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

ABSTRACT 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.