A high-precision RF vector analyzer based on synchronous sampling

An RF/microwave amplitude and phase measurement system of exceptional linearity and stability (0.0001 dB) has been developed. In this system, the signals to be measured are transformed to discrete time digital signals by synchronous sampling and analog-to-digital conversion. These digital signals are then processed by a digital signal processor for vector detection and for computing digital feedback sent to the sampling gates. Digital iterative feedback is used to make the system insensitive to gain variations of the sampling gates. The method resembles that of dc substitution, but with vector capabilities, and is responsible for the high stability of the system. Furthermore, digital processing of the IF signals avoids the various IF imperfections of conventional vector analyzers such as gain range errors and detector circularity errors, which explains the exceptional linearity of the system. It is used as the basis for a high-performance dielectric measurement system working from 10 kHz to 500 MHz