Sutton tube

Last updated
The 5836, a typical reflex klystron used as a low-power microwave source. Note the terminal on the top of the tube, used to power the repeller. RK5836.JPG
The 5836, a typical reflex klystron used as a low-power microwave source. Note the terminal on the top of the tube, used to power the repeller.

Sutton tube was the name given to the first reflex klystron, developed in 1940 by Robert W. Sutton of Signal School group at the Bristol University. The Sutton tube was developed as a local oscillator for the receiver of 10cm microwave radar sets. Due to its geometry and long drift space, it suffered from mode jumping through the tuning range. For this reason, from late 1941 onward, it was replaced in many sets by the Western Electric 707A (also known as McNally tube, named by its developer).

Contents

Here the photos of an unbased Sutton tube used in the development of the external tuner and an Air Ministry 10E7501 complete with the tuner. Sutton tubes.jpg
Here the photos of an unbased Sutton tube used in the development of the external tuner and an Air Ministry 10E7501 complete with the tuner.

The 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 by Britain 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 and Radar 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.

Basic klystron concept

In a two-cavity klystron, the electrons "bunch up" as they move between the cavities, re-creating the original signal. Klystron.enp.gif
In a two-cavity klystron, the electrons "bunch up" as they move between the cavities, re-creating the original signal.

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". [1]

A stream of electrons fired from an electron gun passes through the hole, and the varying field causes them to either accelerate or decelerate depending on the value of the rapidly varying field at the time 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. [2]

The electrons then pass through a second cavity, similar to the first. As they pass, the bunches cause a varying electric field to be induced in the cavity, re-creating the original signal but at much higher current. A tap point on this cavity provides the amplified microwave output. [2]

Local oscillators

The reflex klystron essentially folds the two-cavity design in half, using two opposing accelerating fields. Reflex klystron schematic-en.svg
The reflex klystron essentially folds the two-cavity design in half, using two opposing accelerating fields.

The introduction of the cavity magnetron caused a revolution in radar design, generating large amounts of power from a compact and easy-to-build device. However, it also required several additional developments before it could be used.

Among these was a suitable local oscillator about 45 MHz different than the transmitter signal, which fed the intermediate frequency section of the receiver circuits. [3] The problem was that the magnetron's frequency drifted as it warmed and cooled, enough that some sort of tuneable microwave source was needed whose frequency could be adjusted to match. A second magnetron would not work, they would not drift in sync. [4]

As the receiver circuit requires only very little output power, the klystron, first introduced only two years earlier, was a natural choice. Sutton, a well-known expert in tube design, was asked if he could provide a version that could be tuned across the same range as the magnetron's drift. [5] An initial model available in 1940 allowed tuning with some effort. While it worked, it was not suitable for an operational system. Sutton and Thompson continued working on the problem, and delivered a solution in October 1940. [3] Thompson named it for Sutton, while Sutton referred to it as the Thompson Tube. [6] The former stuck.

Their advance was to use a single resonator and clever physical arrangement to provide the same effect as two cavities. He did this by placing a second electrode at the far end of the tube, the "reflector" or "repeller", which caused the electrons to turn around and start flowing back toward the gun, similar to the Barkhausen–Kurz tube. By changing the voltage of the reflector relative to the gun, the speed of the electrons when they reached the cavity the second time could be adjusted, within limits. The frequency was a function of the velocity of the electrons, providing the tuning function. [5]

This modification effectively folded the klystron in half, with most of the "action" at the center of the tube where the input and output from the single cavity were located. Furthermore, only the interior of the cavity was inside the tube, the outer surface was in the form of a metal shell wrapped around the tube. Larger changes to the frequency could be made by replacing the outer shell, and this also provided a convenient location for mounting. [5]

Unfortunately, the system needed two high-voltage power supplies, one for the initial acceleration in the gun, and a second between the gun and the reflector. And, due to the way it worked, the system was generally limited to milliwatts of power.[ citation needed ]

