A Compact Differential Filtering Quasi-Yagi Antenna With High Frequency Selectivity and Low Cross-Polarization Levels

A compact differential filtering quasi-Yagi antenna is proposed for high frequency selectivity and low cross-polarization. The proposed antenna is formed by inserting a double-sided parallel-strip line (DSPSL) filter between the driver and the reflector of the quasi-Yagi antenna. This integration enables the antenna to achieve both high frequency selectivity and compact size. An antenna prototype exhibits a 10-dB return loss bandwidth of 1.77–1.87 GHz, peak gain of 5.6 dBi, and maximum cross-polarization levels of $-22/-17$ dB in E-/H-planes at 1.81 GHz. The out-of-band suppression is enhanced by 14.4 and 11.8 dB at 1.67 and 1.97 GHz compared to the quasi-Yagi antenna itself, respectively.