Multiple passband transmission zeros embedded compact UWB filter based on microstrip/CPW transition

This manuscript presents an ultra-wideband (UWB) bandpass filter (BPF) with dual transmission zeros (TZ) embedded in the passband for interference free operation in indoor environment. Based on the vertical electromagnetic (EM) coupling of microstrip-to-coplanar waveguide (CPW) transition, the structure has two similar microstrips placed adjacent on the top plane whereas a short-circuited CPW forms the ground. The response of this BPF is quasi-elliptical in nature with two TZs at either passband edges which enhances selectivity and improves insertion/return loss. To this basic BPF, novel sectoral folded split ring resonator (SFSRR) and spiral resonator (SR) are appended in the slots of the ground plane which produce dual TZs in the passband at 4.5 and 8 GHz respectively. A prototype of the proposed structure is fabricated and tested. The dual notched BPF is developed on a low cost substrate and is of compact size occupying an area of 21.2 x 16 mm(2).