Experimental verification of target shadow parameter estimation in GPS FSR

Bistatic radars, specifically forward-scatter radars, are proposed as an alternative to standard monostatic radars against targets whose radar cross sections (RCS) have been reduced by passive means. Forward-scatter radars operate by detecting echoes from a targets forward-scatter RCS, which is insensitive to effects of passive RCS reduction techniques. However, the performance of the forward-scatter radar is compromised when the angular separation between the interference, which propagates directly from the transmitter to the receiver, and the target return is less than the Rayleigh resolution limit of the receiving antenna. This research presents the results of a parametric study of the ability of a forward-scatter radar to detect and measure the bearing of a large target, whose RCS is reduced via passive means. Super-resolution array processing techniques, particularly root-MUSIC (multiple signal classification), are used to overcome the traditional limitations resulting from the Rayleigh resolution limit of the antenna. The study compares the received power and the bearing measurement accuracy of the forward-scatter radar to that of an equivalent monostatic radar system. The results indicate that forward-scatter radars enjoy advantages in detection and bearing measurement when the backscatter RCS of the target has been reduced and when the target is close to the baseline. The results also indicate that, through the use of super-resolution array processing the capability of the forward-scatter radar to accurately measure the bearing of the target is dependent upon the amount of interference from the direct wave (i.e., the wave which propagates from the transmitter directly to the receiver) and the correlation between the direct wave and the target echo. Good bearing estimates can be achieved if the correlation coefficient is less than 0.95. Bearing measurements may be improved by suppressing the direct wave by either sidelobe control or null steering techniques. >

This communication presents a physical optics based method developed by CELAR to calculate radar cross section (RCS) in function of the distance separating the target and the radar system. Initially this method has been developed to calculate RCS in the same geometrical configurations than the measurements performed in the CELAR facilities. So, after a short presentation of RCS measurement facilities of CELAR, this paper will expose the method developed to calculate near field RCS. Comparisons between measurements and calculations will be shown to validate the method. Then, some applications will be given on canonical and complex targets. For flat circular and square plates, particular phenomena will be detailed and some analytical approximated formula will be proposed to express their monostatic specular RCS

Adaptive cross approximation (ACA) algorithm as a kind of common matrix compression method is often used to analyze the electromagnetic radiation and scattering problems. In the region of far field, the impedance matrix is compressed by ACA method, and the extracted impedance matrix is accelerated filling by equivalent dipole-moment method (EDM). In the area of near field, the method of moments or the equivalent dipole-moment method is applied for filling the impedance matrix. The iterative near field preconditioning technique is used to solve matrix equation, so that fast calculation of radar cross section (RCS) can be achieved. Numerical results show that the computational efficiency is improved significantly via applying the presented method in this paper without sacrificing much accuracy.

