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Automated antennas measurement systems have evolved significantly since the first Scientific-Atlanta Model 1891 which featured a modified IBM selectric as its output device. Following the trend set by the general purpose instrumentation industry, a calculated based antenna analyzer has been designed. The use of a calculator as the system controller offers two distinct advantages. The calculator and its peripherals are much less expensive than a mainframe minicomputer and for some test installations, easier to use.
Two major functions of the National Bureau of Standards are the development of reliable measurement techniques and the development and maintenance of primary reference standards which provide the basis for accurate measurements of important physical quantities. By this means, and through its various measurement and calibration services, NBS fulfills its obligations to support industry and other federal agencies and to help science prosper in the United States.
A system which simulates the motion of a single jammer relative to an adaptive array is described. Jammer motion is simulated electronically without physically moving the array or the jammer. Electrical simulation in the laboratory is desirable when testing airborne arrays because achievable rotation rates are measured in the hundreds of degrees per second.
Wide aperture noise sources for accurate antenna energy parameters measurements are described. Measurement methods utilizing radiators with high equivalent noise temperature (104-105)K are discussed as well as their construction. Antenna equivalent efficiency, gain and disspation coefficient can be measured with accuracy (5-10%) depending on the frequency range.
A new, major facility is being developed at the NAVAIRDEVCEN to provide a wide range of capabilities for test and evaluation of both antennas and complete avionics systems mounted in full-size fleet aircraft. Under the joint sponsorship of NAVAIR (PMA-253, AIR-5492, and AIR-5334) and NAVAIRDEVCEN, this facility is configured to allow efficient, high speed, high-reliability data acquisition and analysis.
A new generation programmable, phase-amplitude measurement receiver has been developed which advances the state-of-the-art of antenna pattern measurements. The new receiver features microprocessor-based control and data processing systems resulting in improved performance and versatility.
Of the wide variety of antenna parameters and system parameters that are measured in anechoic chambers, not all are compatible with all chamber designs. This paper has been primarily designed to answer the following question; “Knowing the type of measurements one intends to make in a chamber, how does one choose and carry out the chamber design so that the chamber will be well suited?” Secondarily, this paper is designed to answer the corollary question; “Can an existing chamber of a particular design be well-suited to particular measurements?”
A VHF antenna array of the uniform filled-aperture type at 103 MHz has been developed for Interplanetary Scintillation (IPS) studies. The filled-aperture array consists of full-wave dipoles arranged in 64 East-West rows of 16 dipoles each. The rows form the basic units with the dipoles polarized in the North-South direction. A partial reflecting screen is mounted 0.22 wavelength below the dipoles. The array uses two 32-element Butler Matrices to form multibeam patterns along with a correlation receiver. The antenna array has a physical aperture of about 5000 m2. Transits of various radio sources have been taken by this antenna array. Various parameters of the array such as halfpower beamwidth, gain, aperture efficiency, etc. have been determined by the radio source transit method and compared with their theoretical values.
This paper presents a method for determining the measurement cone associated with the measurement of far field antenna pattern using a multiaxis positioner. Using the Piogram, a convenient method for specifying the transformation matrix between two rotating coordinate systems, it is shown how to determine the transformation matrix for any general multiaxis positioner. Given the transformation matrix, the parameters of the measurement cone are then derived in a straightforward manner, which is summerized [sic] by a step by step procedure.
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.
An automated, computer-controlled measurement system capable of conducting transmission and reflection measurements on components over the 40 to 47 GHz frequency range is described. The measurement system utilizes harmonic mixing in conjunction with a phase locked, dual channel receiver to downconvert signals in the 7 GHz bandwidth to a lower intermediate frequency (1 KHz) where phase and amplitude measurements are made. The system is capable of operating over a dynamic range in excess of 50 dB when used with an EHF source producing a minimum –10 dBm output. Following a description of the system and its operation, some performance characteristics are presented. The measurement system accuracy is demonstrated using two types of reference standards: (1) a rotary vane attenuator for the transmission measurements, and (2) a set of reduced-height waveguide VSWR standards for the return loss measurements. Results obtained using these standards have indicated that measurement accuracies of 0.25 dB and 30 are achievable over a 50 dB dynamic range.
