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A review will be made of advances in anechoic chamber technology from the precursors of World War II to the huge complex chamber of today. A glimpse of the technology of the 80’s will be offered.
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.
Currently the Fleet lacks a quantitative description of their electromagnetic (EM) capabilities and vulnerabilities. A ship’s mission can be seriously degraded because of unsatisfactory performance of EM systems due to various factors found in the operational environment. In addition, a ship can become vulnerable to a potential enemy by inadequate emission control (EMCON) of EM energy. The EMPASS measurement platform is capable of collecting and analyzing three-dimensional emission data in the operational environment. The word EMPASS is the acronym of Electromagnetic Performance of Aircraft and Ship Systems. EMPASS consists of a calibrated, special equipped, measurement platform situated on an EP-3A aircraft with complementary ground based data reduction and analysis facilities. The products of the EMPASS program are the effectiveness evaluation of operational EM systems, development of the criteria for the most effective tactical use of EM systems, and the providing of the capability to conduct RDT&E in the operational EM environment. This paper presents a description of the EMPASS capabilities and the results of measurements of some representative EM systems used in the fleet.
The compact antenna range has been recognized as an effective means of testing microwave antennas. Antennas which normally require long outdoor ranges for testing can be tested under far field conditions at an indoor facility, using the compact range. The compact range operates on the principal that a parabolic reflector will transform an incident spherical wave into a collimated plane wave in its near zone. The plane wave produced is suitable for testing antennas, thus simulating far field electromagnetic criteria in the near zone. The typical compact range is housed in a room approximately 20 feet wide, 40 feet long and 20 feet high. The performance of the compact range has been well documented and specified over a frequency range of 3.95 GHz to 18.0 GHz. Now, through recent testing performed at Scientific-Atlanta, the compact range can be specified for operation up through 60.0 GHz. This paper describes the tests that were performed, discussed the results of these tests and establishes performance specifications for operation at these millimeter frequency bands.
A limited number of power gain measurements for some broadband airborne antennas were analyzed by comparing the measured values to the predictions from hypothetical models for the antennas. The difference between the predicted gain and measured gain is defined as the measurement uncertainty. The measurement uncertainties were statistically analyzed to determine the accuracy of the gain measurements. The results indicated that 79 percent of measurement uncertainties were written 1.5dB.
The spectacular growth and developments of microprocessors make it highly likely that they will form the bases for all future data acquisition systems. Microprocessors combined with numeric processor chips even give computational capability comparable to the larger and faster mini computers of only a few years ago. The hardware cost of complete data acquisition microprocessor systems has continued to decline to where this cost is comparable to or less than one of the test instruments it reads.
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.
This paper describes the modifications made to the Scientific-Atlanta 2020 Antenna Analyzer System, to make it more suitable for adaptive antenna testing. Three functional modifications are described: (1) Digital interfacing of a wideband microwave power meter (2) Creation of programs for manipulating stored data files (3) Operating system documentation and permanent program storage The general philosophy of the SA 2020 modification was to make the changes transparent with respect to the original operating system. Thus, although the antenna analyzer now possesses several new features, none of the original features has been degraded. An operator has no indications of the modifications unless he specifically selects the new system modes of operation. Altering the SA 2020 system software has been complicated by limited main frame memory in the 21MX computer. In some cases it has been necessary to limit the flexibility of new programs in order to fit the available memory space. In the future, when more memory becomes available, the routines can be easily expanded. In there present form, the programs are considered quite satisfactory for all planned adaptive antenna tests.
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.
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.
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.
The AEGIS AN/SPY-1A antenna system is an S-band monopulse phased array system designed for monopulse operation. Its high performance and manifold capabilities have placed stringent demands on the test system used in its evaluation. This paper will describe the AEGIS Near-Field Antenna Test Set (ANFATS) currently being implemented for acceptance testing production models of the antenna, a system designed for operation by manufacturing test personnel
Today I would like to describe this unique antenna Test Facility and its background, capabilities, typical tests and problem areas.(Figure 1) First of all by way of introduction: I’m in the Test and Evaluation Branch of the Rome Air Development Center (RADC). We are an R&D laboratory under the Air Force Systems Command. RADC’s prime mission is R&D in the area of Command, Control, Communication and Intelligence often referred to as C3I. We are located at Griffiss AFB which is in the City of Rome, in the center of beautiful upstate New York. The outdoor antenna range which is the subject of this briefing is at the RADC Newport Test Site is located about 30 miles east of Griffiss in the foothills of the Adirondack mountains.(Figure2)
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.
In recent years there has been an increasing requirement for more extensive and precise measurements of the polarization properties of antennas. Some of the more conventional polarization measurement techniques are no longer applicable because of the required measurement time or the achievable accuracy. This presentation is an overview of polarization measurement methods which may be employed on far-field antenna ranges. Instrumentation requirements and sources of error are also included.
A novel application of the variable-range outdoor antenna measurement system is the test and evaluation of various active optical weapons systems such as missile and projectile fuses. These devices are tested as optical-wave length antennas. The entire test program, including positioning, stimulus and measurement, is performed under computer control by the SA 2021A Automatic Antenna Analyzer. Outdoor testing of optical weapons system affords the opportunity to evaluate the effectiveness of various countermeasure and counter-countermeasure 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.
Automatic testing is becoming more and more prevalent in the antenna measurement field. With this new technology, the antenna test engineer is faced with the problem of controlling the antenna test positioner system automatically. Automatic operation may simply consist of driving the test positioner axes to make several scans of a test antenna; or it could involve complete computer control of a multi-axis positioning system to perform a complex routine. This presentation discussed a positioner programmer designed to meet these requirements. The 2012 can be programmed from its front panel to perform common position and raster scan routines. Using the IEEE-488 interface bus, the programmer will accept commands from a digital calculator or computer to control up to six (6) axes of motion through any desired sequence of operation. During record scans, the 2012 will output commands at selected angular intervals to allow the digital processor to update and read measurement instruments and perform other functions such as tuning signal sources and receivers. Various features, options, and accessories for the 2012 enhance its overall flexibility and compatibility in the antenna measurement system.
Near field antenna measurements have long been of interest to the antenna community and of particular interest to those in the design and measurement of antennas. Efforts in this area using analog computers for data reduction were already under way in the late 1950’s. These applications were limited, primarily due to the limitations of the analog computer. Two planar near field probe positioners were built by Scientific-Atlanta during this period and delivered; on to Martin Denver and one to the Georgia Institute of Technology. These units were used for development on planar near field measurements. The unit at Martin Denver was also used by the Bureau of Standards. Experimental work at Georgia Tech led to Dr. Joy’s thesis on spacial sampling and filtering.1 This work on sampling was particularly important because it gave an understanding of the required data density for meaningful transformation by digital computer. Numerical integration is a time and core intensive process and it was the utilization of the Fast Fourier Transform in the early 1970’s that made the digital computer a viable approach to the problem.
This paper will present a basic explanation of the IEEE Standard 488-1978, concerning what it is, and how and why it concerns people in the RF world. In addition, the practical side of the IEEE 488 will be discussed, touching on such topics as the types of instrumentation available with IEEE, custom systems design and installation, the new one-chip interfaces, computer enhancement of measurements and generation of analytical graphic data. This up dated review is made with an eye towards enhancing both speed and accuracy of contemporary antenna testing techniques.