Receiver nonlinear distortion severely impacts modern wireless systems. Traditional power series polynomial models suffer from numerical instability in parameter estimation, especially at high orders or with memory. This paper investigates orthogonal memory polynomial models from the perspectives of memory depth, nonlinear order, input signal distribution, and temporal correlation of the input signal, focusing on effective methods for improving the condition number. Comprehensive analysis reveals that the condition number of the Gram matrix grows rapidly with polynomial order and memory depth for the conventional polynomial, while orthogonal polynomials remain well-conditioned due to their inherent orthogonality and normalization. Notably, orthogonal polynomials maintain robust performance even when the input distribution does not perfectly match the basis weight function. Experiments using OFDM and 3-carrier WCDMA signals confirm that orthogonal polynomials achieve condition numbers orders of magnitude lower than those of power series, along with superior fitting accuracy.

Directional Antenna Modulation (DAM) utilizing 2D conformal phased arrays has been demonstrated to enable secure Multi-directional Independent Transmission (MIT) over a broad angular range. This paper proposes an unbalanced DAM technique that dynamically allocates power according to transmission distance, thereby significantly enhancing transmission efficiency in practical scenarios where receivers are located at varying distances. In particular, a high-efficiency Differential Evolution (DE) optimization algorithm integrated with an “alien species invasion” mechanism is developed to accelerate convergence and optimize the phase delays of each array element. Bit Error Rate (BER) analysis for MIT reveals superior directional security compared to traditional methods, with conformal arrays providing wider angular coverage and spherical sparse arrays overcoming the half-wavelength spacing limitation. The simulation results validate that the proposed system achieves simultaneous secure transmissions in multiple directions while maintaining a BER below −40 dB.

The continuous wave (CW) illuminator, whose fundamentals are related to the theory of loop antennas loaded with ferrite materials, is an important facility for electromagnetic pulse (EMP) susceptibility assessment. However, existing theoretical formulas do not consider cases where ferrite materials are loaded into the loop antenna. This paper provides a new explicit theoretical formula of the impedance of a circular loop antenna loaded with ferrite materials for CW illuminator design and explores the variation regularity of its input impedance. Loading ferrite materials affects the internal impedance of the loop antenna and forces some modifications to the classical calculation procedure, resulting in an asymptotic numerical calculation method and a closed-form solution. The full-wave simulation results from CST Studio Suite show the maximum error is less than 0.99% compared to the classical theory. With ferrite material loaded, the input impedance of the loop antenna is significantly reduced and smoothed in a wide range (0< ??< 2.5). For a loop antenna with a fixed circumference, the input impedance indicates that the Q-factor decreases as the thickness of the ferrite material increases. Conversely, for a ferrite-loaded loop antenna with a constant material thickness, a larger loop circumference results in a higher Q-factor. In summary, this study provides a fast and accurate computational method for the input impedance design of CW illuminators, while also offers an effective tool for further research on the performance of ferrite-loaded loop antennas.

The continuous-wave (CW) illuminator, whose fundamentals are related to the theoretical understanding of loop antennas loaded with ferrite materials, is a device which plays an important role in electromagnetic pulse (EMP) susceptibility assessment. However, existing theoretical formulas do not consider cases where ferrite materials are loaded into the loop antenna. This paper provides a new explicit theoretical formula for the impedance of a circular loop antenna loaded with ferrite materials for CW illuminator design, and explores the variation regularity of its input impedance. Loading ferrite materials affects the internal impedance of the loop antenna and forces some modifications to the classical calculation procedure, resulting in an asymptotic numerical calculation method and a closed-form solution. The full-wave simulation results from CST Studio Suite show a maximum error of less than 0.99%, compared to the classical theory. With ferrite material loaded, the input impedance of the loop antenna is significantly reduced and smoothed in a wide range of normalized radii. For a loop antenna with a fixed circumference, the input impedance indicates that the Q-factor decreases as the thickness of the ferrite material increases. Conversely, for a ferrite-loaded loop antenna with a constant material thickness, a larger loop circumference results in a higher Q-factor. In summary, this study provides a fast and accurate computational method for the input impedance design of CW illuminators, while also offering an effective tool for further research on the performance of ferrite-loaded loop antennas.

The traditional radio wave propagation models exhibit several limitations when they are employed to predict the path loss for vehicular ultra-shortwave wireless communication. To addresses these challenges, an optimized approach for Egli model based on the high-resolution remote sensing satellite image is proposed in this study. The optimization process includes three components. First, a method for calculating the actual equivalent antenna height is introduced, utilizing high-precision remote sensing satellite imagery to obtain communication path profiles. This method accounts for the antenna’s physical length, vehicular height, and local terrain characteristics, thereby providing an accurate representation of the antenna’s effective height within its operational environment. Second, an equivalent substitution method for ground loss is developed, utilizing surface information derived from high-precision remote sensing satellite images. This method integrates ground loss directly into the Egli model’s calculation process, eliminating the need for separate computations and simplifying the model. Third, leveraging the Egli model as a foundation, the least squares method (LSM) is employed to fit the relief height, ensuring the model meets the requirements for ultra-short wave communication distances under line-of-sight (LOS) conditions and enhances suitability for real-world vehicular communication systems. Finally, the validity and accuracy of the optimization model are verified by comparing the measured data with the theoretical calculated values. Compared with the Egli model, the Egli model with additional correction factors, and the measured data, the average error of the optimized model is reduced by 8.98%, 2.09%, and the average error is 0.45%.

With the expansion of urban areas and the increase in the number of vehicles, the complexity and harshness of the electromagnetic environment for vehicular communication in cities have significantly intensified. Traditional methods for evaluating the electromagnetic compatibility (EMC) of vehicular communication systems face substantial limitations. With the advancement of high-resolution satellite remote sensing image technology, the acquisition of high-precision urban models has become more accessible, significantly enhancing applications in the field of communication systems. Therefore, a novel EMC evaluation method for vehicular wireless communication systems based on urban high-resolution satellite remote sensing images is proposed in this paper. By analyzing the characteristics of such systems and integrating the requirements of practical urban communication scenarios and vehicular tasks, EMC evaluation indicators were selected, and a hierarchical evaluation indicators system was constructed, comprising target, criterion, and sub-criterion layers. The proposed method leverages the strengths of TOPSIS, AHP, and FCE methods, utilizing quantitative TOPSIS and qualitative AHP to determine the weights of the criterion and sub-criterion layers, respectively. The FCE method was employed to evaluate the EMC of the vehicular wireless communication system. The rationality and feasibility of the method were validated through practical communication experiments conducted with a vehicle in an urban environment.