This thesis investigate design techniques for multilayer Frequency Selective Surfaces
(FSS) and its applications in quasi-optical (QO) systems. Design challenges that involve
higher order filter and practical implementation of multilayer FSS at higher frequencies
are reviewed. Multilayer FSS structures are commonly realized by cascading two or more
FSS panel to achieve higher order responses, which usually rely on dielectric substrates
to support the FSS arrays. It is noted that existing design approaches involved elaborate
manufacturing processes as well as the requirement of custom dielectric thickness for the
implementation of multilayer FSS. These design issues poses practical problems in the
realization of multilayer FSS of higher order and its demonstration at higher frequencies.
Furthermore, realization of higher order multilayer FSS with custom dielectric
thicknesses are not feasible with low cost Printed Circuit Board (PCB) technology. As a
result of this investigation, a novel design and synthesis technique is developed to address
the aforementioned design issues. Equivalent circuit modelling and full wave
electromagnetic simulation are employed for this purpose. The developed design
technique enable practical realization of QO filter to have all transmission lines of
predefined fix length. As a result, the proposed technique is able to resolve the limited
availability of custom dielectric thicknesses, thus enable demonstration of multilayer FSS
of higher order at higher frequencies. Particularly, the proposed design methodology
allow rectification by design to adapt to any small variations in the dielectric thicknesses.
Subsequently, based on this technique, a novel QO reflector design is developed to
demonstrate proof of concept for time delay multiplexing that are employed in a radar
system. The implementation of time delay between two polarization multiplexed beams
initially requires true time delay structures that are difficult to integrate due to their
electrically large structure. In order to address this problem, the designed QO reflector is
able to perform same functionalities, i.e. a significant group delay difference for the two
orthogonal linear polarization. Specifically, the designed QO reflector has the capability
to de-multiplex an incoming wave into two linear polarized waves, whereby one of the
reflected wave is time delayed while the other wave is unaffected. A synthesis method
for QO reflector design with time delay multiplexing has been presented. Based on the
design procedures reported in this thesis, prototypes for both QO filter and QO reflector
of fourth order has been developed to operate at 15 GHz with 5% and 3.5% bandwidth
respectively. The performances of the developed prototypes are verified with free-space
measurement setup. The measured insertion loss of the QO filter is observed to be in the range of 0.5 dB – 2.83 dB, while the measured return loss of the QO reflector is the range
of 1.5 dB – 2.3 dB. In order to demonstrate the effect of the group delay from the QO
reflector, frequency domain analysis is performed by post-processing the measured data
to obtain the required time domain signals. Overall the experimental measurement results
corroborate well with both full-wave and circuit simulation
