Compact UWB PCML bandpass filter with L- and C-shaped resonator

A novel ultra-wideband (UWB) bandpass filter with four resonant modes is proposed based on a parallel coupled microstrip line (PCML) with L- and C-shaped resonators. The coupling factor of the PCML structure depends on the impedance of the feeding network. The PCML coupling factor can be enhanced by using a feeding network with smaller characteristic impedance. With an L-shaped feeding network and C-shaped middle microstrip line a non-uniform resonator is constructed with the first two resonant modes falling within the UWB. The other two resonant modes within the UWB can be obtained by adjusting the width of both the L- and C-shaped resonators. Overall the designed filter exhibits good UWB passband behaviour with insertion loss < -0.2 dB and group delay < 0.15 ns.