AMTA Paper Archive
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Scale Model Shipboard Antenna Measurements with a Computer Automated Antenna Analyzer System
This paper discusses some of the more unique problems involved in the performance of measurements on a ground plane type of antenna range generally required for the study and design of multiple antenna shipboard systems. The discussion concentrates on the installation and use of a computer automated antenna analyzer system on this type of range. The methods and results of various range calibration measurements are presented with emphasis on the use of the system’s computerized capability to perform measurements, analyze data, and produce various graphic output formats. The test results obtained from a pair of monopole antennas mounted on a simplified model ship hull are also presented and discussed.
Microwave Antenna Measurement Services at the National Bureau of Standards
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.
Design, calibration and performance of a full-sized aircraft antenna range from 30 MHz to 40GHz
This paper summarizes the results of work performed for the Naval Air Development Center (NADC) on a new full-sized aircraft antenna range located in Warminster, PA. Because of the ever-increasing sophistication of aircraft systems, a facility capable of testing full scale mock-ups has become necessary to fully characterize the system in its operating environment. There are, however, several unique problems associated with such a range. Many systems of interest have a wing-tip to wing-tip baseline, which requires that the incident illumination be “uniform” over a significant aperture (approximately 40x15 feet for tactical aircraft). Differential path loss between wing-tip ends, as the aircraft is rotated, can be a source of large error, as can the parallax created by off-center rotation. Also, since today’s military aircraft carry a wide variety of systems, the range is required to be a “general use” range, operational over a wide frequency spectrum from 30 MHz to 40 GHz. A thorough examination of design trade-offs was performed relating the critical parameters of source beamwidth, specular reflection, path loss, phase error, and receive aperture size in order to choose the proper source antenna type, source height, and separation distance between source and test antennas for each frequency band of interest. Other factors in the range design were a maximum possible source height of 40 feet (approximately the height of the pedestal), and a desire to keep the separation distance fixed over the entire frequency range. Results are presented with indicate excellent performance over an 18 x 18 foot aperture for various polarizations. It was found that the range operates effectively as a ground reflection range from 30 MHz to 3 GHz, and as an elevated range at higher frequencies. Peak-to-peak amplitude ripples over the test aperture of 1.0 dB (corresponding to a reflection level of –25 dB) were acheived over a significant portion of the frequency spectrum.
A Partial loop source of E and H fields for antenna factor calibration (a loop cell)
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.
Automatic gain measurement system
A common method for determining gain on an antenna pattern range is to use the substitution method which involves comparing the response of the test antenna with that of an antenna of known gain. For situations where a standard gain horn is the appropriate reference, this does not present a problem. Calibration curves of these horns are available covering all frequencies for which horns are available, and the horns themselves can be conveniently stored in a cabinet or on a wall rack.
Antenna calibration at the TUD-ESA spherical near-field range
Since 1976 the Technical University of Denmark (TUD), sponsored by the European Space Agency (ESA), has developed a facility for spherical near-field scanning of antennas. This range has been in operation since April 1979 and has undergone continuous refinement. Some of the measurement results obtained with the facility as well was various aspects of the measuring system itself have been published from time to time (Ref. 1-5).
Calibration measurements of an 80 element linear phased array antenna
An 80 element linear phased array antenna was measured in the nearfield. The insertion phase and amplitude for each element were measured while the 8-bit ferrite phase shifters were individually stepped through their degrees for freedom.
Design and calibration of a 250 MHz antenna test range at Canada's David Florida Laboratory
This paper deals with the design, calibration and performance of a new antenna test range facility at the David Florida Laboratory in Ottawa, making use of an existing 40 foot cube anechoic chamber and a Scientific-Atlanta 2020 system. The main purpose is to use the same test range for the calibration of a nominal seven foot by five foot Standard Gain Horn and ultimately for gain and pattern testing of an eight foot space qualified axial mode helix, which must be maintained inside the anechoic chamber. This rules out a completely outdoor test range.
A New antenna test facility at General Electric Space Systems Division in Valley Forge, PA.
This paper describes the new antenna test facility under construction at General Electric Space Systems Division in Valley Forge, PA. The facility consists of a shielded anechoic chamber containing both a Compact Range and a Spherical Near-Field Range. In addition, it provides for a 700’ boresight range through an RF transparent window. The facility will be capable of testing antenna systems over a wide frequency range and will also accommodate an entire spacecraft for both system compatibility and antenna performance tests.
Design and Calibration of Standard Gain Horns in the 200-400 MHz Range
Paper not available for presentation.
Automated wideband, phase coherent polarimetric radar cross section measurements
This paper describes the equipment, mechanics and methods of one of the outdoor ranges at Teledyne Micronetics. A computer controlled microwave transceiver uses pulsed CW over a frequency range of 2-18 GHz to measure the amplitude, phase and polarization of the signal reflected off the target. The range geometry, calibration and analysis techniques are used to optimize measurement accuracy and characterize the target as a set of subscatterers.
