Design of Novel 4-GHz Bandpass Filter Using a Combination of Defected Ground Structure Resonators and Admittance J-Inverter

Abstract

A wideband quasi-elliptical bandpass filter with enhanced reject-band performance is presented. The proposed bandpass filter utilizes a new asymmetric defected ground structure (DGS) under a pair of end-coupled microstrip line. The DGS consists of two square headed slots connected transversely with a rectangular slot. The DGS-microstrip resonator provides band-accept filtering characteristics. To be equivalent to the circuit DGS is demonstrated. The presented equivalent circuit shows both resonant and anti-resonant properties. The equivalent circuit parameters are extracted using the modeling method of proposed DGS. A better selectivity in lower transition band in comparison to upper transition band is observed in the frequency response. To improve the roll-off in upper transition band, a pole is created by putting an additional DGS unit under the same microstrip line. The combined structure shows bandpass characteristics with deep and wide stopband on both sides of the passband. The bandwidth and centre frequency of the filter is controlled by the dimensions of both DGS cells. The article presents some promising patents on Defected Ground Structure Resonators and Admittance J-Inverter.