Slotted section standing wave meter

The formal theory of a single discontinuity is briefly stated and developed in terms of the complex reflection coefficient. The concept of multiple reflections is used to extend the theory to cover a transmission line having two discontinuities. Expressions are derived which are then used to analyse the effect of the reflection from the travelling detector in a slotted section on the measurements of standing waves. A convenient method of analysing errors in measurement due to the probe reflection factor is described and charts are given which enable the errors to be calculated. The techniques for making accurate measurements of v.s.w.r. are discussed for both small and large ratios. Attention is then turned to the problem of accurately determining the position of the standing wave in the line and different techniques are given for small ratios and for large ratios. Methods are suggested for eliminating the inherent errors of the measuring instrument. The determination of normalized impedance or admittance is considered in some detail. Causes of inaccuracy in the results are discussed and techniques for avoiding them are given. The electrical and niechanical problems involved in the design of waveguide slotted section standing wave meters are discussed and some relations are evaluated. An instrument design by the author is analysed critically in order to demonstrate some of the ways in which the problems may be solved. The methods of test used are described, illustrating the application of the theory outlined.