GLOSSARY OF TERMS

Albaloy: A plating finish comprised primarily of copper, tin and zinc which provides good electrical performance, but unlike silver, albaloy is highly resistant to tarnish.  Being non-magnetic, it also provides excellent passive intermodulation (PIM) performance comparable to silver.

Amplifier: An active device where a signal is fed to the input of the amplifier and an amplified, higher power level, signal of the same frequency as the input signal, exists the amplifier. A measure of how much the signal was amplified is called the amplifier gain.

Amplitude Balance: The maximum peak-to-peak amplitude difference (in dB) between the output ports of a power divider or hybrid coupler over the specified frequency range.

Attenuation: Loss of signal amplitude or power measured in dB.

Attenuation Accuracy: The amount of variation in magnitude from the nominal value across the entire frequency band.

Attenuator: A passive device or network that absorbs part of the input signal and transmits the remainder with minimal distortion.  Attenuators are used to extend the dynamic range of devices such as power meters and amplifiers, reduce signal levels to detectors, match circuits and are used daily in lab applications to aid in product design.  Attenuators are also used to balance out transmission lines that otherwise would have unequal signal levels.

Bandpass Filter: A filter that passes a band of frequencies and rejects higher and lower frequencies outside the band.

Bandwidth: The with of the pass band of a bandpass filter.  It is bounded by the upper and lower frequencies of the pass band pass filter.

Base Station: A fixed transmitter/receiver with which a mobile radio transceiver establishes a connection link to gain access to the public-switched telephone network.

Bias Tees: A passive device used in applications to inject/remove DC voltages in RF circuits without affecting the RF signal through the main transmission path.  Ideal for remote powering of bi-directional amplifiers (BDAs), repeaters and tower top amplifiers (TTAs) by BTS control modules.

Center Frequency: It is the center frequency (mid-point) of the pass band of a band pass filter.

Circuit: The strip line element (or sometimes microstrip) that forms a resonator with the ground plane.  This circuit element has 120° symmetry, may be circular or triangular, and may have cuts and shapes to adjust its RF properties.  Three transmission lines match and connect the circuit to the three input/output connectors.

Circulator: An RF device with three ports that allows the input signal to be directed with low loss to a second port, with none coming out of the third port.  The device is symmetrical, and any port may be selected for the input port.  Circulators are made in coaxial, waveguide, drop-in, and surface mount configurations.

Coaxial: A transmission line in which the ground conductor surrounds the center conductor, the two being coaxial and separated by a continuous dielectric such as air or PTFE.

Connector: Coax units are equipped with SMA or N-Type connectors (other types can be fitted by request).

Contact Resistance: The electrical resistance across closed contacts as measured at their associated external terminals.

Coupling: Is a measure of the radio, in dB, of the input power of a coupler to power picked up by the coupler port.

Coupling Variation (dB): The Maximum peak-to-peak variation in coupling expected over the specified frequency range.

Cutoff Frequency: The upper frequency edge of the pass band of low pass filters.

CW (Continuous Wave): Signal of constant amplitude.  In contrast, pulsed signals are discontinuous.

dB (Decibel): A comparison of two power levels equal to ten times the common logarithm of their ratio, or the ratio of two voltage levels equal to 20 times the common logarithm of their ratio.

dBc: The ratio in dB of a power level that is being compared to the power level of the reference carrier signal. Normally used for comparing noise and distortion products present on a carrier signal.

dBm: The number of decibels related to 1mW – the standard unit of power level used in the microwave industry.  Example:  0 dbM = 1mw, +10dBm = 10mw, +20dBm = 100mw, etc.

DC Block: An in-line device primarily used in applications to block DC voltages in RF circuits without affecting the RF signal through the main transmission path.  The three basic types are:

1. Inner – Blocks DC voltages on inner conductor only
2. Outer – Blocks DC voltages on outer conductor only
3. Inner/Outer – Blocks DC voltages on both conductors

Directional Coupler: A passive device used for sampling incident and reflected microwave power conveniently and accurately with minimal disturbance to the transmitted signal.  Some general applications for directional couplers include line monitoring, power measurement and load source isolators.

Directivity (dB): Directivity is a measure of how well a coupler isolates forward and reverse signals. An ideal coupler has only the forward signal coupled into the coupled port.  Directivity is determined by taking the value of isolation and subtracting the specified coupling (including all variations).

DPDT (products/coaxial – switches): Double-Pole-Double-Throw switch. A switching with two inputs and two outputs, providing a ON – OFF switch function.  Cab be thought of as two Singe Pole Single Throw (SPST) switches mechanically linked together.

Drop in: A component that does not require connectors, but has tabs that are typically soldered in place.  The component housing may be bolted to the system ground plane.

