Glossary of Terms used in Wireless and Mobile Communication - Masinde Muliro University of Science and Technology

MASINDE MULIRO UNIVERSITY OF SCIENCE & TECHNOLOGY

GLOSSARY OF TERMS & STANDARDS USED IN MICROWAVE ENGINEERING


	Antenna beam width	The (full) angle at which the antenna's radiation pattern (in power units) is at half its maximum value. It is also known as the “Half-power full width” (HPFW), or simply the "Half-power beam width," (HPBW). In engineering convention, it is also known as the "3 dB beam width." Antenna radiation pattern depends on the specific plane of cut, and two principal planes are generally given. For a linearly polarized antenna they are the E-plane (the plane containing the radiation maximum and the E-field) and the H-plane (the plane containing the radiation maximum and the H-field, which plane is perpendicular to the Eplane).
	Antenna gain (G(θ,φ)):	The ratio of the radiation intensity in a given direction, to the radiation intensity that would be obtained if the antenna pattern were isotropic. Note: This is equivalent to the commonly used definition that the antenna gain is the product of the directivity and the antenna ohmic efficiency, or radiation efficiency. If the direction is not specified, the direction of maximum radiation is implied.

	Backward wave oscillator (BWO)	A vacuum tube that is used to generate microwaves up to the terahertz range. It belongs to the traveling-wave tube family
	Boresight	The beam-maximum direction of a highly directive antenna.
	Circulator	A three-port ferromagnetic passive device used to control the direction of signal flow in an RF circuit.
	Conversion Loss	The ratio in dB of the IF output of a mixer to the rf input power. All conversion loss measurements and specification are normally based on the mixer being terminated on all ports and a stated LO signal power level being applied
	dBm	Decibels related to 1mW – the standard unit of power level used in the microwave industry. Example: 0 dBm = 1mw, +10 dBm = 10mw, +20dBm = 100mw, etc.
	Directivity	(1) Directivity (of antenna in a given direction (D(θ,φ)): the ratio of the radiation intensity in a given direction from the antenna to the radiation intensity averaged over all directions. Notes: The average radiation intensity is equal to the total power radiated by the antenna divided by 4π. If the direction is not specified, the direction of maximum radiation is implied. (2) A measurement of the desired signal strength to the undesired signal strength. Determined by taking the value of isolation and subtracting the specified coupling (including all variations). Directivity is a measure of how good the couplers performance is (similar to the Q factor of a coil).
	Dynamic Range	The range, from the minimum, which is at a level 3 dB above the amplifier's internally generated floor, to a maximum input signal level that a component can accept and amplify without distortion. Dynamic Range = P1dB - PMDS Where: PMDS = Minimum detectable signal 3 dB above the noise floor
	Directional Coupler	A passive device used for sampling incident and reflected microwave power conveniently and accurately with minimal disturbance to the transmission line. Some general applications for directional couplers include line monitoring, power measurements and load source isolators.
	Gain	Gain is the ratio of the power output to the power input of the amplifier in dB. The gain is specified in the linear operating range of the amplifier where a 1 dB increase in input power gives rise to a 1 dB increase in output power. Gain = 20*log(S21)
	Gunn Diode	A Gunn diode, also known as a transferred electron device (TED), is a type of diode with negative resistance, used in high-frequency electronics. It is based on the "Gunn effect" discovered in 1962 by physicist J. B. Gunn. The negative differential resistance, combined with the timing properties of the intermediate layer, are responsible for the diode's largest use, i.e in electronic oscillators at microwave frequencies and above. A microwave oscillator can be created simply by applying a DC voltage to bias the device into its negative resistance region. Gunn diodes are mainly used at microwave frequencies and above. They can produce some of the highest output power of any semiconductor devices at these frequencies.
	Half-power bandwidth	The width at which the power response is half the maximum value; also called the 3-dB bandwidth.
	Hybrid Coupler	A passive four-port device that is used either to equally split an input signal with a resultant 90° phase shift between output signals or to combine two signals while maintaining high isolation between them.
	Insertion Loss	The drop in power as a signal enters an RF component. This value not only includes the reflected inconming signal, but also the attenuation of the component. Insertion Loss (dB) = 10 * LOG₁₀(Output Power/Incident Power)
	Klystron	A klystron is a specialized linear-beam vacuum tube, invented in 1937 by American electrical engineers Russell and Sigurd Varian, which is used as an amplifier for high radio frequencies, from UHF up into the microwave range.
	LSA (limited space-charge accumulation) diode	A transferred-electron diode similar to the Gunn diode except that it is intended to operate at frequencies that are determined by the microwave cavity in which the diode is mounted and that are several times higher than the transit-time frequency so that the formation of charge packets (or domains) is limited.
	Magnetron	The cavity magnetron is a high-powered vacuum tube that generates microwaves using the interaction of a stream of electrons with a magnetic field while moving past a series of open metal cavities (cavity resonators). Bunches of electrons passing by the openings to the cavities excite radio wave oscillations in the cavity, much as a guitar's strings excite sound in its sound box. The frequency of the microwaves produced, the resonant frequency, is determined by the cavities' physical dimensions. Unlike other microwave tubes, such as the klystron and traveling-wave tube (TWT), the magnetron cannot function as an amplifier, increasing the power of an applied microwave signal; it serves solely as an oscillator
