Synthesis Method for Even-Order Symmetrical Chebyshev Bandpass Filters With Alternative $J/K$ Inverters and /spl lambda//4 Resonators

This paper proposes a unified synthesis method for the bandpass filters based on the alternative J/K inverters and λ/4 microstrip line resonators. Firstly, an even-order Chebyshev bandpass filter prototype with equal terminations is transformed to two dual networks based on hybrid J/K inverters and λ/4 resonators. In this work, two adjacent λ/4 resonators are coupled with each other through a semi-lumped via-hole as the K inverter; the tailored method is employed and effectively demonstrated to extract the J/K inverters' values and their respective associated effective lengths. As its application examples, the proposed synthesis method is applied to design two classes of even-order Chebyshev bandpass filters with fourth and sixth order on microstrip-line topology, which operate at 2.4 GHz with the fractional bandwidths of 10% and 15%, respectively. Finally, both classes of filters are fabricated and measured. Simulated and measured results provide a good verification for the theoretical counterparts.