New developments in waveguide mode matching techniques are considered, in particular the efficient modeling of waveguide cavity coupled detectors. This approach is useful in far-infrared astronomical instrumentation and cosmic microwave background experiments in which bolometers feeding horn antennas or Winston cones are often employed for high sensitivity, good control of stray light and well behaved beam patterns. While such systems can, in theory, be modeled using full wave FEM techniques it would be desirable, especially for large structures in terms of the wavelength, to exploit more efficient mode matching techniques, particularly for initial design optimization. This would also be especially useful for cavities feeding partially coherent multi-mode horns or Winston cones. The mode matching approach also allows for straightforward modeling of the complete coupling structure including the horn, waveguide cavity and absorbing layer of the bolometer, thus marking a significant advance in the ability to predict the optical efficiencies of cavity coupled bolometers. We consider typical single mode and multi-mode examples that illustrate the power of the technique.