Study on Electromagnetic Scattering Characteristic of Hypervelocity Model with SBR Method

In this paper, an outdoor massive MIMO (Multiple-Input and Multiple-Output) system with $40\times 40$ planer array is simulated based on the SBR (Shooting and Bouncing Ray) method. The propagation characteristics, including PAP (Power Angle Profile), receive power, delay spread and PDP (Power Delay Profile), are studied in both LoS (line-of-sight) and NLoS (non-line-of-sight) links. The near-field effect is also discussed.

Two ray shooting methods for computing the EM scattering by large open-ended cavities

The spectral theory of diffraction (STD) is well known for its ability to deal with complex fields (creeping waves, shadow limit fields, caustics fields) and their transformations through multiple diffractions. We present a fully numerical and 3-D implementation of this method. This implementation is based on a ray-tracing representation of plane waves propagation and it takes advantage of the simplicity of the plane waves transformation formulas at dielectric or conducting interfaces. The geometrical optics ray-tracing part of the procedure is quite similar to what is done in the shooting and bouncing rays (SBR) method, which has been applied to scattering calculations. However, the final evaluation of the field is performed through a spectral domain integration in our spectral domain ray tracing (SRT) method, instead of a physical optics integration in the SBR method. We give an outline of the principles of the method, and present the application of the method to substrate-lens antenna analysis. Simulated results obtained through this method are compared to results obtained through a more classical physical optics analysis, and to measured far-field radiation patterns of the antenna.

A new efficient hybrid technique is presented, which combines the method of moments (MoM) and the shooting and bouncing ray (SBR) for analyzing scattering of complex large structures. By applying the SBR method for the whole structures, a corrected incident field including not only the direct incident field but also the multi-bounce field from the SBR region contributes to the integral equation in the MoM region. For the SBR region, it also considers the interaction from MoM region and then a physical optics (PO) type integration is performed to calculate the scattered field. For complex electrically large electromagnetic problems, the proposed technique is more efficient and simpler to implement in a general-purpose computer code. Numerical results are presented to show the efficiency and accuracy of the method.

Radar detectability reducing for complex shape military or civil object is very important problem of contemporary radar theory. Solution of this problem is unthinkable without providing numerical estimations of the investigated object Radar Cross Section (RCS) and its reduction with some cloak. In this paper a new method for the semitransparent cloak modeling is proposed. This method is realized in the framework of Shooting and Bouncing Ray (SBR) method. General stages of SBR method and the cloak modeling introduction into its algorithm are discussed. The proposed approach was tested on an example of complex shape object.

This letter proposes new usage of the binary tree constructed by fundamental GO ray components in shooting and bouncing rays (SBR) for indoor propagation analysis. The node number of the binary tree is here considered as an important parameter. A couple of small size arrays that can store the passing ray information of both the node number and the position of the pixel considered, and the corresponding ray classification algorithm are newly introduced, not to double-count the same ray with slightly different bouncing angle. Consequently, we realize the big reduction of the computer memory resources consumed for the ray classification especially for wide area analysis, keeping the high accuracy of the SBR method.

Terahertz communication is considered as a potential solution to alleviate the communication blackout. However, it is not clear how the shape parameters of the vehicle affect the propagation of terahertz communications in the plasma sheath. In this article, the influence of half-angle on the plasma flow and terahertz propagation characteristics around blunt cone vehicle was investigated using the numerical hypersonic hydrodynamic model and multilayer transmission model. The maximum electron number density in the plasma sheath near the antenna decreases with the decreasing half-angle. The thickness of the high-density section in the plasma sheath is almost unaffected by the half-angle. As a result, the terahertz wave attenuation decreases with the decreasing half-angle. The half-angle is reduced from 20° to 5°, and the attenuation of electromagnetic waves is reduced by about 25 dB. Therefore, reducing the half-angle of blunt cone vehicle can effectively reduce the attenuation of electromagnetic waves. Finally, the feasibility of lowering the half-angle to solve the blackout problem during the whole reentry process was discussed; the results show the operating frequency of terahertz wave that maintains normal communication when the half-angle is 1° is reduced by 0.1 THz compared with the half-angle of 9°. Based on the study, a new scheme combining the reduction of half-angle of blunt cone vehicle and terahertz communication was proposed in this article to mitigate the RF blackout.

This paper proposes a method to compute the near-field RCS and Doppler spectrum of a target when the distances to the antennas are comparable to the target size. By dealing with a small piece of the target surface at a time, the transmitting antenna, and the receiving antenna are in the far-field zone of the small piece of the induced currents. The electromagnetic field produced by this small piece of induced currents can be written as a spherical wave. Sum up all spherical waves produced by every small piece of induced currents and we can obtain the total scattered field at the receiving antenna. The physical theory of diffraction (PTD) and the method of shooting and bouncing rays (SBR) are modified to evaluate the received signals. Numerical results based on these techniques are obtained and discussed. The formulation applies the simple concepts of "equivalent" image and vector effective height, which are believed to be novel.

In this letter, we employ a time-domain physical optics (TDPO) method using a Radon transform (RT) interpretation to obtain the high-resolution range profile (HRRP) of a near-space hypersonic vehicle under various conditions. Through a comparative analysis of the results, we observe that the high-resolution range profile of the target shows systematic changes in response to variations in the temperature and pressure inside the plasma sheath. Moreover, variations in flight conditions, such as reentry altitude and flight speed, significantly affect the target's high-resolution range profile, thereby complicating the accurate imaging and identification of the target. The research presented in this letter introduces a novel approach for studying the radar imaging and electromagnetic scattering characteristics of hypersonic targets covered by inhomogeneous plasma sheath.