A cylindrical near-field antenna range has been designed, implemented and tested recently at the Cobb County Research Facility of Georgia Tech’s Engineering Experiment Station. While Georgia Tech has had an operational planar scanner since 1974 [1], the relocation of a portion of the Experiment Station to an off-campus site, together with the need for measurements of antennas not practical with the existing planar scanner, prompted the addition of a cylindrical near-field range. Provision was made in the range instrumentation for planar-polar and spherical near-field measurements. Computer software was written to effect the conversion from cylindrical near-field measurements to far-field patterns.
This paper describes a method for determining the radiation patterns of all possible operating modes of multi-element antennas without using the normally-required mode-forming networks. For the general case of non-symmetrical antennas, the radiation pattern amplitude and phase characteristics of each antenna element is digitally recorded with all other elements in their normal operating positions and their output ports terminated in a matched load. The patterns of all possible operating modes of the antenna are then computed by phasor summation of the element patterns using the same amplitude and phase offsets which would be imparted by a mode-forming network. This approach significantly reduces hardware requirements for testing broadband multielement antennas, particularly during early development stages. Symmetry in the antenna can be used to reduce the number of elements that need to be measured. If the antenna is rotationaly symmetric (for example, log-spirals, log-periodic monopole arrays and some cavity backed monopole arrays), only one element needs to be measured. Significant data reduction is achieved since all the orthoganal mode patterns can be derived from the field of one element. An eight-arm, constant electrical radius spiral was used as a test antenna for comparison of patterns generated by the following three methods: 1. Direct measurement with mode forming network present. 2. Computational phasor summation of all spiral arms. 3. Computational rotation, superposition and phasor summation of the output of a single arm. High correlation of results between the three methods is demonstrated. A discussion of possible error sources is included.
In principle, spherical near-field scanning measurements are performed in the same way as conventional far-field measurements except that the range length can be reduced. This provides a natural advantage to scanning in spherical coordinates over other coordinate systems due to the steady availability of equipment. However, special considerations must be given to near-field range design because of the necessity for phase measurement capability, mechanical accuracy and the need to handle large quantities of data. Based on experience with spherical near-field measurements carried out during verification testing of a spherical near-field transformation algorithm, we discuss the practical aspects of constructing a near-field range. In particular we will consider range alignment procedure, engineering of the RF signal path and times for data collection and processing.
Over the past year an extensive set of verification tests has been made on a particular test antenna in order to confirm the design and operation of a spherical near-field algorithm. The measurement checks included data taken at two frequencies at three range lengths, with two coordinate orientations and with two types of probe horns. Comparisons were made against the compact range and among the various spherical near-field tests. In this talk we show examples from this program of measurements and summarize the results which demonstrate the operation of the spherical near-field scanning technique.
Research on the near-field antenna measurement technique is now in its 15th year at Georgia Tech. Current research is supported by the Army Research office, by the Joint Services Electronic Porgram [sic], and the National Science Foundation. An overview of the current research activities will be given including a description of the Georgia Tech Planar, Cylindrical and Spherical Surface near-field ranges. A recently developed technique for analytic compensation of near-field probe positioning error will be presented.
