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.)
A monostatic C.W. radar cross-section facility in the X-band at the Radar and Communication Centre, Indian Institute of Technology, Kharagpur, India is described. This set up is capable of automatically measuring the c.w. monostatic radar cross-section over the range of aspect angle 0 to ±180o for both TE and TM polarizations. The transmitting/receiving antenna and the rotating target is housed on the roof-top of the building and the microwave circuit with recording arrangement is in the air-conditioned laboratory. It is capable of handling a target of arbitrary shape of maximum size equal to 70 cm and uses a two-stage background (without target) cancellation technique employing Magic-T. A typical value of effective isolation between the transmitted and received signals is of the order of 70 dB and a dynamic range of 35 dB. Measurements made in this set up with different types of targets show a fair agreement with the results obtained by analytical investigations. The same set-up with necessary modifications for measuring the phase of the scattered field along with the amplitude data is expected to provide the amplitude and phase information for target identification and classification problems.
The loop cell is fabricated using two intersecting metal sheets joined at the intersection and forming a 36 deg angle. A section of a loop is mounted between two coaxial panel jacks, one on each sheet at a distance equal to the loop radius from the intersection. A known current through this section of electrically small loop produced calculable E and H fields between the sheets in the plane of the loop. These known fields may be used to determine the antenna factor of small E and H antennas placed in the field if the mutual impedance due to the antenna images in the sheets is negligible and the antenna is not close to the open edges of the cell. Measured and calculated antenna factors agree within ±2 dB between 0.25 MHz and 1000 MHz.
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.
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.
Scientific-Atlanta, Inc. was selected by the United States Air Force to design and install a complete turn-key test facility for depot maintenance support of the F-16 fighter aircraft. These facilities have been installed at Hill Air Force Base, Utah. Four complete facilities have been supplied, each consisting of a Series 2020 Antenna Analyzer and a Series 5750 Compact Antenna Range. Two facilities are configured for antenna testing and two for radome testing. This paper describes the equipment furnished for this program. The hardware is discussed as well as the special software designed to perform specific radome and antenna tests.
An instrument has been built which allows the electromagnetic measurement of the surface accuracy of a large millimeter-wavelength antenna. The University of Texas 4.9 m radio telescope has been measured with this technique at 86.1 GHz to an accuracy of 4 µm at the surface. Our technique is an interferometric one which is fast, accurate, and able to measure the whole antenna surface at once. While the technique is illustrated by its use on a large antenna, it could be used in a near field measurement of a smaller antenna. Several antenna surface maps are presented. A comparison of run-to-run repeatability was made. The technique itself was tested by deforming the antenna surface in a known way and subsequently detecting the deformation. In addition, important factors which influence the overall error budget have been identified. These include errors in setting the antenna angular position and fluctuation noise in the atmosphere and electronics. An instrument has been built which allows the electromagnetic measurement of the surface accuracy of a large millimeter-wavelength antenna. The University of Texas 4.9 m radio telescope has been measured with this technique at 86.1 GHz to an accuracy of 4 µm at the surface. Our technique is an interferometric one which is fast, accurate, and able to measure the whole antenna surface at once. While the technique is illustrated by its use on a large antenna, it could be used in a near field measurement of a smaller antenna. Several antenna surface maps are presented. A comparison of run-to-run repeatability was made. The technique itself was tested by deforming the antenna surface in a known way and subsequently detecting the deformation. In addition, important factors which influence the overall error budget have been identified. These include errors in setting the antenna angular position and fluctuation noise in the atmosphere and electronics.
This paper explored the details of the mechanical and electrical design of a multipurpose scanner. Planar, cylindrical and spherical scans as well as separation scanning (for extrapolation gain method) are accomplished by allowing any two of the five axes to be selected for program control. Special laser interferometers are available for the X-Y planar scanning. However, all axes are fitted with two-speed synchros. The method of driving and counter-weighing the X-Y probe carriage reduced the moving mass significantly which helps in the areas of start-stop agility, resonances, bearing wear and structual bending.
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.
This paper reviews established design principles and techniques for control of electromagnetic characteristics of an antenna test environment. In particular, the discussions here relate to test facilities which are intended for use in direct measurement of the free-space far-zone performance of antennas. The bulk of the material presented here was excerpted by permission from reference 1.
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.