A novel bandpass filter design using cascaded CPW/Slotline ring resonators with tapered step impedance CPW fed structure

A novel bandpass filter using the cascaded CPW/Slotline ring resonators with tapered step impedance CPW fed structure is proposed. This fed structure not only provides two transmission zeros for the bandpass filter at the lower and upper passband edges but also makes the filter with very compact size. The CPW/Slotline ring resonators utilize a pair of anti-coupled lines to create poles. Moreover, the central frequency and coupling coefficient can be obtained by adjusting the anti-coupling gap. In this paper, two kinds of bandpss filters with CPW/Slotline ring resonators are demonstrated which have fabricated on conventional FR-4 substrate. The measured insertion loss is less than 3 dB and the return loss is better than 15 dB across 10% bandwidth. The measured results show good agreement with HFSS simulated results.