150 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 49, NO. 2, FEBRUARY 2001
A Shared-Aperture Dual-Band Dual-Polarized
Microstrip Array
David M. Pozar, Fellow, IEEE and Stephen D. Targonski, Member, IEEE
Abstract—This paper describes the design and testing of a
prototype dual-band dual-polarized planar array operating at L-
and X-bands. The primary objectives were to develop new antenna
technology with dual-band and dual-polarization capability in a
shared aperture, featuring low mass, high efficiency, and limited
beam scanning. The design of a prototype planar microstrip array
of 2
2 L-band elements interleaved with an array of 12 16
X-band elements that meets these requirements is discussed in
detail and measured results are presented. The array is modular
in form and can easily be scaled to larger aperture sizes.
Index Terms—Dual-frequency, dual-polarized, microstrip
arrays.
I. INTRODUCTION
HE trend in microwave remote sensing radars and radiome-
ters is to perform simultaneous measurements at different fre-
quencies,preferablywithdualpolarizationcapability.TheSIR-C
shuttle imaging radar, for example, operated at L- and C-bands
with dual linear polarization at each frequency, but these two an-
tennas did not share a common aperture [1]. Future systems re-
quirecomparablecapabilities,butwithreducedmassandreduced
size,drivinganeedfordual-frequencydual-polarizationantennas
using a shared aperture.In addition, beam scanningin one ortwo
planes, over a few beamwidths, may be required. This presents
theantennadesignerwithachallengingproblem,asthefollowing
considerations are critical.
1) The avoidance of grating lobes (particularly if scanning
is required) places an upper limit on element spacings at
eachband,whilemaximumelementspacingsarepreferred
to minimize cost. This precludes the use of dual-band or
wide-band elements, such as spirals or notches.
2) Operating frequencies are usually widely separated (typi-
cally some combination of L-, C-, or X-bands), requiring
different array element spacings to avoid grating lobes.
This implies that an interleaved arrangement of elements
at each band is optimum.
3) System bandwidth requirements areon the order of3–8%,
so printed antenna elements having bandwidths greater
than the simple single-layer microstrip element are re-
quired.
4) Duetolayoutconstraints,asinglemicrostripfeedsubstrate
is limited to two independent feed networks (e.g., two po-
larizationsor twofrequencies).Thus, atleasttwosubstrate
Manuscript received June 1, 1999; revised February 15, 2000.
The authors are with the Electrical and Computer Engineering Department,
University of Massachusetts at Amherst, Amherst, MA 01003 USA.
Publisher Item Identifier S 0018-926X(01)02283-9.
Fig. 1. Basic subarray element, consisting of an L-band proximity-fed
perforated patch and a 4
2
4 subarray of aperture coupled microstrip patches.
layersarerequiredfordualpolarizationattwofrequencies.
Isolationrequirementsare not likelytobemetunlessthese
feed networks are separated by a ground plane.
5) System considerations usually dictate comparable
beamwidths at the two operating frequencies, so the
radiating aperture at the higher frequency will be smaller
than that at the lower frequency. This means that the
dual-frequencyarray aperture will not be uniformly filled.
Because of the difficulty in satisfying the above constraints,
reported work in the area of dual-band dual-polarized arrays
with a common aperture is limited. One recent paper describes
such an antenna operating at C- and X-bands [2], using inter-
leaved printed slots and microstrip patches. Although good re-
sults were obtained, the coplanar-fed microstrip patches limited
the bandwidth toa fewpercent at C-band,and the X-bandslot el-
ements requireda reflecting ground plane. In addition, since this
design used two layers of solid teflon-based substrates, scaling
to L-band frequencies would result in a relatively thick and
heavy structure. A similar dual-polarized array operating at L-
and C-bands was reported in [3]. That array used L-band slots
and C-band microstrip patches with foam substrates, resulting
in a very lightweight structure, but the large slots led to some
spurious radiation and degraded isolation.
This paper describes the design and testing of a prototype
L/X dual-band dual-polarizedplanar array forsynthetic aperture
radar (SAR) applications. The primary objectives of this work
were to develop new antenna technology with dual-band and
dual-polarization capability in a shared aperture, featuring low
mass, and capable of being scaled to a large radiating aperture.
0018–926X/01$10.00 © 2001 IEEE