This paper presents a new integrated double-shell lens antenna to be used as a single feed for a quasi-optical imaging reflector system at 500GHz. The use of the double-shell configuration favors power transmission across the lens, being the main challenge to design a double shaped high permittivity integrated lens antenna with good scanning characteristics and low reflection losses that can produce multiple virtual foci compatible with a wide reflector focal arc. The proposed lens antenna was designed and evaluated with the ILASH software tool, which was developed at Instituto de Telecomunicações (IT), in the framework of an European Space Agency (ESA/ESTEC) funded project. A remarkable agreement between measurement and simulations was obtained for the lens radiation patterns for the different feed positions, both in terms of amplitude and phase, confirming the ILASH software tool reliability and accuracy.