Welcome to the AMTA paper archive. Select a category, publication date or search by author.
(Note: Papers will always be listed by categories. To see ALL of the papers meeting your search criteria select the "AMTA Paper Archive" category after performing your search.)
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.
An S-band telemetry antenna system was designed and fabricated using a 30-inch diameter lightweight Luneberg lens as the aperture. It is equipped with four feeds in the azimuth plane to achieve single beam patterns or multiple beam patterns. Initial measurements with the lens without a radome were made with various feeds and feed combinations in the compact range of the Georgia Tech Engineering Experiment Station. The final design also done by Georgia Tech to Kentron Specifications, uses a custom designed quad ridged circular feed with orthogonal linear polarization outputs which are converted to left- and right-hand circular polarization using 90o hybrid couplers. A control panel permits the operator to manually select a single beam coverage of 11o x 11o, twobeams combined for 22o x 11o sector coverage, or four beams combined for 44o azimuth x 11o elevation sector coverage. A automatic mode permits the full gain of a single beam, about 22 dB, to be attained and switched automatically to the RF feed containing the greatest signal power as sensed by eight total power radiometer receivers; one for each orthogonal polarization for each of the four antenna feeds. Selectable integration time constants are 0.1, 1, 10, and 100 milliseconds. Dependable switching is obtained for signals of -99 dBm or greater. The RF switching is achieved by PIN-diode switches in 10 nanoseconds. The system employs eight state-of-the-art gain and phase matches GaAs FET low-noise preamps which have a noise figure of 1.1 dB and gain of 51 dB. External limiters at the input of each LNA protect the devices from accidental RF inputs up to six watts average power. The system was designed as a removable package to be flown aboard the U.S. Army’s C-7A Caribou aircraft with an opened rear cargo ramp to collect terminal TM data from missile reentry vehicles (RV’s) impacting near the Kwajalein Missile Range. Flight testing of the system against target of opportunity missions began the third week of June 1982. The system is expected to be declared an operational system in support of ballistic missile testing by December 1982.
This paper presents the results of research conducted to compensate near field measurements for known errors in near field probe position. The complete solution for probe position error compensation and associated computer algorithm developed by Corey as a Ph.D. dissertation resulted in a large computer memory and computation time requirements. Corey’s results showed, however, that the prime effect of probe positioning error was a change in the near field measurement phase in the direction of main beam propagation. It was also shown that the sinusoidal components of the probe position error produced spurious sideband propagation directions in the calculated far field patterns. This information has been used to develop a simplified probe position error compensation technique which requires negligible computer storage and computation time. An early version of this technique has recently been implemented at RCA for the Aegis near field measurement facility. The technique and sample results are presented for a small probe position errors and for a low sidelobe level antenna measurement.
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.
The Naval Underwater Systems Center has under construction an antenna pattern arch for measuring the radiation pattern of submarine antennas protruding above the sea water surface. The 70-foot radius tripodal arch is constructed of laminated wood members located over a 66-foot by 93-foot concrete pool which will contain a six inch depth of sea water. A well is located off-center in the pool for mounting the antenna under test. Pattern measurements will be made from 20 MHz to 2 GHz and at antenna heights of up to 15-feet above the sea water. Heretofore this over-sea water pattern information has been unobtainable. The important criteria for far-field antenna measurements are mentioned. The Numerical Electromagnetic Code (NEC) was used to model typical submarine antennas at various frequencies in order to predict the accuracy of the arch range. NEC uses moment methods to determine the arch patterns and the far-field patterns.
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.
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.
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.
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 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.
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.
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.
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.
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.
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 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.