The paper presents the results of theoretical justification of the appearance of combinational pulses in the time responses of coupled transmission lines with inhomogeneous dielectric filling. Combinational pulses are of interest because their arrival times do not correspond to the per-unit-length delays of the modes propagating in the lines, but consist of their combinations. They appear because of the asymmetry of the line cross section or boundary conditions. In this study, we formulated analytical expressions for calculating time responses that include combinational pulses, which extends the theory of transmission lines and the development of protection devices based on modal decomposition of pulses. Additionally, we optimized asymmetric structures according to amplitude and time criteria and considering combinational pulses to increase the attenuation of interfering UWB-pulses. We also designed layouts of asymmetric transmission lines with broad-side and edge couplings and investigated them experimentally. The time responses obtained by electrodynamic simulations and measurements confirm the appearance of combinational pulses, which has previously been shown only by quasi-static lossless simulations.

The paper presents a new method for experimental studies of typical prototypes with triple modal reservation. The authors propose to define the investigated devices in the frequency domain and then by using Advanced Design System software to redefine their characteristics in the time domain. The paper contains recommendations for the preparation and conduction of such experimental studies. Using these recommendations, the authors conducted measurements of the complex S-parameters of the circuits with triple modal reservation in the frequency range from 10 MHz to 18 GHz before and after failures. Then, to analyze the response to ultra-wideband interference, a pulse in the trapezoidal waveform with a duration of 150 ps was excited in Advanced Design System to the input of the reserved circuit. The maximum amplitude value at the end of the reserved circuit is obtained for all the faults studied. The authors also present the optimal order of switching the reserving circuits. This paper proposes the methods for analyzing the frequency and time characteristics. It makes possible to analyze the characteristics of circuits with multiple modal reservation and to determine the optimal switching order for reserving circuits. The proposed method requires commonly used equipment and a minimum set of technical tools that can reduce economic expenditures and time costs.