From Practical MMIC Design

5.7 Phase Shifters

Phase shifters are used to delay or shift the phase of an RF signal by a fixed or variable amount. The phase shift can be continuously variable, as in an analog phase shifter, or it can be switched in discrete steps, as in a digital phase shifter. Analog phase-shifter designs include the reflective and the loaded-line styles, and digital phase-shifter designs include the switched-delay-line and switched-filter styles.

5.7.1 Reflective Phase Shifters

The reflective style of phase shifter [134 137] is constructed from a 90 hybrid coupler, such as a Lange coupler, connected to two varactor diodes that are de-biased through decoupling inductors, as in Figures 5.136 and 5.137. The Lange coupler splits the input power equally between the two diodes and couples the power reflected from the diodes to the output port. The phase of the reflected power from the varactor diodes is a function of their capacitance, which is varied by the control voltage.


Figure 5.136: Reflective analog phase shifter.

Figure 5.137: Reflective-type phase-shifter MMIC. (Courtesy of Alcatel Alenia Space France.)

5.7.2 Loaded-Line Phase Shifters

The loaded-line phase shifter [138 141] is constructed from a quarter-wavelength length of transmission line with a reactive load at each end, such as a varactor diode, as shown in Figure 5.138. The phase change along the transmission line varies according to the voltage on the varactors, which determines their capacitance. The varactor diodes at either end of the transmission line can be replaced with a switch connected to different lumped reactances in...

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