Design of a modified hairpin bandpass filter using embedded radial stubs featuring ultrawide stopband

Abstract

The analysis and design of a microstrip bandpass filter featuring an ultrawide stopband are presented and investigated in this paper. In this filter, single radial stubs are exploited in combination with a regular hairpin structure to achieve suppression of harmonic responses of the filter passband up to 10f0. The passband of the filter remains almost intact compared to the conventional hairpin filter. A 3rd-order BPF with a central frequency of 2 GHz and a bandwidth of 44% is designed and the simulation results are verified with the measurement results. The proposed filter shows more than 32 dB rejection from 3 GHz to 20 GHz in S21 and the measured passband insertion loss is 1.3 dB. The filter structure is simple, without the need for defected ground structures, multilayers, lumped elements, and even vias. The proposed filter can be in demand anywhere easy fabrication, low cost, ultrawide stopband together with a good rejection level are considered crucial.