Improvements in microwave power measurements through the use of feedback

The measurement of microwave power by calorimetric and bolometric methods, together with problems inherent in these types of measurements, are discussed. The methods have high inherent accuracies but in their simplest form suffer from abnormally long time-constants and the effect of ambient-temperature changes. Methods are discussed for lessening the effect of these problems. The long time-constants associated with measurements of this type can be greatly decreased by the proper use of feedback. The effect of ambient-temperature changes can be minimized by the use of a balanced structure in which two identical power-sensing elements are exposed to the same environmental conditions.