Analysis and Design of Quasi-Optical Multipliers using Lumped Element (LE)-FDTD Method

The millimetre and sub-millimetre wave frequency ranges are becoming widely used in a number of communications, radar and remote sensing applications. In these frequency ranges the use of guiding structures can he quite inefficient and single high power sources are difficult to produce. One possible solution to these problems is the use of quasi-optical circuits. One of the problems of quasi-optical circuits is the difficulty of their design. This arises from the fact that they often have many active devices embedded in radiating structures and hence pose great problems for conventional circuit simulators. Quasi-optical circuits thus require a global simulation tool that can simulate all parts of the circuit, including active, passive and radiating elements. A promising method is the lumped element finite difference time domain (LE-FDTD) method. This approach allows for the incorporation of lumped element models including passive, active and non-linear devices directly into the traditional FDTD grid structure. The method is used in this paper to investigate the analysis and design of quasi-optical multipliers using diodes mounted in slot antennas. The conventional approach to slot multiplier design is to place the diode centrally in the slot, however, using LE-FDTD the diode can be offset in the slot to add an extra degree of freedom to the design process. It is felt that by placing the diode towards the end of the slot, in the low impedance region of the slot, improvements in performance may be possible.