| dc.description.abstract | Millimetre and sub-millimetre wave systems have been applied in many areas, such as
radio astronomy, remote sensing of the atmosphere, plasma diagnostics, material
exploration. A Quasi-optical Network (QoN) is the most efficient approach to transport
signals within such systems.
The Gaussian beam summation method has proven to be a useful ray-tracing-based
solution in designing the complex configurations of QoNs. An efficient approach,
diffracted Gaussian beam analysis (DGBA) has been developed at Queen Mary,
University of London. However, this version of DGBA can be only used for a 2.5-D
analysis, for the following reasons: (1) the input Gaussian beams (GBs) should be
stigmatic (circular); (2) all incident beams are approximated as normally incident,
unable to treat oblique polar angles of incidence. So in this regard, there is a need to
develop a 3D treatment of diffraction in DGBA.
In this thesis, a 3D diffracted GB approach (3D-DGBA) to the analysis of multireflector
QoNs is presented. This new approach expands the input beam/field into a set
of elementary GBs by using windowed Fourier transforms (WFT). The ensuing GBs
propagate to the reflector. Reflected and diffracted beams are respectively handled by a
phase-matching method and a 3D GB diffraction method. In addition, it is modular and
suitable for analysis of large, multi-element, QoNs.
A specific design procedure of multi-path, multi-reflector, QoNs is presented and two
different kinds of dual-path QoNs are built and assessed. By analysing one of these
QoNs, the new 3D-DGBA approach is verified experimentally, as well as compared to
the original DGBA and GRASP predictions. It is observed that 3D-DGBA is more
accurate than the original DGBA. For example, in one of the simulated cases, the farfield
deviation between 3D-DGBA and GRASP within 20˚ stays in the range of ±8.0 dB
in comparison with ±23.0 dB of the original DGBA. | en_US |
