Matched feeds for offset reflector antenna using circular microstrip patch antenna

Abstract

This article presents two designs of matched feed for an offset fed reflector. Circular microstrip patch antennas are used in the proposed designs. Both the matched feeds achieve conjugate field matching by generating TM21 mode at an appropriate ratio to the fundamental TM11 mode. The first matched feed generates the required dual mode field distributions using a dual layer stacked patch antenna. The second matched feed is a novel design using centered circular array with the central element generating the required TM21 mode and the surrounding circular ring antenna elements operating in the TM11 mode. Both the designs are studied analytically using cavity model and are implemented in High frequency System Simulator (HFSS) and Computer Simulation Technology (CST). The matched feed designs are investigated for an offset reflector with the projected diameter, D = 50λ, focal length, F = 30λ and clearance height, H = 5λ operating at 20 GHz. The secondary field patterns of the offset reflector fed by the matched feeds are evaluated numerically using a MATLAB code based on geometrical optics technique and verified by HFSS-PO results. Offset reflector performance such as cross-polarization, −30 dB cross-polar bandwidth, gain, and first side-lobe level are investigated for the both matched feeds.