Coordinate System Plotting for Antenna Measurements
Authors: Gregory F. Masters, Stuart F. Gregson
Publication: AMTA 2007
Copyright Owner: NSI-MI Technologies
Antenna measurement data is collected over a surface as a function of position relative to the antenna. The data collection coordinate system directly affects how data is mapped to the surface: planar, cylindrical, spherical or other types. Far-field measurements are usually mapped or converted to spherical surfaces from which directivity, polarization and patterns are calculated and projected. Often the collected coordinate system is not the same as the final-mapped system, requiring special formulas for proper conversion. In addition, projecting this data in two and three-dimensional polar or rectangular plots presents other problems in interpreting data. This paper presents many of the most commonly encountered coordinate system formulas and shows how their mapping directly affects the interpretation of pattern and polarization data in an easily recognizable way.
Techniques for Reducing the Effect of Measurement Errors in Near-Field Antenna Measurements
Authors: Allen C. Newell, Greg Hindman
Publication: EuCAP 2007
Copyright Owner: IEEE
The NIST 18 term error analysis has been used for some time to estimate the uncertainty in the far-field antenna parameters determined from near-field measurements. Each of the error terms is evaluated separately to estimate the uncertainty it produces in parameters such as gain, directivity, side lobe level, cross polarization level and beam pointing angle. This identification and evaluation of uncertainties has led to the development of procedures that can be used to reduce the effect of individual error sources and therefore improve the reliability of the results.
Automated, real time systems have been added to the measurement hardware and electronics that can reduce the effect of such things as probe position errors and cable flexing. Measurement and special computer processing techniques have also been developed to self-calibrate and correct for transmission path differences of dual mode probes.
More recently, a number of techniques have been developed that provide a means to reduce the effect of measurement errors without the need of special hardware or additional measurements. These procedures often involve additional data processing steps to identify and reduce the presence of the error in the measured data, but the processing time is small and the improvement in some parameters can be very significant. In some cases, the error signal level can be reduced by 10 to 20 dB. Such techniques have been developed for errors due to bias error leakage in the receivers, non-ideal rotary joints, spherical rotator misalignment, and room scattering. Further improvements can be realized by making additional measurements to reduce multiple reflection effects, position errors and room scattering in spherical systems.
Examples of these techniques will be presented to illustrate the methods and demonstrate typical improvement.
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Copyright 2007 IEEE. Reprinted from The Second European Conference on Antennas and Propagation (EuCAP 2007) 11-16 November 2007.
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