A parabolic equation (PE) based method for analyzing composite scattering under an electromagnetic wave incidence at low grazing angle, which composes of three-dimensional (3-D) electrically large targets and rough surface, is presented and discussed. A superior high-order PE version is used to improve the accuracy at wider paraxial angles, and along with the alternating direction implicit (ADI) differential technique, the computational efficiency is further improved. The formula of bistatic normalized radar cross section is derived by definition and near-far field transformation. Numerical examples are given to show the validity and accuracy of the proposed approach, in which the results are compared with those of Kirchhoff approximation (KA) and moment of method (MoM). Furthermore, the bistatic scattering properties of composite model in which the 3-D PEC targets on or above the two-dimensional Gaussian rough surfaces under the tapered wave incidence are analyzed.

The prediction of radar target echo signal in a large-scale complex environment is of great significance in target detection, radar design and other applications. In this paper, a novel PE/FDTD hybrid model is proposed to predict monostatic radar target echo signals in large-scale complex environments. The target echo signal can be regarded as the output response of the transmitted signal which passes through a linear time invariant system composed of complex environment and target. The transport function of the complex environment is computed by the parabolic equation (PE) method and the scattering characteristics of the target are calculated by finite difference time domain method (FDTD). The combination of PE and FDTD is realized through the system response function. In combination with the ''stop-go'' method, the prediction of moving target echo signal is realized. In addition, the error of combining PE with FDTD is analyzed, and the result shows that the error is less than 0.1% when the target distance is more than 10km. Additional numerical examples are given to demonstrate the correctness of the method in semi-space, rain, fog and atmospheric duct environments. The calculated results are compared with those of theoretical method, time-domain shooting and bouncing ray (TDSBR), multi-level fast multi-pole method (MLFMM) and waveguide mode theory, and good agreement among them is observed. Finally, the simulation analysis of the missile echo signal in the mixed sea-land environment with surface duct is carried out. The simulation results show that this model can be used to predict the echo signal of airborne targets in a large-scale complex environment. It is a promising option for multi-scale computing involving radar target and large-scale environment. INDEX TERMS Monostatic radar target echo, parabolic equation (PE), PE/FDTD hybrid model, large-scale complex environment.

Wireless channel analysis is essential in the design, performance evaluation, and error correction of radar system. In this paper, an efficient parabolic equation (PE) method, which employs the split-step Fourier transform (SSFT) solution and Fourier synthesis technique, is developed for the propagation and parameter estimation of pulse-compression signals in the troposphere considering anomalous propagation conditions. A sliding window method is applied to reduce computational loads for long-distance propagation in time-domain PE. The signal delay is obtained via searching the peak of the correlation function of the received signal and a known reference signal according to the autocorrelation of the signals.The numerical examples indicate that the presented method is well suited for pulse-compression signals. Beyond that, a multiple signal classification (MUSIC) algorithm with spatial smoothing technique is introduced to obtain the signal direction of arrival (DOA) in PE model, where the covariance matrix is constructed via the array fields obtained from PE and the curvature of wavefronts due to the atmospheric refraction is considered in the array steering vector. The numerical examples verify the accuracy of the presented method. The simulation experiments in a typical sea-to-land scenario are presented to analyze the sensitivity of pulse-compression signals to evaporation ducts, including pulse waveform, time delay, and DOA, utilizing the presented methods.INDEX TERMS Parabolic equation (PE), troposphere, radio wave propagation, pulse-compression signal, parameter estimation.

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Analysis of electromagnetic wave coupling to thin-wire structures plays a very important role in electromagnetic compatibility (EMC). In this paper, a hybrid method, which is integrated parabolic equation (PE) and two-potential integral equation (TPIE), is presented to analyze the coupling problems in terrain environments. To model the realistic scenarios, PE based on the split-step Fourier transform (SSFT) technique is applied to solve the three-dimensional field distribution to obtain the external excitations for the wires. According to the boundary conditions, the high-precision TPIE solved via the moment method (MoM) is developed to simulate the induced currents on the wires. The hybrid method takes the terrain influences into account and provides a more reasonable result compared to the traditional approaches. Numerical examples are given to demonstrate correctness of the proposed method. Simulation experiments of field-to-transmission lines with different frequencies, radiation source heights, conductor radii, and lengths, in a realistic scenario constructed by a digital map, are carried out to investigate the coupling properties.