Module 11 − Microwave Principles
APERTURE - See slot.
BOUNDARY CONDITIONS - The two conditions that
the E-field and H-field within a waveguide must meet before energy will travel down the waveguide. The E-field
must be perpendicular to the walls and the H-field must be in closed loops, parallel to the walls, and
perpendicular to the E-field.
BEARING - An angular measurement that indicates the direction of an object in
degrees from true north. Also called azimuth.
BUNCHER CAVITY - The input resonant cavity in a conventional
BUNCHER GRID - In a velocity-modulated tube, the grid which concentrates the electrons
in the electron beam into bunches.
CATCHER GRID - In a velocity-modulated tube, a grid on which the spaced
electron groups induce a signal. The output of the tube is taken from the catcher grid.
CAVITY RESONATOR - a
space totally enclosed by a metallic conductor and supplied with energy in such a way that it becomes a source of
electromagnetic oscillations. The size and shape of the enclosure determine the resonant frequency.
JOINT - a joint between two sections of waveguide that provides a good electrical connection without power losses or
COOKIE-CUTTER TUNER - Mechanical magnetron tuning device that changes the frequency by changing
the capacitance of the anode cavities.
COPPER LOSS - Power loss in copper conductors caused by the internal resistance of the conductors to current
flow. Also called I2R loss.
CROWN-of-THORNS TUNER - See Sprocket Tuner.
CUTofF Frequency - The
frequency at which the attenuation of a waveguide increases sharply and below which a traveling wave in a given
mode cannot be maintained. a frequency with a half wavelength that is greater than the wide dimension of a
Dielectric CONSTANT - The ratio of a given dielectric to the dielectric value of a vacuum.
LOSSES - The electric energy that is converted to heat in a dielectric subjected to a varying electric field.
DirectIONAL COUPLER - a device that samples the energy traveling in a waveguide for use in another circuit.
DirectIVITY - The narrowness of the radiated beam from an antenna.
DOMINANT Mode - The easiest mode to produce in a waveguide, and also, the most efficient mode in terms
of energy transfer.
DRIFT SPACE - In an electron tube, a region free of external fields in which relative
electron position depends on velocity.
Dummy Load - a device used at the end of a transmission line or
waveguide to convert transmitted energy into heat so no energy is radiated outward or reflected back.
E-FIELD - Electric field that exists when a difference in electrical potential causes a stress in the dielectric
between two points.
E-TYPE T-JUNCTION - a waveguide junction in which the junction arm extends from the main
waveguide in the same direction as the E-field in the waveguide.
ELECTRIC FIELD - See E-field.
ELECTRONIC TUNING - In a reflex klystron, changing the frequency and output power of the tube by altering the
ELECTROLYSIs - Chemical changes produced by passing an electrical current from one
substance (electrode) to another (electrolyte).
ELECTRON ORBITAL MOVEMENT - The movement of an electron around the nucleus of an atom.
ELECTRON SPIN - The
movement of an electron around its axis.
ELEVATION ANGLE - The angle between the line of sight to an object
and the horizontal plane.
FARADAY ROTATION - The rotation of the plane of polarization of electromagnetic
energy when it passes through a substance influenced by a magnetic field that has a component in the direction of
FERRITE - a powdered and compressed ferric oxide material that has both magnetic properties and resistance
to current flow.
FERRITE Switch - a ferrite device that blocks the flow of energy through a waveguide by
rotating the electric field 90 degrees. The rotated energy is then reflected or absorbed.
TUNING - a method of changing the center frequency of a resonant cavity by physically changing the distance between
the cavity grids.
GROUP VELOCITY - The forward progress velocity of a wave front in a waveguide.
H-FIELD - Any space or
region in which a magnetic force is exerted. The magnetic field may be produced by a current-carrying coil or
conductor, by a permanent magnet, or by the earth itself.
H-TYPE T-JUNCTION - a waveguide junction in which
the junction arm is parallel to the magnetic lines of force in the main waveguide.
Helix - a spirally wound transmission line used in a traveling-wave tube to delay the forward progress
of the input traveling wave.
HORIZONTAL Plane - An imaginary plane tangent to and touching the Earth's
surface as established by a stable element, such as a gyroscope.
HORN - a funnel-shaped section of waveguide used as a termination device and as a radiating antenna.
HOT CARRIER - a current carrier, which may be either a hole or an electron, that has relatively high energy
with respect to the current carriers normally found in majority-carrier devices.
HOT-CARRIER DIODE - a
semiconductor diode in which hot carriers are emitted from a semiconductor layer into the metal base. Also called
a hot-electron diode. An example is the Schottky-Barrier diode.
HYBRID JUNCTION - a waveguide junction that
combines two or more basic T-junctions.
HYBRID RING - a hybrid-waveguide junction that combines a series of
E-type T-junctions in a ring configuration.
IDLER Frequency - In a parametric amplifier, the difference
between the input signal and the pump signal frequency. Also called the lower-sideband frequency.
INTERACTION SPACE - The region in an electron tube where the electrons interact with an alternating electromagnetic
Interelectrode Capacitance - The capacitance between the electrodes of an electron tube.
LOSS - See Copper Loss.
IRIs - a metal plate with an opening through which electromagnetic waves may pass. used as an impedance matching device in waveguides.
LEAD Inductance - The inductance of the lead wires connecting the internal components of an electron tube.