 

Dual Directional Coupler: A passive 4 port device where the power enters through the main line from port 1 to port 2 and a fraction of the power is picked up by the coupled port, port 3. A small fraction is also picked up by port 4, in case of matched load, the smaller the amount of power picked up by port 4, is a measure of a good coupler directivity.  If port 2 of the directional coupler is not terminated with the characteristic impedance of the coupler, mismatch load condition, some power will be reflected back to port 1, and is picked up by isolated port, por 1.

Duty Cycle: The ratio representing the length of time RF power will pass through the switch and the length of time between RF on and off cycles.  Usually represented as the percentage of time at full RF power.

EMI (Electromagnetic Interference): Unintentional interfering signals generated within or external to electronic equipment.  Typical sources could be power line transients and electromechanical switching equipment.

Energization: The application of power to an actuator coil winding of an electromechanical switch or relay.  Use of this word assumes enough power to operate the relay, unless otherwise stated.

Failsafe: A switch with an actuator that contains a spring return mechanism to provide RF connection to one selected output when no voltage is supplied to the actuating terminals.  Failsafe switches require continuously applied actuator voltage to maintain RF connection at any other position.

Ferrite: The ferrite material is the key component of a circulator.  It is a ceramic material that interacts with the applied RF field depending on the level of stationary magnetic field across it.  As part of a resonator formed by the circuit, the RF fields form standing waves, whose pattern allows energy to flow from the input port to just one of the other two ports.

Frequency Range (MHz): The minimum and maximum frequencies between which the specified component will meet all guaranteed specifications.

Frequency Sensitivity: The maximum peak-to-peak variation in coupling (in dB) of a directional or hybrid coupler over the specified frequency range.  Also referred to as “flatness”.

Gain: Gain is the ratio of the output to the input power of the amplifier in dB. Gain = 20*log(S21)

GHz (Gigahertz): A unit of frequency measure equal to 1000 MHz (Megahertz) or a billion hertz.

Ground Station: As an operating environment for RF switch equipment, a ground station is an indoor, stationary installation where reliability and bandwidth are higher priorities than size or weight.

High Pass Filter: A filter which passes high frequencies and rejects low frequencies.

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 the ports.

IMD: Intermodulation Distortion is the result of two or more RF signals interacting in a non-linear medium.  Power amplifiers produce IMD products at high power levels when amplification begins to saturate and the gain is no longer linear.  Ferrite devices produce IMD since ferrite materials are inherently non-linear.  Dissimilar metal junctions also cause IMD products, but usually at a very low level.  Normally, only third order products are significant.  These have frequencies given by 2F1-F2 and 2F2-F1, where F1 and F2 are the input frequencies.

Impedance (Ohms): Resistance to alternating current.  Most RF and microwave systems are designed to operate with a characteristic impedance of 50 ohms or 75 Ohms.

Input VSWR: A measurement of the signal reflected from the input port over the specified frequency range with all other ports terminated in 50-ohm loads.

Insertion Loss: The transmission loss from input to output, measured in dB.  Typically quoted as the highest loss over the passband.

Iridite (14-2): A chemical film (typically clear or yellow in color) which provides a barrier medium to prevent corrosion on aluminum surfaces and enhance adhesion of subsequent coatings such as paints and primers.

Isoadapter: An isolator that includes a coax to waveguide transition.  The isolator is usually contained in the coax section.  This device has the advantage of reducing VSWR between the transition and the isolator.

Isolation: A unit of measure (in dB) that compares the power level of a signal entering the output port with the level of that signal exiting the input port.

Isolator: An RF device that allows RF energy to flow with low loss in one direction, but presents high attenuation in the other direction. Typically, an isolator is made by terminating one port (3) of a circulator. Any power reflected back into the output port (2) is absorbed by the termination on port 3.

Latching: A switch with a self-cut off actuator that contains a mechanism, either electrical, mechanical, or magnetic, that will stop the chosen RF contact path once voltage is maintained on the control terminals after switching is accomplished.

Linear Phase Filter: A filter where the phase response versus frequency is a straight line. This filter displays a constant delay in its passband.

Low Pass Filter: A filter which passes low frequencies and rejects high frequencies.

Magnet: Powerful ceramic magnets provide the stationary field that causes the ferrite material to exhibit circulator properties. Typically, a magnet is placed on both sides of the ferrite components.

MHz (Megahertz): A unit of frequency measure equal to 1000 kHz (Kilohertz) or a million hertz.

Microstrip (Microstrip line): A transmission line consisting of a metalized strip and solid ground plane metallization separated by a thin, solid dielectric.  Microstrip is a popular transmission medium 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 strip line technology.

Millimeter Wave Frequency Range: The frequency range where the electromagnetic wavelength is between approximately one centimeter and millimeter in length.  Traditionally from approximately 30 GHz to 300 GHz.

