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

In this paper, a new via-less ultra-wideband (UWB) bandpass filter design based on a composite right/left-handed transmission line (CRLH-TL) unit cell is presented. Microstrip capacitive patch is used to provide virtual ground and replace the via in the conventional CRLH TL. Via fabrication complexity can be avoided for large-scale and cost-effective production by using microstrip patch. 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 achieved. SSRR DGS was used to obtain wider upper-stopband and sharp roll-off rate. The filter has compact size (15.6 × 13 mm²) and exhibits a rejection level greater than 20 dB at both upper and lower stopband. The filter has an insertion loss of 0.9 dB, a return loss better than 14 dB, and a fractional bandwidth of more than 100% at center frequency of 6.8 GHz.