The problem of protecting radio electronic equipment from ultrashort pulses is of utmost importance nowadays since conductive interference poses the biggest danger to its proper functioning. The article considers the issue of protecting equipment by means of modal filters (MFs) and analyzes the structures of multiconductor microstrip MFs. We present the results of a complex study of the possibility to conduct the optimization (both separate and simultaneous) of a multiconductor MF by different criteria and the formulation of the basic (electrical) optimization criteria for MF. We have formulated the amplitude and time criteria for optimizing an MF (with any number of conductors) in an analytical form and obtained a general multicriteria objective function for optimizing an MF by different criteria. As a result, we have formed a hybrid model consisting of heuristic search and GA. The results demonstrated the topicality of further research in this field.

The paper considers the protection of critical radio-electronic equipment (REE) from ultrashort pulses (USP) by means of modal filters (MFs). A new approach to improve modal filtration by using reflection symmetry is analyzed. The results of a sophisticated research into protective devices based on reflection symmetric MFs are presented: improving the characteristics of four MFs through optimization both by one and simultaneously by several criteria; calculating the per-unit-length time delays matrix of a reflection symmetric MF using the obtained analytical expressions; calculating the time and frequency responses of an MF with and without losses in conductors and dielectric; developing the laboratory evaluation board; analyzing the effect of moisture protection on the characteristics; analyzing the features of reflection symmetry structures; comparing microstrip and reflection symmetric four-conductor MFs. The obtained results allow us to argue that the reflection symmetric MF protects REE from a USP due to its decomposition into a sequence of pulses with pairwise equalized voltage amplitudes and close time intervals between decomposition pulses with an attenuation coefficient of four times with a controlled bandwidth of a useful signal. This research helps take advantage of the possibilities of using the symmetry to improve modal filtering and opens the ways to create a large number of new MF designs, applying only the principles of the symmetry described in the work.

For the first time, the paper considers in a unified work the possibility of the appearance of additional pulses in various structures based on modal filtration technology, which is used to improve protection against ultrashort pulses (USP). We analyzed meander lines (ML) with broad-side coupling, structures with modal reservation (MR), reflection symmetric MLs, and modal filters (MF) with a passive conductor in the reference plane cutout and obtained the following results. It was found that the main reason for the additional pulses to appear in these structures is the introduction of asymmetry (of the cross-section, boundary conditions, and excitation). It is theoretically and experimentally established that additional pulses are a new resource for increasing the efficiency of protective devices with modal decomposition, but the highest effectiveness could be achieved through careful optimization.

This article presents a novel routing technique for designing microwave transmission lines (TLs) that provide improved functionality. Unlike traditional practices, we propose locating two independent traces close to each other, resulting in strong electromagnetic coupling and potential unwanted crosstalk between traces. However, we show that the suggested routing schemes can significantly increase the ultra-wideband interference immunity of electrical circuits by using modal distortions and reflections, as demonstrated in our study of four prototypes of TLs in the form of serpentine and spiral designs with strong and weak coupling between pairs. To better predict and analyze the microwave behavior in such TLs, we used new simulation techniques based on the $N$ -norms study. Our investigation of these TLs in a transverse electromagnetic cell in the frequency range from 10 MHz to 5.3 GHz showed a low level of radiated emissions. The results indicate that the serpentine scheme with strong coupling between pairs provides the best protection of two independent TLs against ultra-wideband interferences. Moreover, the used electrodynamic approach is in full agreement with the experimental study, further validating the effectiveness of the proposed routing technique.

An experimental confirmation of modal filtration based on multiconductor microstrip lines is executed. Authors designed four- and five-conductor prototypes of modal filters (MF), which have the maximum amplitude of the decomposition pulses of 12.6 and 15.3 times less in comparison with the initial signal. The results showed the prospect of research of multiconductor MF because addition of conductors to the initial structure additionally (up 2.3 times) decreases the amplitude of the initial signal at the end of the active conductor.

This work is devoted to the research of new asymmetry effects in symmetric protective structures with triple modal reservation. We analyzed the structures with different cross-sectional locations of the reference conductor: in the center (unshielded structure), around (shielded structure), at the top and bottom (multilayer printed circuit board), and in the form of side polygons (double-sided printed circuit board). First, a preliminary quasi-static simulation was performed in the range of parameters. It was revealed that in all structures, except for the shielded one (in the form of a cable), the deviations of the output voltage amplitude, bandwidth, and frequency of the first resonance were insignificant, whereas in the shielded structure there were significant deviations in the time and frequency responses. The attenuation of the output voltage in relation to the input for each structure was also estimated. In addition, we performed a parametric optimization of the structures under consideration using a heuristic search, which made it possible to improve their characteristics. Finally, the switching order between the conductors in these structures with the original and optimized parameter sets was investigated in detail. The optimal conductor switching order in the case of a component failure was determined, and the best (according to protective characteristics) parameter configuration for each structure was found.