# Phase shift module

A phase shift module is a microwave network module which provides a controllable phase shift of the RF signal. Phase shifters are used in phased arrays.

## 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.
* 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

### 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 (S$_{11}$ phase shifters)
** Distortion:
*** Distorted if S$_{21}$ phase shifter, because of 3 dB coupler
*** Undistorted and TTD if S$_{11}$ 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$^2$/nm]
* Gain [dB] if active, loss [dB] if passive
* Linearity: IP3, P1dB [dBm]
* Phase shift / noise figure [°/dB] (phase shifter) or time delay / noise figure [ps/dB] (TTD phase shifter)
* Power handling [mW, dBm]
* Reliability [cycles, MTBF]
* Size [mm$^2$]
* Switching time [ns]