Soft Sutton tube

Replicas of World War II allied (left) and German T/R switch tubes Replicas of WWII TR tubes, 1946.jpg
Replicas of World War II allied (left) and German T/R switch tubes

One of the advantages of using microwaves for radar is that the size of an antenna is based on the wavelength of the signal, and shorter wavelengths thus require much smaller antennas. This was vitally important for airborne radar systems. German aircraft, using longer wavelengths, required enormous antennas that slowed the aircraft between 25 and 50 km/h due to drag. [7] Microwaves required antennas only a few centimetres long, and could easily fit within the aircraft nose.

This advantage was offset by the lack of a switching system to allow a single antenna to act as both a transmitter and receiver. This is not always a major problem; the Chain Home system made do with two sets of antennas, as did early airborne radars like the Mk. IV. In 1940 Bernard Lovell developed a solution for microwave radar by placing two sets of dipoles in front of a common parabolic dish and placing a disk of metal foil between them. However, this was not terribly successful, and the crystal diodes used as detectors frequently burned out as the signal bled through or around the disk. [8] A solution using two spark gap tubes was also used, but was less than ideal. [9]

A better solution was suggested by Arthur H. Cooke of the Clarendon Laboratory, and production development was taken up by H.W.B. Skinner along with A.G. Ward and A.T. Starr at the Telecommunications Research Establishment. [9] They took a Sutton tube and disconnected the electron gun and reflector, leaving just the cavity. This was filled with a dilute gas, initially helium or hydrogen, [10] but eventually settling on a tiny amount of water vapour and argon. [11]

When the transmission signal was seen on the input, the gas would rapidly ionize (helped by a heater coil or radium). [12] The free electrons in the plasma presented an almost perfect impedance source, blocking the signal from flowing to the output. As soon as the transmission stopped, the gas de-ionized and the impedance disappeared very rapidly. [10] The tiny echoes caused by reflections from the target, arriving microseconds later, were far too small to cause the ionization, and allowed the signal to reach the output. [3]

The usable soft Sutton tube arrived in March 1941, and was put into production as the CV43. [3] It was first used as part of the AI Mk. VII radar, the first production microwave radar for aircraft. [10] The system was widely used from then on, appearing in almost all airborne microwave radars, including the H2S radar and ASV Mark III radar. [10]

Post-war intelligence revealed that the Germans were baffled by the purpose of the soft Sutton tube. Several examples fell into their hands, notably in the Rotterdam Gerät, an H2S that was captured in fairly complete form in February 1943. Interviews with German radar engineers after the war demonstrated that they could not understand the purpose of the unpowered tube. [9]

The soft Sutton tube was used in a circuit known as a "T/R switch" (or many variations on that theme). Other spark tubes had been used for this purpose, in a design known as the "Branch-Duplexer". This consisted of two short lengths of waveguide about 1/4 of a wavelength, both of which turned on when the signal arrived. Because of the geometry of the layout, the two paths resulted in a reflection of the signal. [13] Sutton tubes were used in a simpler design known as the "shunt branching circuit", which was T-shaped with the transmitter and antenna located at either end of the horizontal portion of the T, and the receiver at the end of the vertical portion. By locating the Sutton tube at the right location along the waveguide to the receiver, the same effect as the branch-duplexer could be arranged. [14] [15]

Related Research Articles

<span class="mw-page-title-main">Microwave</span> Electromagnetic radiation with wavelengths from 1 m to 1 mm

Microwave is a form of electromagnetic radiation with wavelengths ranging from about 30 centimeters to one millimeter corresponding to frequencies between 1 GHz and 300 GHz respectively. Different sources define different frequency ranges as microwaves; the above broad definition includes UHF, SHF and EHF bands. A more common definition in radio-frequency engineering is the range between 1 and 100 GHz. In all cases, microwaves include the entire SHF band at minimum. Frequencies in the microwave range are often referred to by their IEEE radar band designations: S, C, X, Ku, K, or Ka band, or by similar NATO or EU designations.