	Microstrip – (Microstripline)	A transmission line consisting of a metalized strip and solid ground plane metallization separated by a thin, solid dielectric. Microstrip is a popular material above 400 MHz and below 6 GHz because it permits accurate fabrication of transmission lines on ceramic or PC board substrates. Higher frequencies or broadband devices tend to favor stripline technology.
	MTBF – (Mean Time Between Failure)	The mean (average) time between failures of a component and is often attributed to the “useful life” of the materials used to assemble the device. MTBF assumes that the component can be “renewed” or fixed after each failure and returned to service immediately after failure.
	Noise Factor	The Noise Factor of a transducer at a specified input frequency is the ratio of (a/b) where “a and b” are: (a) the available Signal to Noise Ratio (SNR) at the signal generator terminals per unit bandwidth when the temperature of the input termination (generator or source) is 290°K and the bandwidth is limited by the transducer, to (b) the available SNR per unit bandwidth at the output terminals of the transducer. Traditionally: Noise Figure NF = 10 log(noise factor F) Noise Temperature (Te) = To(F - 1) Where: Te is the noise temperature To is standard temperature 290 K F is noise factor
	Noise figure	Noise figure (of receiver): at a specified input frequency, the ratio of 1) the total noise spectral power density at a corresponding output frequency available at the output port when the noise temperature of the input termination is T0 = 290 K, to 2) that portion of 10 the total output noise spectral power density that is engendered by the input termination. [12] The noise figure depends on the impedance or reflection coefficient of the input termination and on the location of the input reference plane. Unless otherwise stated, the receiver noise figure is assumed to be defined at the receiver input.
	Noise Temperature	The amount of thermal noise in a chain or a component. Noise Factor and Noise Temperature (Te) are related as follows: Noise Temperature (T_e) = (F - 1)T_o Where: T_e is the noise temperature T_o is standard temperature 290 K F is noise factor For example, a noise figure of 2.0 dB is equivalent to a Noise Temperature of 170 K.
	Return Loss	Return Loss (dB) is defined as a ratio of the incoming signal to the same reflected signal as it enters a component. Return Loss (dB) = 10 * LOG10(Reflected Power/Incident Power)
	Scattering Parameters	Better known as S-Parameters, these 4 values help define the performance of several variables at various frequencies. S₁₁(Input Reflection Coefficient ) = b1/a1 S₁₂(Isolation) = b1/a2 S₂₁ (Forward Transfer Coefficient or Gain /Loss) = b2/a1 S₂₂ (Output Reflection Coefficient) = b2/a2
	Phased array antenna	An antenna with many radiating elements each with a phase shifter. Beams are formed by shifting the phase of the signal emitted from each radiating element, to provide constructive/destructive interference so as to steer the beams in the desired direction.
	PIN diode	A microwave PIN diode is a semiconductor device that operates as a variable resistor at RF and Microwave frequencies. nA PIN diode is a current controlled device in contrast to a varactor diode which is a voltage controlled device.
	Poynting Vector	Poynting vector represents the directional energy flux density (the rate of energy transfer per unit area) of an electromagnetic field. The SI unit of the Poynting vector is the watt per square metre (W/m2). It is named after its discoverer John Henry Poynting who first derived it in 1884.
	Reflex Klystron	Reflex Klystron is one of the most commonly used microwave (low power) generators. It converts D.C. power into microwave power.
	Stripline	A transmission line consisting of a conductor above or between extended conducting surfaces. Higher frequencies or broadband devices tend to favor stripline technology
	Travelling Wave Tube	A traveling-wave tube (TWT, pronounced "twit") or traveling-wave tube amplifier (TWTA, pronounced "tweeta") is a specialized vacuum tube that is used in electronics to amplify radio frequency (RF) signals in the microwave range. Two major categories are: (a) Helix TWT In which the radio waves interact with the electron beam while traveling down a wire helix which surrounds the beam. These have wide bandwidth, but output power is limited to a few hundred watts. (b) Coupled cavity TWT In which the radio wave interacts with the beam in a series of cavity resonators through which the beam passes. The cavities function as narrowband power amplifiers.
	Tunnel diode	Tunnel diode is the p-n junction device that exhibits negative resistance. That means when the voltage is increased the current through it decreases. Tunnel diodes are named after Leo Esaki, who in 1973 received the Nobel Prize in Physics for discovering the electron tunneling effect used in these diodes. Esaki reported the first paper on tunnel diodes in Physical Review in 1958.
	Varactor diode	varactor diode(or a varicap diode, variable capacitance diode, variable reactance diode or tuning diode) is a type of diode designed to exploit the voltage-dependent capacitance of a reversed-biased p–n junction. Varactors are used as voltage-controlled capacitors. They are commonly used in voltage-controlled oscillators, parametric amplifiers, and frequency multipliers.
	Voltage Standing Wave Ratio (VSWR)	Voltage Standing Wave Ratio is the ratio of the maximum to the minimum voltage of a standing wave (which is the instantaneous sum of incident and reflected waves). VSWR of 1:1 means that 100% of the incoming signal passed through the component without any reflection. In that case, there would be no standing wave. A VSWR of 2:1 (or mismatch) means that 12% of the incoming signal was reflected.