The Georgia Tech Research Institute (GTRI), under contract to the U.S. Air Force 46 Test Group, Radar Target ScatteringDivision (RATSCAT), at Holloman AFB, NM, has designed and developed a fttlly polarimetric, bistatic coherent radarmeasurement system (BICOMS). It will be used to measure both the monostatic and bistatic radar cross section (RCS) cftargets, as well as create two-dimensional, extremely high-resolution images of monostatic and bistatic signature data.BICOMS consists of a fixed radar unit (FRU) and a mobile radar unit (MRU), each of which is capable of independent monostatic operation as well as simultaneous coherent monostatic and bistatic operation. The two radar systems are coherently locked via a microwave fiber optic link (FOL). This paper discusses the system design requirements and keysystem features ofthe BICOMS and its major radio frequency (RF) subsystems.Keywords: bistatic, RCS, imaging, polarimetric, low observable. 1. INTRODUCTION AND BACKGROUND The use of low-observable technology has significantly reduced the monostatic RCS of aircraft, making their detection byconventional surveillance systems extremely challenging. The principal signature reduction technique employed in low-observable design is vehicle shaping. This technique relies on redirecting the incident radar energy in a direction away fromthe transmitting source, thereby reducing the monostatic signature ofthe vehicle. The laws of physics maintain that energymust be conserved. Hence, if the monostatic RCS is reduced by shaping, the incident energy must be distributed elsewheresuch that the signature is increased at some or all bistatic angles. It is therefore conceivable that a bistatic radar will havebetter performance than a monostatic radar for detection of low-observable targets where shaping is the principal method usedin RCS reduction.' While bistatic surveillance techniques have been proposed for several decades, only recently has thenecessary technology been available to perform both the difficult phase locking needed between the transmitter and receiverand the large volume of data processing required for the coordinate translation and matching between the transmit and receiveradar beams. These new advances in phase locking and data processing have made the development of bistatic surveillancesystems possible. In addition, a number of radar-directed anti-aircraft missiles in use today operate in a bistatic mode duringsome or all oftheir engagement envelope. Thus, there must be concern for the bistatic signatures of even non-low-observableair vehicles. The Department ofDefense (DoD) has therefore undertaken a program to upgrade and expand its bistatic RCSmeasurement capability at RATSCAT. BICOMS will provide the DoD with the capability to conduct monostatic andbistatic exploitation measurements of threat targets and evaluation of the radar signatures of blue targets.

This paper explores the concept of a Forward Scattering Radar (FSR) system with a rotational transmitter for target detection and localization. Most of the research and development in FSR used a fixed dedicated transmitter; therefore, the detection of stationary and slow moving target is very difficult. By rotating the transmitter, the received signals at the receiver contain extra information carried by the Doppler due to the relative movement of the transmitter-target-receiver. Hence, rotating the transmitter enhances the detection capability especially for a stationary and slow-moving target. In addition, it increases the flexibility of the transmitter to control the signal direction, which broadens the coverage of FSR networks. In this paper, a novel signal processing for the new mode of FSR system based on the signal’s joint time-frequency is proposed and discussed. Additionally, the concept of the FSR system with the rotational transmitter is analyzed experimentally for the detection and localization of a stationary target, at very low speed and a low profile target crossing the FSR baseline. The system acts as a virtual fencing of a remote sensor for area monitoring. The experimental results show that the proposed mode with the new signal processing scheme can detect a human intruder. The potential applications for this system could be used for security and border surveillance, debris detection on an airport runway, ground aerial monitoring, intruder detection, etc.

The forward scatter signature of a target provides the radar systems designer with an alternative approach to the detection of 'very low radar cross section (RCS)' targets. This paper outlines the rationale for a forward scatter radar system, the forward scatter principle, and the architecture of a forward scatter radar systems performance model. This model has been developed to analyse the effect of variations in the choice of operating frequency, transmitter and receiver characteristics, detection and tracking algorithms. The paper discusses these aspects with results from modelling and performance predictions for target forward scatter signature, transmit and receive antenna designs, analogue to digital converter (ADC) performance and coverage for a forward scatter radar system operating in the ultra high frequency (UHF) band.

: In a comparison of measured, simulated, and theoretical calculations of radar cross section (RCS), the radar target was a simple missile shape (a cylinder with hemispherical ends). For the measurements, the target was rotated on a turntable from 5 to 365 deg in azimuth, and its RCS was measured with a W-band frequency agile instrumentation radar. (Clutter and noise in the measured RCS data were reduced by spatial filtering.) For modeling the target geometry, the ACAD (advanced computer aided design) geometric modeling program was used to create both an IGES (initial graphics exchange specification) and a facet model. For modeling the RCS, three high frequency prediction codes were used (Xpatch, CADDSCAT, and NcPTD), as well as a point scatter model. Various methods were used to process and simulate the target returns, depending upon the aspect angle. Agreement between the measured and simulated bandwidth averaged RCS values depended on the portion of the target that dominated the radar return: agreement was close for radar returns dominated by returns from the hemispherical ends of the target. However, for aspect angles near broadside to the target (for which the cylindrical part of the target dominated the returns), RCS measurements suggested an interaction between the target and the pylons supporting it.

