IETE Technical Review
Vol 23, No 6, November-December 2006, pp 357-366

Dual Frequency Single Aperture Microstrip Patch
Antenna Element for SAR Applications


Antenna Systems Area, Space Applications Centre, Ahmedabad 310 015, India.

This paper presents the design of a dual frequency microstrip patch antenna. The design is presented at C and X band with centre frequency at 5.35 and 9.6 GHz respectively. The radiating element at C band is a microstrip patch while the radiating element at X band is a slot. Simulated and measured data are presented as a function of geometrical parameters.


THE antenna plays a very important role in determining the overall system performance of air-borne as well as space borne synthetic aperture radar (SAR) systems. The basic driving force for frequency and polarization selection of a SAR system is the application targeted for. SAR systems are generally operated at L, C and X band for most of the applications. There is an increasing demand of simultaneous multifrequency SAR for space-borne and air-borne SAR systems to get images of targets of different signatures during one visit of a particular region of earth. A wholly independent antenna for each frequency band would be inefficient and considerable saving in space and weight can be achieved if multi-frequency band SAR signals can be transmitted and received via a single aperture antenna. Moreover, for airborne applications, SAR data at different frequencies like C and X band can be acquired without landing the aircraft for mounting of different antenna at different frequency bands if a multifrequency SAR system is used on board the aircraft. Antennas at different frequency bands will occupy larger area which may be prohibited by the available
space in the radome of the air craft.

Thus, there is a strong need to develop antennas which fulfils the requirement of multifrequency operation for SAR applications. Pokuls et al, [1] presented a design on dual frequency and dual polarization microstrip antennas using X-band rectangular slot and C-band square patches

Paper No 9-B; Copyright © 2006 by the IETE.



In [1], thedetail of the geometry of the patch/slot and the parametric analysis was not presented.

In the present paper, rectangular as well as dog bone slots have been used as radiator at X-band to investigate the merits and demerits of these two configurations of slots. Inset fed patch [2] has been used as radiating elements at C-band. The simulation was performed using Ansoft Ensemble. A parametric study has been carried out by varying various dimensions of the slot and simulated return loss curves are presented. Similarly the lateral spacing between patch and slot is varied and its effect on return loss is presented. A planar array of two by two microstrip patches at C-band slots at X-band in a single aperture has been designed, fabricated and tested to validate the design.


The schematic of the single element antenna is shown in Fig 1. The bottom layer (region ‘ra’ in Fig 1) is a layer of substrate material of Rohacell foam of thickness 5.0 mm with dielectric constant ~ 1.07 backed by a ground plane. Above this foam layer there is a layer of substrate material of thickness 0.79 mm of RT-Duroid 5880 with dielectric constant 2.2 (region‘rb’ in Fig 1). At the top side of this substrate, slot is cut while the bottom side of this substrate there is a feedline which excites the slot. Above the slot there is another substrate layer of thickness 1.575 mm of RTDuroid 5880 (region ‘rc’ in Fig 1). Microstrip patch is
etched at the top side of this substrate. The patch antenna at C- band is inset fed by microstrip line [2].