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Adaptive antenna measurement techniques
The objective of this paper is to outline test procedures, test set-up, and antenna measurements collected on a multi-element adaptive antenna processor. The elements used are UHF blade antennas located on a pedestal mounted A-10 aircraft at the RADC Newport Test Range. The measurement data to be presented will include basic element, and adaptively weighted element patterns. Methods of interpreting system performance and problems in collecting the data will also be provided.
Digital Antenna Data Collecting System for MIL-A-87136 Testing
The Defense Electronic Supply Center in Dayton, Ohio has recently issued a specification, MIL-A-87136, for testing Airborne Antennas. This specification covers all aspects of testing antennas including a section dealing specifically with radiation pattern tests. Further, this specification defines the data format to be used when antenna pattern measurement data is required to be furnished on magnetic tape. Scientific-Atlanta’s Series 2030 Antenna Data Collection System’s magnetic tape format and test instrumentation meets the requirements set forth in MIL-A-87136. The system is a complete instrumentation/firmware package designed and programmed to perform commonly made antenna pattern measurements. After initial operator set-up, measurements can be made automatically at frequencies in the 1-18 GHz range. The test results are digitally recorded on magnetic tape and may be displayed as radiation distribution plots, data listings, or as conventional data patterns. The presentation describes the Antenna Data Collection System, its application to automatic antenna testing and to the requirements of MIL-A-87136. Features of the Data Collection System are included, as well as advantages of automatic measurement and digital recording of antenna data.
E-2C APS-125 Radar In-Flight Antenna Measurement Techniques
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.
Data processing and display for large quantities of antenna patterns
This paper will briefly describe the RADC Antenna test facilities and their function. Considerable focus will be placed on the large amounts of data generated and the associated requirements for Real Time Data, Digital Data, Data Processing and Display, Quality Control and Fast Turnaround of Data. Also, the current process utilized to satisfy the data requirements will be described, followed by a discussion of techniques presently under development to further enhance the process. The use of 3-D displays with color enhancement will be included.
Computerized antenna measurement system
The Amecom Division of Litton Systems has developed several computerized antenna measurement systems designed to make the so-called standard antenna measurements plus relative and absolute phase and amplitude measurements of interferometer arrays. This paper will outline computerized measurement techniques for VSWR, swept phase and amplitude (vs) frequency (multi-octave bandwidths), phase and amplitude (vs) azimuth, radiation patterns and gain. The new computerized systems have reduced production system measurement time by 80 percent.
Antenna pattern data acquisition
This data acquisition and pattern analysis system uses a standard set of Scientific Atlanta antenna-pattern-taking equipment as the basic operational gear. A Tektronix 4051 or 4052 Graphic System is used as a controller to operate the S/A gear and to obtain and store output data in digital format. The TEK 4051 does this by use of the IEEE General Purpose Interface Bus (GPIB), to which three interface boxes are connected. These three: • HP-59306A Relay Actuator • Model 4883 ICS Instrument Coupler • HP-3455A Digital Voltmeter message or digitize the S/A data and put it on the GPIB lines.
Scale model aircraft antenna measurements
Antennas are an integral part of the communications, navigation, EMC systems installed on aircraft. Aircraft, such as the Douglas DC-9, C-9A, C-9B, DC-10, KC-10A, A-3 and A-4, use approximately 20 antennas. These antennas operate from VLF to approximately 20 GHz. The radiation patterns of these antennas are affected by aircraft structure such as wings, vertical stabilizer, engines, and landing gear. Douglas Aircraft Company measures the radiation patterns of these antennas using scale model aircraft (and/or aircraft sections) to predict the performance of the associated system. This paper describes some of the scale model measurement techniques used by Douglas Aircraft Company to obtain scale model radiation pattern data.
Near-field measurement techniques and equipment at the NAEC facility
The Naval Air Engineering Center has been assigned the task of developing Near Field Measurement Techniques and Equipment for testing Navy Aircraft-mounted antennas. These efforts will be applied to Nose-mounted and Wing-mounted antennas. The ultimate objective is the development of a portable near-field test system for the Navy’s ‘O’ level. The test system will produce far field pattern predictions of installed airborne antennas by measuring and processing near field data. NAEC would, also, like the test system to determine if an installed antenna is mission capable or degraded; and in the event of a failed antenna, the test system will isolate the fault of that antenna. This paper will describe NAEC’s progress in this task by descriptions of the following: I. Electrical Hardware i.e. transmitter, receiver, interfaces, controllers II. Mechanical Hardware i.e. translator, probe carriage III. Mathematical approaches Also, recent laboratory results will be described.
