Page 311 - Radar Technology Encyclopedia

301 phase shifter, continuous phase shifter, field-effect tetrode

A continuous phase shifter is one with a gradual (continu- Electrical phase shifters implement phase control by means
ous) phase shift within the required limits when the external of semiconductor device electrical control, or as the result of
exposure is applied. In semiconductor phase shifters, such an dielectric and magnetic permeability variation when external
exposure is the control voltage, in ferrite phase shifters, it is electrical and magnetic fields are applied to dielectric and
external magnetic field, in some types of phase shifters it is magnetic plates. (See semiconductor phase shifter, ferrite
mechanical force (see mechanical phase shifter). Continu- phase shifter, Fox phase shifter.). In opposition to mechani-
ous phase shifters can be feed-through or reflex phase cal phase shifters, they give the possibility of reaching high
shifters, typically based on varactors and field-effect tetrodes. phase shift speed: hundreds of megahertz instead of hundreds
They enable the receptions of the continuous phase inversion of hertz for mechanical phase shifters. IAM

from 0 to 360°with a high degree of phase linearity. IAM Ref.: Lavrov (1974), p. 340.
Ref.: Skolnik (1970), p. 12.41; Gassanov (1983), pp. 146, 153; Voskresen- A Faraday-rotation phase shifter is a reciprocal phase
skiy (1981), p. 355
shifter based on the Faraday effect, sometimes implemented
A diode phase shifter uses as the control component a semi- in a phase shifting unit (section of waveguide) with l/4 ferrite
conductor PN diode (varactor) or PIN diode. Phase shifters plate. With such a plate it works with both linear and circular
based on PN diodes provide a gradual variation of the reac- polarized waveforms, the direction of circular polarization
tive component of diode resistance in the mode when the PN does not change and the plane of linear-polarized signal shifts
junction is closed. Typically they are used in low-power con- by 90°. To eliminate this effect, two plates with the opposite
tinuous phase shifters of the reflex type. A reflex phase shifter direction of magnetic fields can be used. IAM
based on a single varactor provides phase shift up to 180° Ref.: Skolnik (1970), p. 12-31; Johnson (1984), pp. 20–36, 47.
with a nonlinearity not worse than 5% in 5-band. PIN diode
A feed-through phase shifter changes the phase of the signal
phase shifters are based on switching of diode states with for-
propagating along a transmission line. Phase shifters of this
ward and reverse biases and are used in high-power (up to 50
type are used both for continuous (see continuous phase
kW) discrete phase shifters. The switch time in high-voltage
shifter) and discrete (see discrete phase shifter) phase con-
phase shifters is about several microseconds, in low-voltage
trols. IAM
phase shifters 10 to 100 ns. The most widely used discrete
Ref.: Sazonov (1988), p. 165, Kaganov (1981), p. 74.
feed-through phase shifters provide the phase shift accuracy
of 5° to 8° in a 5 to 10% bandwidth with an insertion attenua- Ferrite phase shifters use the interaction of the electromag-
tion of 1.0 to 1.5 dB. netic field with ferromagnetic materials. (See FERRITE.)
Diode phase shifters have small weight and size and can They are divided into reciprocal and nonreciprocal devices.
be done with hybrid IC technology. IAM The former include Reggia-Spencer phase shifters, stripline
Ref.: Skolnik (1970), pp. 12.45–12.63; Sazonov (1988), p. 162; Kaganov analog latching phase shifters, and Faraday rotation phase
(1981), p. 75. shifters. The latter include twin-slab phase shifters and strip
A discrete phase shifter produces fixed phase shifts that dif- line phase shifters. Nonreciprocal phase shifters have smaller
fer from each other by the specified value. Discrete phase size, insertion loss, and drive power then reciprocal types, but
shifters are based primarily on PIN diodes, field-effect tran- they must be switched between transmit and receive modes in
sistors, and field-effect tetrodes in feed-through or reflex cir- the systems using a single antenna for transmitting and recep-
cuits. There are three main approaches to designing these tion. The main advantage of ferrite phase shifters is high
phase shifters: switched line sections, lines loaded with LC- power handling capability; the main disadvantages are the
filters, and reflex types with switch elements. The first are dependence of ferrite materials performance on temperature
typically used in phased arrays, but the band is comparatively and difficulties in obtaining a high switching rate because the
narrow. These phase shifters have several sections for differ- control magnetic systems have large inductances. Typically,

ent phase shifts (e.g. 22.5, 45, 90, 180°sections). The phase ferrite phase shifters produce a phase shift of 0 to 360°, they

adjustment error up to 16° for a 4-bit phase shifter reduces the have phase errors less than ±5°in a 10% frequency band, and
possibilities for using programmable control for phase-fre- insertion loss is about 1 dB. IAM
quency response correction. Phase shifters based on LC filters Ref.: Skolnik (1970), pp. 12.1–12.55; Johnson (1984), p. 20.32.
use the capabilities of low-pass and high-pass filters for phase A field-effect tetrode phase shifter is a semiconductor phase
inverting. The use of these phase shifters enables the reduc- shifter with active components based on a field-effect tetrode.
tion of the losses (up to 0.3 to 0.8 dB) and the production of There are two configurations: analog (continuous) and dis-
discrete phase control from 0 to 180°. Field-effect transistors crete phase shifters, based on the dependence of phase shift
phase shifters have a more stable phase shift in broader band on bias voltage in a gate electrode or on vector summation of
than PIN diode phase shifters and they have a switch time of several signals. The first have a phase shift up to 180° in a
about an order less. IAM narrow frequency band and gain of more than 8 dB. The latter
Ref.: Skolnik (1970), p. 12.41;Gassanov (1988), pp. 148, 151; Voskresenskiy types realize discrete control in a 0 to 360° range and have a
(1981), p. 360.
bandwidth of about an octave. The advantages of field-effect
tetrodes are low losses, a high speed of phase variation that is