Synthesis of tuneable ring-based bandpass filter

The passband frequency response of the quarter wavelength side-coupled ring resonator can be tuned by adding capacitances along the ring. Synthesis has been developed to define the capacitor value to be used so as to move the central frequency to the desired value. As frequency shift affects matching level inductance-based network was used, and with inductance value determined using specific synthesis. These concepts were validated through experiments for filters which tuned components were realized using stubs.