A millimeter-wave micromachined slow-wave bandpass filter using compact microstrip stepped-impedance hairpin resonator

In this paper, a new microstrip stepped-impedance hairpin resonator with inter-digital capacitor (IDC) slow-wave band-pass filter (BPF) using dielectric supported air-gapped microstrip line (DAML) of surface micromachining on GaAs substrate is proposed. The slow-wave periodic structures utilize the parallel and series resonance characteristics of the resonators to construct a band-pass filter. Unlike conventional slow-wave filters, the proposed bandpass filters are designed to produce a narrow passband at the fundamental mode of the resonators. Using IDC, this filter provides small size and sharp shirt characteristic. The proposed slow-wave band-pass filter with IDC is designed to produce a passband of 7.7 % at the fundamental frequency of 56 GHz. It shows the insertion loss of 3.37 dB, the return loss of better than 15 dB, and the stopband characteristic of greater than 31 dB within 37.03 ∼ 45.51 GHz.