MTBF (Mean Time Between Failure): The mean (average) time between failures of a component; it 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.

Non-Coherent Signals: The limiting factor for most Wilkinson power dividers used as combiners is power dissipation.  When input signals are out of phase, non-coherent, or have amplitude unbalance, cancellation occurs across the isolation resistors resulting in power dissipation.  Since these devices are most commonly used as dividers, typical industry designs utilize low power alumina surface mount resistor chips on a thermally insulating circuit board.  However, maximum input for combining non-coherent signals on adjacent ports is:  (Rated input power of divider * 5%) / “N” # of input channels.  If the rated power is exceeded, the chip resistors will heat up and degrade resulting in loss of port-to-port isolation and VSWR.

Output VSWR: A measurement of the signal reflected from the output port over the specified frequency range with all other ports terminated in 50-ohm loads.

1-dB Compression Point: It is the amount of output power from an amplifier where in the output power verses input power filters linear gain curve, the gain is decreased by 1dB from the linear gain asymptote.

Passband: The frequency range of the passband of a filter.

Passivation: The formation of an insulating layer directly over a metal to protect the surface from contaminants, moisture, or particles.

Phase Balance: The maximum peak-to-peak phase difference (in degrees) between the output ports of a power divider over the specified frequency range.

Phase Velocity: This is the velocity at which the phase of any one frequency component of the wave travels.

PIM (Passive Intermodulation): Passive Intermodulation (PIM) occurs when two or more signals are present in a passive device (cable, connector, coupler, etc.) that exhibits a nonlinear response.  The nonlinearity is typically caused by dissimilar metals or dirty/loose interconnects.  Nonlinearity is typically not troublesome at low input signal levels, but if PIM is generated from a high-power transmitter path to an adjacent receiver channel, desensitization will occur.  A common PIM specification is typically -110 dB or greater.

Pole Piece: Thin plates of steel that are used to help complete the magnetic circuit, maximizing the field in the ferrite material and reducing the stray field outside the device.  Pole pieces are normally placed outside the magnets.

Power (Average) (W): Signals that are modulated or pulsed have instantaneous power levels that change over time. Averaging the power over time provides a measure of the energy that must be dissipated as heat, without causing degradation in performance.

Power (Peak): A pulsed signal is characterized by its instantaneous peak power, the length of each pulse, and the duty cycle or pulse repetition frequency.

Power Combiner: A passive RF/Microwave device that has multiple inputs and a single output.  The input signals enter the input ports and are combined into a single output at the output port.  Some signal loss occurs in the process due to the insertion loss of the combiner.

Power Divider: A passive RF/Microwave device that has a single input and multiple outputs. The input signal enters the input ports and is divided into equal signals at the multiple outport ports.  Some signal loss occurs in the process due to the insertion loss of the divider.  A power divider can be used a power combiner and vice versa, by reversing the input and output ports.

PTFE (PolyTetraFluoroEthylene): Used as an insulator in RF and microwave coaxial connectors because of its low & stable dielectric constant and low loss factor over a wide temperature and frequency range.

Radio Frequency, RF: It is the frequency range of electromagnetic wave transmission, this is normally considered between high HF frequency range, 30 MHz to 1 GHz. Above that range (1000 MHz) is considered Microwave Frequency.

Reactive Splitter: A broadband passive network that equally divides power applied to the input ports between any particular number of output ports without substantially affecting the phase relationship or causing distortion.  Reactive splitters differ from Wilkinson power dividers as they provide no isolation between adjacent ports.  Therefore, power entering any output of a reactive splitter will divide evenly between the adjacent and input ports.

Resonance, Above/Below: Ferrite devices that are designed with the magnetic bias field below the field level causing resonance, are said to operate “below resonance”.  Similarly, if the bias field is high enough to exceed the resonant field, the device is operating in the “above resonance” mode.

Resonance, Ferrimagnetic: When a magnetic bias field is present with an RF field in a ferrimagnetic material, electrons precis about the axis of the bias field.  With sufficient magnetic bias field, the electrons align with the bias field, and exhibit a resonant frequency in the microwave spectrum.  This causes considerable loss to an incident RF signal having this resonant frequency.  The RF frequency ω_{0, (}ω₀ = 2πFo) at which resonance occurs, depends on the magnetic bias field H, according to the relationship Fo= γH, where γ has the value 2.80 MHz/Oersted.

Return Loss: When expressed in dB, return loss is the ratio of reflected power to incident power.  It is a measure of the amount of reflected power in a transmission line when it is terminated or connected to any passive or active device.  Once it is measured, it can be converted by equations to reflection coefficient or to VSWR.

