Explain RF Phase Shifter Circuit working for 90-Degree Shift

An RF phase shifter circuit is a specialized microwave network designed to alter the transmission phase angle of a high frequency signal by exactly 90 degrees. This creates a quadrature signal, which is essential for advanced modulation techniques. Common 90-degree phase shifter designs include branch line couplers, RC networks and delay lines, widely used in phased array antennas and QPSK modulators.

RF phase shifter circuits are integral components in modern RF systems, enabling precise phase control critical for applications like beamforming, signal processing, and communication systems. This guide explores the working principle behind achieving a 90-degree phase shift in RF signals, highlighting the design considerations and practical applications of these circuits.

RF phase shifters are devices that change the phase of the input signal to any desired value without attenuating the input signal. Depending upon the control mechanism, RF phase shifters are classified as follows:

• Mechanical or Electrical
• Continuous type (analog) or step type (digital)

RF Phase Shifter Circuit using RC network & its working

A simple phase shifter is usually an RC network which will cause the 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.

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

RF Phase Shifter Circuit using hybrid & its working

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

There are two major types of phase shifters viz. analog and digital. The analog type are typically narrowband and available in a wide frequency range up to 10 GHz. Digital phase shifters are designed based on PIN diode assembly. Based on digital control, the input signal is routed via different electrical signal lengths. Hence different amounts of phase shift are achieved.

Depending upon the structure of the basic cell, there are different types of RF phase shifters as follows:

• Switched line phase shifter
• Hybrid coupled line
• Periodically loaded line phase shifter

Summary

A 90-degree RF phase shifter is indispensable for creating precision quadrature signals used in complex radar and digital modulation schemes. Implementing the correct circuit design guarantees optimal phase accuracy and robust wireless network performance.