<span class="mw-page-title-main">Cavity magnetron</span> Device for generating microwaves

The cavity magnetron is a high-power vacuum tube used in early radar systems and subsequently in microwave ovens and in linear particle accelerators. A cavity magnetron generates microwaves using the interaction of a stream of electrons with a magnetic field, while moving past a series of cavity resonators, which are small, open cavities in a metal block. Electrons pass by the cavities and cause microwaves to oscillate within, similar to the functioning of a whistle producing a tone when excited by an air stream blown past its opening. The resonant frequency of the arrangement is determined by the cavities' physical dimensions. Unlike other vacuum tubes, such as a klystron or a traveling-wave tube (TWT), the magnetron cannot function as an amplifier for increasing the intensity of an applied microwave signal; the magnetron serves solely as an electronic oscillator generating a microwave signal from direct current electricity supplied to the vacuum tube.

<span class="mw-page-title-main">Radar</span> Object detection system using radio waves

Radar is a radiolocation system that uses radio waves to determine the distance (ranging), angle (azimuth), and radial velocity of objects relative to the site. It is used to detect and track aircraft, ships, spacecraft, guided missiles, motor vehicles, map weather formations, and terrain. A radar system consists of a transmitter producing electromagnetic waves in the radio or microwaves domain, a transmitting antenna, a receiving antenna and a receiver and processor to determine properties of the objects. Radio waves from the transmitter reflect off the objects and return to the receiver, giving information about the objects' locations and speeds.

<span class="mw-page-title-main">Klystron</span> Vacuum tube used for amplifying radio waves

A klystron is a specialized linear-beam vacuum tube, invented in 1937 by American electrical engineers Russell and Sigurd Varian, which is used as an amplifier for high radio frequencies, from UHF up into the microwave range. Low-power klystrons are used as oscillators in terrestrial microwave relay communications links, while high-power klystrons are used as output tubes in UHF television transmitters, satellite communication, radar transmitters, and to generate the drive power for modern particle accelerators.

<span class="mw-page-title-main">Traveling-wave tube</span> Microwave signal amplifier

A traveling-wave tube or traveling-wave tube amplifier is a specialized vacuum tube that is used in electronics to amplify radio frequency (RF) signals in the microwave range. It was invented by Andrei Haeff around 1933 as a graduate student at Caltech, and its present form was invented by Rudolf Kompfner in 1942-43. The TWT belongs to a category of "linear beam" tubes, such as the klystron, in which the radio wave is amplified by absorbing power from a beam of electrons as it passes down the tube. Although there are various types of TWT, two major categories are:

<span class="mw-page-title-main">Resonator</span> Device or system that exhibits resonance

A resonator is a device or system that exhibits resonance or resonant behavior. That is, it naturally oscillates with greater amplitude at some frequencies, called resonant frequencies, than at other frequencies. The oscillations in a resonator can be either electromagnetic or mechanical. Resonators are used to either generate waves of specific frequencies or to select specific frequencies from a signal. Musical instruments use acoustic resonators that produce sound waves of specific tones. Another example is quartz crystals used in electronic devices such as radio transmitters and quartz watches to produce oscillations of very precise frequency.

<span class="mw-page-title-main">H2S (radar)</span> First airborne, ground scanning radar system WWII

H2S was the first airborne, ground scanning radar system. It was developed for the Royal Air Force's Bomber Command during World War II to identify targets on the ground for night and all-weather bombing. This allowed attacks outside the range of the various radio navigation aids like Gee or Oboe, which were limited to about 350 kilometres (220 mi) of range from various base stations. It was also widely used as a general navigation system, allowing landmarks to be identified at long range.

