Tuning circuit using varactor diode for tunable bandstop resonator

A tuning circuit based on the use of varactor is presented to tune the electrical length of an open-circuited stub. The complete circuit with the choice of components is given in the paper, along with its simulation results. The proposed circuit is realized using microstrip technology on FR4 substrate. The experimental results are found to be of good agreement with the ones obtained from simulation. The proposed circuit is expected to be advantageous for future tuning applications of bandpass filter. The experimental result shows the center frequency of tunable filter can be tuned up to 84%.