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Superresolution techniques based on the Multiple Signal Classification (MUSIC) have recently been applied to two-dimensional (2-D) Inverse Synthetic Aperture Radar (ISAR) imaging with demonstrated results. These techniques exhibit much higher spa tial resolution than other approaches using a 2-D Fourier transform. This paper a MUSIC based superresolution algorithm for 3-D radar imaging, which is especially useful for measurements with both small frequency and aspect angle (in azimuth and elevation) spans. This algorithm models the measured 3-D data set as a sum of point source emissions plus noise. Once the positions in the 3-D space of such scattering centers are obtained using the MU SIC algorithm, the weights (or RCS) of the scattering centers are obtained through a pseudo-inverse matrix inversion computed by means of a Singular Value De composition (SYD).
Accurate mechanical-to-electrical axis alignment (boresighting), gain, and pattern testing of radar antennae requires specialized tooling/fixturing. This requirement is often taken for granted and seldom discussed in the EE community. Particularly in a production environment, where rapid change of test configurations to accommodate multiple radar platforms are required, a convenient mounting scheme is mandatory. This paper describes and illustrates a method implemented at the Warner Robins Air Logistics Center to satisfy this demand. Drawings and/or photos of a three-point Universal Adapter fixture and several UUT Specific radar mounting fixtures are discussed. The paper discusses tolerances, materials, manufacturing processes, alignment, and antenna boresight methodologies.
Instrumentation grade, coherent, bistatic, radar cross section (RCS) measurement systems require a reliable low-noise method to link the reference, local oscillator (LO) and intermediate frequency (IF) coherent signals between the transmit and receive subsystems. One approach to this is the use of a fiber optic link (FOL). Phase noise measurements have been performed on a distributed feedback (DFB) type laser transmitter-photodiode receiver link with a delay of up to 2.26 kilometers, operating at 5 GHz, using a standard HP 3048A phase noise test measurement setup. System level tests have been performed, incorporating a FOL into a coherent bistatic instrumentation radar system local oscillator path, and performing image processing on an emulated target A first level analysis was conducted regarding the effects of the thermal noise on the radar perfonnance.
A frequency selective surface has been developed for use as a part of an automatic highway system. The FSS is attached as a stripe along the edge or center of the lane, and is designed to a strong retro-reflective echo for the design frequency, polarization, and elevation angle of the forward-looking radar installed on an automobile. The stripe provides directional information for automated steering, as well as other coded information such as lane number, and exit advance warning. This paper reports on initial development and testing of a prototype FSS highway stripe. The stripe was designed for an operating frequency of 10.5 GHz, and was built and tested using a prototype autonomous vehicle. Both FSS stripe performance, and performance of the vehicle will be reported.
Proper characterization of metal walled chambers or other non-anechoic facilities is normally difficult and time consuming. A novel technique for rapid charac terization is described that is available to high PRF, pulsed, chirp radar systems. A sphere is tethered to a crosspiece mounted on the axis of a motor using a fine cord. The system can be mounted on the ceiling or affixed to a variable height pole. adjusting the motor speed and length of the cord, a stable orbit is achieved having a fixed radius and height above the suspension point. Chirp data can be processed into range-time-intensity (RTI) plots that provide clear evidence of multipath and beam taper. By changing the orbit parameters it is possible to characterize a large volume and remedy problems in a very short period of time.
In the past few years there have been new application of transient, ultra-wide band microwaves include cooperating aircraft identification and ground penetration Radar's, high power microwave weapons and others. These applications typically require the use of ultra-wideband antennas with characteristics suitable to radiate transient pulses. This paper describes the capabilities of the USAF Phillips Laboratory's new Transient Antenna Range. The antenna range can measure the radiated characteristics of sources/antennas wave forms with risetimes in the 75 ps regime, and with greater than 50 ns pulse width. The antenna range incorporates a hardware suite controlled by a powerful software data acquisition system that runs on a PC. Automatic data reduction can yield values of wave form peak electric field, risetime and waveform spectrum at a single point, or across an azimuthal scan. This paper will also describe a unique wave form splicing technique used in the data processing algorithms of the Transient Antenna Range. This splicing technique allows test personnel to record the (typically) very fast early time history of the radiated waveform with an SCD-5000 scan converter (operating at a maximum bandwidth, 5 ns of record available), and the long time history of the waveform with a DSA-602 transient digitizer.
From a study of several radar cross section (RCS) measurement facilities, we identify significant sources of uncertainty and develop methods for estimating their effect. Out goal is to provide a "reasonable" and uniform formalism for evaluating RCS measurements which can be used on a variety of test ranges to produce comparable estimates of uncertainty.
New results from complete scattering matric measurements on string-suspended simple geometric shapes - from the Boeing 9-77 compact range - are presented for the first time.
A novel computer simulation methodology to properly characterize the role of probe directivity/pattern compensation in cylindrical near field scanning geometry is presented. The methodology is applied to a linear test array antenna and the JPIJNASA scatterometer (NSCA1) radar antenna. In addition, error analysis techniques of computer simulation and measured have been developed to determine the achievable accuracy in pattern measurements of the NSCAT antenna in cylindrical near field.
Radar scattering can be modeled as a sum of contributions from a finite number of canonical scattering centers. These canonical scattering centers (edges, corners, specular points) all have different amplitude behavior as a function of frequency. We completely characterize this behavior with a single parameter in a parametric model of the scattering data. The estimation of this amplitude dispersion parameter along with down range location and rela tive amplitudes is presented.
