Terminations are forming two different groups of devices: the Absorptive Devices and the Reflective Devices. Terminations, or loads, are power absorbing devices. They are matched to the characteristic impedance of the transmission line. The power reflecting devices are Short Circuit Terminations and Open Circuit Terminations. Shorts and Opens are both fully reflective, with the difference of a quarter wavelength.
Coaxial Terminations do usually operate over a multi-octave bandwidth. In special applications they may be tuned to certain criteria in narrower bands.
It is desired that the loads are ideal, absorbing the power completely. In reality, the units will show some reflections and discontinuities within the circuit, as no design is perfect, and manufacturing tolerances do not allow perfect designs anyway. VSWR is the ratio of the reflected signal and the incident signal. The power reflecting devices, the Opens and Shorts, are reflecting the signal by 100%, this means that the VSWR will become infinite.
The temperature ranges from -54°C to +85°C, or even wider, depending on the application. High Precision Terminations may have a rather limited temperature range for lowest possible VSWR, while Power Terminations in Systems are usually designed for extreme temperature ranges. The operating temperature will affect the power handling of absorptive units.
This is the maximum allowable CW power to which the unit can be subjected to without suffering permanent damage. The power handling of absorptive units is a function of temperature. High temperature units are supplied with cooling fins or heat sinks or both for better power dissipation.
Terminations are available with a large variety of connectors, meeting the appropriate standard interface specifications, such as MIL-Standards, DIN- or IEC- Specifications, etc.
In addition to the standard terminations, shown in this section, Spectrum Elektrotechnik GmbH has been designing and supplying special terminations to suit particular requirements, such as lowest VSWR, unique mechanical outline, unusual mounting or special connector requirements, higher power dissipation, characteristic impedance other than 50 Ohms, rough environment, etc., etc.
Power absorbing devices are needed during test and measurement, can also be integrated in components, and are used in systems applications as well. At a dual or multiport device, one terminal or the terminals that are not involved in the measurement or the function should be terminated in their characteristic impedance, in order to ensure proper measurement or function. Certain components require terminations at at least one port such as the directional couplers. The Short Circuit and Open Circuit Terminations are mainly used for calibration purposes, to establish measurement planes for known reflection phase and magnitude in a test set. Without these short and open circuit terminations, usually no test set can be calibrated.
Most of the Terminations, Spectrum Elektrotechnik GmbH has been designing and manufacturing, especially the new generations of Terminations, are colour coded for easy identification, especially during calibration sequences. The system is most simple: Bright shiny nickel was chosen for the Shorts, easy to remember, as an electrical short circuit would cause bright lightning. Black endcaps were selected for the Opens, as with an open electrical circuit usually never anything happens, it is rather unexciting, or black. Gold plated endcaps were chosen for the Precision Terminations for convenience.