Waveguide terminators absorb energy and prevent RF signals from reflecting back from open-ended or unused waveguide ports. They are passive devices which dissipate radio frequency (RF) energy by producing heat energy. There are three main performance specifications to consider when selecting waveguide terminators. Frequency range is the range of frequencies over which devices waveguide terminators are designed to operate. Voltage standing wave ratio (VSWR), a unit-less ratio ranging from 1 to infinity, is a measure of the amount of reflected energy at the input of the device. Return loss is a measure of the match between system impedance and the impedance of waveguide terminators.