Design of Compact Differentially-Fed End-Fire Filtenna With High Selectivity

In this letter, a compact differentially-fed end-fire filtenna is developed. The developed filtenna consists of three drivers, a director, a reflector, and a pair of U-shaped strips. Different from conventional Yagi antenna with a single driver, multiple drivers are employed to concurrently broaden the impedance bandwidth and facilitate the filtering response. To further improve the lower frequency selectivity, a pair of split rings is inserted between the driver and the director. And a radiation null at lower frequency is generated due to the out-of-phase surface currents on director and split rings. For verification, a prototype with a center frequency of 3.9 GHz is designed, fabricated, and measured. The measurement results have a good agreement with the simulation ones. The developed filtenna has a fractional impedance bandwidth of 14.4% (3.62–4.18 GHz), a peak realized gain of 5.8 dBi, a front-to-back ratio over 15 dB within the entire operational band. In addition, the filtenna also owns good filtering response with suppression levels higher than 16 and 25 dB for low- and high-stopband, respectively.