Abstract
High-impedance quarter-wavelength (λ/4) coplanar waveguide (CPW) transformer is characterized as an alternative J-inverter element with enhanced coupling degree. After the frequency-related coupling behavior of this transformer is investigated, a novel two-stage λ/4 CPW bandpass filter is constructed with widened passband and good harmonic suppression. Its filtering performance is first studied versus varied inductive coupling at center and then optimally designed toward minimizing the insertion loss in the passband. Predicted filtering characteristics are in final confirmed by our experiment of a fabricated filter circuit over a wide frequency range.
