Lightweight patch radiator antenna

A lightweight patch radiator phased array antenna having a single layer patch construction on an artificial dielectric, such as syntactic foam, which achieves a factor-of-ten weight savings over an array constructed with conventional materials. An additional sixty-five percent weight reduction is achieved by cutting away the dielectric material down to the array antenna's ground plane everywhere except under the patch radiator. This construction allows placement of a thermal control material over the patch and ground plane for space applications.

BACKGROUND OF THE INVENTION 
This invention relates generally to antennas and in particular to a 
lightweight patch radiator antenna for use in an airborne or spaceborne 
phased array antenna. 
It is known in the art that a patch radiator consists of a conductive 
plate, or patch,. separated from a ground plane by a dielectric medium. 
When an RF current is conducted within the cavity formed between the patch 
and its ground plane, an electric field is excited between the two 
conductive surfaces. It is the ,fringe field, at the outer edges of the 
patch, that launches the useable electromagnetic waves into free space. 
Patch elements are advantageous in phased arrays because they are compact, 
they can be integrated into a microwave array very conveniently, they 
support a variety of feed configurations, and they are capable of 
generating circular polarization. They also have the advantage of cost 
effective printed circuit manufacture of large arrays of elements. 
For some applications a major drawback to the use of phased array antenna 
systems is their high cost because of the need for hundreds or thousands 
of antenna elements and associated transmit/receive circuitry. For other 
applications such as a spaceborne application, weight is a critical 
factor. Prior art materials used in patch radiator antennas, having a 
dielectric constant of approximately 2 such as a Teflon-fiberglass 
material known as Duroid 5880, may result in a considerable weight 
contribution to the total weight of an antenna depending on its size. 
Duroid is a registered trademark of Rogers Corporation of Chandler, 
Arizona. A patch radiator antenna using Duroid material is described in 
U.S. Pat. No. 5,008,681, "Microstrip Antenna with Parasitic Elements," 
issued to Nunzio M. Cavallaro et al., and assigned to Raytheon Company of 
Lexington, Massachusetts. The present invention of a lightweight patch 
radiator antenna reduces the weight drawback and thermal control 
considerations related to the array antenna surface coatings in spaceborne 
applications. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a lightweight 
patch radiator antenna for space applications. 
It is a further object of this invention to provide a lightweight phased 
array antenna for space applications. 
These objects are generally attained by selectively reducing the quantity 
of dielectric material used in the antenna and by the use of an artificial 
dielectric such as syntactic foam. 
The objects are further accomplished by providing a patch radiator antenna 
comprising an antenna panel having a ground plane, a thermal control 
material bonded to the ground plane surface of the antenna panel, a 
plurality of patch radiators arranged on the antenna panel in a spaced 
apart manner with no dielectric material between the patch radiators, each 
of the plurality of patch radiators comprising a dielectric means having a 
first surface and a second surface, a patch element disposed on and bonded 
to the first surface of the dielectric means, a flange bonded to the 
second surface of the dielectric means, thermal control material bonded to 
the patch element, and probe means extending from the patch radiator for 
coupling the patch element to an RF signal source. The antenna panel 
comprises an aluminum honeycomb material. The dielectric means comprises a 
low weight, high dielectric, syntactic foam. The thermal control material 
comprises a flexible optical solar reflector or a thermal control paint. 
The objects are further accomplished by providing a phased array antenna 
comprising an antenna panel having a ground plane, a thermal control 
material bonded to the ground plane surface of the antenna panel, a 
plurality of patch radiators arranged on the antenna panel in a spaced 
apart manner with no dielectric material between the patch radiators, a 
transmit/receive (T/R) module coupled to each of the plurality of patch 
radiators, each of the plurality of patch radiators comprising a 
dielectric means having a first surface and a second surface, a patch 
element disposed on and bonded to the first surface of the dielectric 
means, a flange bonded to the second surface of the dielectric means, 
thermal control material bonded to the patch element, and probe means 
extending from the patch radiator for coupling the patch element to the 
T/R module. The antenna panel comprises an aluminum honeycomb material. 
