Filtering amplifiers based on coupled resonator circuits

Terahertz (THz) wireless communication systems over 300 GHz can offer broad bandwidth, but they have limitations, such as high precision fabrication requirements, high fabrication cost and lossy system components. This thesis introduces a THz communication system concept based on low-cost and high precision micromachining techniques, also a new design approach to achieve a low loss system for THz communication components and systems. In order to minimise the components and systems losses, this thesis proposes a design approach for filtering amplifiers which removes the lossy planar matching and interconnection circuits to complete the transistor amplifiers design. The technique also adds filters resulting in a combined filtering amplifier. To enable this, an analytical design method for filtering amplifiers based on the conventional passive coupling matrix for filters is expanded for the filtering amplifiers. Novel coupled resonator circuits, including a general transistor model for the first time is investigated and a new [\(T\)] matrix is introduced to facilitate the transistor element. Complete mathematical formulas are provided in this thesis for the coupled resonator circuits for transistor amplifiers. Two physical design examples at X band are provided in this thesis to demonstrate the usage of the novel coupling matrix with a simple mathematical synthesis. A waveguide filtering amplifier is demonstrated using waveguide resonators. This waveguide amplifier reflects the design considerations and methods for future THz amplifier developments. Good correlations between mathematical synthesis results and physical measurements are achieved for the waveguide filtering amplifier, with 3 clearly observed poles in passband, verifying the order of the filters.