Polarization Enhancement of Microstrip Antennas by Asymmetric and Symmetric Grid Defected Ground Structures

A new approach to controlling cross-polarization (XP), for either suppressing XP or exciting circular polarization (CP), in single-fed microstrip antennas using novel grid defected ground structures (GDGSs) is proposed. The key idea of GDGS is to construct defected ground structures (DGSs) from a grid of etched slots on a ground plane. The properties of each slot can be directly set by using either an open or short with fixed hardwires. The overall fixed hardwire configuration of the GDGS can be found straightforwardly by optimization of the XP or CP characteristics of the microstrip antenna. The importance of the approach is demonstrated by the results achieved. Results from two experimental prototypes are provided that demonstrate XP can be suppressed by 15 dB and CP can be excited with 78 MHz (2.2%) 3-dB axial ratio (AR) bandwidth and 6.6 dBic gain respectively on single-fed microstrip patch antennas.