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In order to employ periodic corrugated microstrip lines for reducing or suppressing electromagnetic interference in high‐speed or high‐frequency circuits, a precise method is necessary to calculate and measure the characteristic impedance of periodic microstrip lines. The equation for characteristic impedance (depending on frequency) of lossless periodic microstrip lines was obtained based on the transfer matrix method. A time domain pulse was used to measure the instantaneous impedance of conventional microstrip lines, and when the instantaneous impedance does not change with distance, it can be identified as the characteristic impedance of microstrip lines. However, when the time‐domain pulses are employed to measure the instantaneous impedance of periodic microstrip lines, rapid oscillations occur with distance. Therefore, a standard for spacing between adjacent grooves in the microstrip line can be suggested by analysing the interaction between the time‐domain pulses and the microstrip line grooves. Once such a standard is satisfied, many grooves etched along the microstrip line would no longer be distinguished by the time‐domain pulses. Such a principle and method can be used to determine the instantaneous impedance for the microstrip lines that have periodic grooves. On the other hand, when several periodic structures with different lattice constants coexist on a microstrip line, they can also be distinguished via the instantaneous impedance. A time domain reflectometer was used for measuring the instantaneous impedance of periodic microstrip lines, and the measured results are in agreement with the theoretical analysis. [ABSTRACT FROM AUTHOR]

It has been proved that a subwavelength periodic microstrip structure can be used to suppress crosstalk between two adjacent microstrip lines and such a microstrip structure can be widely used in the application of high‐speed circuit systems. To further increase the accuracy of the equivalent circuit model of the subwavelength periodic microstrip line (SPML), we focus our attention on a single unit cell with the periodic structure, which is divided into several sub‐regions, and the circuit parameters in each sub‐region are analysed for setting up a complete circuit model of the unit cells. Then the details of the interaction between each sub‐region and the electromagnetic field are clearly indicated. The S $S$‐parameters of the circuit model accord well with full‐wave simulation results, showing a maximum deviation of 0.03973 dB for S21 and 0.1211 dB for S11 below 15 GHz. For the first time, we also study the frequency‐dependence of the mutual capacitance and the mutual inductance for analysing the coupling effect between an SPML and a conventional microstrip line (CML). The instantaneous impedance obtained by the full‐wave simulation of the SPML is consistent well with the experimental results. [ABSTRACT FROM AUTHOR]