A Single/Dual-Polarized $\mathbf{\lambda/4}$ Impedance Transformer Coupled Square Microstrip Patch Antenna for X-band Applications

This study introduces compact single-polarized and dual-polarized printed square microstrip patch antennas optimized for SAR applications in the X-band frequency range. The prototypes, named prototype-I and prototype-II, were effectively simulated, fabricated, and measured. Operating at 9.65 GHz with dimensions of $\mathbf{40\mathrm{x}40\mathrm{x}1.587 \ \text{mm}^{3}}$, they offer impedance bandwidths surpassing 140 MHz (9.56 GHz to 9.7 GHz) with S11 parameters below -10 dB. Prototype-II enhances scattering capability through dual polarization by introducing a horizontal port orthogonal to the vertical port. Measurement results confirm dual polarization achievement at 9.65 GHz, similar to prototype-I. Both prototypes provide low-profile, cost-effective solutions. Prototype-I yields a measured gain of 7.463 dBi with a radiation efficiency of 93%, while Prototype-II achieves gains of 7.345 dBi (vertical port) and 7.302 dBi (horizontal port), with radiation efficiencies estimated at 90.28% and 90.3%, respectively.