Design of ultra-wide bandpass filter using hybrid microstrip/CPW structure

The aim of this paper is to propose a new simple design of a ultra-wide bandpass filter (3.1 to 10.6 GHz) based on the cascading of a low pass and a high pass section. They are separately designed using convenient structures leading to compactness and easy fabrication. A stepped impedance structure providing elliptic response has been used for the low pass filter. The high pass section is implemented using a quasi-lumped LC network consisting of three capacitors and an inductor. Planar circuit implementation is feasible thanks to the simultaneous use of microstrip and coplanar waveguide technologies. The high pass section has been optimized for size reduction and additional transmission zero. Good rejection at low and high frequencies and good band pass impedance matching is achieved. The filter is a useful alternative to other recently proposed structures. Experimental validation is provided.