Inline Bandpass Filtering Waveguide Antenna with Two Transmission Zeros Based on All-resonator Structures

Nowadays, a significant amount of effort is being devoted to miniaturizing the design of filtering antennas for future wireless communication systems. However, there are numerous design strategies documented in the literature, most of which are relevant to specific microwave circuit configurations. Moreover, they often require additional matching circuits, which increase the overall size of the filtering antenna. This study introduces a generic coupling matrix approach for developing a second-order filtering antenna with two transmission zeros operating at cross-band frequencies. The last resonator's output is physically connected to free space, and two inline coupled rectangular waveguide cavity resonators operating in the TE101 mode are employed. Impressive, simulated results have been achieved, demonstrating a fractional bandwidth (FBW) exceeding 5% at a reflection coefficient S11 of -9.9 dB. Additionally, the gain response remains remarkably flat, spanning from 8.9 to 9.3 GHz, with a negligible variation of ±0.07 dB around 3.77 dB. The tiny and low-profile design of the suggested filtering antenna offers significant advantages for radar applications.