Page 87 - Radar Technology Encyclopedia

circuit, linear circulator, ferrite 77

A parametric circuit is one in which at least one of the
t
parameters (resistance, capacitance, inductance) is a function
,
y t () = ò h t t,( ) x t() t , ij , = 1 N
d
i ij i of time. If the circuit parameters do not depend upon the oper-
– ¥ ating mode, then the circuit is linear. Circuits with variable
active impedance are used for detection, amplitude modula-
When the circuit is of inertialess-type configuration (the
tion, and frequency conversion. Circuits with variable reactive
parameters of the circuit do not change with time),
elements are suitable for storing and releasing energy and are
and the circuit characteristics depend
h ( t t, ) h ( t – t )
=
ij ij used in parametric generators and amplifiers. IAM
only on one parameter: time shift, t A linear circuit does not
.
Ref.: Popov (1980), p. 276.
change the probability distribution of the input signal (i.e., if
the input is Gaussian the output will also be Gaussian). Exam- A printed circuit is “a pattern comprising printed wiring
ples of linear lumped circuits are oscillating circuits, filters, formed in a predetermined design in, or attached to, the sur-
differentiating, and integrating circuits. Linear distributed cir- face or surfaces of a common base.” It is a wiring assembly of
cuits are represented by different types of transmission lines electronic components on a printed board, using printed wir-
(e.g., coaxial lines). IAM ing, while the elements themselves can also be produced by
Ref.: Levin (1974), p. 214; Oppenheim (1983), Ch. 3; Gonorovskiy (1986), printing (using attached elements) on the boards using assem-
p. 12. bly openings or by placing planar leads on the contact areas
of the boards. In this case such an assembly is termed a
A lumped circuit is one in which electromagnetic fields are
printed-circuit assembly. IAM
concentrated in discrete elements (capacitors, inductors,
resistors). The elements of the circuit are connected by wires Ref.: IEEE (1993), p. 1,007; Popov (1980), p. 287.
having fields that can be neglected. SAL A sample-and-hold circuit is a sampling circuit whose out-
Ref.: Terman (1955), Ch. 3. put is held at the level of the last sample until the next one
arrives. Typically, it consists of an electric circuit that clamps
A nonlinear circuit (or network) is one performing nonlinear
the potential of a storage element (e.g., capacitor) to the video
transformations of input signals. The generic methods of
pulse amplitude each time the new sample is received. Obso-
analysis are well designed primarily for inertialess nonlinear
lete terms for this circuit are the boxcar detector and boxcar
circuits, in which the input s(t) and output y(t) at any moment
generator. SAL
are related by a single-valued function:
Ref.: Skolnik (1980), p. 156.
=
yt () fx t ()[ ]
A sampling circuit is one “whose output is a series of dis-
This dependence is a good approximation for describing crete values representative of the values of the input at a
many types of radio circuits: limiters, mixers, detectors, and series of points in time.” (See SAMPLING.)
so forth. A characteristic of nonlinear circuits is the presence Ref.: IEEE (1993), p. 1,165.
in the output spectrum of harmonics not present in the input
spectrum. (See also filter, nonlinear.) IAM CIRCULATOR, microwave. A circulator is a decoupling
multichannel structure, in which the electromagnetic waves
Ref.: IEEE (1993), p. 856; Levin (1974), vol. 1, p. 214; Gonorovskiy (1986),
p. 14. propagate from one channel to another only in a particular
order. It is typically a “passive waveguide junction of three or
An oscillatory circuit is one “containing inductance and
more arms in which the arms can be listed in such an order
capacitance so arranged that when shock excited it will pro-
that when power is applied to any arm it is transferred to the
duce a current or voltage that reverses at least once.” Typi-
next on the list, the first arm being counted as following the
cally, oscillatory circuits have one or several resonators and
last in order.” Applied to a radar duplexer, it allows a single
additional circuits to control and maintain oscillations.
antenna to be used for both transmission and reception. It can
According to the character of the electrical and magnetic
be used in parametric amplifiers, circuits that add power from
fields distribution, they are divided into lumped circuits,
several generators, and so on.
based on lumped resonators with capacitance C and induc-
Circulators are categorized as being either wave rotation
tance L, and distributed circuits, based on the sections of dif-
or phase-shift circulators. They are constructed from various
ferent transmission lines (coaxial lines, waveguide lines, strip
types of transmission line (Y-junction circulators). Phase cir-
lines, etc.). According to the operating band, oscillatory cir-
culators are usually used in high-power circuits, while low-
cuits are divided into narrowband circuits with no capabilities
power circuits usually employ Y-junction circulators. IAM
for frequency agility (only limited tuning capabilities), typi-
Ref.: IEEE (1993), p. 190; Skolnik (1970), pp. 8.20–8.24; Lavrov (1974),
cally based on a single resonator, and wideband circuits
p. 355.
employing frequency agility capabilities and based on a set of
resonators. Depending on the type of resonator, the most A ferrite circulator is one based on the interaction of electro-
widely used are oscillatory circuits with coaxial, waveguide, magnetic waves with a magnetized ferromagnetic substance.
and strip line resonators, which are used in microwave filters, Virtually all circulators used in radar systems contain ferrite
antenna radiating elements, and vacuum tubes. AIL elements (pins, disks, or plates) and are thus ferrite circula-
tors.
Ref.: IEEE (1993), p. 896; Gassanov (1988), p. 46; Kovalev (1972), p. 195.