<span class="mw-page-title-main">Naxos radar detector</span> Radar warning receiver in World War II

The Naxos radar warning receiver was a World War II German countermeasure to S band microwave radar produced by a cavity magnetron. Introduced in September 1943, it replaced Metox, which was incapable of detecting centimetric radar. Two versions were widely used, the FuG 350 Naxos Z that allowed night fighters to home in on H2S radars carried by RAF Bomber Command aircraft, and the FuMB 7 Naxos U for U-boats, offering early warning of the approach of RAF Coastal Command patrol aircraft equipped with ASV Mark III radar. A later model, Naxos ZR, provided warning of the approach of RAF night fighters equipped with AI Mk. VIII radar.

<span class="mw-page-title-main">Gyrotron</span> Vacuum tube which generates high-frequency radio waves

A gyrotron is a class of high-power linear-beam vacuum tubes that generates millimeter-wave electromagnetic waves by the cyclotron resonance of electrons in a strong magnetic field. Output frequencies range from about 20 to 527 GHz, covering wavelengths from microwave to the edge of the terahertz gap. Typical output powers range from tens of kilowatts to 1–2 megawatts. Gyrotrons can be designed for pulsed or continuous operation. The gyrotron was invented by Soviet scientists at NIRFI, based in Nizhny Novgorod, Russia.

<span class="mw-page-title-main">Backward-wave oscillator</span>

A backward wave oscillator (BWO), also called carcinotron or backward wave tube, is a vacuum tube that is used to generate microwaves up to the terahertz range. Belonging to the traveling-wave tube family, it is an oscillator with a wide electronic tuning range.

<span class="mw-page-title-main">Barkhausen–Kurz tube</span>


The Barkhausen–Kurz tube, also called the retarding-field tube, reflex triode, B–K oscillator, and Barkhausen oscillator was a high frequency vacuum tube electronic oscillator invented in 1920 by German physicists Heinrich Georg Barkhausen and Karl Kurz. It was the first oscillator that could produce radio power in the ultra-high frequency (UHF) portion of the radio spectrum, above 300 MHz. It was also the first oscillator to exploit electron transit time effects. It was used as a source of high frequency radio waves in research laboratories, and in a few UHF radio transmitters through World War 2. Its output power was low which limited its applications. However it inspired research that led to other more successful transit time tubes such as the klystron, which made the low power Barkhausen-Kurz tube obsolete.

COHO, short for Coherent Oscillator, is a technique used with radar systems based on the cavity magnetron to allow them to implement a moving target indicator display. Because the signals are only coherent when received, not transmitted, the concept is also sometimes known as coherent on receive. Due to the way the signal is processed, radars using this technique are known as pseudo-coherent radar.

Sir John Turton Randall, was an English physicist and biophysicist, credited with radical improvement of the cavity magnetron, an essential component of centimetric wavelength radar, which was one of the keys to the Allied victory in the Second World War. It is also the key component of microwave ovens.

<span class="mw-page-title-main">Type 271 radar</span> British WWII naval surface search radar

The Type 271 was a surface search radar used by the Royal Navy and allies during World War II. The first widely used naval microwave-frequency system, it was equipped with an antenna small enough to allow it to be mounted on small ships like corvettes and frigates, while its improved resolution over earlier radars allowed it to pick up a surfaced U-boat at around 3 miles (4.8 km) and its periscope alone at 900 yards (820 m).

<span class="mw-page-title-main">AI Mark VIII radar</span> Type of air-to-air radar

Radar, Airborne Interception, Mark VIII, or AI Mk. VIII for short, was the first operational microwave-frequency air-to-air radar. It was used by Royal Air Force night fighters from late 1941 until the end of World War II. The basic concept, using a moving parabolic antenna to search for targets and track them accurately, remained in use by most airborne radars well into the 1980s.

