Filtering Endfire Dipole Antenna Based on Resonators

A novel filtering endfire dipole antenna based on resonators is presented in this letter. The two driven elements and the director are composed of half-wavelength microstrip resonators; they not only generate three resonant modes in the frequency band, but also have dual functions of filtering and radiation. The reflector is used to increase the radiation in the endfire direction. The feeding structure is a U-shaped stepped impedance resonator loaded with a matching stub, which produces a radiation null in the low-frequency band to further improve the filtering performance. In addition, a high-frequency radiation null is introduced by the cross coupling to enhance the frequency selectivity of the upper band. A prototype is fabricated and measured to verify the design concept. The designed antenna covers an impedance bandwidth of 14.2%, the maximum gain in the operating frequency range is about 6.2 dBi, and two radiation nulls are located at the edge of the passband. Thus, a simple filtering endfire antenna without any extra intricate filtering circuit is achieved.