Mixer Measurements using Network and Spectrum Analysis

Mixer measurements present a significant measurement challenge due to the inherent non-linearity of the device operation and the desired and undesired frequency conversion that takes place. The mixer needs to be excited by two signal sources at differing frequencies and signals exiting a third port must be analyzed at, as a minimum, a third frequency. Parameters of interest include conversion loss, isolation and leakage, port impedance, 1 dB compression, third order intercept, and amplitude and phase tracking. Scalar and vector network analyzers, spectrum analyzers, and power meters are all useful tools that can be applied to varying degrees to the mixer measurement problem. This paper explores methods for measurement of mixer port impedance, isolation, and conversion loss. Comparisons are made, where possible between measurement results using alternative techniques for two sample mixers, one coaxial, and one MMIC mixer measured on-wafer. With regard to conversion loss measurements, it is shown that careful attention must be paid to the frequency dependence of cable loss and RF input power to minimize errors.