Suspended stripline UWB bandpass filter with adjustable transmission zero

In this paper, a new design of an order-seven suspended stripline (SSL) ultra-wideband (UWB) bandpass filter with high selectivity achieved by an adjustable transmission zero is proposed for improving upper-stopband performance. This type of structural filter is constructed based on a novel tubular filter with quasi-lumped elements. The highest out-of-band rejection of the SSL UWB bandpass filter is more than 70 dB. The design procedure is very simple and flexible, where a transmission zero can be generated and shifted easily above the passband by modifying the paraments of the coupling loop. The function of the cross coupling ring is to enhance the skirt selectivity with not increasing the overall filter size. A discussion on its effects is detailed after the SSL UWB bandpass filter is designed, fabricated and tested. Both simulated and measured results are presented to validate the design concept.