A design of the novel varactor tuned directional coupler

The directional coupler with a parallel LC resonator is proposed to control the operating frequency range. The proposed directional coupler is designed based on even-odd mode analysis technique. It has physically quarter wavelength coupled section at center frequency. A varactor tuned directional coupler is designed and fabricated with a parallel LC resonator. It shows the flexible operating frequency range with 40% tunable. The measured results show good agreement with the simulated characteristics.