Effects of defected ground structure slot tuning on frequency and circuit parameters of bandpass filter

摘要

In this paper the effect of the slot area to an end-coupled bandpass filter (BPF) is presented. The defected ground structure (DGS) technique is applied in the ground plane to accomplish the resonant frequency tuning of the filter. To achieve the passband the slot is designed with the etched DGS pattern consisting of two identical square-loops having open-loop edge height, h together with open-ends, g and a slot-line, d which forms connection between them. The proposed dumbbell shaped DGS is used to tune the bandpass filter down to 2.4 GHz with dimension of 40 mm x 20 mm. The gap, g, is kept constant at 0.4 mm, and w is varied. A wide tuning range of 1.31 GHz is achieved by tuning the width dimension of DGS unit cell. The improvement in center frequency, bandwidth and size of bandpass filters is achieved by the utilization of a specific DGS shape. From the analysis, it is depicted that a decrement of 25-30 % in the size of overall structure is achieved as compared to previously reported design for end-coupled bandpass filters. Meanwhile, a further decrement of 500-700 MHz in bandwidth is attained by downshifting the center frequency. Empirical modeling is achieved for frequency versus length dimensions to produce a generalized equation. With the selected structure, the filter's circuit is simulated to attain its performance corresponds to the filter's parameters setting. The results in terms of insertion and return loss, bandwidth due to the resonant frequency are presented and discussed. Effect of DGS on circuit models is also shown.