RF Terminations Information
RF terminations are used to absorb energy and prevent RF signals from reflecting back from open-ended or unused ports. They may include light emitting diode (LED) indicators for conditions such as “power” or “busy”, or mount with a heatsink. There are three main types of RF terminations: coaxial, waveguide, and chip. Coaxial terminations terminate coaxial ports, and waveguide terminations terminate waveguide ports. Chip terminations have an integrated circuit (IC) chip form factor. Typically, they are manufactured with thin-film technology. Form factors and mounting styles for other types of RF terminators are described as flanged, board-level, leaded, panel mount, screw terminals, surface mount, stand-alone, and through-hole.
There are five main performance specifications for RF terminations: frequency range, power rating, voltage standing wave ratio (VSWR), return loss, and resistance. Frequency range is the range of frequencies over which RF terminations are designed to operate. Power rating is the input rated power. VSWR is a unit-less ratio which expressed the amount of reflected energy at the input of the device. A value of 1 indicates that all the energy passes through. Any other value indicates that a portion of the energy is reflected. Return loss is a measure of the match between the impedance of the RF terminations and the impedance of the system. Choices for resistance include 50 ohms and 75 ohms.
RF terminations use many different connector types. Choices include BMA, BMMA, BNC, Type C, Type F, FME, Type G, MCX, MHV, MMCX, Type N, QMA, QWS, and SC. RF terminators may also use connector types such as SMA, SMB, SMC, SSMA, SSMB, SMP, TNC, Triax, and Twinax. Ultra high frequency (UHF) connectors are economical, all-purpose connectors designed with non-constant impedance for use in low-voltage and low-frequency applications. Mini-UHF connectors are a smaller version of the original UHF connector. There are five metric connectors for RF terminators: 1.85 mm, 2.4 mm, 2.92 mm, 3.5 mm, and 7 mm.
Standards and Certifications
Standards and certifications are important to consider when selecting RF terminators. Products that are destined for sale in Europe should comply with the following European Union (UE) directives: Restriction of Hazardous Substances (RoHS), End-of-Life Vehicles (ELV), and Waste Electrical and Electronics Equipment (WEEE). RF terminators that are sold in the United States should comply with requirements from the Federal Communications Commission (FCC), or bear marks from Underwriters Laboratory (UL). In Canada, RF terminators that meet requirements from the Canadian Standards Association (CSA) bear the CSA Mark, alone or with indicators.