CMA-Driven Polarization Purity Enhancement in Triangular Patch Antennas With Resonance Stability

This letter presents an innovative strategy to improve polarization purity in space-constrained microstrip patch antennas using a low-profile metal-pin-based superstructure. The triangular patch, an inherently compact antenna shape, suffers from high cross-polarized field components, an issue that has been largely overlooked. Using characteristic mode analysis (CMA), the near-field E-field distribution of the $T{M}_{10}$ mode reveals that the $E_x$ and $E_y$ components overlap near the apex, leading to increased cross-polarization (XP). While latest minimally invasive method using partially shorting pins causes a 2.2% upward frequency shift, this noninvasive approach results in a 0.3% downward frequency shift, maintaining compactness and scalability. Experimental results demonstrate normalized peak XP levels of −38 dB in the E-plane, −28 dB in the H-plane, and −18 dB in the diagonal plane, with a peak gain of 7.2 dBi, confirming the effectiveness of the design.