A simple filtering lumped impedance transformer with controllable center frequency and bandwidth for complex load

A simple complex impedance transformer with tunable center frequency and bandwidth that feature bandpass filtering capability for the operative band is proposed in this article. The basic principle of this design is the utilization of resonators, which can introduce transmission poles and zeros into the response. Thus, by controlling the resonant frequency through varactors, the desired function is obtained. The tuning range of the center frequency is 300 to 600 MHz and the bandwidth is 40 to 80 MHz and 80 to 130 MHz at its lower cutoff frequency (means that the left edge of passband keeps stable) and upper cutoff frequency (means that the right edge of passband keeps stable), respectively. Good agreement can be observed between simulated and measured results.