Loaded-line phase shifters

Updated July 4, 2011

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Another category of phase shifter is the loaded-line phase shifter, which is often used for 45 degree or lower phase shift bits. An example of a loaded-line phase shifter is shown below. The loads ZL are synthesized such that they create a perturbation in the phase of the signal when switched into the circuit, while they have only a small effect on the amplitude of the signal. The loads must have a very high reflection coefficient in order to minimize the loss of the phase shifter (they should utilize purely reactive elements). Obviously the loads ZL must not be too close to a short circuit in phase angle, or the phase shifter will suffer extreme loss. By spacing the reactive loads approximately a quarter-wavelength apart, the amplitude perturbation can be minimized and equalized in both states. The phase versus frequency response of a loaded line phase shifter is usually flatter than the switched line phase shifter, but not usually as flat as the high-pass/low-pass phase shifter. Usually only one control signal is required for a loaded-line phase shifter, since the loads can be biased simultaneously.

Loaded-line phase shifter