Efficient illumination for a dielectric lens antenna fed by a spiral antenna for broadband THz systems

Spiral antenna is widely used in THz regime as a ultra wide band-width feed for dielectric lenses. Indeed such antenna show a very flat behavior over a very wide band. Conversely these feeds generate very wide radiation patterns inside the lens which illuminate the lens in an inefficient way. In this contribution we want to show how is possible improving the performances of these types of antenna by using a small air gap between the dielectric lens and the spiral feed.