MICROSTRIP PATCH RADIATOR WITH MEANS FOR THE SUPPRESSION OF CROSS-POLARIZATION

RESEAU RAYONNANT A MICRORUBAN AVEC DISPOSITIF POUR LA SUPPRESSION DE LA POLARISATION CROISEE

English Abstract

A dual polarized microstrip patch radiator
comprising a ground plane, a thin layer of dielectric on
each side thereof, a conductive microstrip patch on a
first of the dielectric layers on a side remote from the
ground plane, first and second feed lines on the side of
the second dielectric layer remote from the ground
plane, first and second pairs of apertures in the ground
plane the second pair of apertures being orthogonal to
the first pair of apertures, the first feed line being
radiatively coupled to one of the first pair of
apertures and not radiatively coupled to the other
aperture of the first pair of apertures nor to the
second pair of apertures, the second feed line being
radiatively coupled to one of the apertures of the
second pair of apertures and not radiatively coupled to
the other of the second pair of apertures nor to the
first pair of apertures, the other aperture of the first
pair of apertures being positioned to provide a
symmetrical boundary condition for power coupled from
the second feed line, and the other aperture of the
second pair of apertures being positioned to provide a
symmetrical boundary condition for power coupled from
the first feed line, whereby cross-polarization of the
feeds is minimized.

French Abstract

Un réseau rayonnant à microruban à double polarisation comprend un plan de masse, une mince couche de diélectrique de chaque côté de ce dernier, un microruban conducteur sur une première couche diélectrique, du côté éloigné du plan de masse, une première et une deuxième lignes d'alimentation sur le côté de la deuxième couche diélectrique éloigné du plan de masse, une première et une deuxième paires d'ouvertures dans le plan de masse, la deuxième paire d'ouvertures étant perpendiculaire à la première paire d'ouvertures, la première ligne d'alimentation étant couplée par rayonnement à l'une des ouvertures de la première paire d'ouvertures et non couplée par rayonnement à l'autre ouverture de la première paire d'ouvertures ni à la deuxième paire d'ouvertures, la deuxième ligne d'alimentation étant couplée par rayonnement à l'une des ouvertures de la deuxième paire d'ouvertures et non couplée par rayonnement à l'autre ouverture de la deuxième paire d'ouvertures ni à la première paire d'ouvertures, l'autre ouverture de la première paire d'ouvertures étant placée de façon à fournir une frontière symétrique pour la puissance provenant de la deuxième ligne d'alimentation, et l'autre ouverture de la deuxième paire d'ouvertures étant placée de façon à fournir une frontière symétrique pour la puissance provenant de la première ligne d'alimentation, la polarisation croisée des alimentations étant réduite au minimum par ce moyen.

Claims

I CLAIM:
1. A dual polarized microstrip patch radiator
comprising a ground plane, a thin layer of dielectric on
each side thereof, a conductive microstrip patch on a
first of said dielectric layers on a side remote from
said ground plane, first and second feed lines on the
side of said second dielectric layer remote from said
ground plane, first and second pairs of apertures in
said ground plane said second pair of apertures being
orthogonal to said first pair of apertures, said first
feed line being radiatively coupled to one of said first
pair of apertures and not radiatively coupled to the
other aperture of said first pair of apertures nor to
said second pair of apertures, said second feed line
being radiatively coupled to one of said apertures of
said second pair of apertures and not radiatively
coupled to the other of said second pair of apertures
nor to said first pair of apertures, said other aperture
of said first pair of apertures being positioned to
provide a symmetrical boundary condition for power
coupled from said second feed line, and said other
aperture of said second pair of apertures being
positioned to provide a symmetrical boundary condition
for power coupled from said first feed line, whereby
cross-polarization of said feeds is minimized.
2. A dual polarized microstrip patch radiator as
defined in claim 1 wherein said pairs of apertures are
etched into said ground plane, said patch is
photolithographically deposited on said first dielectric
layer, and said feed lines are photolithographically
deposited on said second dielectric layer.

