PhDNew Quasi-optical sensor technology, based on the millimetre and submillimetre band of the
electromagnetic spectrum, is actually being implemented for many commercial and scientific
applications such as remote sensing, astronomy, collision avoidance radar, etc. These novel
devices make use of integrated active and passive structures usually as planar arrays. The
electromagnetic design and computer simulation of these new structures requires novel
numerical techniques.
The Finite Difference Time Domain method (FDTD) is well suited for the electromagnetic
analysis of integrated devices using active non-linear elements, but is difficult to use for large
and/or periodic structures. A rigorous revision of this popular numerical technique is
performed in order to permit FDTD to model practical quasi-optical devices. The system
impulse response or discrete Green's function (DGF) for FDTD is determined as a
polynomial then the FDTD technique is reformulated as a convolution sum. This new
alternative algorithm avoids Absorbing Boundary Conditions (ABC's) and can save large
amounts of memory to model wire or slot structures. Many applications for the DGF can be
foreseen, going beyond quasi-optical components. As an example, the exact ABC based on
the DGF for FDTD is implemented for a single grid wall is presented.
The problem of time domain analysis of planar periodic structures modelling only one
periodic cell is also investigated. Simple Periodic Boundary Conditions (PBC) can be
implemented for FDTD, but they can not handle periodic devices (such as phased shift arrays
or dichroic screens) which produce fields periodic in a 4D basis (three spatial dimensions plus
time). An extended FDTD scheme is presented which uses Lorentz type coordinate
transformations to reduce the problem to 3D.
The analysis of non-linear devices using FDTD is also considered in the thesis. In this case,
the non linear devices are always model using an equivalent lumped element circuit. These
circuits are introduced into the FDTD grid by means of the current density following an
iterative implicit algorithm. As a demonstration of the technique a quasi-optically feed slot
ring mixer with integral lens is designed for operation at 650 GHz
