Note: Descriptions are shown in the official language in which they were submitted.
CA 02389161 2002-04-26
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STEERABLE-BEAM MULTIPLE-FEED DIELECTRIC RESONATOR
ANTENNA OF VARIOUS CROSS-SECTIONS
This invention relates to dielectric resonator antennas with steerable receive
and
transmit beams and more particularly to an antenna having several separate
feeds
such that several separate beams can be created simultaneously and combined as
desired, the dielectric resonator antenna including a dielectric resonator of
various
different cross-sections.
Since the first systematic study of dielectric resonator antennas (DRAB) in
1983
[LONG, S.A., McALLISTER, M.W., and SHEN, L.C.: 'The resonant cylindrical
dielectric cavity antenna', IEEE Trans. Antennas Propagat:, AP-31, 1983, pp
406-
412], interest has grown in their radiation patterns because of their high
radiation
efficiency, good match to most commonly used transmission lines and their
small
physical size [MONGIA, R.K. and BHARTIA, P.: 'Dielectric resonator antennas -
A
review and general design relations for resonant frequency and bandwidth',
Int. J.
Microwave & Millimetre Wave Computer-Aided Engineering, 1994, 4, (3), pp 230-
247]. Most configurations reported have used a slab of dielectric material
mounted
on a ground plane excited by either an aperture feed in the ground plane or by
a
probe inserted into the dielectric material. A few publications have reported
on
experiments using two probes fed simultaneously in a circular dielectric slab.
These
probes were installed on radials at 90° to each other and fed in anti-
phase so as to
create circular polarisation [MONGIA, R.K., ITTIPIBOON, A., CUHACI, M. and
ROSCOE D.: 'Circular polarised dielectric resonator antenna', Electron. Lett.,
1994,
30, (17), pp 1361-1362; and DROSSOS, G., WU, Z. and DAVIS, L.E.: 'Circular
polarised cylindrical dielectric resonator antenna', Electron. Lett., 1996,
32, (4), pp
281-283.3, 4] and one publication included the concept of switching probes on
and
off [DROSSOS, G., WU, Z. and DAVIS, L.E.: 'Switchable cylindrical dielectric
resonator antenna', Electron. Lett., 1996, 32, (10), pp 862-864].
One method of electronically steering an antenna pattern is to have a number
of
existing beams and to switch between them, or to combine them so as to achieve
the
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desired beam direction. A circular DRA may be fed by a single probe or
aperture
placed in or under the dielectric and tuned to excite a particular resonant
mode. In
preferred embodiments, the fundamental HEMIS mode is used, but there are many
other resonant modes which produce beams that can be steered equally well
using the
apparatus of embodiments of the present invention. The preferred HEMIis mode
is a
hybrid electromagnetic resonance mode radiating like a horizontal magnetic
dipole
and giving rise to vertically polarised cosine or figure-of eight shaped
radiation
pattern [LONG, S.A., McALLISTER, M.W., and SHEN, L.C.: 'The resonant
cylindrical dielectric cavity antenna', IEEE Trans. Antennas Propagat., AP-31,
1983,
pp 406-412]. Modelling by the present Applicants of cylindrical DRAs by FDTD
(Finite Difference Time Domain) and practical experimentation has shown that
if
several such probes are inserted into the dielectric and one is driven whilst
all the
others are open-circuit then the beam direction can be moved by switching
different
probes in and out. Furthermore, by combining feeds in different ways, sum and
difference patterns can be produced which allow continuous beam-steering and
direction fording by amplitude-comparison, monopulse or similar techniques.
Many of these results are described in the present inventors' co-pending US
patent
application serial no 09/431,548 and in the paper KINGSLEY, S.P. and O'KEEFE,
S.G., "Beam steering and monopulse processing of probe-fed dielectric
resonator
antennas", S P Kingsley and S G O'Keefe, IEE proceedings - Radar Sonar and
Navigation, 146, 3, 121 - 125, 1999, the disclosures of which are incorporated
into
the present application by reference.
It has been noted by the present applicants that the results described in the
above
reference apply equally to DRAs operating at any of a wide range of
frequencies, for
example from 1 MHz to 100,000 MHz and even higher for optical DRAs. The
higher the frequency in question, the smaller the size of the DRA, but the
general
beam patterns achieved by the probe/aperture geometries described hereinafter
remain generally the same throughout any given frequency range. Operation ax
frequencies substantially below lMHz is possible too, using dielectric
materials with
a high dielectric constant.
