Radar Cross Section / Scattering

NASA Almond RCS in
Time-Domain

In this application note, simulation of the Radar Cross Section (RCS) in time-domain is described in WIPL-D Software suite. The products used are WIPL-D Pro and WIPL-D Time Domain Solver. Well known metallic object NASA almond was illuminated by plane wave using Gaussian modulated sine. Near field results in time domain are shown.

Object is about 60 wavelengths long, about 4 wavelengths high and about 0.2 wavelengths thin. Polarization is parallel to the longer semi axes of the almond’s cross section. Two symmetry planes are used in order to reduce required number of unknowns for current approximation. It is made using pre-defined object named BoR (Body of Rotation).

Simulation is performed on the inexpensive desktop machine (any regular desktop or laptop will do). One can conclude that WIPL-D Time-Domain Solver combined with extremely efficient MoM solver WIPL-D Pro is very applicable for the time domain simulation. Simulation time is measured in minutes for over 100 frequency points.

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Reduction of Unknowns Over Electrically Large Scatterers

Calculation of monostatic scattering from electrically large metallic objects\aircrafts is often a subject of interest of scientific, military, or engineering working groups. Simulations of large, pure metallic scatterers still require significant attention as airplanes of the 4th generation are still operational and objects like, helicopters, missiles, and metallic spheres are used for calibrations or verification of the results.

This application note deals with the calculation of monostatic RCS of the metallic aircrafts at 2.00 GHz. The aim is to demonstrate highly efficient utilization of WIPL-D software for RCS calculation with a special attention given to a method of reduction of a number of unknowns. The reduction is performed by decreasing Reference frequency to 87.5% of the initial value resulting in a decreased number of unknowns and consequently significantly reduced simulation time. The high accuracy is preserved as the calculated RCS is almost unaffected by the reduction i.e., is in a good agreement with the results obtained using a higher number of unknowns.

WIPL-D Pro CAD, a full wave 3D electromagnetic Method-of-Moments (MoM) based software on an affordable desktop PC empowered with GPU cards has been used for the simulations.

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Monostatic, Bistatic, and Multistatic Radar Scenarios

The motivation behind this application note is to help various readers to understand basic concept of monostatic and bistatic radar scenarios. Examples explaining realistic monostatic, bistatic, and multistatic scattering scenarios are provided. The explanations were supported with WIPL-D Pro CAD, a full wave 3D electromagnetic (EM) Method-of-Moments (MoM) based software and DDS, which is used for solving very large EM structures.

Very basic explanations of monostatic and bistatic scattering were presented in Part 1 of this document. Part 2 contains some advanced examples which can be recognized in some of real-life scenarios. Majority of presented scenarios are supported with results from the simulations, which is very useful for illustrating radar systems operations. The basic principles outlined here relate to radars and EM propagation. Similar principles can be applied with scenarios related to acoustic underwater sonar operation.

All systems and frequencies presented used here are for demonstration purposes, only. The dimensions of radar targets and other structures are approximate but comparable to real life devices.

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RCS Convergence Study on Electrically Large Corner Reflector in WIPL-D Software

An electrically large corner reflector is well-known structure used in numerous applications where emulation of a large Radar Cross Section (RCS) is required from a reasonably sized object. In this application note we present the analysis of an electrically large corner reflector to illustrate the process of simulation results convergence study in WIPL-D software. By following the changes in RCS related to PEC corner reflector from several, carefully selected simulations, the convergence can be established and high reliability of the calculated results confirmed. The simulations differ in some kernel parameters settings which are thoughtfully explained in the text. The changes in reflector RCS obtained after the simulations can be easily compared for the sake of convergence analysis using WIPL Graph module in polar or Cartesian coordinate systems.

WIPL-D Pro CAD and WIPL-D Pro are used for modelling and simulations. It will be shown that WIPL-D Software, a full wave 3D EM Method-of-Moments (MoM) based solver, applying Surface Integral Equations (SIEs) and Higher Order Basis Functions (HOBFs) can be used effectively to simulate the corner reflector scenario in reasonable time using more or less standard computer workstation configuration. The models will be simulated at 10 GHz – a frequency which is important for some military radars.

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RCS Estimation of Generic Airplane Scale Model

This paper presents modeling and simulation results of monostatic Radar Cross Section (RCS) for scaled model of generic airplane in WIPL-D software. We present simulation times, memory requirements and hardware used for two types of solvers: CPU and GPU.

The airplane is modeled from the sketch in WIPL-D Pro CAD which provides simple and fast solid modeling of complex geometries using built-in primitives, Boolean operations and other features. Length of the model is 310 mm. The simulation was performed in WIPL-D Pro at frequency of 30 GHz.

The model is simulated using both CPU and GPU solvers. CPU solution has been prominent feature of WIPL-D software for many years, but last several years the GPU technology has been flagship product for large scale examples. The PC used for simulation is a regular configuration, rather than an expensive workstation, with simulation time measured in minutes.

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Lowering Ship RCS

This application note outlines utilization of WIPL-D Pro Software, a full wave 3D electromagnetic Method-of-Moments (MoM) based software. The software is used to simulate three models of the electrically large ship in monostatic scattering operating mode at the operating frequency of 1 GHz without any reduction applied.

Obtained results could be very useful for studying the influence of the ship shape to RCS. Monostatic RCS calculated for the first two versions of the shape is unacceptably high, while the third version brings significant reduction. The significance of this results is that the RCS of the ship can be reduced with relatively simple modification of the shape of the ship contour without any radar absorbing materials involved and could indicate a good point to start a ship design.

In spite of very large electrical size of the ship models, all the results were calculated in relatively short time. In addition, the workstation used for the calculations was powerful but affordable desktop PC empowered with GPU cards.

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Trees, Foliage and Complex Sceneries

Scattering of EM waves from trees and foliage as well as the propagation of EM waves in the presence of forests plays an important role in many civil and military applications (such as Foliage Penetrating Radar for detecting potential targets in the forest).

Computationally efficient modeling of trees and foliage can be done with metallic wires for branches and metallic plates for leaves with distributed loadings over them. The approach is valid up to approximately 150 MHz (considering that the tree trunk has diameter less than about 2 ft / 60 cm). The number of unknowns needed for the simulation is reduced approximately 100 times! Only ~100 unknowns are needed for the modeling of a single tree.

On a standard desktop, the simulation of the entire forest with 100 randomly placed trees and additional objects lasts under a minute. The presented approach opens the possibility for a rapid full  3D EM simulation of complex sceneries involving trees, foliage, and potential targets inside forests.

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