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An alternative technique for collecting the cylindrical near-field data is suggested here. The linear axis is scanned with the antenna under test rotating simultaneously. This results in the near-field data being collected along non-vertical lines. The near-field data over a rectangular grid are calculated by multiplying the spectrum of the near-field along a circular cuts by a factor that produces the desired shift in the location of the data samples. A software package was developed to simulate the cylindrical near-field measurements and was used to test this technique. The software was used to produce simulated near-field data of a rectangular array of dipoles. The technique was applied to simulated data of non-vertical scan and compared to simulated data on vertical scan. The near-field was reconstructed on vertical scan from non-vertical simulated measurement data. For each field component, the peak error was better than -70 dB relative to the peak field level.
This paper reports on the results of computer simulations of planar near-field scanning and its ability to achieve an high accuracy test-zone field over a wide range of pattern angles. An quality test-zone field was defined for this study to have less than 0.2 dB peak-to-peak amplitude variation and less than 1.5 peak-topeak phase variation. This investigation sought the minimum scan length, for a given critical angle, ec and separation, S. The minimum scan length determined from this investigation is given by: L = D + 2S(tan(0c)) + 20/cos(0c). This scan length is approximately 60),, larger, for a critical angle of 70 degrees, than previously accepted. It is suggested that the maximum practical value of Sc is between 60 and 70 degrees. The use of raised cosine amplitude and/or quadratic phase windows to the edges of the measurement plane is shown to provide test-zone field quality improvement and/or allow scan lengths approximately 10),, smaller.
This paper examines the possibility of increasing the speed of Near-Field measurement of an Antenna, by reducing the number of measurement points and by determining the degree of truncation permissible while maintaining a prescribed degree of precision of the reconstructed far-field. The Near-Field of a planar radiating array is analysed in depth. A formulation and a procedure to correct the spectral domain of the field are established. It is shown that correction in the spectral domain can improve the accuracy of the Far-Field while using the same amount of Near-Field data. The technique has a good potential to be applied to Near Field data of large radiating Antennas leading to new information about the accuracy and speed of measurement achievable.
Portable scanners used for near-field antenna measurements are usually incapable of providing a large scan area with a high degree of probe position accuracy. This paper discusses a 4.5m x 2.0m portable scanner developed by NSI with a probe position accuracy on the order of 2 mils (0.050 mm) rms. An NSI patented optical measurement system measures the X, Y, and Z position, and provides real time position correction capability. This lightweight, portable scanner combined with optical correction provides enhanced accuracy while reducing overall antenna measurement system costs and improving test chamber flexibility.
This paper discusses results of a recent attempt to measure aperture distribution of a small active steerable array antenna at 60 GHz using planar near-field measurements and the back transform. Using a procedure which exercises every phase shifter without steering the antenna beam, it is possible to isolate problems with individual bits in the phase shifters. From calculation of the aperture fields for each case we hope to infer the individual phase shifter bit loss. We will also discuss problems which arose in the measurement because of the short wavelength, signal-to-noise ratio and small number of elements.
Measurement of active array high-power transmit patterns in an indoor near-field facility raises significant issues concerning safe microwave power levels and absorber power-handling capability. An extension of the planar near-field measurement technique for the safe and accurate measurement of active array high power transmit patterns is considered to address these issues. This new technique involves sequentially turning on groups of elements around each probe position while making measurements for each group of activated elements. Simulation results indicate that this technique is potentially feasible for safely and accurately measuring low sidelobe active array transmit patterns.
An analytic technique recently developed at NIST [1] [2] to correct for probe position errors in planar near-field measurements has been implemented to arbitrary accuracy. The nth-order correction scheme is composed of an mth-order ordered expansion and an n - m higher-order approximation, where both n and m are arbitrary. The technique successfully removes very large probe position errors in the near-field, so the residual near-field probe position errors are substantially below levels that can be measured on a near-field range. Only the error-contaminated near-field measurements and an accurate probe position error function are needed for implementation of the correction technique. The method also requires the ability to obtain derivatives of the error-contaminated near field defined on an error-free regular grid with respect to the coordi nates. In planar geometry the derivatives are obtained using FFTs [1], giving an approximate operation count of (3 • 2=- 1 - 1 + (n - m)) N log N, where N is the number of data points. Efficient computer codes have been developed to demonstrate the technique. The results of simulations are more accurate than those obtained us ing the well-known k correction [3), which can correct for position errors in some direction in k space, but further contaminates the sidelobe levels.
An analytic technique recently developed at NIST [1] [2] to correct for probe position errors in planar near-field measurements has been implemented to arbitrary accuracy. The nth-order correction scheme is composed of an mth-order ordered expansion and an n - m higher-order approximation, where both n and m are arbitrary. The technique successfully removes very large probe position errors in the near-field, so the residual near-field probe position errors are substantially below levels that can be measured on a near-field range. Only the error-contaminated near-field measurements and an accurate probe position error function are needed for implementation of the correction technique. The method also requires the ability to obtain derivatives of the error-contaminated near field defined on an error-free regular grid with respect to the coordi nates. In planar geometry the derivatives are obtained using FFTs [1], giving an approximate operation count of (3 • 2=- 1 - 1 + (n - m)) N log N, where N is the number of data points. Efficient computer codes have been developed to demonstrate the technique. The results of simulations are more accurate than those obtained us ing the well-known k correction [3), which can correct for position errors in some direction in k space, but further contaminates the sidelobe levels.
