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This paper discusses some of the applications of high-resolution coherent radar image processing techniques in unimproved indoor facilities. The techniques are particularly useful in situations where traditional indoor range chambers are unavailable or impractical. Experiments in an 18-foot-high warehouse building have shown that useful measurements can be made at close quarters, in a high-clutter environment.
System-2000 instruments were created for pattern range applications. The SD-2000 Synchro Monitor was developed in 1983, the MC-2000 Motor Controller in 1984, and System-2000 Host Processor in 1985. Dual black and white video monitors are being used both for graphics and closed circuit television. A rigid body motion application written in FORTH includes graphic primitives to simulate range components. In this paper, a simple aircraft model is installed on a model tower. A square hole in the vertical stabilizer simulates where a probe or antenna is to be located. The hole is offset from the inter-section of model and tower rotation axes, for discussion. Raster and spiral scanning are examined. Spiral scanning required simultaneous control o two drive motors. Emphasis is placed on using System-2000 dual axis features for motor control and graphic imaging of successive model positions.
The accurate measurement of radar target scattering properties is becoming increasingly important in the development of stealth technology. This paper describes a low cost imaging Radar Cross Section (RCS) instrumentation radar capable of measuring both the amplitude and phase response of low RCS targets. The RCS instrumentation radar uses wideband FM wave-forms to achieve fine range resolution providing RCS data as a function of range, frequency and aspect. With additional data processing the radar can produce fully focused Inverse Synthetic Aperture Radar (ISAR) images and perform near field transformations of the data to correct the phase curvature across the target region. The radar achieves a range resolution of 4 inches at S-band and a sensitivity of –70 dBsm at a 30 ft range.
Inverse synthetic aperture radar (ISAR) imaging is used to produce high cross-range and down-range resolution on objects undergoing a change of aspect angle relative to the radar. In this application, the ISAR technique was used on an outdoor ground-bounce radar cross-section (RCS) measurement range. The objective is to locate, identify, and quantify the scattering properties of the target-under-test (TUT). The TUT is mounted well above ground on a target pole and can rotate in azimuth and elevation. The TUT’s rotational motion about an axis perpendicular to the radar line of sight is used to produce the cross-range resolution. For range resolution, a high-bandwidth frequency stepped waveform is used. The data are processed entirely in the digital domain with an algorithm that consists of a procedure to remove the dispersive properties and amplitude variations of the complete end-to-end range response, followed by a two-dimensional, polar-to-rectangular resampling filter and a two-dimensional fast Fourier transform (FFT). The processor has achieved images with amplitude and distortion products that are below the system’s noise floor with up to 48 dB of processing gain. The radar imagery is presented to the RCS engineer on a high-resolution color graphics terminal with true-perspective color-coded RCS displays in logarithmic amplitude or linear phase scales. The design of the ISAR processing algorithm is described in this paper as are the results for both simulated and actual radar data.
This paper describes a digitally controlled receiver-recorder capable of time division multiplexing in the frequency domain at a 400 KHz rate and in the amplitude domain at a 20 MHz rate. Good sensitivity and interference rejection are other features of this receiver which operates over the 2-18 GHz band. It is utilized to obtain a measure of antennas performance as impacted by air frames upon which the antenna(s) are mounted.
Wideband RCS instrumentation systems can provide a high degree of range resolution. By combining wideband RCS data with a synthetic-aperture or Doppler processing, the spatial distribution of radar reflectivity can be determined. These systems provide diagnostic capabilities which are useful for locating scattering sources on complex objects and for assessing the effectiveness of modifications. The Proceedings of the 1983 meeting included a paper which described a linear-FM system operating over a 3 GHz bandwidth capable of measuring RCS vs range, cross range, and frequency using a single measurement set-up. This paper analytically demonstrates a procedure for extracting CW RCS patterns from the wideband data obtained using the linear-FM system. By combining the latter and the former processing, it is possible to obtain from a single data array both wideband responses showing the spatial distribution of scatterers and narrowband responses which are the traditional CW RCS patterns. The paper includes experimental verifications of these assertions by comparing results of CW measured data with data extracted from wideband RCS measurements.
