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# Module 11 - Microwave Principles Navy Electricity and Electronics Training Series (NEETS)Chapter 3:  Pages AI-1 through AI-6

APPENDIX I

GLOSSARY

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 klystron oscillator.

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.

CHOKE JOINT - A joint between two sections of waveguide that provides a good electrical connection without power losses or reflections.

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 waveguide.

DIELECTRIC CONSTANT - The ratio of a given dielectric to the dielectric value of a vacuum.

DIELECTRIC 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.

AI-1

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 repeller voltage.

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 propagation.

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.

GRID-GAP 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.

AI-2

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 field.

INTERELECTRODE CAPACITANCE - The capacitance between the electrodes of an electron tube.

I2R 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 direction.

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.

LOOSE 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.

AI-3

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.

NEGATIVE-RESISTANCE 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 transistors.

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.

POWER 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.

REFLEX 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 (dielectric).

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.

AI-4

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.

STAGGER 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 given frequency.

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 mode.

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 ELEMENT.

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.

VERTICAL 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.

WAVEGUIDE MODE 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).

AI-5

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.

AI-6