In this paper, microstrip stepped-impedance hairpin resonator (SIR) low-pass filter (LPF) and slow-wave band-pass filter (BPF) using dielectric supported air-gapped microstrip line (DAML) of surface micromachining on GaAs substrate are proposed. The DAML structure, which is a new low-loss micromachining transmission line, is useful for the integration of MEMS and/or MMIC components. Design parameters for the proposed SIR low-pass and slow-wave band-pass filters are derived based on stepped-impedance theory. The proposed slow-wave BPF is designed to produce a passband of 10% at the fundamental frequency of 60 GHz. and a new SIR LPF with aperture and IDC (inter-digital capacitor) is designed for 3-dB cutoff frequency of 33 GHz. The measurement results of the BPF filter and LPF filter agree well with simulation results. These filters are useful for many millimeter-wave system applications.
This paper mainly presents a briefly review for recent progress in MEMS-based transmission lines for use in microwave and millimeterwave range. MEMS-based transmission lines including different transmission line structure such as membrane-supported microstrip line microstrip line, coplanar microshield transmission line, LIGA micromachined planar transmission line, micromachined waveguides and coplanar waveguide are discussed. MEMS-based transmission lines are characterized by low propagation loss, wide operation frequency band, low dispersion and high quality factor, in addition, the fabrication is compatible with traditional processing of integrated circuits (IC’s). The emergence of MEMS-based transmission lines provided a solution for miniaturizing microwave system and monolithic microwave integrated circuits.