Forward scatter radar detection

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.

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.

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.

This letter presents a compact dual-polarized over-the-air testing antenna with low radar cross section (RCS) for the fifth-generation and emerging wireless communication systems. The proposed antenna design is achieved by slotting two orthogonal Vivaldi antennas in a cross-shaped form into a two-part three-dimensional printed radome and loading microwave-absorbing materials (MAMs) at the antenna's outer edges. The proposed antenna has a rocket-nest shape with a diameter of 63.4 and 113.68 mm length. The -10 dB impedance bandwidth (S11) is obtained from a range of 2.1 up to 6 GHz. The two-part radome is formed by polylactic acid and acrylonitrile butadiene styrene dielectric materials, respectively. Their respective dielectric constants are approximately 2.6 and 4.5 within the -10 dB impedance bandwidth. The MAMs geometry and distribution location are optimized to suppress induced current over the antenna. An antenna prototype has been fabricated and measured. The measured results agree reasonably well with the simulated results. The results show that the use of the two-part radome enables the achievement of low RCS with compact form factor. Furthermore, a low bistatic RCS of between 2 and 6 GHz is observed in simulation for angular ranges of θ ∈ [-30°, +30°] and Φ ∈ [-90°, +90°].

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. >

In recent years, the use of shore or buoy mounted forward scatter radar transceivers for the detection of small, low radar cross section, slow speed (otherwise termed low detectability) maritime targets has been proposed and investigated. Work has focused on the fundamental development of the single baseline link, which would form the basis of any netted system and has mostly been investigated at the lower end of the sea state scale. However as sea state increases, one of the main issues for target detection becomes the visibility time due to line of sight interruption. With a single line chain, this could be a major drawback for the system function as a whole, restricting its use to lower sea states. The formation of multiple baselines using multi-static transceivers could however improve the situation greatly. This paper investigates target observability in both single baseline and multi-baseline systems in an effort to estimate the level of improvement possible.

The use of a monostatic radar for the detection of cosmic rays was first suggested by Blackett and Lovell in 1941. Over the years that followed it became clear that this type of radar would require extremely high power transmitters and high gain antennas for its operation. The low Radar Cross Section (RCS) is due to the details of electromagnetic wave scattering by the ionization electrons in the dense terrestrial atmosphere. A less known type of radar, bistatic radar, exhibits a strong enhancement in the RCS at forward directions. We present results of expected received power calculations for a bistatic radar used in the detection of extensive cosmic ray showers. The rapid movement of the shower front followed by extinction of ionization by electronegative oxygen contributes to the formation of a phase modulated signal at the receiver. The signal frequency versus time signature is characteristic for the ionization produced by extensive cosmic ray showers and will provide an optimal discrimination against spurious events.

In this paper we analyze the power budget and calculate signal to noise ratio (SNR) and radar cross section (RCS) for different ground targets using a forward scattering radar (FSR) system, which consists of a transmitter mounted on a satellite of GPS and a receiver located on the Earth's surface. The FSR is a specific bistatic radar system where the bistatic angle is near 180o, and the target is located near the transmitter-receiver baseline. Theoretical and numerical calculations of SNR and RCS are presented for different ground targets when the GPS L1 signal is transmitted by satellites. The SNR and RCS are also estimated by using real records of the GPS signal shadows from different targets. The obtained numerical and experimental results are analyzed and discussed.

The ultra high frequency (UHF) band spectrum will likely be congested in near future since the next generation wireless as well as Radio Frequency Identification (RFID) system users will witness the use of UHF band technology with increased demand of bandwidth, bit rate, frequency spectrum and power consumption. The alternate solution is the use of millimeter-wave band technology. It is possible to improve data throughput, range resolution and multi-user capability in mm-wave band RFID system. ‘Higher power reception efficiency and lower side lobe level (SLL) of radiation pattern’ is required for RFID system that will increase the tag range and transmission bit rate. At the same time lower SLL will minimize the interference level. Beam pointing error is another problem of UHF band antenna which reduces the tag range and bit rate. These problems can be minimized by using large number of antenna elements. But with UHF band signal it is practically difficult to construct large array antenna; since the array size becomes tremendously larger with the increase of antenna elements. ‘Higher power reception efficiency and lower SLL’ can practically be obtained by using non-uniform power distribution of large number of antenna elements in millimeter wave band. A new and technically better method of beam forming by implementing the concept of staircase power distribution (SPD) of antenna elements at 60 GHz has been investigated and presented in the paper. The SPD method is compared with Gaussian edge tapering method. It was found that the maximum SLL (MSLL) is the lowest in case of SPD. The beam efficiency of SPD is also equivalent to that of Gaussian edge tapering method. It is easier to fabricate a larger number of antenna elements within smaller area with SPD at 60 GHz system; since the antenna size is smaller and the number of different power distribution in SPD case is less and stepwise uniform. Uniform and less number of different power distribution of SPD also minimizes other technical errors.