Compact Antenna Ranges (C.R.) proved to suitable for indoor measurements of antennas of moderate size (up to about 4 feet) in the frequency ranges from 4-18 GHz. Where less accurate measurements are allowed, the upper frequency limit can be as high as 60 GHz in current C.R. design. Dimensions of such a range are approximately 4 times larger (in linear dimension) than those of the test antenna. This is due to the face that there is a considerable taper in the amplitude over the aperture of the C.R. Considerable improvements in the electrical performance may be expected for ranges in which two crossed parabolic cylindrical reflectors are used. Due to the increased focal length the uniformity of the amplitude distribution across the final aperture is increased considerably compared to conventional design. Furthermore, an asymmetrical plane-wave zone can be created which makes it possible to measure the patterns of asymmetrical antennas or devices including the direct environment (antennas on aircraft or spacecraft). A compact range which consists of a main reflector with overall dimensions of 2x2 metres has been used for experimental investigation in the 8-70 GHz frequency band. At 10 GHz the plane-wave zone has a slightly elliptical shape (100x90cm). The amplitude variations are in this case less than 0.3dB; the corresponding phase errors are less than 4 degrees. It has been shown that the reflectivity level can be kept below –60dB. Only a minor degradation in performance was found at 70 GHz. In conclusion, the performance of this new compact range is as good as, or better than that of most outdoor ranges. The upper frequency limit is about 100 GHz for ranges of moderate size (up to 3 metres). Summarizing, the main advantages compared to other compact ranges are: -Larger test zone area (up to 2x) for the same C.R. reflector size -better crosspolar performance -considerably higher upper frequency limit The last-named is due to the cylindrical reflector surfaces, which are easier and cheaper to manufacture than double-curved surfaces.
The mechanical alignment of a reflector antenna involves both the reflector shape and also the relative orientation of the feed and subreflector. The requirements for alignment are derived from the system requirements for antenna functional performance, including pointing. A typical alignment plan includes the following alignment operations: • Component inspection of reflector, subreflector and feed. • Antenna assembly, including a final baseline measurement. • Alignment to a positioner for antenna range tests. • Alignment checks before and after environmental exposures. • Installation on spacecraft, including receiving inspection, adjustment to a specific orientation, and structural distortion checks • Alignment checks on spacecraft. Six tooling balls on the back of the reflector are commonly used as a reference for both pointing and structural distortion. Additional references may be provided by mirrored surfaces, auxiliary tooling balls, machined edges, scribe lines and mounting surfaces. Special fixtures for holding the antenna throughout its test sequence have proved useful. These fixtures are designed to provide a rigid support with a minimum of mounting stresses. They also have provisions for fine angular adjustments on antenna positioners. Analytic aids include: • Calculations of the Best-Fit-Paraboloid to the measured points on the reflector surface. • Use of beam deviation factors to calculate the predicted electrical beam from mechanical measurements. • Transformation of coordinates from one system to another. The measurement methods and analytic techniques that are used for a typical set of alignment operations are described.
This paper summarizes the results of work performed for the Naval Air Development Center (NADC) on a new full-sized aircraft antenna range located in Warminster, PA. Because of the ever-increasing sophistication of aircraft systems, a facility capable of testing full scale mock-ups has become necessary to fully characterize the system in its operating environment. There are, however, several unique problems associated with such a range. Many systems of interest have a wing-tip to wing-tip baseline, which requires that the incident illumination be “uniform” over a significant aperture (approximately 40x15 feet for tactical aircraft). Differential path loss between wing-tip ends, as the aircraft is rotated, can be a source of large error, as can the parallax created by off-center rotation. Also, since today’s military aircraft carry a wide variety of systems, the range is required to be a “general use” range, operational over a wide frequency spectrum from 30 MHz to 40 GHz. A thorough examination of design trade-offs was performed relating the critical parameters of source beamwidth, specular reflection, path loss, phase error, and receive aperture size in order to choose the proper source antenna type, source height, and separation distance between source and test antennas for each frequency band of interest. Other factors in the range design were a maximum possible source height of 40 feet (approximately the height of the pedestal), and a desire to keep the separation distance fixed over the entire frequency range. Results are presented with indicate excellent performance over an 18 x 18 foot aperture for various polarizations. It was found that the range operates effectively as a ground reflection range from 30 MHz to 3 GHz, and as an elevated range at higher frequencies. Peak-to-peak amplitude ripples over the test aperture of 1.0 dB (corresponding to a reflection level of –25 dB) were acheived over a significant portion of the frequency spectrum.
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.