Basics and types of RF Phase shifter for phased array antennas
This article covers RF phase shifter basics and RF phase shifter types used in phased array antennas and for other applications.
What is RF Phase Shifter ?
The RF device which shifts the phase angle of input RF signal given at its input and keeps its amplitude constant is called RF phase shifter.
Types of phase shifters based on their control and mechanical constructions are analog phase shifter,
digital phase shifter and mechanical phase shifter.
Analog phase shifter : In this type of phase shifter, phase shift is controlled using analog control voltage.
Digital phase shifter : In this type, phase shift is controlled using digital data bits by microcontroller/microprocessor
or via computer interface. USB and ethernet controlled phase shifters have been developed under this type. They are also called as programmable phase shifters.
Mechanical phase shifter : In this type, phase shift is controlled by tuning the knob manually.
The figure depicts digital phase shifters used in phased array transmitter system. These phase shifters are used to change the phase angle of individual beams provided to individual antennas used in an antenna array. Hence it generates required beamformed output as per system requirement. There are four types of array antennas viz. linear array, planar array, circular array and conformal array based on position and shape of antenna elements. Refer Phased Array Antenna basics >> for more information on 4G/5G Basestation Array Antenna and 4G/5G Smartphone Antenna.
RF Phase Shifter specifications
Following are the generic specifications of RF phase shifter to be considered before making purchase decision.
• Phase range (in units of degrees)
• Phase shifter control type (Analog Voltage, Digital bits, Mechanical knob, Programmable control)
• Insertion Loss (dB)
• Operating frequency range
• Power at input and output
• Supply voltage
• Package type (Surface mount, module, benchtop, rackmount)
Comparison between RF Phase Shifter types
RF Phase shifters based on materials used in their construction and their design methods are ferroelectric phase shifter, MMIC based phase shifter, ferrite phase shifter and MEMS phase shifter. Following table mention difference between them based on various comparison parameters.
| Features | Ferroelectric based | MMIC (Semiconductor based) | Ferrite based | MEMS based |
|---|---|---|---|---|
| Power handling | > 1 Watt | Tens of Watts | KW | < 50 mWatt |
| Linearity | IMD (Intermodulation distortion) intersect at +60 dBm | IMD (Intermodulation distortion) intersect between +35 to +40 dBm | IMD (Intermodulation distortion) intersect at +80 dBm | |
| Switching speed | Intrinsically fast, in ns range | Fast, < 10-9 seconds | 10 to 100 µs | 10 to 100 µs |
| DC power consumption | Low, µW range (<1 µA current) | Low, <10 mWatt | High, 10 Watt range | Negligible |
| RF loss | Approx. 5 dB/36o @ K band | Approx. 2 dB/bit @ Ka band | < 1 dB / 360o @ X band | Approx. 2.3 dB/337.5o @ Ka band |
| Size | Very small | Small | Large | Small |
| Reliability | Good | Very good | Excellent | Good |
| Cost | Low | Expensive | Very expensive | Low |
Reference : Information provided in the table has been derived from pdf document on "Array Phase Shifters : Theory and Technology" Source : NASA Center for Aerospace Information.