Noncontacting measurement of reflection coefficient and power in planar circuits up to 40 GHz

This paper describes the use of loop-coupler probes for noncontacting measurement of power and reflection coefficient in microstrip circuits up to 40 GHz. The inherent directivity of the loop-coupler probe makes it suitable for use with scalar measuring instruments such as power meters and spectrum analyzers. The probe coupling and directivity and their sensitivity to probe positioning errors are investigated. The results are summarized in a simple uncertainty budget. Measurements of reflection coefficient with a vector network analyzer are also presented and verified by coaxially contacting measurements.