Load IsOLATOR - a passive attenuator in which the loss in one direction is much greater than that in the
opposite direction. An example is a ferrite isolator for waveguides that allows energy to travel in only one
Loop - a curved conductor that connects the ends of a coaxial cable or other transmission line and projects into
a waveguide or resonant cavity for the purpose of injecting or extracting energy.
Coupling - Inefficient coupling of energy from one circuit to another that is desirable in some applications. Also
called weak coupling.
MAGIC-T JUNCTION - a combination of the H-type and E-type T-junctions.
Magnetic FIELD - See H-field.
METALLIC INSULATOR - a shorted quarter-wave section of transmission line.
Microwave REGION - The
portion of the electromagnetic spectrum from 1,000 megahertz to 100,000 megahertz.
Modulator - a device that
produces modulation; i.e., varies the amplitude, frequency, or phase of an ac signal.
ELEMENT - a component having an operating region in which an increase in the applied voltage increases the
resistance and produces a proportional decrease in current. Examples include tunnel diodes and silicon unijunction
NONDegenerative-PARAMETRIC Amplifier - a parametric amplifier that uses a pump signal frequency
that is higher than twice the frequency of the input signal.
Phase SHIFTER - a device used to change the
phase relationship between two ac signals.
Power Gain - The ratio of the radiated power of an antenna compared to the output power of a standard antenna. a
measure of antenna efficiency usually expressed in decibels. Also referred to as Power RATIO.
RATIO - See Power Gain.
PROBE - a metal rod that projects into, but is insulated from, a waveguide or resonant
cavity and used to inject or extract energy.
PUMP - Electrical source of the energy required to vary the
capacitance of a parametric amplifier.
RANGE - Distance, as measured from a point of reference, such as a
radar, to a target or other object.
REACTANCE Amplifier - a low-noise amplifier that uses a nonlinear
variable reactance as the active element instead of a variable resistance. Also called a parametric amplifier.
RECIPROCITY - The ability of an antenna to both transmit and receive electromagnetic energy.
KLYSTRON - a klystron with a reflector (repeller) electrode in place of a second resonant cavity to redirect the
velocity-modulated electrons back through the cavity which produced the modulation.
REFRACTIVE Index - The
ratio of the phase velocity of a wave in free space to the phase velocity of the wave in a given substance
REPELLER - Sometimes called a reflector. An electrode in a reflex klystron with the primary
purpose of reversing the direction of the electron beam.
ROTATING JOINT - a joint that permits one section of a transmission line or waveguide to rotate continuously
with respect to another while passing energy through the joint. Also called a rotary coupler.
SKIN EFFECT - The tendency for alternating current to concentrate in the surface layer of a conductor.
The effect increases with frequency and serves to increase the effective resistance of the conductor.
SLOT - Narrow opening in a waveguide wall used to couple energy in or out of the waveguide.
Also called an
aperture or a window.
SPROCKET TUNER - Mechanical tuning device for magnetron tubes that changes the
frequency of the cavities by changing the inductance. Also called a crown-of-thorns tuner.
TUNING - a method of klystron tuning in which the resonant cavities are tuned to slightly different frequencies to
increase the bandwidth of the amplifier.
Standing WAVE RATIO - The ratio of the maximum to the minimum amplitudes of corresponding components of a
field, voltage, or current along a transmission line or waveguide in the direction of propagation measured at a
SYNCHRONOUS TUNING - In a klystron amplifier, a method of tuning which tunes all the resonant cavities to
the same frequency. High gain is achieved, but the bandwidth is narrow.
TRANSIT TIME - The time an electron
takes to cross the distance between the cathode and anode.
TRANSVERSE ELECTRIC Mode - The entire electric
field in a waveguide is perpendicular to the wide dimension and the magnetic field is parallel to the length. Also
called the TE mode.
TRANSVERSE Magnetic Mode - The entire magnetic field in a waveguide is perpendicular to
the wide dimension ("a" wall) and some portion of the electric field is parallel to the length. Also called the TM
TUNNELING - The piercing of a potential barrier in a semiconductor by a particle (current carrier) that does
not have sufficient energy to go over the barrier.
TUNNEL DIODE - a heavily doped junction diode that has
negative resistance in the forward direction over a portion of its operating range. See Negative-Resistance
VARACTOR - a PN-junction semiconductor designed for microwave frequencies in which the capacitance varies with
the applied bias voltage.
VARIABLE ATTENUATOR - An attenuator for reducing the strength of an ac signal
either continuously or in steps, without causing signal distortion.
VELOCITY MODULATION - Modification of
the velocity of an electron beam by the alternate acceleration and deceleration of electrons.
Plane - An imaginary plane that is perpendicular to the horizontal plane.
WAVEGUIDE - a rectangular, circular,
or elliptical metal pipe designed to transport electromagnetic waves through its interior.
of Operation - Particular field configuration in a waveguide that satisfies the boundary conditions. Usually divided
into two broad types: the transverse electric (TE) and the transverse magnetic (TM).
WAVEGUIDE POSTS - a rod of conductive material used as impedance-changing devices in waveguides.
WAVEGUIDE SCREW - a screw that projects into a waveguide for the purpose of changing the impedance.
WINDOW - See Slot.
WOBBLE Frequency - The frequency at which an electron wobbles on its axis under the
influence of an external magnetic field of a given strength.
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