A Compact Filtering Quasi-Yagi Antenna With Wide Reflectionless Bandwidth

A compact planar quasi-Yagi antenna is presented in this letter, featuring integrated filtering radiation and broadband reflectionless performance. The filtering ability is directly achieved by a driven dipole and two strongly-coupled parasitic patches, to suppress the out-of-band reflection coefficient across a wide frequency range, an absorptive feeding network is devised by employing a π phase shifter (PS) together with two parallel bandstop filters (BSFs) loaded with grounded resistors. The frequency responses of the two BSFs are designed to be complementary to that of the filtering antenna, thereby achieving broadband out-of-band reflection absorption without in-band radiation degradation. A prototype is fabricated and measured for verification. Measured results show that the proposed antenna can achieve 3-dB gain bandwidth of 3-4.6 GHz (42.1% fractional bandwidth) and -10-dB impedance bandwidth of 1.1- 10 GHz. Meanwhile, the realized gain gives a high bandpass selectivity with measured out-of-band suppression more than 21.1 dB. The average in-band efficiency is up to 85% with a stable endfire radiation beam.