COMPACT MICROSTRIP BPF WITH HIGH SELECTIVITY USING EXTENDED TAPPED LINES

This paper proposes a compact microstrip bandpass filter (BPF) with high selectivity. A folded stepped-impedance resonator (SIR) of which the high impedance part is realized by a coplanar waveguide on the ground layer is introduced to the filter design for miniaturization. Furthermore, source-load coupling is implemented by extended tapped lines (ETL5). High selectivity with four transmission zeros (TZs) can be achieved. The analysis of the filter is presented based on a transmission line circuit model and even- and odd-mode analysis method. An experimental filter with the size of 0.15 lambda(g) * 0.13 lambda(g) (where lambda(g) is the guide wave-length at the center frequency) is designed to validate our methods.