A wider range of operating frequencies, lower supply voltage levels, and increased circuit density of radio-electronic equipment (REE) increase its susceptibility to electromagnetic interferences. Elements of REE are becoming more sensitive to electromagnetic environment especially to ultra-short pulses (USPs) penetrating through front door or back door channels. There is a large variety of noise suppressing devices, but their construction characteristics lead to limited efficiency. Modal filters (MFs), which are based on modal distortion, protect REE from USPs. In this article, the authors present the results of the study of a new method for implementing a MF with a passive conductor in a reference plane cutout and propose two prototypes of the MF with strong and weak couplings. The article presents the results of full-scale and computational experiments in time and frequency domains. For the first time, the decomposition of a USP in the proposed MF configurations is experimentally shown. Besides, we experimentally demonstrated the arrival of additional pulses, the time of which is determined by a linear combination of per-unit-length delays multiplied by the line length. Thus, the proposed approach allows implementing a simple and inexpensive technique for protection against USPs in multilayer printed circuit boards.

This paper presents a novel technique for improving modal filter (MF) performance by using an electromagnetic absorber which shows a significant improvement in attenuation of ultra-wideband interference. The authors analyzed the effect of the absorber on the MF performance in suppressing conducted and radiated interferences (in the near and far fields). As an excitation, the authors used an ultra-wideband pulse of 155 ps (at 0.5 level) and then employed $N$ -norms to estimate and characterize the decomposed pulses. It was experimentally demonstrated that the value of $N_{1}$ decreased by a factor of 4.31, $N_{2}$ – by a factor of 6.52, $N_{5}$ – by a factor of 1.87. In terms of radiated interference in the near field, the improvement in attenuation of each norm achieved at least 2.81 times. The analysis of the characteristics in the far field showed that the use of the electromagnetic absorber allows reducing the transmission coefficient on average by 2.25 times at a distance of 1 m.

This article presents the results of an experimental study of a structure with single modal reservation (MR). The decomposition of an ultrawideband (UWB) pulse in such a structure before and after failures has been demonstrated for the first time. For this case, authors used two bell-shaped pulses with a total duration of 0.15 and 1.5 ns. The frequency dependences of the transmission coefficient magnitude | S ₂₁ | were measured for the manufactured prototype in the range from 10 MHz to 18 GHz. The results demonstrate that the structure before and after failures acts as a low-pass filter. To confirm the results of the experiment, its numerical simulation was carried out using two approaches: quasistatic and electrodynamic. In doing so, we took into account losses in conductors and dielectrics. To numerically estimate the criticality of the voltage waveforms obtained during the experiment at the output of the reserved circuit before and after failure, we calculated the N -norms. The simulation and experimental results in the time and frequency domains agree quite well. It was shown experimentally that after failures the maximum changes in the cutoff and the resonant frequencies are 45% and 19%, respectively. This suggests that after failures, the results may not coincide with the predicted ones, which must be taken into account when designing real structures with MR. It was found that in the time domain after failures, the maximum amplitudes of the decomposition pulses at the far-end of structure with a single MR change, and these changes depend on the duration of the UWB pulse at the input. This influence is explained by the length of the traces to SMA connectors. If the double delay in the trace is greater than the total pulse duration, then after failures, the amplitudes will not change, since the reflected pulses will not be superimposed on the main ones. However, as the length increases, the UWB pulse will be superimposed on the main ones and will change the maximum amplitude. This effect must be taken into account during design process as it can affect the interference immunity and functional safety of the device. This is shown in the analysis of N -norms.

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.

The paper considers reservation structure implemented by using modal filtering. Such reservation is called modal reservation (MR) for short. To ensure certainty, we took a PCB layout with a single MR. It is shown that in quasi-static simulation, for the structure with losses in conductors and dielectrics, the cut-off frequency for an OC and an SC at one end of the passive conductor is 5.5 and 1.6 %, respectively, lower than for the circuit in operating condition, and the resonance frequencies are 8 and 11.6 %, respectively, lower. In electrodynamic simulation, for the conductor-loss structure and dielectrics, the cut-off frequency for an OC and an SC at one end of the passive conductor is 1.3 and 2.7 %, respectively, lower than for the circuit in operating condition, and the resonance frequencies are 7.3 and 10.65 % lower. The differences of resonance frequencies (f ₀), cut-off frequencies (f _cu) in quasi-static and electrodynamic simulations are no more than 5.66 and 1.6 %, respectively.

This article presents 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 MF frequency responses were converted into time domain responses in the Advanced Design System. At the MF output, the responses to an ultra-wideband pulse, a high-frequency damped sinusoid, and a sinusoid with Gaussian modulation were 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 different types of interference by separating them in time and decreasing their effect on the components. Finally, signal integrity was evaluated for two data rates. It was found that the MF under investigation may be used in signal circuits up to 1 Gb/s.