2
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The concept of hemispherical dielectric resonator antennas is known from
[McALLISTER, M.W. & LONG, S.A.: "Resonant hemispherical dielectric antenna",
Electronics Letters, 1984, 20, (16), pp 6~7-659; MONGIA, R.K. and BHARTIA, P.:
"Dielectric Resonator Antennas - A Review and General Design Relations for
Resonant Frequency and Bandwidth", International Journal of Microwave and
Millimetre-Wave Computer-Aided Engineering, 1994, 4, (3), pp 230-247; and
KISHK, A.A., ZHOU, G. & GLISSON, A.W.: "Analysis of dielectric resonator
antennas with emphasis on hemispherical structures", IEEE Antennas Propag.
Mag.,
1994, 36, pp 20-31]. These references make no mention of hemispherical
dielectric
resonator antennas with a plurality of probes or steerable receive and
transmit beams.
A hemispherical dielectric resonator antenna has the advantage of a simple
spherical
interface between itself and free space [LEUNG, K.W., LUK, K.M., LAI, K.Y.A. &
LIN, D.: "Theory and experiment of a co-axial probe fed hemispherical
dielectric
resonator antenna", IEEE Transactions on Antennas and Propagation, AP-41,
1993,
pp 1390-1398] and of being capable of being rigorously analysed which
simplifies
design procedures [LEUNG, K. W., NG, K. W. LUK, K.M. & YUNG, E.K.N.,
"Simple formula for analysing the centre-fed hemispherical dielectric
resonator
antenna", Electronics Letters, 1997, 33, (6)].
According to a first aspect of the present invention, there is provided a
dielectric
resonator antenna including a grounded substrate, a dielectric resonator
disposed on
the grounded substrate and a plurality of feeds for transferring energy into
and from
different regions of the dielectric resonator, the feeds being activatable
individually
or in combination so as to produce at least one incrementally or continuously
steerable beam which may be steered through a predetermined angle,
characterised in
that the dielectric resonator has a cross-section that varies along an axis
extending
substantially perpendicularly from the grounded substrate.
3
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It will be appreciated that where the grounded substrate is other than
substantially
planar, then the axis may be defined as substantially perpendicular to a plane
which
is tangential to a surface of the grounded substrate at a point from where the
axis is
taken. The cross-section may vary in size or in shape or in both size and
shape along
the axis.
Advantageously, the dielectric resonator antenna includes electronic circuitry
adapted to activate the feeds individually or in combination so as to produce
at least
one incrementally or continuously steerable beam which may be steered through
a
predetermined angle.
In a first embodiment, the dielectric resonator has the form of a cone or a
truncated
cone. The cone may be a right cone or a non-right cone, and may be configured
such
that its cross-section increases or decreases in area along the axis. In
comparison to a
dielectric resonator antenna including a resonator of constant cross-section,
such
conical resonators may have increased bandwidth and, in the case of non-right
conical resonators, may allow a generated beam pattern to vary about the axis.
In a second embodiment, the dielectric resonator has the form of a pyramid or
a
truncated pyramid. The pyramid may be a right pyramid or a non-right pyramid,
and
may be configured such that its cross-section increases or decreases in area
along the
axis. The pyramid may be a 3-pyramid, a 4-pyramid, a 5-pyramid or an n-
pyramid,
where n is a positive integer. In comparison to a dielectric resonator antenna
including a resonator of constant cross-section, such pyramidal resonators may
have
increased bandwidth and, in the case of non-right conical resonators, may
allow a
generated beam pattern to vary about the axis. Furthermore, it has been found
that an
oblong resonator has two resonant frequencies associated with the dimensions
of the
two differently-sized sides. Accordingly, it is expected that a resonator
having a
greater number of differently-sized sides will have a greater number of
resonant
frequencies. These resonant frequencies may be selected to be closely spaced
so as ,
to increase bandwidth, or to be widely spaced so as to permit operation in
different
frequency bands.
