Compact QMSIW bandpass filter using composite right/left‐handed transmission line in grounded coplanar waveguide

Abstract

A novel compact quarter-mode substrate integrated waveguide (QMSIW) bandpass filter based on composite right/left-handed transmission line (CRLH TL) in grounded coplanar waveguide (GCPW) is proposed in this work. Two unit cells CRLH TL is implemented at the inductive window of two coupled QMSIW resonators, does not occupy any extra area and minimizes size of the proposed filter. The characteristics of the CRLH unit cell are analyzed in order to get one transmission zero (TZ) at the lower stop band and one pole at the center frequency of the filter. Therefore two unit cells CRLH TL gives two poles at the center frequency and one TZ at the lower stop band of the filter. In addition to this, the proposed structure of the filter gives two more TZs at upper stop band to obtain better selectivity and wide stop band performance. To validate the proposed method, a fourth-order bandpass filter (BPF) is designed and fabricated on a single layer Rogers RO3003 substrate. The measured results are 14% fractional bandwidth (FBW) with 8.4 GHz center frequency, a return loss (RL) better than −18 dB, and an insertion loss (IL) less than −1.55 dB. Three TZs are obtained at 7.42, 9.97, and 13.42 GHz with rejection levels of −31.51, −28.43, and −53.56 dB, respectively. The simulation result shows a good match with measured S-parameters.