A Frequency Tunable Quadrature Coupler With Wide Tuning Range of Center Frequency and Wide Operating Bandwidth

To solve the problems of existing frequency tunable quadrature couplers with limited tuning range and narrow bandwidth, a frequency tunable 3-dB quadrature coupler with wide tuning range and wide bandwidth is proposed and is based on the vertically installed planar (VIP) structure. Varactor diodes are loaded between vertical patches to achieve frequency tuning. Due to the strong coupling characteristics of the VIP structure, broad bandwidth is maintained during the frequency tuning process. For validation, a frequency tunable coupler is designed, fabricated, and measured. The center frequency of the designed coupler can be varied from 1.3 GHz to 2.7 GHz covering a frequency range of 70%. For each operating mode, more than 40% bandwidth defined by 1 dB amplitude imbalance between output ports, 10 dB return loss and isolation, and phase variation of 5°, can be achieved.