RF terminations are one of the most common RF components used in nearly every application and use case where RF systems are employed. An RF termination is simply a terminating impedance that is designed to match the impedance of the transmission line or waveguide used in the signal chain. For instance, if a 50 Ohm coaxial path is to be properly terminated, say at the reverse port of a directional coupler, then the appropriate termination would be a 50 Ohm coaxial termination that matches the connector type of the directional coupler. Another example may be an extra test port that is generally unused but may be useful during maintenance or diagnostic troubleshooting. If unterminated the test port would return undesirable reflections and otherwise leak signals out of the open-ended port. An RF termination would safely prevent signal leakage and absorb the signal energy that would otherwise be reflected in an open port.
Another use case for an RF termination is if a transmit and receive signal chain are connected to an antenna via a switch as opposed to a diplexer or circulator. This is how many time domain duplex (TDD) and some radar operations. During a switching operation the transmitter signal energy would still be present for a short period of time. Hence, if the switch also changes the transmitter path to an RF termination with the appropriate ratings, the high-power RF from the transmitter can be safely terminated and absorbed. Otherwise potentially damaging reflections could occur as the input of an RF power amplifier or other transmission hardware has a limited reflected power handling capability.
RF terminations are also commonly used to terminate unused test ports in RF test and measurement equipment, such as a VNA. This is to prevent accidental reflections if a port is accidentally energized. If left open, the test port could cause damaging reflections to the sensitive test equipment receiver circuitry.
Given the various use cases of RF terminations, there are numerous types of RF terminations to better suit these use cases. For instance, there are some RF terminations meant for particularly high-power use cases. These RF terminations are generally larger in size and include a heat sink, often made from anodized aluminum. In more extreme high-power cases, an oil-filled terminator may be used, which uses oil to dissipate excess thermal energy. Some RF terminations even include active cooling systems for extremely high-power absorption.
However, many RF terminations are meant for lower power applications, such as those used with test and measurement equipment. These dummy loads are generally small and resemble an RF adapter. Some of these RF terminations may be multi-purpose and have two types of coaxial interface, one on either side. These are particularly useful in test and measurement applications where multiple coaxial connector types may be used in the same system.
Waveguide terminations are also common. Like with coaxial RF terminations, a waveguide termination may either be a simple length of waveguide with RF absorbing materials inside or include large heatsinks and even active cooling depending on the power rating of the termination.
Some RF terminations may also have other features, such as embedded O-rings for enhanced environmental performance, and clips/chains to ensure that a termination isn’t accidentally misplaced when temporarily removed.