Measurement of the Impedance of a Microstrip Line with a Vector Network Analyzer

A method of measuring the impedance of a microstrip transmission line using a vector network analyzer is proposed. The problem of determining the frequency dependence of the impedance of a microstrip line is very important in order to create circuit models of the electronic components and touchstone-files in the virtual strip channel with a reference impedance of 50 omega. Circuit models of the components and files are used in computer-aided design systems of integrated microwave devices. It is proposed to solve the problem of measurement by a vector network analyzer in the entire frequency range of operation, by the LTR method. From the measurement results, for a network analyzer in the coaxial channel, of the S-parameters and coefficients of reflection of two segments, short and electrically long microstrip transmission lines, the phase velocity and a damping factor of an electromagnetic wave propagating in the strip line transmission were determined, as well as the converted S-parameters of two distorting adapters modeling contact fields of the coaxial and strip lines. Over the range 0.02-2.00 GHz, the impedance was found from the coefficients of reflection from the coaxial ports of the distorting adapters at two fixed frequency points, at which the reactive capacitive component of the complex impedance is compensated by the inductance of the contact fields of the coaxial and strip lines. The frequency dependence of the real part of the impedance, passing through these frequency points, is determined over the range of frequencies of operation of the network analyzer, by means of the circuit model of the microstrip Beatty standard in the NI AWR Design Environment computer-aided design system. The model of this standard of a line with an air section between two segments of strip lines with an insulation foundation was derived by means of an MLIN circuit analog, suitable for the physical prototype of the line. The importance of the measurement of impedance of the microstrip line is shown by a vector network analyzer on the example of identifying the characteristic parameters of the chip resistors.