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Antenna coordinate system transformations for far field measurements of vehicle mounted antennas
J.S. DeRosa (Rome Air Development Center), November 1982

Far field antenna radiation patterns of vehicle mounted antennas are often recorded on the antenna range by rotating the entire vehicle/antenna system with a multiple axis vehicle positioner. Antenna patterns, obtained in this manner, consider the antenna and vehicle as a system and include the effects of the vehicle structure. These patterns are more representative of the operational antenna patterns than the “free space” patterns of the antenna itself. When the antenna is arbitrarily directed on the vehicle, standard antenna pattern cut trajectories, recorded in the coordinate system of the vehicle, become skewed when referenced to the coordinate system of the antenna. With proper adjustment of the fixed angles of the vehicle positioner however, selected standard antenna pattern cut trajectories, referenced to the antenna, may be obtained. The required fixed vehicle positioner angles are obtained from solutions to systems of equations representing the coordinate transformations for the positioner/vehicle/antenna system. In this paper, two general methods of obtaining the coordinate transformation equations are reviewed. These equations are then solved to obtain expressions for the positioner angles necessary for specific cut trajectories. A practical example of a six axis transformation associated with measurements of a three axis gimballed aircraft mounted radar antenna and a three axis vehicle positioner is used to illustrate the techniques (This example was taken from a recent RADC/Newport measurement program.

Conceptual Analysis of Radar Cross-Section Measurements on Compact Ranges
D.W. Hess (Scientific-Atlanta, Inc.),Richard C. Johnson (Georgia Institute of Technology), November 1982

A strong emphasis is now being placed on techniques for reduction of radar cross-section. A missile or aircraft which is invisible to radar has an important strategic advantage. With this fact in mind, the user of a weapons system may place an upper limit on the radar cross-section that he will permit his missile or aircraft to have. The designer must then make use of “stealth technology” to reduce the cross-section to an acceptable level. In order to verify the design, radar cross-section measurements must be made. Thus the current emphasis on cross-section reduction leads to an important need for accurate and reliable methods of measuring radar cross-section.

High sensitivity millimeter wave instrumentation
R.B. Dybdal (The Aerospace Corporation),T. T. Mori (The Aerospace Corporation) H. E. King (The Aerospace Corporation), November 1981

This paper describes a technique to increase the millimeter-wave sensitivity of the popular 1740-1750 series SA (Scientific-Atlanta) receivers. The frequency coverage is conveniently extended with harmonic mixing techniques which reduce the sensitivity. Phase-locked circuitry was developed to allow the receiver to operate in a fundamental mixing mode which permits the measurement of millimeter-wave antennas and radar targets with the same sensitivity achieved at microwave frequencies. At Ka-band a 30 dB enhancement in sensitivity results with the phase-locked circuitry compared with the conventional instrumentation.

US Army Electronic Proving Ground
US Army, November 1981

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.

An Automated Precision Microwave Vector Ratio Measurement Receiver Offers Solutions for Sophisticated Antenna Measurement Problems
F.K. Weinert, November 1980

This paper describes a new, automated, microprocessor controlled, dual-channel microwave vector ratio measurement receiver for the frequency range 10 MHz to 18 GHz. It provides a greater than 120 dB dynamic range and resolutions of 0.001 dB and 0.1 degree. Primarily designed as an attenuator and Signal Generator Calibrator, it offers solutions to antenna measurement problems where high accuracies and/or wide dynamic measurement ranges are required such as for broadband cross-polarization measurements on radar tracking antennas, highly accurate gain measurements on low-loss reflector antennas, frequency domain characteristics measurements on wide-band antennas with resulting data suitable for on-line computer conversion to time domain transient response and dispersion characteristics data and wideband near field scanning measurements for computing far field performances. The measurement data in the instrument is obtained in digital form and available over an IEEE-488 bus interface to an outside computer. Measurement times are automatically optimized by the built-in microprocessor with respect to signal/noise ratio errors in response to the measurement signal level and the chosen resolution. Complete digital measurement data amplitude of both channels and phase, is updated every 5 milliseconds.

E-2C APS-125 Radar In-Flight Antenna Measurement Techniques
J. Seale (Naval Air Test Center),D. DeCarlo (Naval Air Test Center), November 1979

The E-2C Hawkeye aircraft is a carrier based airborne early warning sensor platform. The primary sensor is the APS-125 radar which is operated in the 400 to 446 MHz frequency range and utilizes a 10-element, Yagi end-fired array antenna integrated into a rotating, 2,400 pound rotodome mounted on top of the E-2C aircraft. As is the case for most airborne antennas, the performance in free space when the antenna is off the aircraft can be readily measured on a ground antenna range, but the accurate measurement of the antenna’s performance under actual flight conditions presented project engineers with a unique problem: Pattern interaction between the rotating rotodome and the aircraft fuselage and turning propellers could not be evaluated using existing ground range facilities. The proposed improvements to these facilities to accomplish this task were estimated to cost in excess of five million dollars.
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