Waveguide flange

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Figure 1. A UBR320 flange on R320 (WG22, WR28) guide. This type of flange has no choke or gasket grooves. The through-mounted assembly is made evident by the distinct colours of the copper waveguide-tube and brass flange. Waveguide-flange-UBR320.jpg
Figure 1. A UBR320 flange on R320 (WG22, WR28) guide. This type of flange has no choke or gasket grooves. The through-mounted assembly is made evident by the distinct colours of the copper waveguide-tube and brass flange.

A waveguide flange is a connector for joining sections of waveguide, and is essentially the same as a pipe flange—a waveguide, in the context of this article, being a hollow metal conduit for microwave energy. The connecting face of the flange is either square, circular or (particularly for large [1] or reduced-height rectangular waveguides), rectangular. The connection between a pair of flanges is usually made with four or more bolts, though alternative mechanisms, such as a threaded collar, may be used where there is a need for rapid assembly and disassembly. [1] Dowel pins are sometimes used in addition to bolts, to ensure accurate alignment, particularly for very small waveguides.

Waveguide (electromagnetism) waveguide for the transmission of electromagnetic waves; linear structure that conveys electromagnetic waves between its endpoints

In electromagnetics and communications engineering, the term waveguide may refer to any linear structure that conveys electromagnetic waves between its endpoints. However, the original and most common meaning is a hollow metal pipe used to carry radio waves. This type of waveguide is used as a transmission line mostly at microwave frequencies, for such purposes as connecting microwave transmitters and receivers to their antennas, in equipment such as microwave ovens, radar sets, satellite communications, and microwave radio links.

Microwave form of electromagnetic radiation

Microwaves are a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter; with frequencies between 300 MHz (1 m) and 300 GHz (1 mm). Different sources define different frequency ranges as microwaves; the above broad definition includes both UHF and EHF bands. A more common definition in radio 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.

Bolted joint type of fastener

Bolted joints are one of the most common elements in construction and machine design. They consist of fasteners that capture and join other parts, and are secured with the mating of screw threads.

Contents

Key features of a waveguide join are; whether or not it is air-tight, allowing the waveguide to be pressurized, and whether it is a contact or a choke connection. This leads to three sorts of flange for each size of rectangular waveguide.

For rectangular waveguides there exist a number of competing standard flanges which are not entirely mutually compatible. [2] Standard flange designs also exist for double-ridge, reduced-height, square and circular waveguides.

Pressurization

The atmosphere within waveguide assemblies is often pressurized, either to prevent the ingress of moisture, or to raise the breakdown voltage in the guide and hence increase the power that it can carry. Pressurization requires that all joints in the waveguide be airtight. This is usually achieved by means of a rubber O-ring seated in a groove in the face of at least one of flanges forming each join. Gasket, gasket/cover or pressurizable flanges (such as that on the right of figure 2), are identifiable by the single circular groove which accommodates the O-ring. It is only necessary for one of the flanges in each pressurizable connection to be of this type; the other may have a plain flat face (like that in figure 1). This ungrooved type is known as a cover, plain or unpressurizable flange.

Paschens law

Paschen's law is an equation that gives the breakdown voltage, that is, the voltage necessary to start a discharge or electric arc, between two electrodes in a gas as a function of pressure and gap length. It is named after Friedrich Paschen who discovered it empirically in 1889.

Breakdown voltage

The breakdown voltage of an insulator is the minimum voltage that causes a portion of an insulator to become electrically conductive.

O-ring mechanical, toroid gasket that seals an interface

An O-ring, also known as a packing, or a toric joint, is a mechanical gasket in the shape of a torus; it is a loop of elastomer with a round cross-section, designed to be seated in a groove and compressed during assembly between two or more parts, creating a seal at the interface.

It is also possible to form air-tight seal between a pair of otherwise unpressurizable flanges using a flat gasket made out of a special electrically conductive elastomer. Two plain cover flanges may be mated without such a gasket, but the connection is then not pressurizable.

Gasket type of mechanical seal

A gasket is a mechanical seal which fills the space between two or more mating surfaces, generally to prevent leakage from or into the joined objects while under compression.

Electrical continuity

Figure 2. A UG-1666/U (MIL-standard) choke flange (left), and matching gasket/cover flange (right). These flanges are aluminium and are socket-mounted onto aluminium WG18 (WR62) waveguide. Waveguide-choke-flange-UG-1666-U.jpg
Figure 2. A UG-1666/U (MIL-standard) choke flange (left), and matching gasket/cover flange (right). These flanges are aluminium and are socket-mounted onto aluminium WG18 (WR62) waveguide.

