English: Horn antenna with dielectric lens, used in the Atacama Large Millimeter Array, a radio telescope being built in Chile. It is used as a "feed horn", to collect the radio waves reflected from the large parabolic dish and funnel them to the radio receiver. The telescope will operate at millimeter wavelengths, from 9.6 mm to 0.3 mm. In use it is installed in a cryostat and cooled by liquid nitrogen to very low temperatures to lower the electronic noise level and make the radio telescope more sensitive to weak signals.