New formulas for synthesizing microstrip bandpass filters with relatively wide bandwidths

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