Wideband SIW Filtering Antenna With Controllable Radiation Nulls Using Dual-Mode Cavities

A wideband fourth-order filtering antenna consists of two substrate integrated waveguide (SIW) dual-mode cavities is presented in this letter. The first SIW cavity creates two resonant nodes and one radiation null (RN) located on the upper stopband. The second SIW cavity integrated with a slot cannot only achieve radiation function but also realize dual-mode resonance, which can produce another lower out-of-band RN. These two RNs can be controlled to improve frequency selectivity and design flexibility. The coupling matrix theory is adopted to guide the design of the filtering antenna, and the generation principle of these two RNs can be explained by cross coupling. Finally, such a filtering antenna operating at the center frequency of 5.4 GHz with a fractional bandwidth of 7.64% and a maximum gain of 5.3 dBi is fabricated and measured.