Vented radio frequency shielded enclosure

Claim 1

A ventilated enclosure providing shielding of electronic equipment from external radio frequency energy up to frequencies of the order of 3000 megahertz, comprising an inner metal container forming a chamber surrounding the equipment, hollow rectangular input and output ducts connected to said chamber, the ducts being parallel to each other and forming the end walls of the inner container, the ducts having openings within the container, an outer fully enclosed container surrounding the metal container and the ducts, the outer container forming a chamber between the outer ends of the ducts, the outer container having openings opposite the outer ends of the ducts, the openings being larger than the ends of the ducts, and means directing air into the outer container through one of said openings, a portion of the air being directed through the outer container and out the other opening and a portion of the air being directed through said ducts and said inner container for cooling the equipment in the chamber, the ducts operating as waveguide means having a cutoff frequency above the frequencies of said external radio frequency energy, the length of the ducts forming the waveguide means being of the order of at least twice the freespace wavelength at said cutoff frequency of the radio frequency energy.