suitable order, either alone or in
conjunction with software.
Features of the present invention which are described in the context of
separate embodiments may also be provided in combination in a single
embodiment.
Conversely, features of the invention, including method steps, which are
described for
brevity in the context of a single embodiment or in a certain order may be
provided
separately or in any suitable subcombination or in a different order. "e.g."
is used
herein in the sense of a specific example which is not intended to be
limiting.
Devices, apparatus or systems shown coupled in any of the drawings may in fact
be
integrated into a single platform in certain embodiments or may be coupled via
any
appropriate wired or wireless coupling such as but not limited to optical
fiber,
Ethernet, Wireless LAN, HomePNA, power line communication, cell phone, PDA,
Blackberry GPRS, Satellite including GPS, or other mobile delivery.