The compact range is an electromagnetic measurement system used to simulate a plane wave illuminating an antenna or scattering body. The plane wave is necessary to represent the actual use of the antenna or scattering from a target in a real world situation. Traditionally, a compact range has been designed as an off-set fed parabolic reflector with a knife edge or serrated edge termination. It has been known for many years that the termination of the parabolic surface has limited the extent of the plane wave region or, more significantly, the antenna or scattering body size that can be measured in the compact range. For example, the Scientific Atlanta (SA) Compact Range is specified to be limited to four foot long antennas or scattering bodies as shown in their specifications. Note that the SA compact range uses a serrated edge treatment as shown in Figure 1. This system uses a parabolic reflector surface which is approximately 12 square feet so that most of the reflector surface is not usable based on the 4 foot square plane wave sector. As a result, the compact range has had limited use as well as accuracy which will be shown later. In fact, the compact range concept has not been applied to larger systems because of the large discrepancy between target and reflector size. In summary, the target or antenna sizes that can be measured in the presently available compact range systems are directly related to the edge treatment used to terminate the reflector surface.
The US Army Electronic Proving Ground is in Southeastern Arizona with outlying facilities located throughout Southern Arizona. The Proving Ground is an independent test and evaluation activity under the command of the US Army Test and Evaluation Command. It was established in 1954. EPG’s role in the material acquisition cycle is to conduct development (DT I & II), initial production (first article), and such other engineering (laboratory-type) tests and associated analytical studies of electronic materiel as directed. The results (reports) of these efforts are used by the developer to correct faults, and by Army and DOD decision-makers in determining the suitability of these materiels/systems for adoption and issue. Customer tests to satisfy specific customer requirements and foreign materiel exploitations are also done. EPG is assigned test responsibility for Army ground and airborne (aircraft-mounted) equipment/systems which utilize the electromagnetic spectrum to include: tactical communications; COMSEC (TEMPEST testing included); combat surveillance, and vision equipment (optical, electro-optical, radar, unattended sensors); intelligence acquisition; electronic warfare; radiac; imaging and image interpretation (camera, film, lens, electro-optical); camouflage; avionics; navigation and position location; remotely piloted vehicle; physical security; meteorological; electronic power generation, and tactical computers and associated software. Facilities and capabilities to perform this mission include: laboratories and electronic measurement equipment; antenna pattern measurement’ both free-space and ground-influenced; unattended and physical security sensors; ground and airborne radar target resolution and MTI; precision instrumentation radars in a range configuration for position and track of aerial and ground vehicles; climatic and structural environmental chambers/equipment; calibrated nuclear radiation sources; electromagnetic compatibility, interference and vulnerability measurement and analysis; and other specialized facilities and equipment. The Proving Ground, working in conjunction with a DOD Area Frequency Coordinator, can create a limited realistic electronic battlefield environment. This capability is undergoing significant development and enhancement as a part of a program to develop and acquire the capability to test Army Battlefield Automation Systems, variously called C3I, C4, and/or CCS2 systems. The three principal elements of this capability which are all automated include: Systems Control Facility (SCF), Test Item Stimulator (TIS), and Realistic Battlefield Environment, Electronic (REBEEL). In addition to various instrumentation computers/processors, EPG currently utilizes a DEC Cyber 172, a DEC VAX 11-780, a DEC System 10, and has access to both a CDC 6500 and a 6600. Under the Army Development and Acquisition of Threat Simulators (ADATS) program, EPG is responsible for all non-air defense simulators. The availability of massive real estate in Southern Arizona, which includes more than 70,000 acres on Fort Huachuca, 23,000 acres at Willcox Dry Lake, and 1.5 million acres near Gila Bend, is a major factor in successful satisfaction of our test mission. Fort Huachuca itself is in the foothills of the Huachuca Mountains at an elevation of approximately 5,000 feet and has an average annual rainfall of less than 15 inches. Flying missions are practical almost every day of the year. The Proving Ground is ideally situated between two national ranges and provides overlapping, compatible instrumentation facilities for all types of in-flight test programs. The clear electromagnetic environment, the excellent climatic conditions, and the freedom from aircraft congestion make this an unusually fine area for electronic testing. The Proving Ground consists of a multitude of sophisticated resources, many of them unique in the United States, which are an integral part of the USAEPG test facility and have resulted from an active local research and development effort over a 28-year period.