Design and Synthesis of a High-Selectivity and Wide Stopband Suppression Filtering Antenna With Symmetric Coupling Structure

A fourth-order high-selectivity and wide stopband suppression filtering antenna with a symmetric coupling structure is presented. By incorporating resonant units with different structures, harmonics are effectively suppressed due to the resonators’ identical fundamental modes and distinct second-order harmonics. By introducing a cross-coupling path, two controllable radiation nulls are achieved, further enhancing the antenna's selectivity. Additionally, the symmetric coupling structure is employed to minimize cross-polarization. Finally, the theory of coupling matrix is utilized in the synthesis of the filtering antenna, and the relevant physical parameters are obtained. The results demonstrate that the proposed filtering antenna exhibits a bandwidth of 2.40 GHz to 2.66 GHz for |<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub>| < −10 dB, a peak gain of 6.1 dBi, and two radiation nulls at 1.98 GHz and 3.12 GHz, resulting in enhanced selectivity with suppression levels exceeding 37.5 dB and cross-polarization levels below −38.1 dB.