This thesis outlines several different topics associated with the design and analysis of millimetre and submillimetre systems. A major topic is the design, analysis and verification of a 4 mm receiver for the 20 m telescope at Onsala Space Observatory, Onsala, Sweden. The 4mmreceiverwas designed to be installed parallel to the existing 3 mm channel to target new science at that longer wavelength. Gaussian beam mode analysis was used to produce the fundamental optical design. This is computationally efficient, and provides all critical beam characterization through the optical train within the paraxial limit. The design was analysed more accurately with physical optics, using GRASP, a commercial software package developed by TICRA. Following the manufacture of the system, experimental verification was performed at Onsala Space Observatory. Measurements of the beam were compared with simulations to verify the operation at 69 GHz. In addition to this, an investigation was carried out into the development of lens antennae fed by planar antennae with good beam characteristics, as an alternative to horn antennae in the W band. A variety of patch designs were considered, with the effect of a lens placed in front of them. This adds the required directionality to the beam to launch or receive signals efficiently. CST Microwave studio was used for this investigation. Finally, the behaviour of absorbing bolometer detectors housed in waveguide cavities was examined, in particular the effects of varying the absorber and input waveguide position for a number of different cavity geometries. The goal was to analyse the effect of these parameters on the optical coupling: how much incident radiation was absorbed in a thin absorbing layer of tantulum associated with a TES detector. This work was directed towards the SAFARI instrument for proposed SPICA missions. The analysis tool was CSTMicrowave Studio.