Filtering patch antenna on λ /4‐resonator filtering topology: synthesis design and implementation

In this study, a novel filtering patch antenna (FPA) based on quarter‐wavelength or λ /4‐resonator filtering topology is presented, and its frequency response is efficiently synthesised to achieve the prescribed higher‐order frequency selectivity. As the resonant patch radiator is capacitively fed by two inductively coupled λ /4 resonators, three transmission poles are created in the operating band to demonstrate the third‐order bandpass filtering property. In design, two adjacent λ /4 resonators are coupled via a shorting pin as the K inverter, while one of them is coupled with the resonant patch via coupled line as the J inverter. As their equivalent parameters are numerically de‐embedded, the overall equivalent filtering network of this proposed FPA is constituted and synthesised with the Chebyshev‐function filtering response. Next, the relationship between the realisable fractional bandwidth and in‐band return loss is thoroughly investigated for a patch radiator with its constant unloaded quality factor. Finally, a prototype FPA at 4.0 GHz is designed, fabricated, and measured. The measured and simulated results are found in good agreement with each other, demonstrating a few attractive features of the proposed FPA, inclusive of wide operating bandwidth, sharp filtering selectivity, and flat radiation gain, as benefited by the three in‐band poles.