3. A dual polarized microstrip patch radiator as
defined in claim 1 wherein said apertures are either
rectangular or circular.
4. A dual polarized microstrip patch radiator as
defined in claim 3 wherein all of said aperturess are of
the same size and shape.
5. A dual polarized microstrip patch radiator as
defined in claim 1 wherein said apertures are
rectangular, said first pair of apertures being
orthgonal to said second pair of apertures.
6. A dual polarized microstrip patch radiator as
defined in claim 1, wherein apertures are circular.
7. A dual polarized microstrip patch radiator
array comprising a plurality of microstrip patch
radiators as defined in claim 1, wherein the first feed
lines of each of said radiators are connected in series,
and the second feed lines of each of said radiators are
connected in series, each radiator being mounted in said
array in the same orientation.

Description

CA 02218269 1997-10-1~
MICROSTRIP PATCH RADIATOR WITH MEANS FOR THE
SUPPRESSION OF CROSS-POLARIZATION
FIELD OF THE INVENTION
The present invention relates to a dual
polarized microstrip patch radiator including means for
suppressing cross-polarization of the radiation.
BACKGROUND OF THE PRIOR ART
Microstrip patch radiators are well known in
the art. These radiators are used at UHF through to
millimetre wave lengths and are conventionally
manufactured using photolithography techniques.
U.S. Patent 5,043,738 of August 27, 1991
illustrates a patch antenna which is fed by a pair of
orthogonal apertures within the ground plane element of
the antenna. These apertures either linearly or
circularly polarize microwave power from the feed
structures to the patch radiator.
U.S. Patent 5,005,019 of April 2, 1991
illustrates both the use of patches and slots as
radiating elements of a printed circuit antenna. U.S.
Patent 4,489,328 illustrates the use of slot antennas in
place of patch antennas. U.S. Patent 4,692,769
illustrates a patch antenna with a slotted microstrip.
U.S. Patent 4,771,291 shows the use of slots
in the patch to provide an antenna intended for dual
frequency operation.
U.S. Patent 4,929,959 is a compound antenna
structure for transmitting and receiving dual polarized
signals from different layers of the antenna. U.S.
Patent 4,926,189 is a similar antenna structure for
receiving high gain single and dual polarized microwave
signals. U.S. Patent 4,125,838 illustrates a square
shaped patch radiator which may be notched for tuning
purposes. U.S. Patent 4,903,033 illustrates a patch

CA 02218269 1997-10-1~
antenna equipped with various frequency broadening
components and a polarizer which can be used for
converting linear to circular polarization. A cross-
shaped slot is utilized for feeding the antenna.
None of the above microstrip antennas includes
means for the suppression of cross-polarization in a
dual polarized microstrip patch radiator.
SUMMARY OF THE PRESENT INVENTION
Conventional techniques for achieving dual
independent linear polarization from a single slot
coupled microstrip patch radiator result in either
excessive cross-polarization levels, or require complex
feeds having four feed lines exciting four active slots.
The present invention achieves very low cross-
polarization while maintaining a simple two line feedstructure and only two active feed apertures. A single
active feed aperture and a single feed line are combined
with a passive aperture for each polarization.
Asymmetry in the field distributions under the patch is
eliminated through the use of dummy apertures which do
not have feed lines exciting them. This results in a
simpler feed with very low cross-polarization.
The present invention provides for suppression
of cross-polarization in a dual polarized microstrip
patch radiator by providing two active slots and two
dummy slots etched into the ground plane layer beneath a
microstrip patch. The active slots are energized by
feed lines produced on the bottom surface of a lower
dielectric and the patch radiator is metallized on the
top surface of an upper dielectric layer. The two
active slots are coupled to the feed lines and the two
dummy slots do not have coupling through the feed lines
and are not energized by the feed lines. The dummy or
passive slots provide the means for suppression of
cross-polarization as discussed below.