4
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In a third embodiment, the dielectric resonator has the form of a stepped cone
or
pyramid or a truncated stepped cone or pyramid. The term 'stepped' is here
intended
to mean a structure of generally conical or pyramidal shape having a surface
which is
not even, such as a Tower of Hanoi structure corresponding in external shape
to a
stack of discs of diminishing diameter. The stepped cone or pyramid may be a
right
stepped cone or pyramid or a non-right stepped cone or pyramid, and may be
configured such that its cross-section increases or decreases in area along
the axis. In
comparison to a dielectric resonator antenna including a resonator of constant
cross-
section, such stepped conical or pyramidal resonators may have increased
bandwidth
and, in the case of non-right stepped conical or pyramidal resonators, may
allow a
generated beam pattern to vary about the axis.
In a fourth embodiment, the dielectric resonator is generally dome shaped or
has the
form of a sphere or a portion of a sphere. For example, the resonator may be
substantially spherical, hemispherical, semihemispherical,
semidemihemispherical or
the like. Alternatively, the resonator may have the form of an arbitrary
segment of a
sphere. Such shapes allow beamsteering in three-dimensions from the curved
surface portion of the resonator.
A substantially spherical resonator may be made up of two substantially
hemispherical resonator elements, each contacting a grounded substrate and fed
by
monopole feeds. The hemispherical elements may be joined together on either
side
of a shared grounded substrate so as to make a substantially spherical
resonator, or
may each be provided with a separate grounded substrate at their base portions
and
then placed close to each other so as to make a substantially spherical
resonator.
A further advantage of these embodiments is that rounded resonators tend to be
shaped more aerodynamically than, say, a cylindrical resonator, which is
advantageous when a dielectric resonator antenna is to be mounted on an outer
surface of an aircraft, for example.
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In a fifth embodiment, the dielectric resonator is amorphous, i.e. of
irregular or
indeterminate shape. For example, the resonator may be formed as an amorphous
mass of dielectric gel or other appropriate dielectric material such as a
plastics
material. Subject to operating requirements, such an amorphous resonator may
be
moulded as part of a structure such as a casing for a mobile telephone or
other
communications device.
In a sixth embodiment, the dielectric resonator is annular with a hollow
centre (in the
manner of a "Gugelhupf' cake, which has a generally toroidal structure having
an
overall dome-shaped profile). Such a structure may be substantially lighter
and use
less dielectric material than a solid dielectric resonator. The resonator may
have a
base perimeter which is circular, oval or any other appropriate shape. As with
the
previously discussed embodiments, geometries of non-circular cross-section
generally confer the advantage of broad bandwidth operation.
According to a second aspect of the present invention, there is provided a
dielectric
resonator antenna including a grounded substrate, a dielectric resonator
disposed on
the grounded substrate and a plurality of feeds for transfernng energy into
and from
different regions of the dielectric resonator, the feeds being activatable
individually
or in combination so as to produce at least one incrementally or continuously
steerable beam which may be steered through a predetermined angle,
characterised in
that the dielectric resonator has a non-circular cross-section.
Advantageously, the dielectric resonator antenna includes electronic circuitry
adapted to activate the feeds individually or in combination so as to produce
at least
one incrementally or continuously steerable beam which may be steered through
a
predetermined angle.
The dielectric resonator may have a substantially oval cross-section, a
regular or
irregular polygonal cross-section, a lobed cross-section, or any other
appropriate
non-circular cross-section. These cross-sections generally allow the
dielectric
resonator to be lighter and to use less dielectric material than an equivalent
size
6
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cylindrical resonator of truly circular cross-section. Non-circular cross-
sections
generally also provide better bandwidth and, when constructed in segmented
form,
may have low backlobes in predetermined directions. The cross-section of the
dielectric resonator may be substantially constant along an axis extending
substantially perpendicularly from the grounded substrate or may vary. either
in size
or in shape or in both size and shape.
According to a third aspect of the present invention, there is provided a
dielectric
resonator antenna including a dielectric resonator and at least one dipole
feed for
transferring energy into and from the dielectric resonator, the dipole feed
having a
longitudinal axis and being activatable so as to produce at least one
incrementally or
continuously steerable beam which may be steered through a predetermined
angle,
characterised in that the dielectric resonator has a cross-section that varies
along an
axis extending substantially parallel to the axis of the dipole feed.
The dielectric resonator may be in the form of a substantially solid sphere of
a
dielectric material which is fed by at least. one and preferably more than one
dipole
probe and which does not need a grounded substrate. Such a resonator enables
three-
dimensional coverage over the whole sphere since there is no groundplane.
