New formulas for synthesizing microstrip bandpass filters with relatively wide bandwidths

Abstract

New formulas are proposed for designing wideband parallel-coupled microstrip bandpass filters with improved prediction of bandwidth. When a fractional bandwidth Delta is required, a correction theta = (pi / 2) (1 +/- Delta / 2) is incorporated into the formulation for determining the dimensions of each coupled stage. Two filters with Delta = 50% are designed and fabricated to show the improvement. The measurement shows a very good agreement with the simulation.