Circular monopole filtering antenna with improved sideband selectivity and in-band impedance using circular-stub-load resonator

Abstract

Abstract In the design of the filter antenna, the filter unit with the same structure as the radiation patch not only improves the selectivity of the band edge, but also helps to improve the in-band impedance. In this design, a compact circular monopole filtering antenna with improved sideband selectivity and in-band impedance using a circular-stub-load resonator is proposed. To obtain better sideband selection characteristics and in-band impedance characteristics, and reduce the mismatch problem caused by the introduction of the filter, a branch-loaded filter with the same resonance mode as the antenna radiation patch is designed. In addition, different shape branch loading structures of the bandpass filter are also studied. The experimental results show that when the loading unit of the filter and the radiation structure of the antenna have the same structure, both good in-band impedance characteristics and sideband selectivity characteristics can be obtained from the filter antenna. The antenna reflection coefficient bandwidth is from 3 to 11 GHz (114%), and the maximum reflection coefficient is only −15 dB, showing good in-band impedance characteristics and sideband selection characteristics. The filter antenna realizes the integration of antenna filtering without increasing the size, and the final size of the antenna is 30 × 25 mm2.