The microwave reflectometer

Abstract

The technology described in this chapter at one time represented a highly developed art and provided much of the basis for precision microwave metrology. Although failing to yield phase information, the need for this was in some cases circumvented by 'generalised reflectometer techniques' which specifically addressed certain problems of major interest, particularly in the area of power measurement. At best, however, these methods were both frequency sensitive and time consuming. With the increasing interest in broadband systems, and the advent of digital technology, these methods have to a large degree been replaced by others which are more amenable to automation. In the process, a major shift in measurement strategy has also occurred. In particular, the foregoing tuning methods were largely developed in an era where the key to better accuracy was an improved item of hardware. As such, they represent a set of highly developed techniques for making in-situ adjustments of the hardware parameters such that the 'ideal' response is more nearly realised. By contrast, the more recent strategy, as reflected by the 'vector' network analyser, for example, is that of specifically identifying and characterising the hardware imperfections such that they may be eliminated by software corrections. Although much of this earlier technology is still embodied in the 'scalar' network analyser, in other cases the shift in emphasis has been from trying to build a better piece of hardware, to 'smarter' use of that already in existence.