Center Frequency and Bandwidth Controllable Microstrip Balun Bandpass Filter

This work aims for the development of a so-called reconfigurable balun bandpass filter, which is essentially a filter of controllable center frequency and bandwidth, as well as the balun functionality. The modified Marchand-balun structure is adopted as the building block for the proposed reconfigurable filter. Specifically, the two-line coupled-line structure used for Marchand baluns is replaced with the proposed asymmetric three-line coupled-line structure, and the symmetrical second-order bandpass filter prototype based on admittance inverters is adopted for the filter synthesis. And, the center frequency and bandwidth tunabilities are realized with varactor-incorporated three-line coupled-line structure of tunable transmission poles and zeros.