Note: Descriptions are shown in the official language in which they were submitted.
~067Z0Z
This invention relates to a system and method for determining
the radiation pattern of an antenna. The invention is based on the use of
what may be termed RELEDOP (Receiving ELEmentary Dipole with Optional
Polarity).
Generally, the measurement of radiation patterns is a difficult
problem, which requires careful positioning of a radio source of the
correct polarization at a specific distance, elevation angle and azimuth
relative to the antenna being measured. Historically, measurement of VHF
and HF antenna patterns has been neglected because of the inherent difficulty
of making the measurement. Patterns with varying degrees of relevance to real
life applications have been derived using mathematical and scale modeling
techniques. The accuracy of these are limited by the difficulty of precise
modeling of complex environments such as those provided by ships, cities,
etc. This problem is particularly severe at HF frequencies where the ground
is an inherent part of the antenna. Large aperture antennas are currently
utilized, for example, at those frequencies which can be degraded by irregu-
larities and inhomogeneities in the ground. These parameters are easily
measured prior to the installation of the antenna by measuring the pattern
of a standard monopole antenna erected at the proposed antenna site. Proper
engineering of an antenna and its optimum utilization in a communications
circuit requires accurate knowledge of its radiation pattern.
One method which is known involves the use of what has been termed
XELEDOP, or transmitting elementary dipole with optional polarity. This
technique consists of an aircraft towing an aerodynamically stable package
equipped with a short dipole antenna and transmitter that sequentially trans-
mits on a number of frequencies. The signals are received by the antenna
being calibrated and their amplitude recorded. This data defines the radiation
pattern of the antenna after corrections are made for the pattern of the test
dipole, non-linearities in the electronics and variation in distance between
the XELEDOP and the antenna being measured. This system has been found to be
effective in measuring antenna patterns and the results are well documented.
-- 1 --
~067ZOZ
The main disadvantage of the XELEDOP system is that it is difficult
to transmit enough power to generate sufficiently strong fields at the unknown
antenna to measure all aspects of its pattern. This is particularly true
when the measurements must be made at a distance of 30 to 60 miles which is
the case for large aperture antennas. In essence, it is technically very
difficult to couple energy from the low output impedance XELEDOP transmitter
to its short dipole because the dipole has a high input impedance which is
highly reactive.
The object of this invention is to permit sufficient power to
be generated to enable a more thorough measurement of the antenna radiation
pattern to be made. In this invention, the antenna which is being measured
is the transmitting antenna, and the dipole is the receiving antenna. Thus,
instead of transmitting from the airborne dipole, transmissions are made
from the antenna being calibrated and the signals are received by the dipole
and receiver, which are towed behind an aircraft in a set pattern above
the transmitting antenna. The elementary dipole is coupled directly to the
input preamplifier of the receiver, thereby giving a system with high
sensitivity. Coupling the input impedance of the dipole to the high input
impedance preamplifier is much more efficient than coupling it to a power
amplifier with its inherently low output impedance. A VHF telemetry link
is employed with the amplitude of the received signal being telemetered in
real-time either directly to the aircraft towing the dipole and receiver,
or to a ground terminal. The system of this invention is capable of 2,
or more, orders of magnitude more sensitivity than that of the XELEDOP,
although only 1 watt is transmitted from the ground antenna which is being
measured.
Optional polarity is available with the receiving dipole arrange-
ment of this invention. The receiver and dipole are towed sufficiently far
behind the aircraft so as to provide isolation from the distorting effects of
the aircraft fuselage. This allows the polarization of the transmitted signal
to be changed from horizontal to vertical.
1067ZOZ
In accordance with one aspect of this invention there is provided
a system for determining the radiation pattern of an antenna comprising a
transmitter coupled to said antenna, a receiving elementary dipole adapted
to be orien~ed to receive either vertical or horizontal polarized signals
coupled to a receiving means for detecting the amplitude of the signal, and
adapted to be moved in a determined manner about the antenna, means for
recording the position of the dipole with respect to the antenna, a telemetry
transmitter coupled to said receiving means, and a telemetry receiving and
recording arrangement having a recording device adapted to co-ordinate and
record the amplitude of the signal and the position of the dipole to permit
the derivation of the radiation pattern directly from said recording device.