<span class="mw-page-title-main">GL Mk. I radar</span>

Radar, Gun Laying, Mark I, or GL Mk. I for short, was an early radar system developed by the British Army to provide range information to associated anti-aircraft artillery. There were two upgrades to the same basic system, GL/EF and GL Mk. II, both of which added the ability to accurately determine bearing and elevation.

<span class="mw-page-title-main">GL Mk. III radar</span> Family of British radar systems for artillery

Radar, Gun Laying, Mark III, or GL Mk. III for short, was a radar system used by the British Army to directly guide, or lay, anti-aircraft artillery (AA). The GL Mk. III was not a single radar, but a family of related designs that saw constant improvement during and after World War II. These were renamed shortly after their introduction in late 1942, becoming the Radar, AA, No. 3, and often paired with an early warning radar, the AA No. 4, which was also produced in several models.

<span class="mw-page-title-main">ASV Mark III radar</span>

Radar, Air-to-Surface Vessel, Mark III, or ASV Mk. III for short, was a surface search radar system used by RAF Coastal Command during World War II. It was a slightly modified version of the H2S radar used by RAF Bomber Command, with minor changes to the antenna to make it more useful for the anti-submarine role. It was Coastal Command's primary radar from the spring of 1943 until the end of the war. Several improved versions were introduced, notably the ASV Mark VI, which replaced most Mk. IIIs from 1944 and ASV Mark VII radar, which saw only limited use until the post-war era.

<span class="mw-page-title-main">Wireless Set Number 10</span> Worlds first microwave relay telephone system

The British Army's Wireless Set, Number 10, was the world's first microwave relay telephone system. It transmitted eight full-duplex (two-way) telephone channels between two stations limited only by the line-of-sight, often on the order of 25 to 50 miles. The stations were mounted in highly mobile trailers and were set up simply by aiming the two parabolic antennas on the roof at the next station.

<span class="mw-page-title-main">SCR-720</span> Type of aircraft radar

The SCR-720 was a World War II Airborne Interception radar designed by the Radiation Laboratory (RadLab) at MIT in the United States. It was used by US Army Air Force night fighters as well as the Royal Air Force (RAF) in a slightly modified version known as Radar, Airborne Interception, Mark X, or AI Mk. X for short.

References

Citations

  1. Caryotakis 1998, p. 3.
  2. 1 2 Caryotakis 1998, pp. 1–2.
  3. 1 2 3 4 Watson 2009, p. 146.
  4. "Magnetron Theory of Operation", p. 3.
  5. 1 2 3 Lovell 1991, p. 61.
  6. Reg Batt, "The Radar Army: Winning the War of the Airwaves", Hale, 1991, p. 61.
  7. Jean-Denis G.G. Lepage, "Aircraft of the Luftwaffe, 1935-1945", McFarland, 2009, p. 61.
  8. Lovell 1991, p. 62.
  9. 1 2 3 Hodgkin 1994, p. 192.
  10. 1 2 3 4 Lovell 1991, p. 63.
  11. Watson 2009, p. 165.
  12. Robert Buderi, "The Invention That Changed the World", Touchstone, 1998, p.118.
  13. Christian Wolff, "Branch- Duplexer"
  14. C.G. Montgomery, "Microwave Duplexers", MIT
  15. A.L. Samuel, J.W. Clark and W.W. Mumford, "The Gas-Discharge Transmit-Receive Switch", Bell System Technical Journal, 1946, p. 54.

Bibliography

  • Hodgkin, Alan (1994). Chance and Design: Reminiscences of Science in Peace and War. Cambridge University Press. ISBN   9780521456036.
  • Watson, Jr, Raymond (2009). Radar Origins Worldwide. Trafford Publishing. ISBN   9781426991561.
  • Lovell, Bernard (1991). Echoes of War: The Story of H2S Radar. CRC Press. ISBN   9780852743171.
  • Caryotakis, George (April 1998). "The Klystron: A Microwave Source of Surprising Range and Endurance" (PDF). Stanford Linear Accelerator Center.

Further reading