The dielectric means comprises a low weight, high dielectric, syntactic 
foam. The thermal control material comprises a flexible optical solar 
reflector or a thermal control paint. 
The objects are further accomplished by a method for providing a 
lightweight patch radiator antenna comprising the steps of providing an 
antenna panel having a ground plane, bonding to the ground plane surface 
of the antenna panel a thermal control material, arranging on the antenna 
panel in a spaced apart manner a plurality of patch radiators with no 
dielectric material between the patch radiators, providing a dielectric 
means having a first surface and a second surface for each of the 
plurality of patch radiators, disposing a patch element on and bonding it 
to the first surface of the dielectric means, bonding a flange to the 
second surface of the dielectric means, bonding thermal control material 
to the patch element, and coupling the patch element to an RF signal 
source with probe means extending from the patch radiator. The step of 
providing a thermal control material comprises bonding a flexible optical 
solar reflector. 
The objects are further accomplished by a method for providing a phased 
array antenna comprising the steps of providing an antenna panel having a 
ground plane, bonding to the ground plane surface of the antenna panel a 
thermal control material, arranging on the antenna panel in a spaced apart 
manner a plurality of patch radiators with no dielectric material between 
the patch radiators, coupling a transmit/receive (T/R) module to each of 
the plurality of patch radiators, providing a dielectric means having a 
first surface and a second surface for each of the plurality of patch 
radiators, disposing a patch element on and bonding it to the first 
surface of the dielectric means, bonding a flange to the second surface of 
the dielectric means, bonding thermal control material to the patch 
element, and coupling the patch element to the T/R module with probe means 
extending from the patch radiator. The step of providing an antenna panel 
comprises the panel having an aluminum honeycomb material. The step of 
providing a dielectric means includes the dielectric means comprising a 
low weight, high dielectric, syntactic foam. The step of providing a 
thermal control material comprises bonding a flexible optical solar 
reflector.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring initially to FIG. 1, it may be seen that a lightweight phased 
array antenna 10 according to the present invention includes a plurality 
of patch radiators 14 mounted on a top surface 11 of an antenna panel 12 
with no dielectric material between each of the patch radiators. Each 
patch radiator 14 is fed by a corresponding transmit/receive (T/R) module 
15 (shown in FIG. 2) attached to the inner side of the patch radiator 14 
opposite surface 11. T/R modules 15 are driven by an RF feed network of RF 
power dividers 16, 17 which provide RF signals to each of the T/R modules 
15; phase information is supplied to each T/R module 15 through the system 
controller 18. System controller 18 originates the RF feed signals to 
power dividers 16, 17 as well as control signals and voltages to the 
plurality of T/R modules 15. The phased array antenna 10 operates in the 
L-band frequency range (1-2 GHz). 
Referring now to FIG. 2, an end view of an antennule module 13 is shown 
which is positioned by pins 24, 26 into the side 11 of the antenna panel 
12. The antennule module 13 comprises the single layer radiator patch 14 
and the T/R module 15 with the T/R module 15 being attached to the bottom 
side of the patch radiator 14 which touches the surface 11 of antenna 
panel 12. At one end of the T/R module 15 is a coaxial RF connector 19 and 
a flexible circuit cable 20 which are provided for electrically connecting 
the T/R module 15 to a wiring board 22 disposed on a bottom surface 21 of 
antenna panel 12. At the other end of the T/R module 15 which attaches to 
the patch radiator 14 two inserts 43 are provided for insertion of two 
probes 42 extending from the patch radiator 14. By attaching directly to 
the T/R module 15 an intermediate connector is not used, and the 
reliability of the antennule module 13 comprising patch radiator 14 and 
T/R module 15 is improved. The antenna panel 12 which functions as a 
ground plane comprises an aluminum honeycomb material 27 of approximately 
1.5 inches thickness to accommodate acoustic loading during a launch in 
the space application for the present embodiment. The T/R module 15 
comprises a baseplate 28 and a cover 29. The antennule module 13 provides 
for minimal cost to manufacture and maintain such a phased array antenna 
10. 
