Microwave power measurement (introductory lecture)

The physical phenomena which have been made the basis of microwave power measuring techniques are reviewed, and brief descriptions of typical instruments are given. Some of the factors in which the user is likely to be interested are considered next, and an attempt is made to indicate those techniques which have actual or potential advantages for special purposes. For example, response time may be very important in some applications, whereas accuracy may be the chief requirement in others. Similarly, in other circumstances, bandwidth, sensitivity, stability of calibration, simplicity of operation or cost may be the decisive factor. Next, the scaling laws of several types of wattmeter with respect to frequency are considered, and special attention is given to millimetric and submillimetric techniques, existing and proposed. The special problems of power measurement at very high and very low power levels are also discussed. Microwave radiometry is a branch of microwave power measurement of great and growing importance, both directly in radio astronomy and indirectly in measuring the noise factors of microwave receivers. Finally, consideration is given to the direction in which research in microwave measurement might progress in the future. In particular, there are possibilities in one or two physical phenomena hitherto unused for this purpose, and of course there is also scope for the development of existing methods.