Electric current flows on the inside surface of the waveguides, and must cross the join between them if microwave power is to pass through the connection without reflection or loss.

Skin effect

Skin effect is the tendency of an alternating electric current (AC) to become distributed within a conductor such that the current density is largest near the surface of the conductor, and decreases with greater depths in the conductor. The electric current flows mainly at the "skin" of the conductor, between the outer surface and a level called the skin depth. The skin effect causes the effective resistance of the conductor to increase at higher frequencies where the skin depth is smaller, thus reducing the effective cross-section of the conductor. The skin effect is due to opposing eddy currents induced by the changing magnetic field resulting from the alternating current. At 60 Hz in copper, the skin depth is about 8.5 mm. At high frequencies the skin depth becomes much smaller. Increased AC resistance due to the skin effect can be mitigated by using specially woven litz wire. Because the interior of a large conductor carries so little of the current, tubular conductors such as pipe can be used to save weight and cost.

Reflections of signals on conducting lines

A signal travelling along an electrical transmission line will be partly, or wholly, reflected back in the opposite direction when the travelling signal encounters a discontinuity in the characteristic impedance of the line, or if the far end of the line is not terminated in its characteristic impedance. This can happen, for instance, if two lengths of dissimilar transmission lines are joined together.

Contact connection

A contact connection is formed by the union of any combination of gasket and cover flanges, and ideally creates a continuous inner surface from one waveguide to the other, with no crack at the join to interrupt the surface currents. The difficulty with this sort of connection is that any manufacturing imperfections or dirt or damage on the faces of the flanges will result in a crack. Arcing of the current across the crack will cause further damage, loss of power, and may give rise to arcing from one side of the guide to the other, thereby short circuiting it.

Electric arc electrical breakdown of a gas that produces an ongoing electrical discharge

An electric arc, or arc discharge, is an electrical breakdown of a gas that produces a prolonged electrical discharge. The current through a normally nonconductive medium such as air produces a plasma; the plasma may produce visible light. An arc discharge is characterized by a lower voltage than a glow discharge and relies on thermionic emission of electrons from the electrodes supporting the arc. An archaic term is voltaic arc, as used in the phrase "voltaic arc lamp".

Short circuit Electrical circuit, usually with very low or no impedance

A short circuit is an electrical circuit that allows a current to travel along an unintended path with no or a very low electrical impedance. This results in an excessive amount of current flowing into the circuit. The electrical opposite of a short circuit is an "open circuit", which is an infinite resistance between two nodes. It is common to misuse "short circuit" to describe any electrical malfunction, regardless of the actual problem.

Choke connection

Figure 3. E-plane cross-section of connected choke and gasket/cover waveguide flanges from figure 2. The gap between the flange faces has been exaggerated by a factor of four to make it clearly visible.
Legend:
a. waveguide tubing socket-mounted into...
b. choke flange and...
c. gasket/cover flange
d. gap between flange faces (width exaggerated by factor of 4)
e. point of contact of flange faces
f. short at bottom of choke ditch
g. O-ring gaskets to allow pressurization
The choke flange can also be mated with a plain cover flange and still form a pressurizable join Waveguide-choke-flange-cross-section.svg
Figure 3. E-plane cross-section of connected choke and gasket/cover waveguide flanges from figure 2. The gap between the flange faces has been exaggerated by a factor of four to make it clearly visible.
Legend:
a. waveguide tubing socket-mounted into...
b. choke flange and...
c. gasket/cover flange
d. gap between flange faces (width exaggerated by factor of 4)
e. point of contact of flange faces
f. short at bottom of choke ditch
g. O-ring gaskets to allow pressurization
The choke flange can also be mated with a plain cover flange and still form a pressurizable join

A choke connection is formed by mating one choke flange and one cover (or gasket/cover) flange. The central region of the choke flange face is very slightly recessed so that it does not touch the face of the cover flange, but is separated from it by a narrow gap. The recessed region is bounded by a deep choke trench (or ditch or groove) cut into the face of the flange. Choke flanges are only used with rectangular waveguide, and are invariably pressurizable, having a gasket groove encircling [3] the choke ditch. The presence of these two concentric circular grooves makes choke flanges easily recognizable. The left-hand flange in figure 2 is a choke flange.

It is considered wrong to join together two choke flanges; the resulting gap between the flange faces is twice that intended, and the effect is similar to that of having two joins in the guide rather than one. In the absence of unpressurizable choke flanges, all flanges fall into one of three categories: choke, gasket/cover and cover.

