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For over a decade the National Bureau of Standards (NBS) has used the planar near-field method to accurately determine the gain, polarization and patterns of antennas either transmitting or receiving cw signals. Some of these calibrated antennas have also been measured at other facilities to determine and/or verify the accuracies obtainable with their ranges. The facilities involved have included near-field ranges, far-field ranges, and compact ranges. Recently, NBS has calibrated an antenna to be used to evaluate both a near-field range and a compact range. These ranges are to be used to measure an electronically-steerable antenna which transmits only pulsed-cw signals. The antenna calibrated by NBS was chosen to be similar in physical size and frequency of operation to the array and was also calibrated with the antenna transmitting pulsed-cw. This calibration included determining the effects of using different power levels at the mixer, the accuracy of the receiver in making the amplitude and phase measurements, and the effective dynamic range of the receiver. Comparisons were made with calibration results obtained for the antenna transmitting cw and for the antenna receiving cw. The parameters compared include gain, sidelobe and cross polarization levels. The measurements are described and some results are presented.
This paper describes an automated radome test and evaluation system, which very accurately and quickly determines the shift in electrical boresight and loss in antenna gain caused by the presence of a radome in front of a monopulse antenna. The measurement system hardware, which is shown in Figure 1, is based on the Flam & Russell, Inc. ADAM 8003 Antenna and RCS Measurement System and consists of a DEC MicroVAX computer, Hewlett Packard 8510B network analyzer and a highly accurate two axis positioning system. The monopulse antenna and radome are attached to the same positioner. The monopulse antenna is electrically steerable, thus allowing different areas of the radome under test to be examined.
Naval Aviation Depot has completed final testing requirements for its unique antenna/radome test ranges. This paper provides an overview of the Navy's one of the kind test facility. Justification for our compact range facility was based on the requirement of a functional range during adverse weather conditions. Prior to 1986 all testing of antennas was completed at our outdoor range (Figure 1). This mode of operation was inefficient during periods of rain, snow or high wind conditions. These conditions are normally present during the winter months along the east coast (Dec-Mar). Testing antennas under these conditions could possibly lead to inaccurate data and damage to the antenna under test. Another requirement was to reduce the turn around time for repair and testing of radomes. This new test range will provide a significant reduction in the Navy's repair cycle, since no time is lost in certifying repaired radomes.
Texas Instruments' antenna test range complex consists of 15 new indoor ranges at the McKinney site. To meet projected business requirements, Texas Instruments initiated an aggressive antenna test range expansion and upgrade program in 1986. Construction of the new test range facility at McKinney is phase 1 of the plan which will be completed in the first quarter 1988. Phase 2, the construction of a new outdoor facility, will be completed in 1991. When completed the new facilities will be equipped with the latest technology in instrumentation and materials. A staff of antenna measurement experts maintain the ranges; they are equipped to make very short turn-around-time modifications to the range to meet special measurement requirements.
A new spherical near field test facility is under development by Canadian Astronautics Limited at the David Florida Laboratory in Ottawa. It provides for a wide range of antenna measurements, including far-field, far-field from near field, and near-in and very near-in field reconstruction. Many user-friendly, user-interactive, and graphics features are incorporated. This paper outlines some of the underlying concepts for the facility.
A roof-top antenna range has been installed at the Bellcore facility in Red Bank, New Jersey. This facility is used as a far field range to measure highly directive antennas at millimeter wave frequencies. Theoretical and experimental studies were performed to characterize the range environment and identify reflections. Two computer programs were used to analyze the strength and location of interfering signals at both UHF and millimeter wave frequencies. These programs use Geometrical Optics and the Geometrical Theory of Diffraction to predict the location and strength of diffracted and reflected energy from the surrounding structures. Both singly and doubly diffracted interferences were considered. A bi-static radar, with an 850 MHz carrier, bi-phase modulated by a 40 Mbit/s pseudonoise code, was used to measure the impulse response of the environment. The antenna range measurements are compared with the analysis done at 850 MHz and calculated results are printed for the behavior of the range in the millimeter wave regime.
Near-field testing of a very low sidelobe, L-band, 32-element, linear phased array antenna was conducted. The purpose was to evaluate testing and calibration techniques which may be applicable to a much larger, space borne phased array antenna. Very low sidelobe performance in a relatively small array was achieved by use of high precision transmit/receive modules. These modules employ 12-bit voltage controlled attenuators and phase shifters operating at an intermediate frequency (IF) rather than at RF. Three array calibration techniques are discussed. One technique calibrates the array by means of a movable near-field probe. Another method is based on mutual coupling measurements. The last technique uses a fixed near-field source. The first two calibration methods yield substantially the same results. Module insertion attenuation and phase can be set to 0.02 dB and 0.2 degrees, respectively. Near-field measurement derived antenna patterns were used to demonstrate better than -20 dBi sidelobe performance for the phased array. Application of increasing Taylor array tapers showed the limitations of the measurement systems to be below the -35 dBi sidelobe level. The effects of array ground plane distortion and other array degradations are illustrated.
A major problem in direct broadcasting satellite (DBS) communication systems is the interference caused by transmission from adjacent satellite whose signals inadvertently enter a ground station receiver and interference with a desired signal. However, the interference may be as much as 25 dB below the desired signal level. In fact, the interference may be below the thermal noise in the channel. Although weak, these signals because of their coherent nature and their similarity to the desired signal, do cause objectionable interference and must be suppressed. The interference is of the nature of "ghosts" in a television signal.
