Phase shift module

A microwave (6 to 18 GHz) Phase Shifter and Frequency Translator. Picture courtesy of Herley

A phase shifter is a microwave network which provides a controllable phase shift of the RF signal.^[1][2][3] Phase shifters are used in phased arrays.^[4][5][6]

Classification

• Active versus passive: Active phase shifters provide gain, while passive phase shifters are lossy.
  • Active:
    • Applications: active electronically scanned array (AESA), passive electronically scanned array (PESA)
    • Gain: The phase shifter amplifies while phase shifting
    • Noise figure (NF)
    • Reciprocity: not reciprocal
  • Passive:
    • Applications: active electronically scanned array (AESA), passive electronically scanned array (PESA)
    • Loss: the phase shifter attenuates while phase shifting
    • NF: NF = loss
    • Reciprocity: reciprocal

• Analog versus digital:
  • Analog phase shifters provide a continuously variable phase shift or time delay.^[7]
  • Digital phase shifters provide a discrete set of phase shifts or time delays. Discretization leads to quantization errors. Digital phase shifters require parallel bus control.

• Differential, single-ended or waveguide:
  • Differential transmission line: A differential transmission line is a balanced two-conductor transmission line in which the phase difference between currents is 180 degrees. The differential mode is less susceptible to common mode noise and cross talk.
    • Antenna selection: dipole, tapered slot antenna (TSA)
    • Examples: coplanar strip, slotline
  • Single-ended transmission line: A single-ended transmission line is a two-conductor transmission line in which one conductor is referenced to a common ground, the second conductor. The single-ended mode is more susceptible to common-mode noise and cross talk.
    • Antenna selection: double folded slot (DFS), microstrip, monopole
    • Examples: CPW, microstrip, stripline
  • Waveguide
    • Antenna selection: waveguide, horn

• Frequency band

• One-conductor or dielectric transmission line versus two-conductor transmission line
  • One-conductor or dielectric transmission line (optical fibre, finline, waveguide):
    • Modal
    • No TEM or quasi-TEM mode, not TTD or quasi-TTD
    • Higher-order TE, TM, HE or HM modes are distorted
  • Two-conductor transmission line (CPW, microstrip, slotline, stripline):
    • Differential or single-ended
    • TEM or quasi-TEM mode is TTD or quasi-TTD

• Phase shifters versus TTD phase shifter
  • A phase shifter provides an invariable phase shift with frequency, and is used for fixed-beam frequency-invariant pattern synthesis.
  • A TTD phase shifter provides an invariable time delay with frequency, and is used for squint-free and ultra wideband (UWB) beam steering.

• Reciprocal versus non-reciprocal
  • Reciprocal: T/R
  • Non-reciprocal: T or R

• Technology
  • Non semi-conducting (ferrite, ferro-electric, RF MEMS, liquid crystal):
    • Passive
  • Semi-conducting (RF CMOS, GaAs. SiGe, InP, GaN or Sb):
    • Active: BJT or FET transistor based MMICs, RFICs or optical ICs
    • Passive: PIN diode based hybrids

• Design
  • Loaded-line:
    • Distortion:
      • Distorted if lumped
      • Undistorted and TTD if distributed
  • Reflect-type:
    • Applications: reflect arrays (S₁₁ phase shifters)
    • Distortion:
      • Distorted if S₂₁ phase shifter, because of 3 dB coupler
      • Undistorted and TTD if S₁₁ phase shifter
  • Switched-network
    • Network:
      • High-pass or low-pass
      • $\pi$ or T
    • Distortion:
      • Undistorted if the left-handed high-pass sections cancel out the distortion of the right-handed low-pass sections
  • Switched-line
    • Applications: UWB beam steering
    • Distortion: undistorted and TTD
  • Vector summing

Figures of Merit

• Number of Effective bits, if digital [Bit]
• Biasing: current-driven, high-voltage electrostatic [mA,V]
• DC power consumption [mW]
• Distortion: group velocity dispersion (GVD) [ps/(km.nm)]
• Gain [dB] if active, loss if [dB] if passive
• Linearity: IP3, P1dB [dBm]
• Phase shift / noise figure [deg/dB] (phase shifter) or time delay / noise figure [ps/dB] (TTD phase shifter)
• Power handling [mW, dBm]
• Reliability [Cycles, MTBF]
• Size [mm²]
• Switching time [ns]

References

1. Microwave Solid State Circuit Design, 2nd Ed., by Inder Bahl and Prakash Bhartia, John Wiley & Sons, 2003 (Chapter 12)
2. RF MEMS Theory, Design and Technology by Gabriel Rebeiz, John Wiley & Sons, 2003 (Chapter 9-10)
3. Antenna Engineering Handbook, 4th Ed., by John Volakis, McGraw-Hill, 2007 (Chapter 21)
4. Phased Array Antennas, 2nd Ed., by R. C. Hansen, John Wiley & Sons, 1998
5. Phased Array Antenna Handbook, 2nd Ed., by Robert Mailloux, Artech House, 2005
6. Phased Array Antennas by Arun K. Bhattacharyya, John Wiley & Sons, 2006
7. Microwave Phase Shifter information from Herley General Microwave

External links

• Website on Phase Shifters in Microwaves
• Microwave Phase Shifter information from Herley General Microwave
• A low cost electro-mechanical phase shifter design, including a brief summary of solid state methods @ www.activefrance.com