Two-port scalar microwave network analyzer with an analog source and software error correction

A computer controlled analog microwave sweep generator is developed for the use of scalar network analysis. The RF source is based on a free running voltage-controlled oscillator (VCO) which is being tuned by a precision digital-to-analog converter (DAC) in an open loop configuration. A switched directional coupler assembly is implemented to allow for the measurement of the magnitudes of S₂₁ and S₁₁ parameters. Also, a low cost RF power detector is used to measure the power of the transmitted and reflected waves. The system is controlled by a windows based application which plots the S-parameters vs. frequency. Tests show that such a low cost approach combined with the advantages of software control and error correction, provides a low cost solution for making broadband microwave measurements.