In accordance with another aspect of this invention there is
provided a method of determining the radiation pattern of an antenna com-
prising the steps of transmitting a signal from the antenna, receiving the
signal with an elementry dipole coupled to a receiving means adapted to detect
the amplitude of the signal and moved in a determined manner about the antenna,
recording the position of the dipole with respect to the antenna, transmit-
ting the amplitude of said signal from a telemetry transmitter coupled to the
receiving means to a telemetry receiving and recording system having a recor-
ding device, co-ordinating and recording on said device the amplitude of the
signal and the position of the dipole and deriving the radiation pattern
directly from the recording device.
Reference should be had to the drawings which are as follows:-
Figure 1 is a schematic of the RELEDOP, or receiving elementarydipole with optional polarity;
Figure 2 is a sketch of the configuration employed during measure-
ment of the antenna radiation pattern;
Figure 3 is a block diagram of the total system configuration;
Figure 4 is a block diagram of the telemetry receiving and record-
ing arrangement.
1067ZOZ
Referring to Figure 1 it can be seen that a preferredembodiment of the RELEDOR, generally indicated at 20, is
comprised of a 6 foot dipole antenna 10,10' ~ith end spheres
12,12' connected to a receiver (not shown), housed in a fiberglass
spherical chamber 14, having a diameter of six inches. The
spherical chamber 14 is connected to a towing rope 15 by the use
of a FIBERGLAS (trade mark) bridle 16. This allows for adjust-
ment and orientation of the dipole antenna.
Referring to Figure 2, it can be seen that the receiver
and dipole are towed as part of a flight package 20 behind an
aircraft 21, which flies, for the most part, in a circular pattern
at a fixed distance from the antenna 25 at various altitudes.
The dipole can be oriented to accept either vertical or
horizontal polarized signals. A departure from this normal
flight plan is necessarily made to obtain the vertical pattern
of the antenna. The aircraft in this case flies over the
antenna in straight lines at a constant altitude. ~ radar 26,
which can be deployed adjacent to the antenna 25, is used to
measure the position of the aircraft, and consequently, of the
flight package. This information is recorded with time markers,
and the information i5 subsequently analyzed in order to derive
direct readings from the ultimate recording mechanism.
Figure 3 represents a block diagram of the flight
package 20, which comprises the dipole and receiYer. Each
half 10,10' of the six foot dipole antenna is connected to the
high impedance input of a push-pull preamplifier 30. The
output of the preamplifier 30 is stepped down to 50 ohms and fed
into a balanced mixer 31. The signals are then mixed with the
output of a high frequency oscillator 33, and amplified by an
IF amplifier 35. Detection of the signal takes place in the
~ ~ 4
106720Z
linear detector and the output of the linear detector 36 controls
the frequency of the linear voltage controlled oscillator 37
output which in turn modulates the slgnal transmitted by the
telemetry trans~ltter 38. The telemetry transmitter 38 can be
an FM telemetr~ trans~itter. The overall ~oltage gain of the
receiver is in the order of 70 dB.
-4a-
1067ZOZ
Referring to Figure 4, there is shown a blo~k diagram of the tele-
metry receiving and recording arrangement, having a recording device, such as
a chart recorder 40. The audio output of the telemetry receiver 41 drives a
frequency to voltage converter 42 whose output is displayed on the chart
recorder 40. The time markers are also recorded in the chart recorder 40,
and are correlated with the radar fixes recorded during the measurement
interval. Since the linearity of the system is maintained from the input of
the RELEDOP receiver to the output of the telemetry receiver 41 and frequency
to voltage converter 42, the pattern of the antenna can be derived directly
from the chart recorder 40.
