Cavity-Backed Patch Filtenna for Harmonic Suppression

A co-design consisting of a filtering antenna integrating a cavity-backed patch antenna and a low-pass coaxial filter is proposed for size reduction of the RF front-end. The cavity-backed patch antenna is developed to exhibit a broad impedance bandwidth and a unidirectional radiation pattern. The low-pass coaxial filter is implemented to suppress harmonic resonances and gain in the stop-band of the antenna and is embedded directly inside the antenna cavity to realize a compact small-footprint co-designed filtering antenna structure. Two prototypes of the proposed filtering antennas, which integrate cavity-backed patch antennas with 4thand 5thorder low-pass coaxial filters and with the overall dimensions of 0.697λ0× 0.585λ0× 0.236λ0and 0.697λ0× 0.585λ0× 0.320λ0(where λ0is the free space wavelength at 3.15 GHz), respectively, are fabricated and measured. The experimental results show fractional bandwidths of 25% and 23.8% and gain suppression levels exceeding 11 dB and 22 dB in the stop-bands for the filtering antennas with the 4thand 5thorder filters, respectively. The measured gain is more than 6.5 dBi in the pass-band for both filtering antennas. In addition, excellent agreement is obtained between the simulated and measured results.