Indeed, a
dipole feed may be used to drive any shape of dielectric resonator without the
need
for a grounded substrate. Where monopole feeds and a grounded substrate are
used,
the grounded substrate acts as a mirror plane in which the dielectric
resonator sees its
mirror image. An equivalent dielectric resonator antenna may be manufactured
by
providing a dielectric resonator having a shape corresponding to the shape of
the
monopole feed embodiment and its image as reflected in the plane of the
grounded
substrate. As stated above, there is then no need for a grounded substrate in
the
dipole feed embodiment. In general, however, the monopole feed embodiment is
preferred, since it is easier to use a monopole feed inserted into a half
shape
dielectric resonator disposed on a grounded substrate than it is to embed a
dipole
probe and feed cable within a whole shape dielectric resonator.
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The substantially spherical dielectric resonator will generally be made up of
two
hemispherical portions which are stuck together so as to sandwich the at least
one
dipole feed between base portions thereof.
According to a fourth aspect of the present invention, there is provided a
dielectric
resonator antenna including a dielectric resonator and at least one dipole
feed for
transferring energy into and from different regions of the dielectric
resonator, the
dipole feed being activatable so as to produce at least one incrementally or
continuously steerable beam which may be steered through a predetermined
angle,
characterised in that the dielectric resonator has a non-circular cross-
section.
The dipole feed preferably has a longitudinal axis, and the cross-section of
the
dielectric resonator is preferably defined as being substantially
perpendicular to that
axis.
It will be appreciated that equivalents to any of the dielectric resonator
shapes
described above in relation to the grounded substrate embodiment may be made
with
the dipole embodiment by providing a dielectric resonator equivalent in shape
to that
of the grounded substrate embodiment together with its reflection in the plane
of the
grounded substrate.
In all of the embodiments described above, the dielectric resonator may be
substantially solid or may alternatively include at least one cavity therein.
In some
applications, the dielectric resonator may be in the form of a hollow shell of
the
2~ desired shape.
Advantageously, the antenna of the present invention is adapted to produce at
least
one incrementally or continuously steerable beam which may be steered through
a
complete 360 degree circle.
s
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Advantageously, there is additionally or alternatively provided electronic
circuitry to
combine the feeds to form sum and difference patterns to permit radio
direction
finding capability of up to 360 degrees.
The electronic circuitry may additionally or alternatively be adapted to
combine the
feeds to form amplitude or phase comparison radio direction finding capability
of up
to 360 degrees.
Preferably, radio direction finding capability is a complete 360 degree
circle.
The feeds may take the form of conductive probes which are contained within or
placed against the dielectric resonator or may comprise aperture feeds
provided in
the grounded substrate (these are not appropriate for the dipole embodiment).
Aperture feeds are discontinuities (generally rectangular in shape) in the
grounded
substrate underneath the dielectric material and are generally excited by
passing a
microstrip transmission line beneath them. The microstrip transmission line is
usually printed on the underside of the substrate. Where the feeds take the
form of
probes, these may be generally elongate in form. Examples of useful probes
include
thin cylindrical wires which are generally parallel to a longitudinal axis of
the
dielectric resonator. Other probe shapes that might be used (and have been
tested)
include fat cylinders, non-circular cross sections, thin generally vertical
plates and
even thin generally vertical wires with conducting 'hats' on top (like
toadstools).
Probes may also comprise metallised strips placed within or against the
dielectric. In
general any conducting element within or against the dielectric resonator will
excite
resonance if positioned, sized and fed correctly. The different probe shapes
give rise
to different bandwidths of resonance and may be disposed in various positions
and
orientaxions (at different distances along a radius from the centre and at
different
angles from the centre, as viewed from above) within or against the dielectric
resonator so as to suit particular circumstances.
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Where more than feed is provided. different feeds can be driven at different
frequencies so as to make the antenna transmit or receive simultaneously in
different
predetermined directions (e.g. azimuth and in elevation) at the different
frequencies.
Furthermore, there may be provided probes within or against the dielectric
resonator
which are not connected to the electronic circuitry but instead take a passive
role in
influencing the transmit/receive characteristics of the dynamic resonator
antenna, for
example by way of induction.
In one embodiment of the present invention, the dielectric resonator may be
divided
into segments by conducting walls provided therein, as described, for example,
in
TAM, M.T.K. AND MURCH, R.D., 'Compact circular sector and annular sector
dielectric resonator antennas', IEEE Trans. Antennas Propagat., AP-47, 1999,
pp
837-842.
