Modern anechoic chambers are typically shielded and equipped with wedge or pyramidal absorbers. The absorbers are tailored to achieve a “quite zone” around the antenna under test (AUT). However, size constraints and other parameters will limit the frequency band over which low reflections can be achieved.
Traditionally, the highest frequencies of interest have increased with time. However, recently this trend has also been towards expanding into lower frequencies as well. Previously it was common to relegate such measurements to outdoor ranges, but both interference issues and the use of fragile designs rule out this option, especially in the case of space antennas.
The RUAG Space “A6” anechoic chamber is primarily used for frequencies between 0.8 and 40 GHz. The room size is 5 m x 5 m x 9 m, with a probe to AUT distance of 6 m. The reflection properties of the absorbers deteriorate for lower frequencies, but 0.8 GHz is no abrupt cut-off. Recently, antenna projects in the UHF range (400-500 MHz) have necessitated an assessment of the possible use of this chamber at these low frequencies. The goal of this assessment is then to provide viable figures for the measurement accuracy of this chamber in terms of disturbance levels and frequency dependence as well as identification of possible compensation methods that can be used to enhance the chamber performance and measurement accuracies. It is also foreseen that the outcome of the assessment would be an electromagnetic model of the complete chamber to be used for future assessments at different frequency bands (ranging from UHF up to 60 GHz).
Some measurements have been made with reference antennas to obtain a picture of what can be achieved, but a simplified numerical or analytical model of the properties would enhance the understanding of important parameters. The numerical modeling is foreseen to involve FDTD or FEM software, and approaches could range from brute force to equivalent reflectivity absorber modeling. The analytical model would typically involve MATLAB code, and could range from simple to semi-numerical approaches.
The project should comprise:
- A literature study (e.g. anechoic chambers, absorber data, absorber modelling, absorber measurements)
- Antenna measurement, anechoic chamber and absorber theory
- Range and absorber modelling (FDTD/FEM/ Matlab)
- Comparison with measurements
- Identification of compensation methods, if any
- Conclusions and recommendations
The work should be a master thesis of 30 credits and the duration is 20 weeks for one student. The starting time should be as soon as possible in agreement with the student. Understanding of electromagnetic fields and antennas is strongly recommended. Relevant education is engineering, majoring in microwave technology, antennas or technical computations.
For more information about the thesis work contact:
Johan Wettergren, tel: 031-7354034, johan.wettergren(at)ruag.com