Design of a Wide-Beamwidth Circular Patch Antenna Element Based on TM₂₁ Mode for Phased Array Applications

This study presents a wide-beam circular microstrip patch element operating in the TM₂₁ mode for Ku-band phased arrays. In this design, the TM₂₁-mode conical radiation couples to symmetric parasitic dipoles on low- ϵ_r sidewalls, forming a Huygens-type radiator with a stable wide-angle pattern. Fullwave simulations show a resonance at 13.35 GHz with a return loss below -25dB and ∼ 450 MHz bandwidth for |S₁₁|< -10 dB. A flat-gain radiation pattern with a 3 dB beamwidth of ~ 275° is achieved, maintaining < 3 dB gain variation across -137.5°-+137.5°. Infinite-array analysis confirms matching better than -10 dB for elevation scans up to θ=70° within the band. The design provides a simple, array-compatible route toward wide-angle scanning arrays.