Advanced Near-Field Antenna Measurement Techniques

During the past decades, near-field antenna measurements have emerged as one of the most widely preferred methods among engineers for antenna characterization. Some of the unique advantages they offer include accuracy, trustworthiness, and a closed and controlled environment where the measurements take place. Apart from its substantial utilization in the industry, large space organizations, such as the European Space Agency, have long relied on performing near-field antenna measurements on their satellites before the launch of their critical missions. This highlights the importance of these methods for the progress of significant sectors such as space exploration, communications, and connectivity.

In this Ph.D. study, the focus is placed on improving the measurement time of spherical nearfield antenna measurements. Among all the different types of near-field antenna measurements, it can be argued that the spherical type is the most accurate. However, after decades of improvements, the technology has matured, while the specifications from the industry have steadily become more strict, thus pushing its capabilities to the limits. Reducing the required measurement time is probably the most valuable development currently in demand, especially for the space sector which operates on stringent conditions and delays in characterization and testing can be quite costly.

Primarily, three methods are investigated in this Ph.D. study, namely signal derivative sampling, numerical uncertainty estimation and Rydberg atom probes. The first of them concerns the exploitation of the spatial derivatives of the received probe signal in order to extract additional information about the unknown near-field of the antenna. It is shown that this method can reduce the measurement time by up to 50% (or more for stop-go scanning schemes) and has the potential of additional time reductions if higher derivatives are also employed. Numerical uncertainty estimation methods are explored with the aim of eliminating the rather time-consuming common experimental uncertainty estimation methods, without any compromise regarding their accuracy and dependability. This is achieved by carefully exploiting the motion of a probe when it collects samples and predicting the actual locations of these samples if mechanical errors of certain type are present. Finally, the potential of Rydberg sensors in near-field antenna measurements is studied and assessed. These quantum sensors can detect electromagnetic radiation, so they act like “classical” antennas, but they also offer numerous unique advantages, such as extremely wide frequency of operation and almost complete elimination of secondary error sources, such as multiple reflections.

In order to further validate the obtained results, computer simulations and/or physical experiments are conducted for all of the aforementioned methods. The computer simulations are implemented, mainly, with the electromagnetics simulation software WIPL-D and the physical experiments took place at the DTU-ESA Spherical Near-Field Antenna Test Facility, Kgs. Lyngby, Denmark and at the National Institute of Standards and Technology, Boulder, Colorado, USA.