A Series-Fed $2\times 2$ Filtering Microstrip Antenna Array with Second-Order Chebyshev Response

A series-fed 2× 2 Filtering Microstrip Antenna Array (FMAA) with a second-order Chebyshev response is proposed. A feed line is coupled to novel Z-shaped resonators, which are also coupled to U-shaped patch antenna elements. The proposed structure behaves as a second-order Band-Pass Filter (BPF), and the response matches the Chebyshev prototype circuit. Moreover, the structure provides a flat broadside antenna gain response in the pass-band and two radiation nulls in the out-of-band. The measurements are consistent with the simulated results. Notably, the array size can be easily increased without altering the feed structure, and it does not compromise the filtering feature.