Microstrip Coupled Line Filter Design for Ultra Wideband Applications

Abstract

A compact microstrip parallel coupled line filter for ultra wide band applications by means of combining a network of coupled line and defected ground is proposed. The design equations for three and five interconnected networks are derived and implemented. Simulations for three different configurations for filters are optimized. Then three prototype circuits are constructed, a bandpass filter with center frequency 2.25 GHz and two different bandpass filters (in terms of perturbations) with center frequencies 2.33GHz. For 2.25 GHz circuit wide fractional bandwidth of about 90% is obtained but undesired high return loss existed. For 2.33GHz circuit with grooves in sides fractional bandwidth of about 60% is obtained at about 3.4 GHz center frequency. However undesired return loss existed for this circuit whereas good out off band performance is achieved. For 2.33GHz circuit with grooves in whole sections the center frequency got shifted to about 3.4 GHz and about 50% fractional bandwidth is obtained with very good out off band performance observed.