Novel Wideband Quadrature Hybrid Coupler With Tunable Power Dividing Ratio

This paper presents a novel wideband quadrature hybrid with tunable power dividing ratio. It consists of a broadband hybrid power divider and two varactor diodes. By verifying the reverse voltage of the varactor diodes, the power dividing ratios between the two output ports (i.e., port 3 and port 4) of the hybrid can be easily controlled. Analytical design equations are derived using the even-odd mode method. To verify the design concepts, a miniaturized tunable power dividing ratio hybrid working at 1.85 GHz is designed and tested. When verifying the reverse voltage of the varactor diodes from 0 to 16 volt, the power dividing ratios between the two output ports of the hybrid can be tuned from -1 to 7.3 dB within a wide bandwidth (1.7-2.0 GHz). Good isolation and return loss performance have been maintained for different power-dividing ratios. And the output phase difference is nearly 90 degree. Moreover, the working bandwidth is larger than 200 MHz for different values of reverse voltage. The measured results agree well with the simulated ones. The total size of the quadrature hybrid power divider is much small (60.4x26.8x1 mm(3)).