A Comprehensive Theory on Gain and Field of View of Conical Horn for Sensing Applications in the Optical and THz Ranges

The systems with horn elements are widely used as receiving components in applications of solar concentrators, for sensing in biomedicine, THz technology, etc. In many cases, using the horns as focusing elements in radiation detection arrangements is preferable to lenses. The article develops a theory for gain and field of view of a conical horn under normal and oblique illumination applicable in a wide spectrum ranging from ultraviolet to Sub-mm-Wave/Terahertz. The model assumes the introduction of fictional conical horns (identical to the real one) located in fictional concentric spheres. The proposed model makes it possible to determine the gain level for any geometric form of the horn and any number of beam reflections on its internal surface when a reflection coefficient is 1. The results of gain dependence on the incidence angle of illumination are analyzed depending on the configuration of the conical horn. It is shown that with an increase in the horn length relative to the optimal value, the distribution of gain on the angle of illumination tends to be Π-shaped, and the angle of view tends to apex angle.