This research includes theoretical analysis and experimental testing of terahertz systems operating in the w-band range. In modelling these long wavelength systems we use Gaussian Beam mode analysis, a novel technique which can be efficiently used to predict optical behaviour of systems that borrow components from both traditionally established optical and radio receiver techniques. This analytical technique neatly includes diffraction, which dominates propagation in this wavelength range. We are currently investigating the most numerically efficient and stable ways of utilising these modes in optical analysis and present our findings. In parallel, in an experimental campaign, we are characterising standing waves or multiple reflections which occur within terahertz systems. We present the experimental arrangement and outline potential methods to reduce the influence of multiple reflections in terahertz systems.