Miniaturized ultra-wideband bandpass filter based on CRLH-TL unit cell

In this paper, a novel ultra-wideband (UWB) bandpass filter design based on a composite right/left handed transmission line (CRLH-TL) unit cell is presented. The series capacitance of CRLH-TL is realised by the interdigital capacitor, and shunt inductance is provided by the grounded stubs. By cascading the interdigital coupled line with a low-pass filter (LPF) based on symmetrical split ring resonator (SSRR) defected ground structure (DGS), an UWB frequency response is obtained. SSRR DGS was used to obtain wider upper stopband and sharp roll-off rate. The filter has compact size (13 × 8.5 mm²) and exhibits an attenuation level greater than 23 dB at both upper and lower stopband. The filter has an insertion loss of 1 dB, a return loss better than 13 dB, and a fractional bandwidth of more than 100%.