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This paper presents the various aspects involved in the design, development and establishment of Cylindrical Near-Field Measurement(cnfm) facility. A brief description of the hardware and the method of data acquisition are outlined. The capabilities of the CNFM system are brought into focus. The effects of alignment errors are presented. The patterns of various test antennas are presented over different frequency bands.
Accurate multiwavelength radiometric remote sensing of the ocean and the atmosphere from an aircraft requires antennas with the same beamwidth at the various frequencies of operation. Scientists at the National Oceanic and Atmospheric Administration designed an offset antenna with a pressure-compensating corrugated feed horn to meet this criterion. A specially designed fairing was incorporated into the antenna to optimize the aerodynamics and minimize the liquid buildup on the antenna surfaces. The antenna has two positions: the zenith (up) position and the nadir (down) position. The planar near-field facility at the National Institute of Standards and Technology was used to determine the far-field pattern of the antenna. The results show that the antenna beamwidths at 23.87 and 31.65 GHz are nearly the same as expected from the design criterion. This antenna was recently used in an ocean remote-sending experiment and performed according to expectations.
The RMS surface error predicted by holographic measurements is often smaller that the one predicted by radiometric measurements. At the FCRAO, a difference of 40% was observed for the 14-millimeter radio telescope. To find the explanation for this discrepancy, simulations and additional near-field measurements were performed. The near-field measurements were carried out at 91.9 GHz on a part of the aperture of the telescope. This paper describes the near-field measurements and presents a careful comparison between the results from holographic, radiometric and near-field surface error measurements. This comparison and simulations revealed that the main reason for the discrepancy between the radiometric and h9olographic results was the smoothing of the holographic data. The smoothing has been used for reducing the effects of the truncated far-field data in the FFT process.
The MSAT satellite payload [1] included the large L-Band Tx and Rx deployable reflector antenna subsystems, the Ku-Band downlink antenna, and the telemetry and command omni. The technical challenges associated with these antennas required a considerable amount of advanced testing for concept development and design, as well as for customer acceptance. The L-Band feed array breadboards were measured to quantify effects of mutual coupling. The L-Band antenna performance was verified by near-field measurement techniques and computer modelling. The Ku-Band shaped reflector antenna was tested in SPAR's compact range. A short summary is given of the omni antenna tests, and the PIM tests carried out on the L and Ku antennas.
Microwave holography is an important technique for analyzing electromagnetic fields in close proximity to objects such as antennas or radomes. In this paper, data measured in the far-field and near-field are transformed to the surface of a spherical radome using spherical microwave holography. Further, the fields are calculated on a sequence of spheres concentric to the spherical radome to display the spatial distribution of the fields as a function of distance from the surface of the radome out to five wavelengths from the radome, a movie. This progression demonstrates the ability to locate radome surface defects is severely limited without the use of microwave holography. Three sets of radome defects are presented and range in size from three-eights of a wavelength to three wavelengths. This paper shows that near-field measurements alone are not generally capable of locating defects directly.
Large scanners used for near-field antenna measurements require careful attention to the design and fabrication process to maintain probe position accuracy. This paper discusses the design, implementation, and results of a novel optical probe position tracking system used by NSI on a number of large near-field scanners. This system provides measurement of the probe X, Y and Z position errors, and real-time on-the-fly position correction. The use of this correction can significantly enhance measurement accuracy, and can reduce the cost of building large near-field scanners.
Traditionally the Compact Range is not considered a viable method for conducting low frequency (VHF/UHF) antenna or RCS measurements because of the limited electrical size of the collimating reflector system. Normally, compact range measurements are conducted in the extreme near-field or the collimating system where to reflector size is on the order of 25 to 30 wavelengths minimum with at least four wavelength edge treatments. This mode of operation limits measurements to the high UHF band (800 MHz) and above for typical sized reflector systems in use today. Recent research with compact range3s indicates that acceptable VHF.UHF measurements can be conducted in the quasi far-field region of the collimating system with reflectors as small as five wavelengths and with electrically short edge treatments. A good user knowledge of this mode of operation is required to maximize its utility. A qualitative measure of acceptable quiet zone performance must also be established. This paper addresses the theory of operation, practical implementation and inherent limitations of the non-conventional use of the indoor compact range for conducting low frequency measurements.
