Synthesis Design of In-Line Pseudoelliptic SISL Bandpass Filter Employing Non-Resonating Mode in Low-Loss Patch Resonators

This paper presents a novel type of patch resonator suitable for the design of high selectivity in-line pseudoelliptic bandpass filters (BPFs) based on a substrate-integrated suspended line (SISL) platform. The proposed structure is a rectangular patch resonator that allows the propagation of the fundamental mode and high order modes. By controlling the position of input and output feedlines, the proposed resonators can provide both a reflection and a transmission zero simultaneously. Thus, a pole-zero pair can be produced (behaving as a singlet). The position of poles and zeros can be fully controlled by varying the position and orientation of the feeding lines. To verify the proposed concept, a detailed study about the behavior of the patch singlet and a validated third-order filter BPF with three TZs ( canonical BPF) located in the lower and upper passband is presented in this brief. The measured results exhibit an extended stopband with rejection better than 58 dB in the lower passband and 40 dB in the upper passband. The tested return losses and insertion loss are better than -15.7 dB and 1.31 dB, respectively.