Absorbing Load

a terminal device in radio-engineering, used primarily in the microwave range. It provides total or partial absorption of the power of the electromagnetic oscillations. A low-power (< 1 watt) absorbing load can be used for the matching or microwave assemblies and the measurement of characteristics of microwave components, assemblies, and electronic devices. It can also be used in such capacities as a self-calibrating source of low-temperature noise in the microwave range. High-power (1 watt to 10 kilowatts or more) absorbing loads are used, for example, as equivalents of antennas to eliminate radiation into the surrounding space from apparatus undergoing tests.

Absorbing loads are built as sections of a microwave line that are loaded with a resistor or short-circuited and filled with a substance that absorbs the oscillatory power. The standing wave ratio of absorbing loads is usually < 1.1. Absorbing loads have power absorbers either of the surface type or of the bulk type. A surface absorber consists of a dielectric with a layer of an alloy deposited on the dielectric by sputtering; the alloy—for example, nichrome—must have a high resistivity. Bulk absorbers are made of ceramics with a filler of graphite or silicon carbide; compounds containing additives such as carbonyl iron are also used. Absorbing loads for calorimetric power measurements make use of a liquid—for example, water—flowing at a fixed rate.