Tunable impedance transformer using a transmission line with variable characteristic impedance

This paper proposes a new structure for a tunable impedance transformer. The proposed transformer consists of a quarter-wavelength transmission line with variable characteristic impedance. The operating principle of the variable characteristic impedance is based on the use of parallel combinations of multiple transmission lines and by controlling the line connection with RF switches. Multiple switches are inserted at the in/out terminals of each transmission line. Since a parallel microstrip transmission line has a unique structure that involves a partially removed ground plane under the conductor line, it is possible to realize a high characteristic impedance line with a wide linewidth.