It should be noted that the preferred embodiment of the invention shown in 
FIG. 2 shows a T/R module 15 driving the patch radiator 14. However, in 
some applications this may not be necessary when beam scanning is not 
required resulting in an embodiment comprising the RF feed apparatus 16, 
17 of FIG. 1 directly feeding the patch radiators 14. Depending on the 
nature of the RF feed, one or several fixed beams could then be radiated 
by the array of patch radiators 14. However, eliminating the T/R module 15 
removes the capability of electronically scanning or changing these beams. 
Referring now to FIG. 3 and FIG. 4., there is shown in FIG. 3 a 
cross-sectional view of the patch radiator 14 according to the invention. 
A patch element 34 comprising an electrically conducting material such as 
copper is attached to a first side of a dielectric material 36 with a 
bonding material 35. The dielectric material 36 in the present embodiment 
is low weight, high dielectric, syntactic foam. A second side of the 
dielectric material is bonded with a pressure sensitive bonding film 38 to 
an aluminum flange 40. A cylinder of conductive material 46 extends from 
the patch element 34, to which it is electrically attached or soldered, 
through the dielectric material 36 and an insulator 44 in the aluminum 
flange 40, and contained within and extending from the cylinder 46 is a 
conductive probe pin 42 for insertion into the T/R module 15. As shown in 
FIG. 4, which is a plan view of the patch radiator 14 having a portion cut 
away, there are two probe pins 42 extending from the patch radiator 14, 
one for each of the circular polarization RF signals. On top of the patch 
element 34 is a layer of a thermal control material 30 such as a thermal 
flexible optical solar reflector (FOSR); it is attached to the patch 
element 34 with a pressure sensitive bonding film 32. Because there is no 
dielectric material on the antenna panel 12 except within each patch 
radiator 14, FOSR is useable for thermal control over the patch radiator 
14 and the ground plane which is surface 11 of antenna panel 12. As an 
alternative to. FOSR, a thermal control paint may be used depending on 
application requirements. 
The two probes 42 of each patch radiator 14 are fed 90 degrees out of phase 
with RF voltages of approximately equal amplitude. These probes 42 can be 
located on the diagonals of the square patch, as shown in FIG. 4, or 
located on the principal axes of the patch; another variation comprises 
the use of around patch radiator, with the probes located at equal 
distances from the patch. In all configurations the probes are located 
equal distances from a patch radiator center, and angularly displaced 90 
degrees relative to each other as measured from the center of the patch 
reference. Either right handed or left handed waves can be radiated by 
this array by choosing either a +90 degree or a -90 degree relative 
phasing of the 2 probes. The RF drive voltages to the patch radiator 
probes 42 are supplied by the T/R module 15, which comprises a 90 degree 
phase shift network at its output; the T/R module 15 may also contain an 
auxiliary patch radiator matching network, if desired. Alternately, such 
phase shift and matching networks can be provided by the RF feed apparatus 
16, 17 for the configuration noted hereinbefore having the T/R modules 
eliminated. The result is that in all configurations, each patch radiator 
14 in an antenna array is driven at the desired voltage amplitude and 
phase with its probes 42 phased 90 degrees with respect to one another. 
Another variation of this invention has only one probe driving the patch 
radiator 42. In this case the 90 degree phase shift network of the T/R 
module 15 is eliminated, and the T/R module output voltage directly feeds 
the probe 42. Such an antenna array functions identically to the array 
described above, except that it radiates a linearly polarized beam. 