In a further embodiment of the present invention, there may additionally be
provided
an internal or external monopole antenna which is combined with the dielectric
resonator antenna so as to cancel out backlobe fields or to resolve any
front/back
ambiguity which may occur with a dielectric resonator antenna having a cosine
or
'figure of eight' radiation pattern. The monopole antenna may be centrally-
disposed
within the dielectric resonator or may be mounted thereupon or therebelow and
is
activatable by the electronic circuitry. In embodiments including an annular
resonator with a hollow centre, the monopole could be located within the
hollow
centre. A "virtual" monopole may also be formed by the electrical or
algorithmic
combination of any probes or apertures, preferably a symmetrical set of probes
or
apertures.
The dielectric resonator antenna and antenna system of the present invention
may be
operated with a plurality of transmitters or receivers, these terms here being
used to
denote respectively a device acting as source of electronic signals for
transmission by
way of the antenna or a device acting to receive and process electronic
signals
communicated to the antenna by way of electromagnetic radiation. The number of
CA 02389161 2002-04-26
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transmitters and/or receivers may or may not be equal to the number of feeds
to the
dielectric resonator. For example, a separate transmitter and/or receiver may
be
connected to each feed (i.e. one per feed), or a single transmitter and/or
receiver to a
single feed (i.e. a single transmitter and/or receiver is switched between
feeds). In a
further example, a single transmitter and/or receiver may be (simultaneously)
connected to a plurality of feeds - by continuously varying the feed power
between
the feeds the beam and/or directional sensitivity of the antenna may be
continuously
steered. A single transmitter and/or receiver may alternatively be connected
to
several non-adjacent feeds to the dielectric resonator, thereby enabling a
significant
increase in bandwidth to be attained as compared with a single feed (this is
advantageous because DRAs generally have narrow bandwidths). In yet another
example, a single transmitter and/or receiver may be connected to several
adjacent or
non-adjacent feeds in order to produce an increase in the generated or
detected
radiation pattern, or to allow the antenna to radiate or receive in several
directions
simultaneously.
The dielectric resonator may be formed of any suitable dielectric material, or
a
combination of different dielectric materials, having an overall positive
dielectric
constant k; in preferred embodiments, k is at least 10 and may be at least 50
or even
at least 100. k may even be very large e.g. greater than 1000, although
available
dielectric materials tend to limit such use to low frequencies. The dielectric
material
may include materials in liquid, solid or gas states, or any intermediate
state. The
dielectric material could be of lower dielectric constant than a surrounding
material
in which it is embedded.
By seeking to provide a dielectric resonator antenna capable of generating
multiple
beams which can be selected separately or formed simultaneously and combined
in
different ways at will, embodiments of the present invention may provide the
following advantages:
i) By choosing to drive different probes or apertures, the antenna can be made
to transmit or receive in one of a number of preselected directions (in
azimuth, for
CA 02389161 2002-04-26
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example). By sequentially switching round the probes or apertures the beam
pattern
can be made to rotate incrementally in angle. Such beam-steering has obvious
applications for radio communications, radar and navigation systems.
ii) By combining two or more beams together, i.e. exciting two or more probes
or apertures simultaneously, beams can be formed in any arbitrary azimuth
direction,
thus giving more precise control over the beamforming process.
iii) By electronically continuously varying the power division /combination
between two beams. the resultant combination beam direction can be steered
continuously.
iv) On receive-only, the direction of arrival of an incoming radio signal can
be
found by comparing the amplitude of the signal on two or more beams, or by
carrying out monopulse processing of the signal received on two beams.
'Monopulse
processing' refers to the process of forming sum and difference patterns from
two
beams so as to determine the direction of arrival of a signal from a distant
radio
source.
v) In a typical two-way communication system (such as a mobile telephone
system) signals are received (by a handset) from a point radio source (such as
a base
station) and transmitted back to that source. Embodiments of the present
invention
may be used to find the direction of the source using step iii) above and may
then
form an optimal beam in that direction using step ii). An antenna capable of
performing this type of operation is known as a 'smart' or 'intelligent'
antenna The
advantages of the maximum antenna gain offered by smart antennas is that the
signal
to noise ratio is improved, communications quality is improved, less
transmitter
power may be used (which can, for example, help to reduce irradiation of any
nearby
human body) and battery life is conserved.
1?
