High Q bandpass filters on sapphire substrate for atmosphere remote sensing

High Q band pass filters (BPF) on sapphire substrate at 36 and 56.6 GHz for atmosphere remote sensing applications have been developed. The paper describes BPFs with introduced several transmission zeros based on a combination of parallel coupling and end coupling of half-wavelength microstrip resonators. The BPFs exhibit quasi-elliptic response that results in finite frequency transmission zeros, positioned near the passband edges due to the coupling between non-adjacent resonators. At the center frequency of 36 GHz, the 3 dB bandwidth of the BPF is 2.0 GHz, which is almost 5.6%, and the simulated insertion loss is 0.9 dB. The second BPF with the center frequency 56.6 GHz, is designed for the fractional bandwidth less than 1% with simulated insertion losses about 3.8 dB.