F-117 Nighthawk Stealth Fighter Jet is considered as the world's first true ‘Stealth’ aircraft and its considerably low Radar Cross Section (RCS) has been measured in this paper. RCS is an important parameter for radar that improvises on the detectability the target accurately. Varying two of the most important parameters of RCS such as frequency of the radar transceiver and aspect angle, the best outputs are recorded as the results. Using COMSOL Multiphysics software a virtual chamber has been created and the CAD model of F-117A is applied in it. With a planar electric field as the incident radar signal, the RCS has been recorded. In this paper, the bi-static RCS calculation method is considered for simulation. The results clearly depicted that better RCS can be obtained at the upper order frequency of S band wave range (above 3.5 GHz) and at some specific aspect angles the results exhibit higher detectability.

This paper describes the establishment of a test setup for measurement of passive inter-modulation (PIM) products generated by various device(s) under test (DUT(s)) (filters, coaxial cables etc.) at ultra high frequency (UHF) band. The paper begins with a brief discussion of an ideal PIM test setup using a quiet load. It then discusses the establishment of the setup in the absence of quiet load and demonstrates a PIM level of −192 dBc of the test setup. Finally it shows the PIM performance of a band-stop filter, a flexible cable, cascade of band-stop filter, and flexible cable, measured using the established test setup. These components are required for UHF payload of a communication satellite.

A bending dipole RFID (Radio Frequency Identification) tag antenna at Ultra High Frequency (UHF) band is presented to meet the requirements of the antenna miniaturization. The overall dimension of the tag antenna is only 55×12 mm2.The input impedance of the antenna is about 43 + j800Ω with Philips EPC UCODE Gen 2 RFID tag microchip. The simulation results show that the designed antenna has a wide impedance bandwidth, covering 840–845MHz and 920–925MHz UHF band, and has a good return loss value and omni-direction, which can meet the practical requirements of RFID tag antenna.

Field methods based on the finite-difference approximations of the time-domain Maxwell's equations and the potential-flow equation have been developed to solve the multidisciplinary problem of airfoil shaping for aerodynamic efficiency and low radar cross section (RCS). A parametric study and an optimization study employing the two analysis methods are presented to illustrate their combined capabilities. The parametric study shows that for frontal radar illumination, the RCS of an airfoil is independent of the chordwise location of maximum thickness but depends strongly on the maximum thickness, leading-edge radius, and leadingedge shape. In addition, this study shows that the RCS of an airfoil can be reduced without significant effects on its transonic aerodynamic efficiency by reducing the leading-edge radius and/or modifying the shape of the leading edge. The optimization study involves the minimization of wave drag for a non-lifting, symmetrical airfoil with constraints on the airfoil maximum thickness and monostatic RCS. This optimization study shows that the two analysis methods can be used effectively to design aerodynamically efficient airfoils with certain desired RCS characteristics.

Comparison of four different clutter profiles (border, seaside, free space and forest) using Forward Scatter Radar (FSR), which operates in Ultra-High and Very High Frequency (UHF and VHF) bands, is analyzed in this paper. Clutter levels ranging from low, medium, strong and very strong on each profile were studied. Based on the standard deviation of each clutter profile, border suits the best profile as the strongest clutter profile amidst seaside and free space, while the forest is determined as the lowest clutter profile. Subsequently, the characteristics of the clutter are investigated and compared based on the five distribution models (Log-Normal, Log-Logistic, Gamma, Weibull and Nakagami). The parameters of the five distributions are evaluated using Root Mean Square Error (RMSE) in order to prove that the distribution model fits best to the clutter data. It can be concluded that Gamma distribution is the best distribution model for all cases of frequency bands and profiles.

A shared aperture metamaterial (SA-MTM) with partially reflection and absorber characteristics is presented. The SA-MTM is composed of two metallic layers separated by a dielectric spacer; the top absorbing surface (AS) consists of oblique cross metallic pattern loaded with lumped resistances, and the bottom partially reflecting surface (PRS) consists of etched parallel slots in a metallic layer. An SA-MTM with partial reflection and absorption characteristics is fulfilled by making the absorbing surface and partially reflecting surface shared the same aperture in the vertical direction. The SA-MTM is applied to the waveguide slot antenna; the Fabry-Perot resonance cavity constructed by the PRS and the metallic ground layer of the waveguide slot antenna can achieve high gain, while the AS can obtain the low radar cross section (RCS) characteristic antenna by absorbing the incident wave. Simulation and experimental results demonstrate that the antenna with SA-MTM gain is enhanced above 3 dB in the operation frequency range, the backscattering RCS is obviously reduced in a frequency range of 2–9 GHz. This idea can help us design a high gain and low RCS antenna, which overcomes the conflict between scattering and radiation performance of antenna.