Читать книгу Handbook of Microwave Component Measurements - Joel P. Dunsmore - Страница 77

An RF bolometer or thermistor is a system where the RF measuring element is a thermally sensitive resistor used as part of a DC bridge system. The DC bridge is electrically balanced, and when an RF signal is applied to the bolometer element, the element heats and its DC resistance changes. The DC bridge is nulled using an offset voltage, and the measure of the offset voltage can be related directly to the power absorbed by the bolometer. The key aspect of the bolometer is that it is equally sensitive to RF or DC power; thus, a precision DC source can be used to produce a known power at the bolometer, and the balancing circuit is thus calibrated relative to the DC power absorbed. The heating effect of the RF power produces the same offsets as the DC power and thus is easily calibrated. Bolometers have a relatively small dynamic range (the range of input powers over which they operate) but have linearity (the ability to correctly measure differences in input power) derived from a bridge circuit using DC substitution. Typically, bolometers are found only in precision metrology laboratories and are not in common use among RF engineers.