Design of an interdigital band-pass filter for out-of-band rejection improvement

Abstract

In this letter, an interdigital band-pass filter is proposed for out-of-band rejection improvement. Seven quarter-wavelength resonators are employed to form the passband. Three extra transmission zeros (TZs) on both sides of the passband are implemented by introducing source-load coupling and dumbbell defected ground structures (DGS). As demonstrated by the measured results, out-of-band rejection and selectivity are improved by these three TZs, and good performances are achieved. The proposed method of increasing out-of-band rejection is feasible and applicable in the design of modern microstrip filters.