Wide-stopband Millimeter-wave BPF on GaN MMIC Using Asymmetric Feeding Structure

This paper presents a novel compact bandpass filter for 30 GHz millimeter-wave applications in Monolithic Microwave Integrated Circuit (MMIC). The proposed circuit consists of two symmetrical coupled quarter-wavelength transmission-line resonators and two coupled transmission-line feeding structures. Two feeding lines are designed as asymmetrical structures, which are utilized not only to cause mismatch at the third harmonic frequency between the resonator and feeding lines so that the third harmonic can be suppressed but also to provide source-loaded to generate two transmission zeros near the passband, resulting in high selectivity. To verify the proposed idea, an experiment filter has been implemented. High skirt selectivity and wide stopband are observed in the results.