AMTA Paper Archive

Target support interaction terms often drive Radar Cross Section Measurement limitations. These limitations are when mask needed information, or render interpretation difficult. Although support improvement is desirable and studied, there is a fundamental problem. Perhaps we can create a support that is 10 dB better than existing supports. The technology producing that improvement will usually be applicable to targets. Result: The same ratios recur. Modern instrumentation Radar possesses many acquisition agility's. Processing power currently available permits handling huge volumes of data. This paper studies evaluation and/or elimination of interaction terms using these agility's. Interactions within the test article are often significant. Controlled of this method would select and retain, or remove the terms.

Coherent background subtraction is an established method of reducing additive range clutter in radar cross­ section measurements. In some measurement situations, it is neither practical nor convenient to directly make a coherent measurement of the range background. The Environmental Research Institute of Michigan has devel­ oped two methods of synthesizing background measure­ ments for the coherent subtraction of additive clutter in these cases. The first method synthesizes a background for measurements of pylon-supported targets by remov­ ing unterminated pylon returns using software gating. The second method improves background subtraction by compensating for phase drift between target and back­ ground measurements. In this paper, these methods of improving the performance and utility of background subtraction will be described and demonstrated on mea­ sured data.

Forming radar images from large fractional band­width data can often lead to unusual artifacts or resolutions degraded from "expected" theoretical point-target values. The frequency dependencies of typical scatter­ ing mechanisms, such as diffractions, surface waves and speculars, can be significant over processing apertures when data are collected using large fractional bandwidth measurement systems. For example, it is well known that resonant scatterers exhibit blurring in the down­range direction of an image. Other scattering mechanisms have linear or quadratic amplitude dependencies which can also alter the impulse response from that of an ideal point scatterer. This paper will first provide a brief description of the frequency dependencies of various scattering mechanisms. The paper will then describe the corresponding effects seen in the impulse response, primarily in the range profile domain. Impulse response plots will be compared for data with large and small fractional band­widths. Lastly, the effects of frequency dependent scattering on the impulse response will be shown using images generated from data collected in indoor compact ranges.

Several approaches are known for the identification of non­cooperative air-borne targets with radar. Assuming that the tar­ get can be tracked during a certain flight path, observations from different aspect angles will be obtained. High-resolution radar (HRR) systems use these observations to create one-dimensional range profiles. With Inverse Synthetic Aperture Radar (ISAR) the data from all observed aspect angles are combined to obtain two-dimensional images. In recent years, techniques for resolution enhancement have been developed for both techniques. The choice for one of the two approaches should depend on the applicability of the target representation for identification. ISAR is the most suitable for reproduction on a display and identification by human observers. In case of identification by a machine, for example an algorithm on a computer, the choice is not straight­ forward. In this paper an overview of the influence of several errors on the performance of HRR and ISAR will be given. The error sources that will be evaluated are: • uncertainty of the absolute distance of the target; • errors in the mutual alignment of observations; • additive noise. The errors are generated numerically and applied to data from simulations and low-noise measurements. The influence of the bandwidth and angular span on the quality of the target reconstruction will be regarded as well as the performance of some high-resolution techniques. Finally, conclusions are drawn concerning the applicability of ISAR and HRR.

The U.S. Air Force 46 Test Group, Radar Target Scattering Division (RATSCAT), at Holloman AFB, NM, in conjunction with the US Army, Navy and Georgia Tech Research Institute (GTRI), has developed a concept for a bistatic coherent radar measurement system (BICOMS). It will be used to measure both the monostatic and bistatic RCS of targets, as well as create two-dimensional images of monostatic and bistatic signature data. It will consist of two mobile radar units, each of which is capable of simultaineously collecting coherent monostatic and bistatic RCS data. This paper will cover the systetn design specificatiovs, layout and design of equipment, and discuss the operating parameters for the radar (power, antenna sizes, sensitivities, timing, etc.).

Modem pulsed phased array radar systems bring new challenges to antenna measurement. These antennas generally consist of hundreds of Transmit-Receive (TR) modules controlled via a beam steering computer to fonn the antenna beam. Attempting to operate these modules with a CW wavefonn will not only quickly damage the mod­ ules but will not properly characterize the antenna. The Navel Surface Warfare Center, Crane Division, recog­ nized the need to add pulsed capability when specifying their latest antenna measurement system. Scientific­ Atlanta met these requirements by integrating their newly introduced Model l 795P Pulsed Microwave Receiver into their proven 2095 Microwave Measurement System to make the Model 2095P Pulsed Microwave Measurement System.

The Modular Radar System has been developed at the Danish Defence Research Establishment (DDRE) in cooperation with the Danish company CRIMP. The unique system is capable of performing nearly all types of calibrated radar measurements. The modularized highly flexible system is presented along with a number of measurement. RCS of very small targets at short ranges 400'- l 000', medium range measurements of Navy targets, aircraft and chaff at ranges from 1-10 nautical miles. The real time high resolution range profiles are used for positive identification of "hot spots" on Navy vessels leading to very efficient RCS reductions.

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.

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.

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.