Absorber material us used in antenna measurements to reduce multiple reflections and multipath effects. However, in some cases the effect of the absorber can still have an uncertainty larger than the desired uncertainty of the measurement. For accurate antenna gain measurements, using the planar, cylindrical and spherical near-field methods and the extrapolation technique, insertion-loss measurements should be accurate to within + 0.03dB. To satisfy this requirement it is important to minimize the multiple reflections between the probe and antenna under test. If the multiple reflections are too large, the insertion loss becomes very position sensitive and uncertainties on the order of 1 dB can occur. It is imperative that absorber be used to cover all metal surfaces of the antenna mounts. Uncertainties can also occur if the absorber is not used carefully. The effects on antenna fain data measured with and without absorber will be shown. Measurement results showing the effect of the placement of the absorber on the antenna under test will also be presented. This will include absorber distance from the antenna's aperture, the rotation of absorber about the antenna's coordinate system, and the use of different types of absorber.
The Three-Antenna gain method is commonly used on far-field ranges to determine an antenna's absolute gain. This is especially true when no other calibrated antenna is available. This method has been used for years by calibration laboratories such as NIST to calibrate probes and gain standards for far and near-field ranges. In some cases, the calibration is too costly or does not meet the schedule requirements of the near-field test range. An alternative is to calibrate the probe or gain standards directly on the near-field range. In this paper we present the results of a study done to show the accuracy of the Three-Antenna gain method when used on a near-field range. An extensive error analysis is presented validating the utility of this method.
The Three-Antenna gain method is commonly used on far-field ranges to determine an antenna's absolute gain. This is especially true when no other calibrated antenna is available. This method has been used for years by calibration laboratories such as NIST to calibrate probes and gain standards for far and near-field ranges. In some cases, the calibration is too costly or does not meet the schedule requirements of the near-field test range. An alternative is to calibrate the probe or gain standards directly on the near-field range. In this paper we present the results of a study done to show the accuracy of the Three-Antenna gain method when used on a near-field range. An extensive error analysis is presented validating the utility of this method.
Two techniques of antenna diagnostics based on the knowledge of partial information about the near field are discussed. In the first approach, the problem of the characterization of the source from the knowledge of the near field over a limited scanning domain is formulated as a linear inverse one. The second problem concerns the antenna diagnostics from the knowledge of only amplitude distributions over limited regions of two planar surfaces. In both cases effective and reliable solution procedures are discussed.
The advantages of mesh antennas include good storability and low mass for large on-board antennas over 10M in diameter. Their weak point is that surface adjustment is necessary to attain high accurate surface. Surface adjustment traditionally involves the repeated measurement of surface node position with a theodolite system and subsequent cable adjustment. These steps take much time. This paper describes a surface adjustment scheme that uses near field measurement for a modular mesh antenna composed of mesh, cable network and supporting structure. The node positions of the antenna are obtained by back projection of the far field pattern generated from the near field pattern. The cable network has low sensitivity to changes in local node position. The results of tests show that the surface accuracy needed to achieve the required RF performance can be obtained quickly without theodolite systems.
Phaseless near-field antenna measurements, and the ensuing required processing for retrieving the phase are becoming an increasingly important part of modern antenna measurements. This paper discusses recent investigations of phaseless near-field measurements using the UCLA bi-polar planar near-field antenna measurement system. A "table-top" implementation of this technique is proposed as a resizable and cost-effective means for performing phaseless near-field measurements at millimeter wave frequencies. This paper will present a brief overview of the phase retrieval problem and the algorithms which have been utilized in the microwave and millimeter wave regimes. A more detailed examination of an iterative Fourier transform algorithm for solution of the phase retrieval problem with application to the bi-polar near-field measurement technique will be given. Measurement results will be presented and compared to results obtained using both the measured amplitude and phase data.
A novel bi-polar near-field range has been constructed at UCLA recently. The purpose of this article is the evaluation of the bi-polar measurement of a large reflector antenna using simulation methodologies. Bi-polar measurement of such an antenna is simulated and a parametric error study is reported. The study shows that a bi-polar near-field range for measuring large reflector antennas can be designed to provide accurate measurements with reasonable hardware requirements. The measured on-axis gain is found to be highly tolerant to probe position errors which occur in the plane of the measurement. The z-positional error has a greater effect on the gain, however, this error can be minimized with careful alignment of the bi-polar axes.
