Matched feed design employing TE01 and TM11 modes in a smooth walled rectangular waveguide for cross-polar reduction in offset reflector antenna systems

Cross polar performance of an offset reflector antenna fed by a smooth walled rectangular matched feed employing TE01 and TM11 modes is presented. When studied with analytical mode field patterns, TE01 + TM11 combination is found to give better cross-polar performance compared to combinations like TE01 + TE11 and TE01 + TE11 + TM11. Physical optics (PO) has been used to compute secondary pattern. Mode coefficients and relative phases of different modes are evaluated using Particle Swarm Optimization (PSO) technique or contour plot. A shifted waveguide junction is used to generate the TM11 mode for realization of the matched feed. The desired mode coefficients are realized by proper choice of shifted waveguide dimensions and relative phase is maintained by proper choice of waveguide lengths. The performance evaluation of the complete antenna system is carried out using HFSS. A −30 dB cross-polar bandwidth of 2.16% is achieved.