Page 314 - Radar Technology Encyclopedia

phase shifter, toroidal POLARIZATION 304

A toroidal phase shifter is a nonreciprocal ferrite phase open structure and operates with the inverse spatial harmonic.
shifter with the transverse magnetic field, using one or several An amplifying or oscillating platinotron is called an
sections of ferrite material having toroidal geometry. It can be amplitron or a stabilitron, respectively.
implemented as an analog or digital unit, typically are based A platinotron is used in decimeter and centimeter wave-
on a waveguide or strip transmission line. Switching time is bands basically in output stages of pulsed-radar transmitters.
about 0.5 to 2 ms, frequency band is 10%, insertion losses are IAM
0.8 to 1.2 dB, and average power handling capability is 0.2 to Ref.: Skolnik (1962), p. 231; Popov (1980), p. 291.
0.4 kW. AIL
PLUMBING. “A colloquial expression for pipelike
Ref.: Skolnik (1970), p. 12.15; Sazonov (1988), p. 178.
waveguide circuit elements and transmission lines.”
A transverse magnetic field phase shifter is a nonreciprocal Ref.: IEEE (1993), p. 963.
ferrite phase shifter providing phase shifting as a result of
POINCARÉ SPHERE. “A sphere whose points are associ-
magnetic permeability variation in ferrite with a transverse
ated in a one-to-one fashion to all possible polarization states
magnetic field created by electromagnets. This phase shifter
of a plane wave [field vector] according to the following
is of the nonreciprocal type. When it uses rectangular
rules: The longitude equals twice the tilt angle, and the lati-
waveguide, two ferrite plates are typically inserted to increase
tude is twice the angle whose cotangent is the negative of the
the phase shift. A coaxial variant with an area between ferrite
axial ratio of the polarization ellipse.” The north pole repre-
plates partially filled by dielectric is also used. Continuous
sents left-hand circular polarization, the south pole right-
phase shifters of this type require a permanent current supply
handed circular, and diametrically opposite points represent
to the control winding. Discrete phase shifters do not have
orthogonal polarizations (Fig. P12). If the angular distance
this disadvantage. (See toroidal phase shifter.) IAM
between two points is 2x, then the polarization efficiency (the
Ref.: Sazonov (1988), p. 177.
fraction of power transferred between antennas having polar-
twin-slab phase shifter (see toroidal phase shifter). izations represented by the points) is
h = cos2x
p
A waveguide phase shifter is based on the variation of elec-
SAL
trical length of a waveguide. According to the type of control
Ref.: IEEE (1993), p. 963; Johnson (1984), p. 1.9.
used they are divided into mechanical and electrical phase
shifters. Mechanical waveguide phase shifters have different
modes of electrical length variation: the variation of geomet-
rical length, the use of a dielectric plate inserted parallel to the
electrical field through a nonradiating slot, or the use of an
elastic section of waveguide made from a springy material.
Typically, waveguide phase shifters are used in the band of 6
to 35 GHz. IAM
Ref.: Skolnik (1962), p. 308; Sazonov (1988), p. 152; Lavrov (1974), p. 340.
PHASOR. A phasor “a complex number expressing the mag-
nitude and phase of a time-varying quantity.” It is used to
describe a signal vector, relative to some arbitrary reference
phase (e.g., the phase of the reference oscillator, or COHO, in
an MTI system). DKB
Ref.: IEEE (1993), p. 946.
PLATFORM. In radar terminology, the platform refers to the
Figure P12 Polarization states on the Poincaré sphere (from
vehicle on which the radar is mounted.
Johnson, 1984, Fig. 1.4, p. 1.9, reprinted by permission of
Platform motion effects are the effects introduced in radar McGraw-Hill).
performance by a movable platform, which may also be
POLARIZATION. In the context of radio-wave propaga-
unstable and deformed (such as ship, aircraft, spacecraft, or
tion, pointing is “the locus of the tip of the electric field vec-
etc.). This effect results in additional measurement errors (see
tor observed in a plane orthogonal to the wave normal.” All
ERROR, platform dependent) and other effects such as
polarizations are special cases of elliptical polarization, which
velocity spread across the antenna beamwidth in airborne
may be divided into right-hand and left-hand. Special cases
MTI), and others. (See SLANT-RANGE EFFECT.) SAL
are circular and linear polarization, and special cases of this
Ref.: Skolnik (1990), pp. 16.3-16.8; Leonov (1990), pp. 174-203.
last are horizontal and vertical polarizations. Complete infor-
A PLATINOTRON is a microwave tube that combines the mation about a backscattered electromagnetic signal (radar
properties of a magnetron and a backward-wave tube with a return) is represented by polarization scattering matrix. (See
transverse magnetic field (M-type). In contrast to the magne- MATRIX.) Techniques using all the information content of
tron, the platinotron, like the backward-wave tube, has an the polarization scattering matrix are called matrix tech-