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RF Phase Shifter Basics

RF phase shifters are devices which changes the phase of the input signal to any desired value without attenuating the input signal. Depending upon control mechanism RF phase shifters are classified as follows:
•   Mechanical or Electrical
•   continuous type (analog) or step type (digital)

A simple phase shifter is usually a RC network which will cause output to either lead or lag the input signal by 90 degrees. Many different types of circuits are designed to produce phase shift of choice. A simple RF phase shifter for the carrier signal is shown in the figure.

RF Phase Shifter Circuit

RF phase shifter

As shown in the figure, R1 and C1 combination produces output which lags the input signal by 45 degrees. R2 and C2 combination produces output which leads the input signal by 45 degrees. The total phase shift between the two outputs is 90 degree.

Another cheaper and faster RF phase shifter is based on 90 degree hybrid junction as shown in the figure-2. This circuit is loaded with biased varactor diodes. In this version, RF signal sees transition capacitance whose value depends on the control voltage applied to the inverse biased varactor diode pair.

RF phase shifter using hybrid

There are two major types of phase shifter viz. analog and digital. The analog type are typically narrowband and available in a wide frequency range upto 10 GHz.

Digital phase shifters are designed based on PIN diode assembly. Based on digital control, input signal is routed via different electrical signal lengths. Hence different amount of phase shift is achieved.

Depending upon the structure of basic cell, there are different types of RF phase shifters as follows.
•  Switched line phse shifter
•  Hybrid coupled line
•  periodically loaded line phase shifter

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