Substrate-Integrated Waveguide Band-Pass Filter and Diplexer With Controllable Transmission Zeros and Wide-Stopband

In this brief, a substrate integrated waveguide (SIW) bandpass filter (BPF) with wide out-of-band rejection is researched and fabricated with the center frequency of 45.8 GHz and 3-dB FBW of 2.18%. Due to the exploitation of electronic excitation, higher order modes mismatch and orthogonal transmission, the simulated and measured out-of-band rejection is better than 20 dB with frequencies up to $7.6f_{0}$ and $2.4f_{0}$ , respectively. Diplexer with stopband suppression better than 30 dB up to $1.87f_{0}$ is proposed based on the theory of the proposed filter. Dual-mode resonator operating with TE301 mode (43.8 GHz) and TE103 mode (45.8 GHz) has been designed to provide the transition of two filter channels. High isolation better than 27 dB over the whole band can be achieved. Transmission zeros (TZs) are generated by spurious resonances under electrical excitation, resulting in high selectively of the passbands. Good agreements between simulations and measurements can be observed.