Design of Dual-Band Quarter-Wave Transforms Using Three Equal-Length Transmission Lines

Design of dual-band quarter-wave transformers based on three equal-length transmission lines is studied in the paper. The dual-band quarter-wave transformers are found to be capable of operating at f1 and kf1 for , where f1 and kfi are the two midband frequencies. Consider the microwave components that are composed of quarter-wave transformers, such as impedance matching network, resonators, power dividers, directional couplers. The use of the dual-band quarter-wave transformers can naturally makes these components dual-band, as demonstrated in Section IV.