Options and considerations for the design of computer aided antenna measurement systems
Rapid advances in digital and micro-computer technology have revolutionized automated control of most measurement processes and the techniques for analysis, storage and presentation of the resulting data. Present-day computer capabilities offer many “user-friendly” options for antenna instrumentation, some of which have yet to be exploited to their full potential. These range from vendor-integrated turnkey systems to innovative designs employing a multitude of subsystem components in custom-interfaced configurations. This paper reviews system and component choices keeping in mind their relative merits and trade-offs. Key design considerations are outlined with particular emphasis on: a) Integration and interfacing of different instrumentation, hardware and software subsystems. b) Upgrading and/or designing of completely new facilities. Various other problems, such as vendor package compatability, and those associated with the analysis and application of measured antenna data are discussed. In addition, suggestions are offered to promote the establishment of a mechanism to facilitate the interchange of data between different antenna measurement laboratories and analysis centres.
Extraction of narrow band responses for wideband RCS data
Wideband RCS instrumentation systems can provide a high degree of range resolution. By combining wideband RCS data with a synthetic-aperture or Doppler processing, the spatial distribution of radar reflectivity can be determined. These systems provide diagnostic capabilities which are useful for locating scattering sources on complex objects and for assessing the effectiveness of modifications. The Proceedings of the 1983 meeting included a paper which described a linear-FM system operating over a 3 GHz bandwidth capable of measuring RCS vs range, cross range, and frequency using a single measurement set-up. This paper analytically demonstrates a procedure for extracting CW RCS patterns from the wideband data obtained using the linear-FM system. By combining the latter and the former processing, it is possible to obtain from a single data array both wideband responses showing the spatial distribution of scatterers and narrowband responses which are the traditional CW RCS patterns. The paper includes experimental verifications of these assertions by comparing results of CW measured data with data extracted from wideband RCS measurements.
Extension of the extrapolation method for accurate swept frequency antenna gain calibrations
For approximately 10 years the National Bureau of Standards has used the Extrapolation Technique (A. C. Newell, et al., IEEE Trans. Ant. & Prop., AP-21, 418-431, 1973) for accurately calibrating transfer standard antennas (on-axis gain and polarization). The method utilizes a generalized three-antenns approach which does not require quantitative a priori knowledge of the antennas. Its main advantages are its accuracy and generality. This is essentially no upper frequency limit and it can be applied, in principle, to any type of antenna, although some directivity is desirable to reduce multipath interence.
The Sandia National Laboratories scatter facility
The two measurements PCAL / PMRC and PTARG / PMRT are ratioed and the PMRC / PMRT term accounts for changes in both power or phase since calibration, because the mid-range is of fixed RCS size and phase. Using this technique, Scientific-Atlanta has been able to hold calibrations to within 0.5 dB amplitude and 8 degrees phase for as long as 12 hours. This includes outdoor range effects.
Calibration techniques used in the Sandia National Laboratories scatter facility
This paper briefly discusses the calibration techniques used in the Sandia National Laboratories Radar Cross-Section Test Range (SCATTER). We begin with a discussion of RCS calibration in general and progress to a description of how the range, electronics, and design requirements impacted and were impacted by system calibration. Discussions of calibration of the electronic signal path, the range reference used in the system, and target calibration in parallel and cross-polarization modes follow. We conclude with a discussion of ongoing efforts to improve calibration quality and operational efficiency. For an overview description of the SCATTER facility, the reader is referred to the article Sandia SCATTER Facility, also in this publication.
AUTOMATING THE 3 ANTENNA GAIN-POLARIZATION MEASUREMENT TO FIND SWEPT RESPONSES
The calibration of gain standards for antenna measurements requires path loss measurements between three antennas if the assumption of identical antennas is not made. The equipment finds the insertion loss for pairs of antennas as if the combination of the antennas and the free space between them were a two port network. The usual setup uses a network analyzer to measure the insertion loss. The Scientific Atlanta 2020 system can be operated as a network analyzer and used for these measurements. Part of the system is a synthesized signal source which allows frequency stepping, and along with leveling, enables the repetition of both amplitude and phase of the signals. The computer control of the equipment provides for rapid stepping through the frequencies, control of the receiver, ability to read amplitude and phase, and means of data storage for off-line analysis.
A Method of making fast high accuracy polarization measurements
A method is presented for making fast multi-frequency high accuracy polarization measurements using a digital computer. This paper will provide a brief review of the IEEE standard polarization definitions, their applicability to the three antenna method, and finally a fast two antenna method.  The fast two antenna method uses a dual polarized orthomode sampling antenna along with a standard antenna whose polarization is known. The dual polarized sampling antenna is calibrated before the test data is acquired using the polarization standard in two different orientations 90 degrees apart. Once the calibration data is acquired the dual polarized orthomode antenna is used as a sampling antenna for the AUT. Since the sampling antenna is dual polarized the AUT polarization data can be obtained rapidly for many frequencies since neither antenna is required to rotate. This method has been used to acquire polarization data for over 500 frequencies in less than 20 seconds.
On the use of the HP-8510 network analyzer for antenna pattern measurements
Enhanced accuracy in antenna pattern measurements using the HP-8510 is possible by using a novel calibration procedure. By circumventing antenna dispersion, this procedure leads to better resolution of multipath responses and thus increases the effectiveness of gated measurements. Measured patterns of a dipole antenna are presented to illustrate the effectiveness of this procedure.
Near-field testing of a low-sidelobe phased array antenna
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.
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