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vi) The addition of an internal or external monopole antenna can be used to
null
out the backlobe of the antenna, thereby reducing the irradiation of a person
near the
device, or to resolve front/back ambiguities in radio direction fording.
vii) By choosing to drive different feeds (probes or apertures) at different
frequencies, the antenna can be made to transmit or receive simultaneously in
one
predetermined direction (in azimuth, for example) on one frequency in other
predetermined directions on other frequencies.
For a better understanding of the present invention and to show how it may be
carried into effect, reference shall now be made by way of example to the
accompanying drawings, in which:
FIGURE 1 a is a top view of an existing mufti-feed dielectric resonator
antenna using
probe feeds;
FIGURE lb is a side view of the mufti-feed dielectric resonator antenna of
Figure la;
FIGURE 2a is a top view of an existing mufti-feed dielectric resonator antenna
using
aperture feeds;
FIGURE 2b is a side view of the mufti-feed dielectric resonator antenna of
Figure 2a;
FIGURE 3a is a top view of an existing mufti-probe dielectric resonator
antenna with
the addition of a central monopole;
FIGURE 3b is a side view of the mufti-probe dielectric resonator of Figure 3a;
FIGURES 4 to 7 show measured azimuth radiation patterns for the antenna of
Figures la and lb as various combinations of probes are driven;
13
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FIGURE 8 shows a measured azimuth radiation pattern for the antenna of Figures
3a
and 3b as it is simultaneously driven with a monopole antenna;
FIGURE 9a is a side view of a generalised multi-feed hemispherical dielectric
resonator antenna of the present invention using probe feeds;
FIGURE 9b is a top view of the multi-feed hemispherical dielectric resonator
antenna of Figure 9a;
FIGURE 10 shows measured azimuth radiation patterns for the antenna of Figures
9a
and 9b for probes 7a, 7c, and 7a and 7c simultaneously;
FIGURE 11 a is a side view of a generalised multi-feed hemispherical
dielectric
resonator antenna of the present invention using probe feeds and a central
monopole
antenna;
FIGURE I 1 b is a top view of the mufti-feed hemispherical dielectric
resonator
antenna of Figure 11 a;
FIGURE 12a is cross-sectional view on a segmented mufti-feed dielectric
resonator
antenna made up of four lobes;
FIGURE 12b is a cross-sectional view on a dielectric resonator antenna formed
from
a single lobe of the Figure 12a embodiment;
FIGURE 13 shows the measured azimuth pattern for a single lobe of the
dielectric
resonator antenna of Figure 12;
FIGURES 14 to 17 show various spherical and hemispherical dielectric resonator
antennas according to the present invention; and
1~
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FIGURE 18 shows various shapes of dielectric resonator that may be used in the
present invention.
Figures 1 to 8 relate mainly to a dielectric resonator antenna having a
cylindrical
shape as described, for example, in co-pending US patent application serial no
09/431,548 from which the present application claims priority.
Referring now to Figures la and 1b, there is shown a substantially circular
slab of
dielectric material 1 which is disposed on a grounded substrate. 2 having a
plurality
of holes to allow access by cables and connectors to a plurality of internal
probes 3a
to 3h. The probes 3a to 3h are disposed along radii at different internal
angles.
Figures 2a and 2b show a substantially circular slab of dielectric material I
which is
disposed on a grounded substrate 2 having a plurality of aperture feeds 3a to
3h
1 S disposed along radii at different internal angles. The aperture feeds are
fed by
microstrip transmission lines 4.
Figures 3a and 3b show side plan and side views respectively, as for Figures
la and
1b, but with the addition of a central monopole antenna 4(i) above the
dielectric slab
1 used to cancel out the backlobe or resolve the front/back ambiguity that
occurs
with dynamic resonator antennas having cosine or 'figure of eight radiation'
patterns.
In Figure 3 the monopole 4(i) is shown as an external device above the
dielectric slab
1, but a central probe 4(ii) within the dielectric slab 1 will also act as a
suitable
monopole reference antenna, as will a central probe 4(iii) below the slab 1.
The basic concept for a multiple-beam dielectric resonator antenna using a
plurality
of feeds is given by the present Applicants in the paper KINGSLEY, S.P. and
O'KEEFE, S.G., "Beam steering and monopulse processing of probe-fed dielectric
resonator antennas", S P Kingsley and S G O'Keefe, IEE proceedings - Radar
Sonar
and Navigation, 146, 3, 121 - 125, 1999. This paper confirms by practical
experimentation the present Applicants' FDTD simulation results that multiple-
feed
CA 02389161 2002-04-26
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operation is possible and that the feeds do not mutually interact electrically
in any
significant way that prevents the formation of several beams simultaneously.