RF Couplers: RF/Microwave Couplers are passive devices that are used to sample high frequency signals. It takes one single as the input and provides two outputs- One being the direct output and the other being the coupled output. Based on the application requirement, the power level of the coupled signal can be varied when designing the device. Couplers have many applications and are used for sampling signals.  They are used in signal generator and power amplifier feedback loops to control gain, measure incident or reflective power and to determine VSWR.  Couplers are also used for unequal power splitting.  The devices have many other applications.

RFI: Radio Frequency Interference.  In order to minimize radiated emissions of RF energy, the seams of coaxial devices can be sealed with conductive sealant.

RF Leakage: The amount of RF energy which “leaks” or radiates from a connector and/or device.  Typically tested at one frequency and expressed in dB.  Large negative values indicate that the device does not radiate much energy.

Ripple: Generally referring to wavelike variations in the amplitude response of a filter. Chebyshev and elliptic function filters ideally have equi-ripple characteristics, which means that the difference in peaks and valleys of the amplitude response in the passband are always the same.

RoHS: (Restriction of Hazardous Substances) Directive adopted by the European Union in February 2003 with the specified limits for the following elements in the manufacture of various types of electronic and electrical equipment:

1. Lead (Pb) < 0.1%
2. Mercury (Hg) < 0.1%
3. Cadmium (Cd) < 0.01%
4. Hexavalent Chromium (CrVI) < 0.1%
5. Polybrominated Biphenyls (PBB) < 0.1%
6. Polybrominated Diphenyl Esters (PBDE) < 0.1%

Stop Band: The area of frequency where it is desirable to reject or attenuate all signals as much as possible.

Strip line: 
A transmission line consisting of a conductor between extended conducting surfaces.  Higher frequencies or broadband devices tend to favor strip line technology.

Surface Mount: Surface mount components are soldered directly to circuit traces.  Solder pads on the component may be under the component.

3-dB Compression Point: It is amount of output power from the amplifier where in the Pin verses Pout linear gain curve, the linear gain asymptote is deceased by 3 dB.

3-dB Hybrid Coupler: It is a passive four-port device that is used either to equally split an input signal with a resultant 90* phase shift between outputs or to combine two 90* degree out of phase signals in-phase while maintaining high isolation between them.

Temperature (operating): The minimum and maximum ambient temperatures a given component can operate at and still meet all guaranteed specifications unless otherwise noted.

Temperature Compensation: Ferrite and magnet materials are selected to minimize variations of circulator properties with temperature.  Where excessive variation occurs, inserts of temperature compensation steel are used to reduce the variation.  These steels show considerable reduction in permeability with temperature and compensate for varying magnetic field in the ferrite material.

Termination: A load at the end of a transmission line, which matches the transmission line impedance, normally 50 Ohms in coax.  A termination must be able to handle all the power transmitted through the transmission line.

Time Delay: Is the delay between the time the signal enters the input port and exists the output port of a filter, or other microwave components.

Torque: Recommended mating torque for industry standard connectors:

1. SMA – 7 to 10 in-lbs
2. Type-N – 12 to 15 in-lbs
3. TNC – 12 to 15 in-lbs
4. 7/16 DIN – 220 to 300 in-lbs

Transmission Line: The conducting components between circuit elements (such as amplifiers and isolators) which carry signal power.  Wire, coaxial cable, microstrip, strip line, and waveguide are common examples.

Uni Directional Coupler: A passive 3 port device where the power enters through the mainline from port 1 to port 2 and a fraction of this power is picked up by the coupled port, port 3.

VSWR (Voltage Standing Wave Ratio): The ratio of the incident signal voltage compared to the reflected signal voltage in a transmission line.  VSWR cannot be directly measured, so a return loss measurement (expressed in dB) is taken of reflected power to incident power.  Once it is measured, it can be converted by equations to reflection coefficient or to VSWR.

Waveguide: A metal tube (normally rectangular) which passes RF energy with extremely low loss.  The waveguide cross section determines the operating frequency range, which is about 20% of the nominal center frequency. Waveguide circulators are made with a Y geometry, in which the ferrite is placed close to the center of the Y.  Waveguide flanges are used to connect the device to other components.

Wilkinson Power Divider: A passive device that equally splits an input signal to each output port or combines input signals to a common output port.  Wilkinson power dividers differ from reactive splitters because the output ports are isolated Signals entering one of the output ports will not interfere with signals on the adjacent port.  The limiting factor for Wilkinson power dividers used as combiners is power dissipation.  When input signals are out of phase, non-coherent, or have amplitude unbalance, cancellation occurs across the isolation resistors resulting in power dissipation.

Wrap: Thin plates that are wrapped around coax and waveguide circulators (typically around 3 sides) to complete the magnetic circuit, maximizing the field in the ferrite material, and reducing the stray magnetic field outside the device.