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 article presents the study of a reflection symmetric modal filter (MF) and meander lines (ML) based on a four-layer printed circuit board (PCB). Their prototypes were made, and the transmission coefficients were measured in the frequency range from 10 MHz to 10 GHz. At the output of the structure, the response to an ultra-wideband (UWB) pulse was analyzed. The results of post-processing showed four decomposed pulses at the output of the MF and the ML with two-turns, and six decomposed pulses in the ML with one-turn, which is in complete agreement with the modal theory and analytical models. The N-norms were used to characterize the output voltage waveforms. Both MLs demonstrated better attenuation of the UWB pulse than MFs of the same PCB size. More specifically, the value of N1 decreases by at least 2 times, N2 by at least 1.6 times, and N5 by at least 1.36 times. The values of N3 and N4 remained unchanged. The post-processing method for detecting combinational pulses in the time responses of ML is presented.

This article analyzes novel, adventurous routing schemes employed in designing microwave transmission lines (TL). In contrast to traditional schemes, we propose to locate two independent traces close to each other. The strong electromagnetic coupling thus formed can cause unwanted crosstalk between traces. However, if their level is acceptable, we can use the suggested routing schemes to significantly increase the powerful interference immunity of the electrical circuits by using modal distortion. Two prototypes of such TLs in the form of a serpentine and a spiral were made in which the far-end crosstalk voltage waveforms do not exceed 4.4% of the useful signal amplitudes. We performed electrodynamic simulations and measurements of such TLs in a transverse electromagnetic cell in the frequency range from 10 MHz to 5.3 GHz. The investigated lines have a low level of radiated emissions. Experimental results show that the proposed TLs decrease the voltage amplitude of the ultra-wideband pulse by at least 4 times and the voltage change rate by 10.7 times and more. In addition, the effective voltage value on the load is decreased by at least 2.2 times. The spiral scheme was found to be better than the serpentine scheme in almost all parameters. Simultaneously, the electrodynamic approach is in full agreement with the experimental study.

The article presents the results of a study of a modal filter (MF) based on a microstrip line with two side conductors grounded at both ends. New analytical expressions for calculating the time response in such a structure are given. For their validation, an MF prototype was made and the transmission coefficient was measured in the frequency range from 0 to 12 GHz. In addition, the full-wave electrodynamic simulation and the analysis based on the transmission line theory were carried out. The frequency responses of the MF were converted into time domain responses in the ADS system. At the MF output, the response to an ultra-wideband (UWB) pulse was analyzed. The results for the analytical model are in good agreement with the results of measurements and simulations by the two approaches. It was experimentally proven that the structure under study provides the protection of electrical circuits from a UWB pulse by separating it in time and decreasing its effect on the components.