History Claimants to the invention of the choke connection include Norman Ramsey with the assistance of Shep Roberts while the two were working at the MIT Radiation Lab during World War II. Winfield Salisbury also claims to have made the invention while leader of the Radio Frequency Group at the MIT Radiation Lab between 1941 and 1942. The invention was not patented. Performance Choke connections can achieve a VSWR of 1.01 (a return of −46 dB) over a useful bandwidth, and eliminate the danger of arcing at the join. Nevertheless, better performance is possible with a carefully made contact-connection between undamaged plain flanges. Attachment to waveguide Flanges are either through-mounted or socket-mounted on the end of the waveguide tube. Through-mounting In through-mounting, the waveguide tube passes all the way through to the front face of the flange. Initially the tube is allowed to protrude slightly beyond the face of the flange, then after the two pieces have been soldered or brazed together, the end of the tube is machined down so that it is perfectly level with the face. This type of construction can be seen in figures 1, 4 and 5. Socket-mounting In socket-mounting, the aperture in the front face of the flange matches the inside dimensions of the waveguide. At the back, the aperture is rabbeted to form a socket which fits onto the end of the waveguide tubing. The two pieces are soldered or brazed together to ensure an uninterrupted conducting path between the inside surface of the waveguide tube and the mouth of the flange. This type of construction can be seen in figure 2, and is shown diagramatically in figure 3. A variation on this is butt-mounting, in which the waveguide tube abuts the back face of the flange. The back of the flange has a number of protrusions, sufficient to align the tube, but without forming an unbroken socket-wall around it. Socket mounting avoids the need to machine the face of the flange during attachment. For choke flanges this means that the depth to which the face is recessed, and the width of the resulting gap is fixed when the flange is manufactured and will not change when it is attached. MIL-spec choke flanges are socket-mounted. Standards MIL-spec is a United States Military Standard giving detailed descriptions of choke, gasket/cover and cover flanges for rectangular waveguide. describes flanges for double-ridge waveguide, and formerly also