Antenna test facility at ISAC-Bangalore
The paper describes a simple but unique antenna test facility suitable for aerospace antenna developments. The total idea can be easily adopted by organizations who wish to carry out antenna measurements with minimum required instrumentation. The facility majorly caters for omni and wide beam antenna measurements, has been set up at ISRO Satellite Centre, Bangalore, India. It has been extensively used for omnidirectional antenna developments in VHF, UHF, L, S, and X-bands for India’s various space programs. Radiation pattern, gain, polarization and impedance measurements can be carried out both in near free space conditions as well as the ground reflection modes. The main feature of the facility is the use of large fiber-glass mounting structures for avoiding reflections and perturbations in radiation patterns due to impressed surface currents, specially in VHF ranges. Field probing is done by the use of a fiber-glass X-Y probe positioner. The facility used Scientific Atlanta 1752 Receiver and 1540 Recorder. Suitable software has been added to the facility for contour plotting of radiation levels, calculation of efficiency isotropy, and polarization properties.
Antenna pattern interpolation via digital signal reconstruction
Digital signal processing techniques provide a method by which a finely resolved antenna pattern can be reconstructed from coarsly sampled data. Antenna pattern reconstruction offers several advantages over the direct measurement of a finely resolved pattern, and is applicable whenever a computer is available for implementation of the reconstruction algorithm. As computerized pattern measurement equipment becomes more prevalent, pattern reconstruction algorithms will become more common place. The advantages of pattern reconstruction include higher quality presentation of antenna patterns due to increased resolution, decreased data acquisition time due to coarser sampling, and decreased data storage requirements. The mean square error or a reconstructed antenna pattern is smaller than that of the directly measured pattern. In the context of near-field to far-field pattern transformations, pattern reconstruction becomes essential. The transformation is performed at a coarse spacing for maximum computational speed without compromising the quality of output data. This paper provides an introduction to the technique of antenna pattern reconstruction. Key concepts and terminology are discussed A generic reconstruction algorithm is developed. Examples of interpolated antenna patterns are shown.
A New Generation Programmable Phase/Amplitude Measurement Receiver
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.
Radio Astronomical Technique to Measure Antenna Parameters of IPS Telescope at 103 MHz
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.
A Method for Obtaining the Measurement Cone When Using A Multiple Axis Positioner In the Measurement Of Far Field Antenna Pattern
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.
Cylindrical Near-Field Techniques with Application to Array Antennas
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 , 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.
Element measurements of multimode antennas
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.
New class in compact ranges
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.
US Army Electronic Proving Ground
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.
The Orbiting Standards Package: A Recalibratable Satellite Instrument Assembly for Measuring Large Earth Station Antennas
The concept of an Orbiting Standards Package (OSP) has been discussed as a means of making direct measurements of fields, patterns, and polarization states of signals radiated from large earth station antennas. It would also have the capability of producing test field of known intensities and arbitrary but well-defined polarization states, thereby enabling the determination of such parameters as G/T and Effective Receiving Area of earth stations. Recent developments in microwave six-port networks and in standard antennas would permit the all-electronic generation and detection of these signals. Moreover, it appears possible to recalibrate the satellite standards package to laboratory state-of-the-art accuracy following launch.
Antenna pattern measurements of large aperture, low sidelobe space antennas
There is a growing interest, for developing large, high performance communication antennas for use in space. Such antennas employ many new technologies and are very expensive to design, build, and deploy. These high risk projects require thorough ground testing before becoming operational. Unfortunately, accurately measuring the far field pattern of a large, structurally weak, high performance antenna on the ground is a difficult problem. The antenna’s extraordinary characteristics place severe tolerances on an antenna measurement range. This paper examines many of the problems encountered with measuring the far field pattern of these antennas. Several possible techniques are reviewed and the errors, tolerances, and limitations associated with each technique are analyzed.
Measurement of surface coupled antennas for subsurface radar probing
The experimental techniques presented here can be used to obtain the approximate time domain transfer function and pattern of underground radar antennas. These techniques provide an easy approach to obtaining relative antennas performance. The experimental setup which is used to perform these experiments consists of slanted hollow plastic pipes bored in the ground, the receiver unit, transmitter unit, controller and processor units etc. A buried antennas is used to transmit to a test antenna on the ground surface. The data obtained from two separate test antennas are presented and compared.
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