A Compact and High Selectivity Bandpass Filter Based on Substrate Integrated Coaxial Line Technology

A compact and high selectivity bandpass filter (BPF) consisting of parallel-coupled three-line (PCTL) units and shorted stubs is proposed using substrate integrated coaxial line (SICL) technology. Single via transitions are adopted to connect the BPF with the grounded coplanar waveguides (GCPWs). Moreover, an equivalent circuit model is built to understanding the properties of the BPF. Two transmission zeros (TZs) are created by the shorted stubs and the gap between the PCTL units. The locations of the TZs are closed to the passband edges of the proposed BPF as the gap capacitance increased and the electrical length of the shorted stubs decreased, so a compact size and high selectivity can be obtained. Finally, a BPF prototype is fabricated by PCB process and the results indicate that the proposed BPF centered at 25.9 GHz is realized with compact size of
$0.42\lambda_{g}\times 0.28\lambda_{g}$
and high selectivity factor of 0.554, where
$\lambda_{g}$
is the wavelength at 25.9 GHz.