Ultra-Wideband Bandpass Filter Based on Parallel-Coupled Microstrip Lines and Defected Ground Structure

Abstract

A compact planar microstrip bandpass filter with 3.1 GHz ? 10.6 GHz bandwidth, below 1 dB in-band insertion loss, 0.2 ns ? 0.6 ns group delay and out-of-band rejection level better than - 10 dB is presented for ultra-wideband (UWB) applications. The desired UWB is realized by etching a defected ground structure (DGS) in the ground plane and loading a folded steppedimpedance stub by one of the coupling microstrip lines. This can offer two transmission zeros at lower and upper edges of the passband, which improve the passband selectivity and out-of-band rejection significantly. An equivalent lumped circuit model is introduced; the result of the circuit model fits the EM model well. The simulated and measured results are in good agreement