Bandwidth and transmission zero control for compact dual-mode resonator filter by extraction of EM coupling

The electric coupling and magnetic coupling are extracted for a dual-mode resonator filter. The resonator is a half-wave section with its center being shorted to ground. The extraction relies on an equivalent circuit model. With properly tuning of the coupled-line sections, the electric and magnetic coupling coefficients of the two quarter-wave resonators can be adjusted, and hence both the filter bandwidth and zero frequency can be controlled. Two experimental filters are fabricated and measured for validation. Good agreement between measurement and simulation is obtained.