Design and performance of a noncontacting probe for measurements on high-frequency planar circuits

Optimal design of a noncontacting magnetic probe for measurements on the interior of planar high-frequency circuits has been studied, and performance of the probe has been determined. The design was studied using enlarged models tested at frequencies 100 times lower than those of the actual intended use. The nature of its errors has been investigated, and some techniques for error reduction have been found. The accuracy of measurements on circuits with SWR <3.0 is typically 0.8 dB in magnitude and 7° in phase. S-parameter measurements on general two-ports can also be made by using the probe at several different positions on the associated transmission lines. The technique effectively eliminates the problem of de-embedding that arises in other kinds of S-parameter measurements. Examples of measurements with the large model probe are presented and compared with theory. Performance appears to be acceptable for the intended applications