Referring again to FIG. 1 and FIG. 3, a 30 times (30 X) reduction in weight 
of the antenna panel 12 is achieved with the present invention. Part of 
this weight savings is obtained by cutting away all dielectric material on 
the array top surface 11 (approximately 65%) except for where it is needed 
underneath the patch element 34 of the patch radiator 14. This approach 
has the further advantage of allowing the placement of the thermal control 
material 30 on the array ground plane or panel 12, thereby improving 
thermal performance. Since the patch radiator 14 only covers approximately 
35% of the antenna panel 12 surface area, this results in a 3 times 
reduction in the dielectric which is virtually the entire patch radiator 
14 weight above the surface of the panel 12. The use of syntactic foam 
artificial dielectric 36 for the patch radiator substrates results in less 
weight by a factor of 10 compared to the prior art teflon-based 
dielectrics such as Duroid. This results in a total of 3.times.10 or a 30 
X weight reduction in the patch radiator 14. Such weight reductions are 
critical for cost-effective space applications. 
The dielectric material 36 may be embodied by a low weight, high dielectric 
constant, syntactic foam such as those manufactured by Emerson and Cumming 
of Canton, Massachusetts or by APTEK Corporation of Valencia, California. 
The bonding film 32, 35, 38 may be embodied with FM 73 manufactured by 
American Cyanamid of Havre de Grace, Maryland. The thermal control 
material, FOSR, is manufactured by Sheldahl Corporation of Northfield, 
Minnesota. Alternatively, a thermal control paint may be embodied by 
S13GLO manufactured by IIT Research Institute of Chicago, Illinois. 
Referring now to FIG. 5 and FIG. 6, FIG. 5 shows the patch radiator 14 
elevation radiating pattern at 1.622 GHz compared relative to the ideal 
cos .theta. pattern (solid line) and FIG. 6 shows the patch radiator 14 
azimuth radiating pattern at 1.622 GHz compared to the ideal cos .theta. 
pattern (solid line). The benefits of the present invention are primarily 
realized in the frequency ranges of L-band or S-band. When the operating 
frequency is below 4 GHz the patch radiator 14 size and weight savings are 
significant. The present invention achieved a major weight decease in the 
L-band phased array antenna 10 operation whereas at higher frequencies 
less weight savings are achieved. 
The patterns shown in FIGS. 5 and 6 are significant in that they 
demonstrate the proper operation of the patch radiator of the present 
invention. An ideal patch radiator, when excited by an RF drive signal and 
with all other radiators terminated in their usual output impedance, 
exhibits a cos .theta. radiated power pattern in all planes. FIGS. 5 and 6 
show the corresponding elevation plane and azimuth plane radiated power 
patterns of the patch radiator of this invention, taken in a small array 
with all other patch radiators resistively terminated. The driven patch 
radiator probes 42 are fed 90 degrees out of phase, resulting in a 
circular polarization of the radiated wave. The measurement is taken by a 
rapidly rotating linearly polarized horn (as is customary practice) 
located in the far field whose angular location relative to the array is 
slowly varied to measure the appropriate radiated field pattern. The 
closely spaced peaks and minima of the patterns of FIGS. 5 and 6 show the 
major and minor axes of the polarization elipse, whereas the slower 
variations show the pattern variation with angular position of the far 
field horn. The difference in decibels between the successive maxima and 
minima of this pattern represents the local axial ratio of the array at 
that radiation angle. From FIGS. 5 and 6 it can be seen that the patterns 
exhibit nearly cos .theta. variations with radiated angle and axial ratios 
of approximately 1 db over most of the scan volume. The radiated power of 
the azimuth pattern only falls off near the azimuth grating lobe onset 
location, as expected. This azimuth grating lobe onset location is set by 
the azimuth spacing of the radiators in the array, and is closer in angle 
to boresight than the elevation plane grating lobe onset angle. These 
patterns demonstrate the proper operation of the patch radiator invention 
described herein. 
This concludes the description of the preferred embodiment. However, many 
modifications and alterations will be obvious to one of ordinary skill in 
the art, such as the type of thermal control material 30 to be used in a 
particular application, without departing from the spirit and scope of the 
inventive concept. Therefore, it is intended that the scope of this 
invention be limited only by the appended claims.