Improvement and applications for nonlinear transmission lines

A NLTL is a high impedance transmission line periodically loaded with Schottky varactor diodes. In this synthetic structure, the small signal propagation velocity depends on the voltage variable capacitance of the diodes working as a voltage dependent delay line. On the other hand, when a large signal propagates through the NLTL, it is distorted due to the nonlinearity of the NLTL and generates a shock wave containing harmonics of the fundamental frequency. Utilizing these characteristics of the NLTL, we designed and tested a compact and inexpensive network analyzer, and THz scanning and detection system. The device shows very promising results, but with some limitation in the output power generated and the frequency range.; To overcome the limitations, we pursued two different approaches. One was fabrication of MOS based varactors and the other was fabrication of an air-bridge NLTL. Both showed very promising results in the performance improvements of the NLTL. Based on the theories and experiments reviewed in this thesis, we propose to further refine the critical interface between the insulating layer and the GaAs substrate as a means of improving the MOS varactor characteristics, and integrating the varactor into the an air-bridge transmission line. In that way, we will have a very compact and inexpensive THz scanning and detection system capable exhibiting a significantly large contrast.