2012) Broadband and wide range tunable phase shifter based on composite right/left handed transmission line, Journal of Electromagnetic Waves and Applications, 26: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 π-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°. The relative bandwidth is 40%, while the input return loss is not large than 10 dB.
IntroductionPhase shifters are widely applied to microwave and communication systems, especially in phased array antennas and radars. For different engineering applications, different kinds of tunable phase shifters were proposed using ferrite materials [1-4], p-i-n diodes [5-7], varactor diodes [8-11], etc. The phase shifters based on ferrite materials usually have large insertion loss and hard to be integrated, while p-i-n diodes are popular in designing digital phase shifters. For an analog phase shifter in microwave frequency band, varactor diode-based structures are widely adopted. The capacitance of varactor diode varies continuously when the DC voltage is changed. The quality factor Q is acceptable to reduce loss, hence it is suitable for designing tunable analog phase shifters with good performance, such as compact size, low cost, and broad bandwidth.More recently, metamaterial-based phase shifters have also received considerable attention in both scientific and engineering communities [12][13][14][15][16][17][18][19][20][21][22]. In [12], the tunable phase shift reaches 342°by cascading 13 left-handed metamaterials (LHMs) units with operation frequencies from 8 to 10 GHz. In [14], a phase shifter is cascaded by four LHMs units with an adjustable phase ranging more than 150°, but the relative bandwidth is less than 20%. In [15], a digital phase shifter is fabricated by cascading five composite right/left handed (CRLH) transmission line (TL) unit cells. The relative bandwidth is only 10% at X-band. In