Norden Inc. has developed and instrumented its JSTARS 1000' Outdoor Antenna Range with a multi-port antenna measurement system designed to acquire antenna data (patterns and other related signals) at the antenna's respective radar system's intermediate frequency (IF). The measurement system utilizes the JSTARS RF microwave receivers attached to the multiple channels of the JSTARS antenna. These receivers obtain the RF signal from these multiple channels and provide the IF signals to the measurement system.
This paper demonstrates a high speed antenna measurement capability recently developed in the MDTI Radar Measurement Center. Originally constructed as a Radar Cross Section facility, the RMC has added the capability to measure antenna patterns on apertures up to 40-feet in length in the far field. Data will be presented to demonstrate system performance through the use of modern output formats, such as global plots and videotape presentations.
Three-dimensional imaging capability has recently been added to METRATEK's Model 200 RCS Diagnostic Radar. This paper describes the rationale and methodology for producing three dimensional images and gives sample images taken with the system.
Radar with the 2-D Fourier trans- form of the scattered field data in frequency and/or have poor resolution. A modified brid method and a modified 2-D AR technique are proposed to high radar images us- limited backscattered field data. The final image presents the scattering properties of the target in a quantitative way. The peaks in the image represents the positions of centers contributing to the backscattered field. Furthermore, the amplitudes of the peaks correspond to the intensities of the scattering centers.
The Naval Command, Control and Ocean Surveillance Center, Research, Development, Test and Evaluation Division (NRaD) is tasked by the Navy to collect and evaluate full-scale radar cross section (RCS) measurements on ships and aircraft. The Radar Branch at NRaD, operates a radar range west of Pt Loma, San Diego, CA. This radar range has been used to collect X-band and Ku-band calibrated data on Naval ships for the past seven years. The NRaD radar calibration helicopter procedures are the focus of this paper. Using helicopters to suspend and measure "isolated" spheres in space as the primary reference is a major calibration element. A 1700-ft Kevlar line is used to suspend the sphere from the helicopter. This length of line is sufficient to isolate the helicopter from the sphere; thus, the helicopter is not in the significant antenna sidelobes.
A versatile millimeter wave imaging radar is presented to conduct polarimetric doppler as well as wide band RCS measurements. The aim of the system is not only to acquire doppler measurements of determine the distance of an object but also to generate image-like information for classification purposes. A hardware gate controller is incorporated in the system to perform pulsed measurements. This controller can drive three different frequency extension modules covering frequency ranges from 8 to 18 GHz, 70 to 80 GHz and 75 to 77 GHz respectively. In all bands, dual polarized horns are used to allow fully polarimetric measurements. A network analyzer and a FFT analyzer are used as receivers. For both concepts the advantages and disadvantages are discussed. The transmit and the receive antenna are mounted on a positioner. Thus, a radar image using the real aperture of the antennas can be generated by mechanical scanning in azimuth and elevation.
RCS measurements of representative strategic targets in the resonant scattering regime are presented in this paper. The frequency and aspect dependent RCS signatures of various targets are shown to have close agreement to method-of-moment calculations which are based upon the known target shape and composition. Using the resonant scattering signatures, non-cooperative target recognition can be performed with high confidence using a discrete frequency sampling approach. The target set included cones, spheres, and canonical shapes which have been characterized in the VHF and UHF bands. Measurements made at the Lockheed Space Missile Company Rye Canyon facility have recorded calibrated RCS of representative hardware as a function of both frequency and aspect in the resonant region. These data compare well with prediction, and their use for non-cooperative target recognition will be explained. This effort is being conducted to develop signature models, laboratory measurements and useful discrimination algorithms which exploit the frequency variation of the resonant scattering RCS.
The need for practical solutions to radar scattering in high-frequency regime have led to the development of a number of approximation methods. The high-frequency asymptotic methods use approximations based on physical optics (PO), geometrical theory of diffraction (GTD) or physical theory of diffraction (PTD) and their variations. Radar scattering from electrically large conducting surface includes traveling surface wave contributions which are not accounted by the high-frequency asymptotic methods. A hybrid method integrating GTD and traveling wave theory (TW) is used for verification and to illustrate important scattering mechanisms that influence radar cross section (RCS) of a wedge. Analysis of the wedge RCS signature identifies significant contributions of the traveling surface waves to the total RCS. Both measured and predicted RCS of the wedge are considered. Using hybrid GTD-TW method very good agreement between the predicted and measured RCS patterns is observed for all angles.
The Benefield Anechoic Facility, Edwards AFB, California contains a large anechoic chamber for avionic integration test and evaluation. Because of the large chamber size, operational tests can require high-power aircraft radar emissions. To define the range of energy safely accommodated by currently installed radar absorbing material (RAM), a detailed analysis was performed and the results presented. The incident radar energy generates a heat transfer to the RAM. The RAM boundaries dissipate heat through convection, conduction, and radiation. A finite-difference solution demonstrates the temperature distribution in the material varies with the angle and polarization of the incident electric field. Discussions include the use of the RAM thermal characteristic's pretest evaluation to improve operating capability determinations and to facilitate assessment of customer requirements.
The design of wide-band, multi-layer radar absorbing materials involves the solution of what is essentially an N-dimensional optimization problem. Genetic algorithms appear to offer significant advantages over conventional optimization techniques for this type of problem due to their robustness and independence of performance function derivatives. To illustrate their use, the paper considers the optimum design of wideband, multi-layer, Jaumann radar absorbers for normal and oblique incidence.