Broadband and wide range tunable phase shifter based on composite right/left handed transmission line

In this paper, an improved tunable phase shifter with broadband and wide range of the phase shift is proposed. The structure consists of two improved tunable composite right/left handed (CRLH) transmission line (TL) unit cells. A pi-shape circuit model is adopted for each unit cell, and its phase characteristic is discussed in detail, based on which a varactor diode parallel to a lumped capacitor in series circuit and two varactor diodes series with other lumped capacitors in shunt circuits are carefully designed to tune the shifted phase as well as the nonignorable lumped inductors. After that, the phase shifter is finally fabricated using two tunable CRLH-TL unit cells. All of the varactor diodes are controlled by only one bias voltage which also leads to a compact size. The simulated and measured results agree well with a continuously tunable phase range more than 170 degrees. The relative bandwidth is 40%, while the input return loss is not large than 10 dB.