In this paper, an accelerated hybrid method of physical optics (PO) shooting and bouncing ray (SBR)–physical theory of diffraction (PTD) is proposed to deal with the electromagnetic scattering of a complex target on rough ground. To accelerate the ray tracing progress, the ray marching technique based on octree structure is employed. In this technique, only the nodes passed by the ray are detected successively until the first facet intersected by ray is found or the ray passes through the bounding box, which greatly decreases the intersection test. Then, based on the accelerated PO-SBR-PTD method, the spotlight synthetic aperture radar (SAR) echo data of the composite target–ground model is obtained by the vector superposition of the echo on each meshed patch. Furthermore, the spotlight SAR image of the composite model is simulated by the polar format algorithm (PFA). In numerical simulations, both the EM scattering of the target and composite model are calculated and evaluated by comparing with the multilevel fast multipole method (MLFMM) in FEKO software. Meanwhile the spotlight SAR image of the composite target–ground model is also compared with the real image in MSTAR data, and a satisfactory similarity between them is obtained. In addition, the SAR images of two targets on rough ground for different pose angles are also presented and analyzed.

In this paper, we analyze a 28 GHz suburban channel using a hybrid ray-tracing simulation. Hybrid ray-tracing technique is a combination of image method and shooting-and-bouncing rays (SBR) method. The SBR method finds a rough propagation path and the image method predicts the exact propagation path. The hybrid ray-tracing simulation is compared with a measurement campaign conducted in Wolpyeong-dong, Daejeon, Korea, and its performance is verified. The transmitter is placed on a 29m building; the heights of the other buildings are between 10m and 12m. Based on a reasonable agreement between the results of ray-tracing and the measurement results, five streets of Wolpyeong-dong were analyzed using ray-tracing simulation. The path loss, power delay profile, root mean square delay spread, angle of arrival and angular spread were obtained.

A plasma sheath will be generated around the hypersonic vehicle during reentry, and a large number of electrons in the plasma sheath will seriously affect the communication between the vehicle and the ground station. In order to reduce the electron number density of the hypersonic vehicle plasma sheath, a method of using pulsed discharge active actuation to regulate the plasma sheath is proposed. Based on the air dissociation and ionization model including 11 components and 32 chemical reactions, the reduction effect of pulsed discharge actuation on the electron density of plasma sheath is studied by numerical simulation. A first test is performed in which the pulsed discharge is compared with the plasma jets' experimental data. Then, a second test compared the plasma flow field around the RAMC-II vehicle with the flight test and NASA data. In these two tests, the simulation results are basically consistent with the experimental results. Finally, the effect of pulsed discharge with different energy density on the plasma sheath electron density is studied. The numerical results show that the interaction between the high-pressure aerodynamic actuation generated by the actuator and the plasma sheath produces an obvious shock wave, which blocks electrons from flowing downstream, reduces the velocity and pressure of the flow field behind the shock wave, and, finally, makes the electron density downstream of the actuator attenuate significantly, with the maximum attenuation amplitude of about 35%. Compared with the traditional method, the method proposed in this paper requires less space, load, and source power and has certain engineering feasibility.

A new electromagnetic (EM) calculation model, the inhomogeneity zonal medium model (IZMM) (based on the physical optics (PO) method), is proposed to calculate and analyze the EM scattering characteristics of hypersonic vehicle covered with a plasma sheath. First, the flow field of the plasma sheath is divided into nonuniform calculation subregions with different spacing sizes. The shape of the external flow field of the aircraft is modeled by fitting with a paraboloid and circular platform with different radii. Then, the electron density, temperature, and pressure distribution are obtained by collecting data from different points in the flow field of the sheath. Finally, a piecewise PO method is used to calculate the backscattering radar cross section (BRCS) of the hypersonic vehicle covered with plasma sheath from L-band to X-band. The numerical results show that the EM scattering characteristics of a target spacecraft covered with a plasma sheath can be described more accurately by using zoned medium model simulation. Under different flying conditions, the BRCS of hypersonic vehicle covered with a plasma sheath appears to be reduced to different degrees in the S-band and the band range of 7-11 GHz, and a large attenuation of BRCS occurs in the head area of the aircraft. The research results enrich the EM modeling method of hypersonic vehicles, overcome some shortcomings of the existing PO method, and provide technical support and innovative ideas for the accurate analysis of the EM scattering characteristics of hypersonic targets.

The “black-out” phenomenon of reentry vehicles has been a bottleneck problem that has plagued people for many years. Based on the basic interaction mechanism between electromagnetic wave and plasma, researchers have carried out a series of studies in order to overcome the “blackout” phenomenon essentially, and solving the Communication between Reentry Vehicle and ground radar station. In this paper, the shift operator finite difference time domain (SO-FDTD) method is applied to calculate the echo amplitudes of one-dimensional inhomogeneous plasma sheath in time and frequency domain. The physical mechanism of plasma sheath and electromagnetic (EM) wave is elaborated by analyzing the echo characteristics of EM wave, which provides some meaningful reference for the study of plasma sheath and target monitoring.

The theory of the collisionless plasma sheath with a weak magnetic field is presented. Both planar and cylindrical geometries are considered. Two forms for the ion‐electron pair generation function are considered—a constant function and a function which is proportional to electron density. These are applicable to beam‐generated plasmas and to positive columns. Numerical results are given for the plasma limit when the generation function is constant.