A tri-mode low cross-polarized circular matched feed for offset reflector antenna system

The cross polar power resulting due to illumination of an offset reflector by a linearly polarized circular feed operating in TE₁₁ mode can be suppressed considerably by employing TE₂₁ and TM₁₁ modes having proper mode coefficients and relative phases. This paper presents the design and performance evaluation of such a smooth walled circular tri-mode matched feed. Using an analytical pattern for the tri-mode feed and physical optics (PO) for computation of far field, mode coefficients and relative phases are estimated using particle swarm optimization (PSO) technique. Through a parametric study in HFSS, matched feed dimensions to achieve required mode coefficients and phases at the design frequency are determined. HFSS is used to evaluate the performance of the matched feed in terms of cross-polarization and beam squinting. A -30 dB cross-polar bandwidth of 2.73% is achieved at the design frequency.