Design of bandpass filters with parallel three-line coupled microstrips

Abstract

Bandpass filters are designed based on parallel coupled three-line microstrip structures. The relation between the circuit parameters of a three-line coupled microstrip section and an admittance inverter is established. A design graph for substrate with epsilon(r) = 2.2 is provided. Two Chebyshev filters, of order 2 and 1dB passband ripple, with fractional bandwidths 40% and 60% are fabricated and measured. Good agreement between prediction and measurement is obtained.