Spherical near-field antenna measurement is an established method for characterizing the electrical properties of antennas. Compared to far-field measurements, however, a mathematical transformation of the near-field data is necessary to determine the desired far-field characteristics. In order to obtain accurate and complete transformation results, it is necessary to acquire near-field data on a closed surface (e.g. a sphere) around the test antenna. This significantly increases the measurement time compared to far-field measurements. This is particularly relevant in view of the increase of mobile communication devices and the associated measurement burden.
After introducing the theory and the transformation algorithms, several possibilities for accelerating the near-field measurements are investigated and evaluated. A simple approach is the reduction of measurement points by truncation of the measurement surface. This method aims to determine only certain, selected areas of the far field correctly. Due to the lack of information however, approximation errors always occur.
The main contribution of this thesis to the state-of-the-art is the investigation of non or minimally redundant sampling grids and the development of the associated transformation methods. It is shown that the number of measurement points can always be minimized by a suitable selection of the transformation origin. Furthermore, it is comprehensively analyzed which scanning grids enable time-efficient and accurate measurements. Using the proposed methods, a measurement time reduction between 5% and 50% has been achieved for the investigated examples. The determined uncertainties show that this does not reduce the measurement accuracy significantly.
In summary, different acceleration methods can be used and combined. Truncation can considerably reduce the measurement time in certain cases, but has the disadvantage that the antenna properties can only be approximated and not completely determined. In comparison, non-redundant sampling grids reduce the measurement time without significantly reducing the measurement accuracy. In general, the spherical mode spectrum can be determined with the developed methods from measured data on any closed measurement surface. The methods presented can therefore also be used to develop novel measuring systems that are adapted to the corresponding measuring task, since a spherical measuring geometry is generally not required.
Elektro- und Informationstechnik
Fast Spherical Near-Field Antenna Measurement Methods
In this thesis, different methods for accelerating spherical near-field antenna measurements are investigated and evaluated. The work focuses on time-efficient sampling grids. Measurement time reduction up to 50% can be achieved without significant reduction of the accuracy. In general, the spherical mode spectrum can be determined with the developed methods from measured data on any closed measurement surface. This increases the degrees of freedom in antenna measurement applications.