A technique for estimating measurement errors in near field facilities is presented. Known mechanical and electrical errors can be accounted for in simulation and such results are presented here. Unknown factors like chamber reflection and instrumentation drift can be estimated via selective measurement and the error induced by such anomalies may be combined with the simulated findings to provide error patterns for a particular test antenna and facility. Results are shown where these patterns are used to calculate measurement error limits. The software presented here also allows the generation of parametric curves which show the impact of a parameter of interest.
We investigated two methods of probe-position error correction to determine how well the corrected results compare to the uncorrupted far field: the k-correction method and the Taylor-series method. For this investigation, we measured a 1.2 m dish at 4 GHz and a 1.2m by 0.9m phased array at 2.2 GHz. Measurements were made first without position errors and then with deliberate z-position errors. We perfonned probe position error correction using both methods and compared the results to the error-free far field. For errors up to A/4, the fifth-order implementation of the Taylor series correction was slightly better than the k-correction. For errors of ')..J2, the k-correction was better than the Taylor-series correction.
Hologram measurements are becoming more and more popular as a reliable method for identifying bad elements and the tuning of active phased array antennas. Relying on holographic data to adjust phase shifters and attenuators in these antennas can give undesired results if the accuracy of the data is poor. Often measurements can be improved if the error sources can be isolated and quantified. This paper presents an approach to producing a hologram accuracy budget based on the NIST 18-term error budget created for near-field measurements. A set of hologram accuracy terms is identified and data is presented showing the typical hologram accuracy that can be expected from a near-field scanner.
Far-field patterns obtained from planar near-field measurements of a prototype of the AMSU-B radiometer antenna by phase retrieval at 94 GHz are presented in this paper. Comparison with results from a compact range facility show good agreement within the main beam A modified algorithm takes into account any misalignments of the two intensity data sets so that the RMS near-field error metric comparing retrieved and measured values converges to < -30 dB. Phase retrieval is revealing itself as a useful technique to be applied to electrically large antennas at frequencies extending into the millimetre and sub millimetre bands.
The feasibility of realizing a 500 GHz hologram type of compact antenna test range (CATR) for testing the 1.1 m antenna of the Odin satellite is studied. The quiet-zone field is analyzed theoretically by us ing an exact near-field aperture integration method. Due to fabrication errors the slots of the hologram are wider or narrower than in the ideal case. How ever, with reasonable value of fabrication errors the quality of the quiet-zone field is not degraded deci sively. The effect of the displacement of the different parts joined together to form a large hologram is the inclination of the amplitude and phase in the quiet zone. The analysis of the CATR feed scanning in the focal plane to avoid the need to rotate the AUT showed that at least a ±1° change of the direction of the plane wave in the quiet-zone is feasible.
Daimler-Benz Aerospace AG (Dasa) in Munich, Germany designed, developed, build and tested most of the INTELSAT VIII antennas. RF test requirements and results are presented for the Hemi/Zone antennas. These tests cover the Beam Forming Networks (BFN), the feed array in the cylindrical near field facility at ambient temperature and in a temperature range from -61 to +85 deg centigrade, and finally the complete antenna sub system, without and with satellite mock-up, in the large Compensated Compact Range. Dasa and TICRA software was used to calculate the far field results from the measured BFN coefficients and from the feed array results measured in the near field facility. Also alignment aspects are considered.
Earlier measurement results are reviewed to understand the result that cross -polarized patterns agree well when compared between a point-source compact range and spherical near-field scanning. By taking account of the symmetry of the aperture distribution, one can see how the cross-polarized pattern can be affected only moderately by the classic polarization feature of an offset reflector geometry.
This paper details the evaluation of a major aerospace company's tapered anechoic chamber. Using an NSI 3' x 3' near-field scanner and software, the chamber was evaluated at 11 frequencies and two polarizations. SAR imaging techniques were used to map the chamber reflections. A new addition to the software provided the ability to map the difference between the measured phase front and the theoretical spherical phase front; the software also derives the x,y,z phase centers of the source. Error estimates for all aspects of the evaluation will be discussed.
In this paper it is presented the measurements performed on the prototype of the ERS-1 SAR antenna to verify the behaviors of the CASA-Space Division test range described during 1992 AMTA Symposium [1]. The prototype was provided by European Space Agency for this purpose and it has been measured in three different modes supported by the test range (spherical near field, planar near field and fresnel zone field). Results are compared with previous measurements available from other laboratories (TUD, ERICSSON).
A novel computer simulation methodology to properly characterize the role of probe directivity/pattern compensation in cylindrical near field scanning geometry is presented. The methodology is applied to a linear test array antenna and the JPIJNASA scatterometer (NSCA1) radar antenna. In addition, error analysis techniques of computer simulation and measured have been developed to determine the achievable accuracy in pattern measurements of the NSCAT antenna in cylindrical near field.
A novel computer simulation methodology to properly characterize the role of probe directivity/pattern compensation in cylindrical near field scanning geometry is presented. The methodology is applied to a linear test array antenna and the JPIJNASA scatterometer (NSCA1) radar antenna. In addition, error analysis techniques of computer simulation and measured have been developed to determine the achievable accuracy in pattern measurements of the NSCAT antenna in cylindrical near field.
The radiation characteristics for an active phased array receive antenna operating at K Band were measured at the Ipswich Research Facility. On-pole and cross-pole radiation patterns were measured for several scan angles. In this paper we'll discuss the general design of the antenna and the instrumentation ensemble used to perform the far field and near field characterization of this antenna. Measurements taken on a 2600 foot far field range vs. a near field planer scanner are compared.