A Compact and Sharp Ultra Wide Band Pass Filter with use of Short Stub Loaded Rectangular Ring and Split Ring Resonators

A compact and sharp-rejection ultra-wideband (UWB) microstrip bandpass filter (BPF) is presented. The proposed filter is constructed with multiple-mode resonator (MMR) and split ring resonator (SRR). Moreover, proposed structure consists of two doublets parallel cou-pling gaps at each side of a microstrip ring. In comparison with some other filters, this struc-ture shows a significantly wider passband due to the introduction of a cross-coupling be-tween the feed lines (input and output) which generate four pairs of attenuation zeros in the passband. In order to control the transmission zeros in the pass band and adjust the transmis-sion zeros near the lower edges of the filter, a Short Stub, Loaded on microstrip Rectangular Ring Has Been Used. Also, In order to sharpen the upper edge of the filter, we used SRRs in both side of the doublets parallel coupling gaps that leads to the addition of one extra trans-mission poles at the upper edge of the filter. Consequently, a compact four-zero and one pole ultra-wide bandpass filter is designed which exhibits extremely sharp rejection skirts around the target passband. The proposed filter has a passband covers 2.8 to 10 GHz and its meas-ured 3 dB fractional bandwidth is about 112.5%. Furthermore, rejection level better than 20 dB in upper stopband is extended to around 18 GHz. To our knowledge, the size of proposed ultra-wideband filter is more compact in comparison with known similar filters.