A New Method of Measuring Very Small Standing Waves in Waveguides

Abstract

Waveguide systems are usually matched by matching terminations. These terminations will absorb all the incident power and there should be no reflection from the termination. Similarly when components are added to a waveguide system they are usually matched as far as possible. Hence in properly matched systems the reflected wave should be zero. However, it may happen that there is a small reflected wave which gives rise to a standing wave in the guide system. This is usually measured by a standing wave detector with crystal assembly and meter. If the matching is very nearly perfect the reflected wave is so small that the standing wave ratio is of the order of 1·01 or much less. · Under such circumstances the method described below becomes very useful.In this method a short piece of waveguide containing a small probe is introduced into the system. This probe causes a reflected wave which will augment the reflection from the termination. Hence the standing wave becomes very large and it can be easily measured by the standing wave detector. From this the small reflection of the termination or mismatch can be easily calculated.