Measurement of the impedance of a microstrip line with a vector network analyzer

A method for measuring the wave impedance of a microstrip transmission line with a vector network analyzer is proposed. The problem of determining the frequency dependence of the wave impedance of a microstrip line is relevant for creating circuit models of electronic components and touchstone fi les in a virtual strip channel with a standard wave impedance of 50 Ohm, used in computer-aided design systems for integrated microwave devices. The problem of measuring with a vector network analyzer in the entire frequency range of the device operation is proposed to be solved by the LTR method. This method makes it possible to determine, from the results of measurements by a network analyzer in a coaxial channel, the S-parameters and reflection coefficients of two segments: a short and an electrically long microstrip transmission line: phase velocity and attenuation coefficient of electromagnetic waves propagating in a stripline transmission line; transformed s-parameters of distorting adapters, simulating the contact areas of coaxial and strip lines. In the range from 0.02–2.00 GHz, the impedance is determined by the reflection coefficients from the side of the coaxial ports of the distorting adapters at two fixed frequency points. At these frequency points, the reactive capacitive component of the complex wave impedance is compensated by the inductance of the contact areas of the coaxial and strip lines. The frequency dependence of the real part of the wave impedance passing through the frequency points in the frequency range of the network analyzer is obtained using the circuit model of the Beatty microstrip standard in the NI AWR Design Environment computeraided design system. The model of this standard for a line with an air section between two segments of strip lines with an insulating base was obtained using a circuit analog of MLIN, which is adequate to the physical prototype of the line. The relevance of measuring the wave impedance of a microstrip line with a vector network analyzer is shown by the example of identifying the intrinsic parameters of chip resistors.

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