Electronic variable delay line filters using two in-line varactor-controlled four-input couplers allowing variable delay

摘要

A delay circuit for the secondary path of a feed-forward high power amplifier is disclosed. A first 3 dB quadrature hybrid coupler is coupled to first and second resonator circuits that each includes a varactor circuit and are resonant at a first resonant frequency. The output of the first hybrid coupler is coupled to the input of a second 3 dB quadrature hybrid coupler. The second hybrid coupler is coupled to third and fourth resonator circuits that each includes a varactor circuit and are resonant at a second resonant frequency that is greater than the first resonant frequency. The overall combined delay response of the first hybrid coupler and the second hybrid coupler appearing at the fourth node of the second hybrid coupler is substantially constant between the first resonant frequency and the second resonant frequency.