At the National Bureau of Standards (NBS) we have examined the out-of-band response of array antennas from both a theoretical and experimental point of view. Theory shows that the out-of-band response of an antenna depends primarily on two factors: the antenna's input impedance, and its directivity. Experiment shows that, for most practical purposes, the out-of-band response of an antenna can be estimated from a measurement of the antenna's input reflection coefficient alone. If the reflection coefficient is low, the antenna response will be good; if the antenna coefficient is high, the antenna response will be poor.
The evaluation of adaptive antenna systems expands the scope of conventional antenna testing. In addition to the conventional antenna parameters, the evaluation of an adaptive antenna system measures the effectiveness with which the adaptive antenna reduces interference. Adaptive antenna testing is conducted on a system level rather than the component-level tests of conventional antennas. The expanded scope of adaptive antenna testing requires more general test facilities, instrumentation, and test procedures. The additional requirements for adaptive antenna testing will be discussed.
A general theoretical approach is formulated to describe the complex electromagnetic environment of an N-element array. The theory reveals the element-to-element interactions and multiple reflections within the array. To experimentally verify some features of the theory, measurements on experimental array panels in various configurations were made. These array panels consisted of 256 microstrip radiating elements. In each of the configurations both the near-field and portside signals were measured to study the interactions between these panels. In particular, the effects of open-circuited array panels on the radiation pattern of a single panel are observed both in the near field and in the far field. It is found that internal scattering is the main mechanism of interaction between panels, rather than reradiating of signals received from adjacent panels. The effects of scattering are observable at the -50 dB level.
Harris Corporation is in the final stages of implementing the Model 1640 compact range for the Boeing Corporation. This paper provides an overview of the development, fabrication, and test activities on this very significant advance in the compact range state-of-the-art. This range represents a significant increase in the quiet zone size over past available equipment. It features the wide dynamic range, low noise floor, and high quality quiet zone that is achievable using the Harris-Proprietary shaped compact range technique. In this technique, a dual reflector system is used so that quiet zone characteristics may be completely optimized. Another feature of this range is the completely panelized construction techniques. This allows the production of a very large, very precise reflector system. When completed in the winter of 1987-1988, the Model 1640 will represent a new dimension in compact range technology. Primary technical features are a 40 foot quiet zone, a -70 dBsm noise floor, and a frequency range extending from VHF to millimeter-wave frequencies.
A method for the calculation of the errors induced through target-wall-target interactions is presented. Both near-field and far-field situations are considered. Far-field calculations are performed both with Fraunhoffer diffraction theory and target antenna analogies. Absorber is considered as both a specular and a diffuse scatterer. The equations developed permit trade studies of chamber size versus performance to be made.
The direct far field pattern measurement of an aperture antenna becomes more difficult as the size of the aperture increases. Recent measurements on reflector antennas with 2D2/? =1500’ at The Ohio State University ElectroScience Laboratory have demonstrated the usefulness of the compact range in obtaining the complete far field pattern of antennas with large far field distances.
Techniques developed for the design of shaped, off-set reflector antennas have been applied to the design of compact ranges. Shaped optics which map an axially symmetric feed pattern into an elliptical aperture distribution have been designed. Some of the major design considerations for this type of system are examined in this paper. The design has been verified both analytically and experimentally.
This paper reports on work conducted to improve the test zone performance of an offset-fed point-source compact range by shaping the edge serrations of the paraboloidal range reflector.
When performing antenna pattern measurements on far-field antenna test ranges or in anechoic chambers, one of the main problems concerning the pattern accuracy is range reflections. Previous works dealing with this have been limited to the one-dimensional case.
A technique has been developed to characterize the illuminating signal present within an antenna test zone. Information of angular multi-path distribution as well as relative signal amplitudes of various paths can be ascertained by transforming phase and amplitude data measured at numerous intervals across the lineal aperture probe apparatus. An experiment was carried out to test the technique using a ten-foot linear aperture probe installed to probe an antenna test zone located at one end of a one-half mile range. During the experiment several measurements were carried out at two different locations within the far-field antenna range and at two different frequency bands. This paper discusses the results of the experiment as well as the practical aspects of this technique.
This paper presents a test method showing it is practical to bench-test antennas to uncover gain-related deficiencies. Design considerations for the small chamber are given along with a brief error analysis.
This paper describes a novel technique for acquisition of far-field antenna patterns from a very low side-lobe antenna. The low side-lobe requirement imposes stringent multipath restrictions on the measurement range and to accommodate this requirement a vertical range configuration is employed rather than the more conventional range which is parallel to the earth's surface. To assure accurate measurement of side-lobe levels, multipath levels were specified at minus seventy dB (-70 dB) relative to the direct-path, peak-of-the-beam level. In this novel range configuration, an Antenna Under Test (AUT) is oriented to face skyward and operated in a receive mode with E-Field illumination provided from an airborne source. An optical tracker provides data of airborne source location and time-division multiplexing of both frequency and antenna beam position enable optimization of data acquisition efficiency. Post-acquisition processing provides de-interleaving of the desired beam(s)/frequency(s). This paper will present a discussion of the problems encountered and the techniques employed to overcome them in the design of this range. A description of the range will also be presented.