CA 02218269 1997-10-1
BRIEF INTRODUCTION TO THE DRAWINGS
Figure 1 is a cross-sectional view of a patch
antenna in accordance with the invention.
Figure 2 is a bottom view showing the feed
lines for the active apertures and the dummy apertures
in its second place,
Figure 3 is a schematic view of an alternative
embodiment of micropatch antenna having a dual polarized
feed using active and passive circular apertures.
Figure 4 is a schematic diagram illustrating a
series fed array of radiators using active and dummy
apertures.
DETAILED DESCRIPTION OF THE INVENTION
Referring to Figure 1, there is shown in
cross-section a dual polarized microstrip patch radiator
in accordance with the invention. A ground plane 10 is
surmounted by an upper dielectric layer 11 carrying a
metallized photolithographically applied patch 13. A
lower dielectric layer 12 below the ground plane 10
carries photolithographically applied feed lines
designated generally by 14.
Figure 2 is a bottom view of the microstrip
patch radiator of Figure 1 for dual polarization. In
this view, both the upper and lower dielectric layers 11
and 12 and the ground plane 10 have been removed for
clarity. The apertures 17, 18, 19 and 20 in the ground
plane 10 have been highlighted. The first feed line 15
and the second feed line 16 are arranged at right
angles, feed line 15 extending across active aperture
17. Similarly, feed line 16 exténds across active
aperture 19. In addition, dummy apertures 18 and 20 are
provided on the ground plane 10. These dummy apertures
18 and 20 are not engaged by the feed lines 15 and 16.
The microstrip patch 13 is smaller than its ground plane
10, which is indicated in dotted outline.

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The feed line 15 is the input port for the
power to be radiated in one sense of linear
polarization, for example, vertical polarization. The
feed line 15 crosses over the aperture 17 causing fields
to be coupled through the slot into the space beneath
the microstrip patch. These fields induce currents into
the patch which then result in radiation into space.
Similarly, feed line 16 is the input port for the power
to be radiated in the other sense of linear
polarization, for example, horizontal polarization. The
feed line 16 crosses over the active aperture 19 causing
fields to be coupled through the aperture 19 into the
space beneath the microstrip patch 13. These fields
also induce currents into the patch which then result in
radiation into space.
The fields excited into the space below the
microstrip patch 13 by feed line 16 would find the
boundary conditions of that space to be asymmetrical if
dummy aperture 18 was not used. This asymmetry is what
introduces high cross-polarization in existing
implementations using only two feed lines and two slots.
The dummy aperture 18 thus provides a symmetrical
boundary condition for power coupled from feed line 16
to the microstrip patch 13.
In the same way, the fields excited into the
space below the microstrip patch 13 by feed line 15
would find the boundary conditions of that space to be
asymmetrical if dummy aperture 20 was not present. As
before, this asymmetry introduces high cross-
polarization in existing implementations using only two
feed lines and two slots. Aperture 20 thus provides a
symmetrical boundary condition for the power coupled
from feed line 15.

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As previously mentioned, apertures 17 and 19
provide a means for coupling power from the feed lines
into the space below the microstrip patch.
As illustrated in Figure 1, the upper
dielectric layer supports the microstrip patch 13 above
the ground plane 10 at a constant height. The
permittivity of the dielectric 11 affects the required
dimensions of the microstrip patch 13 for resonance and
the corresponding real input impedance. The lower
dielectric layer 12 supports the feed lines below the
ground plane 10. The ground plane 10 is a conductive
layer which acts to separate the fields under the
microstrip patch 13 from the fields under the feed lines
15 and 16. The apertures 17, 18, 19 and 20 are gaps in
the ground plane 10 formed for example by etching.
Figure 3 is a bottom view of a dual polarized
feed using active and passive circular apertures. As
before, a first feed line 15 is positioned orthogonal to
a second feed line 16, feed line 15 extending across
active aperture 17. The second feed line 16 extends
across active aperture 19. Dummy aperture 18 is
positioned to provide a symmetrical boundary for the
feed from second feed line 16, and dummy aperture 20 is
positioned to provide a symmetrical boundary for second
feed line 16.
Figure 4 illustrates a series fed array of
microstrip patch radiators 30, 40 and 50 using dummy
apertures illustrating how the separate feed lines 15
and 16 can be positioned so that they do not intersect
the dummy apertures and that the first feed line only
crosses the first active slot and the second feed line
only crosses the second active slot of each microstrip
patch radiator.

Representative Drawing