Sutton tube

A Sutton tube, or reflex klystron, is a type of vacuum tube used to generate microwaves. It is a low-power device used primarily for two purposes; one is to provide a tuneable low-power frequency source for the local oscillators in receiver circuits, and the other, with minor modifications, as a switch that could turn on and off another microwave source. The second use, sometimes known as a soft Sutton tube or rhumbatron switch, was a key component in the development of microwave radar during World War II. Microwave switches of all designs, including these, are more generally known as T/R tubes or T/R cells.

The Sutton tube is named for one of its inventors, Robert Sutton, an expert in vacuum tube design. The original klystron designs had been developed in the late 1930s in the US, and Sutton was asked to develop a tuneable version. He developed the first models in late 1940 while working at the Admiralty Signals Establishment. Sutton tubes were widely used in a variety of forms during World War II and through the 1960s. Their role has since been taken over by solid state devices like the Gunn diode, which started to become available in the 1970s. "Rhumbatron" refers to the resonant cavity design that was part of many klystrons, referring to the rhumba because of the dance-like motion of the electrons.

Klystrons share the basic concept that the microwave output is generated by progressively accelerating then slowing electrons in an open space surrounded by a resonant cavity. The easiest klystron designs to understand have two cavities.

The first cavity is connected to a source signal, and is designed to resonate at the desired frequency, filling its interior with an oscillating electric field. The cavity's dimensions are a function of the wavelength, most are flat cylinders the shape of a hockey puck of varying sizes. A hole is drilled through the middle, at the center of the "puck".

A stream of electrons fired from an electron gun passes through the hole, and the varying field causes them to either accelerate or decelerate as they pass. Beyond the cavity the accelerated electrons catch up to the decelerated ones, causing the electrons to bunch up in the stream. This causes the stream to re-create the original signal's pattern in the density of the electrons. This area of the tube has to be fairly long to allow time for this process to complete.

...
Wikipedia