The feasibility of an X-ray Forward Scatter Radar (FSR) system, which exploits X-ray pulsars as opportunity transmitters, is examined. We provide a power budget estimate for detection of large cosmic objects using such a FSR system and assume the use of the high-resolution X-ray telescopes mounted on a satellite as the receivers. The numerical results are obtained for three types of pulsars and small asteroids, whose diameters equal and overcome 50m.

Radar Cross Section (RCS) essentially relates to low-observable technology. Most of the aerospace structures are close to cylindrical shape. The scattering problems often involve objects that are quite large in terms of wavelength, hence the matrix equations obtained using numerical methods such as Method of Moments (MoM) are large in size and computationally complex. In this paper, RCS of circular, elliptic and semi elliptic dielectric cylinder is computed using MoM. In order to reduce computational cost, conjugate gradient-based accelerating algorithm is employed. It is shown that the computational time is reduced significantly when accelerating algorithm is incorporated into RCS computations.

In a forward scatter radar system, the forward scatter shadow ratio to characterize a target is introduced as the ratio of the total received power density to the incident power density for a receiver at a certain location. Numerical simulations show that the forward scatter shadow ratio is related to the size of the target as well as the position of the receiver relative to the target. It is a more suitable parameter for studying target detectability than the radar cross-section.

Based on the assumption that plasma medium is cold, unmagnetized, collisional and inhomogeneous, a Radar Cross Section (RCS) calculation model for complex targets shielded with plasma is presented. In high frequency region, the plasma that defilading a target can be treated as layered media. In each layer, the plasma is equivalent to a uniform dielectric. Physics Optics (PO), Ray-Tracing method and Wentzel-Kramer-Brillouin (WKB) method are applied to calculate the backscattering field, which is implemented by visual Graphical Electromagnetic Computing (GRECO) platform. Numerical results illustrate that shielding the targets with plasma is a valid way to reduce the RCS of targets. This conclusion has a broad prospect for plasma stealth and anti stealth

Accurate sub-entire-domain (ASED) and simplified sub-entire-domain (SSED) basis function methods are introduced and compared in this paper for radar cross section (RCS) computation of large-scale periodic structures. The detailed algorithms are presented and the number of unknowns, CPU time and precision of the two methods are discussed respectively. Numerical results are given to show the differences of the two methods, so that a flexible choice can be acquired for further researches and wider applications of SED method.

An essential characteristic of any radar target is the measure of its ability to reflect energy to the receiving antenna. The parameter used to describe this ability is the radar cross section (RCS) of the target. Stealth techniques and technologies, which affect the efficiency of early warning radar systems currently in operation, are described in ref [1]. The problem is to find countermeasures that fully integrate new requirement capabilities into the current long-range radar net and infrastructure, keeping research & development, and maintenance costs, low. The netcentric approach recently proposed in ref [2] using VHF-based multi-band radar systems is a new concept for Recognized Air Picture production based on long-range radars, which offers a powerful solution for the surveillance of large areas at a reasonable cost. Target RCS behaviour, fluctuations due to aspect angle and frequency are of particular interest in these systems, because the antenna beam positioning of the "VHF", "L" (or "S") and "X" band radars should be synchronised in azimuth and elevation. Targets could change orientation, course and kinematical characteristics during the time required for beam positioning. Advance knowledge and accurate prediction of target RCS is therefore desirable in order to design and develop efficient (robust) discrimination algorithms for the optimisation of target detection, tracking and non-cooperative target recognition. This paper reviews the target RCS aspects in current radar systems of interest, and examines RCS behaviour for use in future multi-band radar system applications.

