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Accuracy

Automated, broadband antenna measurements
R.E. Hartman, November 1983

Today’s broadband electronic warfare systems are more sophisticated and complex than ever before. Many systems require that component and subsystems be characterized more extensively than in the past. This leads to the need for high-speed automated antenna measurement over a broad frequency band. For example, a program currently in progress requires that phase and amplitude measurements be made on the antenna system for four different polarizations at approximately 400 frequencies over a 9:1 bandwidth. This is achieved with an automated test system using broadband instruments which are capable of rapidly stepping through frequencies while maintaining measurement accuracy. This paper will review some of the current trends in test requirements, the problems associated with this increased demand for data and alternative solutions. Data will be presented to illustrate achievable performance.

The Orbiting Standards Package: A Recalibratable Satellite Instrument Assembly for Measuring Large Earth Station Antennas
A.J. Estin,R. C. Baird, November 1982

The concept of an Orbiting Standards Package (OSP) has been discussed as a means of making direct measurements of fields, patterns, and polarization states of signals radiated from large earth station antennas. It would also have the capability of producing test field of known intensities and arbitrary but well-defined polarization states, thereby enabling the determination of such parameters as G/T and Effective Receiving Area of earth stations. Recent developments in microwave six-port networks and in standard antennas would permit the all-electronic generation and detection of these signals. Moreover, it appears possible to recalibrate the satellite standards package to laboratory state-of-the-art accuracy following launch.

Automated digital antenna measurements
R.E. Hartman (Flam & Russell, Inc.), November 1982

The Automated Digital Antenna Measurement (ADAM) System developed by Flam & Russell, Inc. (FR) relieves the antenna engineer and technician from the constraint of designing a test plan/procedure dictated by the architecture of his automated test system. By contrast, ADAM’s flexibility allows the user to design a test configuration and interface with that instrumentation which is optimum for the performance evaluation of the antenna system under test in terms of data rate and accuracy. Further, as the test needs and configurations change, ADAM changes with them. For instance, if the engineer is testing antennas for a phase/amplitude interferometer, the test set-up might include a Systron-Donner frequency synthesizer and a Scientific-Atlanta receiver – thus sacrificing speed for accuracy. The same facility could be used later in the day for production testing where frequency accuracy is less critical and high data rates are the objective. In this case the signal source might be a voltage controllable Wiltron sweeper and the receiver an HP network analyzer. ADAM accommodates this change by merely identifying the test equipment through a menu.

Millimeter wavelength measurements of large reflector antennas
J.H. Davis (University of Texas at Austin), November 1982

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.

An Antenna pattern arch for measurements over sea water
D.E. Fessenden (New London Laboratory),D.C. Portofee (New London Laboratory), November 1982

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.

Wide aperture microwave noise oscillators for antenna parameter measurements
V. Lander (Airtron Corp.), November 1981

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.

Automated Phase/Amplitude EHF Measurement System
B.M. Potts (Massachusetts Institute of Technology), November 1981

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.

Configuration of spherical near-field ranges
D.W. Hess (Scientific-Atlanta, Inc.),Joseph J. Tavormina (Scientific-Atlanta, Inc.), November 1981

In principle, spherical near-field scanning measurements are performed in the same way as conventional far-field measurements except that the range length can be reduced. This provides a natural advantage to scanning in spherical coordinates over other coordinate systems due to the steady availability of equipment. However, special considerations must be given to near-field range design because of the necessity for phase measurement capability, mechanical accuracy and the need to handle large quantities of data. Based on experience with spherical near-field measurements carried out during verification testing of a spherical near-field transformation algorithm, we discuss the practical aspects of constructing a near-field range. In particular we will consider range alignment procedure, engineering of the RF signal path and times for data collection and processing.

Estimating the accuracy of gain measurements
S.J. Caprio (EG&G), November 1980

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.

Antenna Polarization measurements
R. Heaton, November 1979

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.

IEEE 488 System Concepts
J. Hassel (John Fluke Mfg. Co., Inc.), November 1979

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.







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