Microstrip patch antenna feed for offset reflector antenna for dual band application

Abstract

In this article, details of a dual band microstrip patch antenna (MPA) array feed for an offset reflector antenna is presented. The main objective of the proposed structure is to achieve low cross-polarization at Φ = 90° plane in the reflector pattern. Low cross-polar levels in the reflector pattern are achieved by illuminating the reflector with fields of the proposed dual band feed structure. A centered circular array as the dual band feed structure is proposed in which the central radiating element is a dual mode circular MPA operating at 6 GHz and the surrounding circular ring of eight circular MPA elements operating at 4 GHz in the dominant mode. The dual mode central antenna uses the concept of conjugate field matching for cross-polarization reduction. TM21 mode is excited at an appropriate ratio with the TM11 mode to achieve the proper field matching at 6 GHz. The radius of the surrounding circular array is varied to obtain cross-polarization better than −30 dB at both the resonant frequencies. The offset reflector gain is found to be better than 37 dB with a 2.5 m parabolic reflector and F/D = 0.8 at both the operating frequencies.