A metamaterial approach to wideband radar cross section reduction that is thin, low-cost and doesn't dictate object shaping is presented in work from Iran. The approach uses principles potentially applicable to infrared and visible light as well as radar. The wideband RCS reducing surface is produced on a commercial high-frequency circuit substrate using conventional printed circuit manufacturing techniques Reducing an object's detectability to radar systems is now a well established priority for military applications, most famously in aircraft applications. ‘Stealth’ aircraft that were once well kept secrets are now a familiar concept to the general public and even fly in air shows. The radar cross section (RCS) of an object is essentially a measure of how detectable an object is to radar systems and so reducing an object's RCS is the basic goal of radar focused ‘stealth’ technologies. There are three main approaches to reducing RCS; radar absorbing material (RAM), object shaping and reflected wave cancelling by object coating. RAM materials, as the name suggests, are designed to reduce radar reflections back to the detector by absorbing the electromagnetic energy transmitted by the radar system, converting it into heat. However, they can be bulky and high maintenance. Object shaping works by shaping the surface of the object to minimise reflections of the radar waves back to the radar system, instead reflecting them in other directions. The obvious disadvantage to this approach is that it dictates the shape of the object, which can compromise the performance of the object for its primary purpose. For example, above all an aircraft must be shaped to enable it to fly, an aircraft that is very hard to detect but cannot take off is of no use to anyone. The work reported in this issue, by researchers at Iran University of Science and Technology (IUST) uses the third approach, in which a surface coating reflects the radar waves in such a way as to reduce the amount of radar energy that returns to the detector. This approach is low profile, low bulk and doesn't dictate the shape of the object. In the IUST team's work it can also be cheaply and simply manufactured using printed circuit board manufacturing techniques. Their proposed structure consist of a chessboard arrangement of two different artificial magnetic conductor (AMC) unit cell patterns, each of which reflects the radar waves differently. The key difference in the reflections is a 180° phase shift, which causes the reflections from the two different AMC cell types to interfere destructively and so significantly reduces the useful energy returned to the radar system's detector. “Since radar systems usually send out a short pulse signal in the time domain, wide bandwidth of the RCS reducer is necessary. The proposed AMC structure achieves a RCS reduction over a very wide bandwidth, about 85%,” said Dr Seid Hasan Sedighy, one of the IUST researchers on this project. The wide bandwidth achieved is possible because the critical 180° phase difference in the reflections is produced by the AMC unit cells over a wide frequency range, from 9.4 GHz to 23.28 GHz, providing 10 dB RCS reduction in that range. The peak RCS reduction is in excess of 40 dB, at 15 GHz. Printed circuit manufacturing techniques were used to create the AMC patterns on a commercial high-frequency circuit substrate, providing a low-cost manufacturing method. As flexible circuit board technologies are now available and continue to develop, this AMC-based, effective and relatively cheap approach to RCS reductions could be applied to arbitrary shapes. AMCs are metamaterial structures that behave as perfect magnetic conductors in a limited range of frequencies. The two unit cell AMC patterns used in this work are an arrangement of ‘E’ shapes and saltire arrows. The patterns were optimised to achieve the desired 180° phase difference in their reflections by simulation before being confirmed by experiment. The RCS reducer consists of a chessboard pattern of AMC patches using two different AMC unit cell designs, which produce reflections 180° out of phase with each other. The resulting destructive interference provides the intended RCS reduction The principles of AMCs and using destructive interference to reduce reflected energy are of course applicable to other frequencies of the EM spectrum, not just the band used for radar. This means that similar effects could be achievable in very different frequencies if the structures can be manufactured. Dr Sedighy expects this to lead to developments closer to photonic frequencies “It seems that this design approach will develop in the other frequency bands such as visible and infrared frequencies, which have many civil and military applications.”

Radar detection of small maritime targets is of great interest in the context of coastal and port security for prevention of activities such as smuggling and piracy. Multistatic radar and forward scatter radar offer detection advantages compared with conventional monostatic systems, such as advantageous multi-perspective target view for the former and target radar cross-section enhancement for the latter. In this study, experimental results are presented to characterise simultaneous measurements investigating the detection of a small inflatable boat by a multistatic radar and a forward scatter radar. These results are believed to be the first example of simultaneous experimental comparison of such systems.