Filtering Microstrip Patch Antenna Design Using Coupling Matrix Approach for ISM Applications

This paper presents a novel design approach for a filtering microstrip patch antenna inspired by a bandpass filter (BPF). It is based on the coupling matrix approach, where the magnitudes of the matrix elements are utilized to extract the physical dimensions. Two rectangular microstrip patch resonators (RMPRs) are directly coupled via an air-gap to realize a second-order BPF and a filtering microstrip patch antenna. For the BPF, a 50-Ω microstrip feedline is employed at the input/output ports and extended into the center of the RMPRs to ensure strong impedance matching within the passband of interest. For the filtering antenna, the output feedline port is removed, and the second RMPR is modified to obtain the required radiation quality factor and provide radiation within the passband frequency range. To validate the proposed approach, both designs are fabricated and experimentally tested, showing excellent agreement with the simulation results. The measured 10-dB fractional bandwidth (FBW), passband peak gain, and total efficiency are 4.05%, 6.0 dBi, and 74.0%, respectively. These results demonstrate that the proposed designs offer a compact size, high gain, and high efficiency, making them promising candidates for ISM band applications.