A High Selectivity and High Efficiency Filtering Antenna With Controllable Radiation Nulls Based on Stacked Patches

A high selectivity and high efficiency filtering antenna is presented in this paper. A double-layer filtering patch antenna is first proposed, which can generate a radiation null due to the mixed electric and magnetic coupling between the two patches. By changing the length of the slot line on the patch, the position of the radiation null can be flexibly set at the lower band edge or upper band edge. Based on this mechanism, a three-layer patch antenna with two radiation nulls is designed. Two radiation nulls are introduced on both sides of the passband, consequently, a quasi-elliptic bandpass response can be obtained. Moreover, the proposed antenna features high efficiency since no extra filtering circuit is utilized. A prototype antenna operating at 1 GHz is designed, fabricated, and measured for validity verification. The measured results agree well with the simulated one, showing that the prototype antenna has a fractional impedance bandwidth of 16% (0.91-1.07 GHz), a flat passband gain response with peak value of 8.83 dBi, a high efficiency about -0.41 dB in the passband. The band-edge selectivity is highly improved by the radiation nulls near the passband edge.