Since the publication of this paper an 8-probe circular dielectric resonator
antenna,
having the form shown in Figures 1 a and 1 b has been constructed and tested.
In a
further development, an 8-probe circular dielectric resonator antenna with an
external
monopole antenna, having the form shown in Figs 3a & 3b, has also been
constructed and tested.
In Figures 4-$, the circular lines represent power steps of 5 dB (decibels)
and the
arrow shows the direction of the principal beam direction or 'boresight'. The
radial
lines represent the angle of the beam; this being the azimuth direction when
the
antenna is placed on a horizontal plane.
Results are given here for a cylindrical dielectric resonator antenna fitted
with 8
internal probes 3a to 3h disposed in a circle. When probe 3a is driven (in
either
transmit or receive mode) and the remaining probes 3b to 3h are open-circuited
or
otherwise terminated, but not connected to the feed, then the measured azimuth
radiation pattern shown in Figure 4 is obtained.
When probe 3b is connected instead of probe 3a, the measured azimuth radiation
pattern is as shown in Figure 5. It can be seen that the beam has been steered
incrementally by roughly the same angle as the probes are disposed internally
(45
degrees in this case).
When probes 3a and 3b are driven simultaneously with equal power from a single
source, using a power splitter/divider or similar power sharing device and
with the
remaining 6 probes open-circuited, the resulting measured azimuth radiation
pattern
is as shown in Figure 6. It can be seen that the beam has been steered roughly
to an
angle between the angles by which the probes are disposed internally (22.5
degrees
in this case). This method can be used to continuously steer the beam by
continuously varying the feed power being shared between probes. For example,
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where the power splitter is operated in such a way so as incrementally to
transfer
power from probe 3a to 3b, the direction of the transmitted or received beam
will be
steered correspondingly in proportion to the transfer of power. As the entire
azimuth
radiation pattern rotates with the beam, the direction of any nulls also
changes in a
corresponding fashion. In many applications (e.g. missile tracking) it is the
null or
nulls which are used rather than the beam or beams, particularly since
antennas of
this type can be made to have deep nulls.
If probes 3b and 3h are driven simultaneously with the remaining 6 probes
being
open-circuited, this should produce an azimuth radiation pattern with a
boresight
(that is, a direction of maximum radiation on transmit, or a direction of
maximum
sensitivity on receive) in the same direction as probe 3a (probes 3b and 3h
being
disposed in angle either side of probe 3a). Figure 7 is an experimental result
that
confirms this. The advantage of feeding two probes this way is that a
significant
increase in bandwidth can be obtained compared obtained with a single probe.
It can be seen that the patterns of Figures 4 to 7 have a significant
backlobe, being
substantially cosine (figure-of eight) shaped in form. When transmitting in a
given
direction this implies a loss of power, when receiving this implies a loss of
sensitivity
and when direction finding there is a front-to-back ambiguity. The addition of
a
central internal or external monopole 4, as shown in Figures 3a and 3b, can be
used
to resolve the ambiguity or, by driving the monopole 4 and one or more of the
dielectric resonator steering probes 3 simultaneously, the backlobe can be
significantly reduced. This is shown experimentally by the measurements in
Figure
8, where probes 3e and 3f and the monopole 4 are driven. It is possible to
choose
whether to cancel out or reduce either the backlobe or a corresponding front
lobe by
driving the monopole either in phase or in antiphase with the probes 3.
Referring now to Figures 9a and 9b, there is shown a slab of dielectric
material 5,
substantially hemispherical in cross-section, which is disposed on a grounded
substrate 6 having a plurality of holes to allow access by cables and
connectors to a
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plurality of internal probes 7a to 7f. The probes 7a to 7f are disposed along
radii at
different internal angles.
In Figure 10, the circular lines represent power steps of 5 dB (decibels) and
the
arrows show the direction of the principal beam directions or "boresights". It
can be
seen that the pattern for probes A and C separately are disposed roughly 120
degrees
in angle from each other and that the pattern for probes A and C excited
simultaneously represents a new beam, formed electronically, with a boresight
roughly half way between the two separate probe patterns.