This paper describes a 550 GHz planar near-field measurement system developed for flight qualification of the radio telescope carried onboard the NASA submillimeter wave astronomy satellite (SWAS). The very high operating frequency required a new look at many near-field measurement issues. For example, the short wavelength mandated a very high precision scanner mechanism with the accuracy of a few microns. A new thermal compensation technique was developed to minimize errors caused by thermally induced motion between the scanner and spacecraft antenna.
A system performance upgrade program of Taiwan CSIST 26' by 20' horizontal planar near-field measurement system was completed recently. The program includes replacement of the original RF subsystem with new HP8530A based microwave receiver and HP83630A synthesized sweepers in external mixers configuration. Other parts of the program introduce new data acquisition computer, HP9000/382 work station, running X-windows under U-NIX environment providing better networking capability and friendly user graphic interface. Efforts has been made to handle the operation between host computer and RF subsystem and to incorporate with the system hardware, in particular on timing requirement and synchronization among processes. This paper briefly introduces the upgraded system hardware configuration and software architecture and describes the results of system overall RF performance along with the upgrade program.
The Spherical Near-Field measurement technique has been in existence for a number of years. The cost associated with this type of measurement system has often been assumed to be substantial. Herein is presented the system configuration for a low cost Spherical Near-field System whose design goals include the capability for production line testing while retaining simplicity in approach. NSI has been contracted to provide a Spherical Near-field antenna measurement system. This paper focuses upon the design considerations undertaken during the prototype development of that system.
The Sacramento Air Logistics Center at McClellan AFB has developed near-field (NF) antemia test capability over the past three years. With assistance from the National Institute of Standards and Teclmology (NIST), McClellan has assembled a modem planar near-field antenna range using components from various vendors. Although the LH( division of McClellan AFB) team's current range has been operating for over a year, it is being continuously improved for measurement accuracy, user-friendliness, and safety. This paper will briefly discuss the evolution of McClellan's near-field program, and then focus on the building of the LH near-field antenna range. Radio-frequency (RF) issues, such as RF design and electromagnetic shielding will be covered. Precision measurement teclmiques such as positioning accuracy and temperature control are discussed. Finally, relevant safety and constrnction issues affecting the McClellan facility will be examined.
One of the world's most sophisticated antenna test ranges is now fully operational. This was designed by the Deutsche Aerospace (DASA) and is operated by Siemens Plessey Systems (SPS). The presented paper will describe the pioneering design philosophy adopted to ensure the stringent performance features. Although this facility is located outside, it allows extremely high precision probing of cylindrical near field of large and very complex antenna systems, with turning diameters up to 16 meters and up to 20 GHz. Besides the RCS optimized 36 m large scanner tower the significant highlights of this facility consist of a comprehensive air-conditioning system for all accuracy dependent components, a permanent autoalignment system, which ensures high precision cylindrical measurements and an interleaved high speed data collection system, which delivers a maximum of data performance within a minimum time frame. Test results including a pattern comparison of the Ref erence Antenna between measurements in DASA facilities and the SPS Cylindrical Near-Field Test Facility show good range performance. The evaluation of the range performance data demonstrates the measurement integrity of the facility and proves to be qualified to characterize a wide range of antennas.
One of the world's most sophisticated antenna test ranges is now fully operational. This was designed by the Deutsche Aerospace (DASA) and is operated by Siemens Plessey Systems (SPS). The presented paper will describe the pioneering design philosophy adopted to ensure the stringent performance features. Although this facility is located outside, it allows extremely high precision probing of cylindrical near field of large and very complex antenna systems, with turning diameters up to 16 meters and up to 20 GHz. Besides the RCS optimized 36 m large scanner tower the significant highlights of this facility consist of a comprehensive air-conditioning system for all accuracy dependent components, a permanent autoalignment system, which ensures high precision cylindrical measurements and an interleaved high speed data collection system, which delivers a maximum of data performance within a minimum time frame. Test results including a pattern comparison of the Ref erence Antenna between measurements in DASA facilities and the SPS Cylindrical Near-Field Test Facility show good range performance. The evaluation of the range performance data demonstrates the measurement integrity of the facility and proves to be qualified to characterize a wide range of antennas.