Results for an example of the present invention are given here using a
hemispherical
dielectric resonator antenna fitted with internal probes. When probe 7a is
driven (in
either transmit or receive mode) and the remaining probes are open-circuited
or
otherwise terminated but not connected to the feed, then the measured azimuth
radiation pattern labelled 'Probe A' in Figure 10 is obtained.
When probe 7c is connected instead of probe 7a, the measured azimuth radiation
labelled 'Probe C' in Figure 10 is obtained. It can be seen that the beam has
been
steered incrementally by roughly the same angle as the probes are disposed
internally
(120 degrees in this case).
When probes 7a and 7c are driven simultaneously from a single source, using a
power splitter/divider or similar power sharing device, and with the remaining
probes
open-circuited, the resulting measured azimuth radiation pattern is as
radiation
labelled 'Probe A&C' in Figure 10. It can be seen that the beam has been
steered by
roughly the angle bisecting the probes (60 degrees in this case). This method
can be
used to steer the beam continuously by continuously varying the feed power
being
shared between probes.
It can be seen that the patterns of Figure 10 have a significant backlobe,
being
substantially cosine (figure-of eight) shaped in form. When transmitting, this
implies a loss of power in the desired direction and the possibility of
causing
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interference in the opposite direction. When receiving, this implies a loss of
sensitivity in the desired direction and the possibility of suffering
interference from
the opposite direction. When direction finding, there is a front-to-back
ambiguity.
The addition of a central internal or external monopole 8, as shown in Figures
l la
and 1 1b, can be used to resolve this ambiguity or, by driving the monopole 8
and one
or more of the dielectric resonator steering probes 7 simultaneously, the
backlobe can
be significantly reduced.
Figure 12a shows a cross-section through an embodiment of the present
invention
comprising a dielectric resonator 10 having a four-lobe cross-section, the
cross-
section being reminiscent of a four-leaf clover. The resonator 10 is disposed
on a
grounded substrate 12, and includes probes 13a, 13b, 13c and 13d, one in each
lobe
11. The radiation patterns of this device are essentially cosine patterns of
the type
already shown in Figures 4 and 5.
This structure may be divided into segments and a single segment version is
shown
in Figure 12b, which depicts a grounded substrate 12 and one lobe 11 of the
dielectric resonator 10 of Figure 12a, the lobe 11 being driven by a probe
13a. The
lobe 11 is shown as bounded by generally vertical conducting walls 14, which
are
disposed at substantially 90° to each other. The advantage of such a
single-probe
quarter 'cloverleaf antenna is that when the probe 13a is driven, the measured
azimuth radiation of Figure 13 is obtained. The radiation frequency is 1378MHz
at a
bandwidth of 169MHz, and it can be seen that there is a significant reduction
in
backlobe in the direction from the probe 13a towards the centre of the
dielectric
resonator 10.
Figure 14 shows a solid spherical dielectric resonator 15 incorporating a
dipole feed
16, thus obviating the need for a grounded substrate. This resonator 15 gives
full
beamforming coverage in all directions about the sphere.
Figure 15 shows a solid hemispherical dielectric resonator 16 disposed on a
grounded substrate 17 and incorporating a monopole feed probe 18.
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Figure 16 shows two solid hemispherical dielectric resonators 16 each provided
with
a monopole probe 18 and mounted back-to-back on either side of a shared
grounded
substrate 17. As with the embodiment of Figure 14, full beamforming coverage
is
provided in all directions.
Figure 17 shows two solid hemispherical dielectric resonators 16 each provided
with
a monopole probe 18 and each provided with a separate grounded substrate 17.
The
respective resonators 16 are then placed back-to-back such that the grounded
substrates face each other but do not touch, the overall shape of the
composite
resonator being substantially spherical.
Finally, Figure 18 shows representations of the various shapes of dielectric
resonator
which are used in the present invention, including: right conical 20; non-
right conical
21; truncated 22; non-truncated 23; stepped 24; non-stepped 25; non-circular
cross-
section 26; conical 27; pyramidal 28, 29; domed 30; spherical 31; part-
spherical 32;
amorphous 33; toroidal 34, 35; solid 36; cavity 37; hollow shell 38; oval
cross-
section 39; regular polygonal cross-section 40; irregular polygonal cross-
section 41;
lobed cross-section 42; and non-constant cross-section 43.