An E-plane cross section of an assembled choke connection is shown in figure 3. This is the plane cutting each of the broad walls of the waveguide along its centre-line, which is where the longitudinal surface currents—those that must cross the join—are at their strongest. The choke ditch and the gap between the flange faces together form a somewhat convoluted side-branch to the path of the main guide. This side branch is designed to present a low input impedance where it meets the broad walls of the waveguide, [3] so that the surface currents there are not obstructed by the gap, but instead flow onto and off of the separated faces of the flanges. Conversely, on the outer edge of the choke ditch, at the point where the two flanges come into physical contact, the ditch presents a high series impedance. The current through the contact point is thus reduced to a small value, [3] and the danger of arcing across any crack between the flanges is likewise reduced.

Theory

At the operational frequency of the choke flange, the depth of the ditch is approximately one quarter [3] of a wavelength. This is somewhat longer than a quarter of the free-space wavelength, since the electric field also varies in going around the ditch, having two changes of polarity, or one complete wave in the circumference. The ditch thus constitutes a quarter-wave resonant short-circuit stub, and has a high (ideally infinite) input impedance at its mouth. This high impedance is in series with the metal-to-metal connection between the flanges, and minimizes the current across it. The distance from the main waveguide through the gap to the ditch is likewise one quarter [3] of a wavelength in the E-plane. The gap thus forms a quarter-wave transformer, transforming the high impedance at the top of the ditch to a low (ideally zero) impedance at the broad wall of the waveguide.

Figure 4. Plastic caps over disconnected flanges prevent dirt and moisture entering the waveguide, in addition to protecting the face of the flange from damage. Protective-plastic-cap-on-waveguide-flange.jpg
Figure 4. Plastic caps over disconnected flanges prevent dirt and moisture entering the waveguide, in addition to protecting the face of the flange from damage.

Frequency dependence

Because the working of a choke connection depends on the wavelength, its impedance can be zero at at most one frequency within the operating band of the waveguide. However, by making the gap extremely narrow, [1] [3] and the choke ditch relatively wide, [1] the input impedance can be kept small over a broad frequency band. For gap and ditch widths in a fixed proportion, the connection input impedance is approximately proportional to either width (doubling both widths is like having two connections in series). Increasing just the ditch width, increases its input impedance proportionately, and to a some extent decreases the transformed impedance, though the effect is limited when the gap-length is not exactly one quarter wavelength. The MIL-spec choke flanges have a gap width of between 2% and 3% of the waveguide height (the smaller inner dimension of the guide), which for WR28 waveguide (WG22) amounts to a gap of just 3 thousandths of an inch. The choke ditch in these flanges is some 8 times wider (around 20% of the waveguide height), although the proportions vary considerably, as the width-to-height ratio of the standard mid-size guides deviates from 2:1. MIL-Spec choke flanges are intended for use over the full recommended operational frequency band of the waveguide [5] [6] [7] [8] [9] (that is roughly from 1.3 to 1.9 time the guide cutoff).

History

Claimants to the invention of the choke connection include Norman Ramsey [10] [11] 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. [12] The invention was not patented. [10]

Performance

Choke connections can achieve a VSWR of 1.01 [13] (a return of -46 dB) over a useful bandwidth, and eliminate the danger of arcing [13] at the join. Nevertheless, better performance is possible with a carefully made contact-connection between undamaged plain flanges. [13]

Attachment to waveguide

Figure 5. RCSC 5985-99-083-0003 choke flange through-mounted on WG16 (WR90) waveguide. Machining down the end of the waveguide tube has left a clear pattern across the recessed face and the end of the tube. The flats on either side of the flange are to allow a threaded collar to be manoeuvred over it, while the notches at the top and bottom are for alignment. The O-ring for pressurization is in place. Waveguide-choke-flange-through-mounted.jpg
Figure 5. RCSC 5985-99-083-0003 choke flange through-mounted on WG16 (WR90) waveguide. Machining down the end of the waveguide tube has left a clear pattern across the recessed face and the end of the tube. The flats on either side of the flange are to allow a threaded collar to be manoeuvred over it, while the notches at the top and bottom are for alignment. The O-ring for pressurization is in place.

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. [14] 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. [5] [6] [7] [8] [9]

Standards

Figure 6. Non-standard quick-disconnect (threaded collar) flanges on WR102 guide Waveguide-flange-with-threaded-collar.jpg
Figure 6. Non-standard quick-disconnect (threaded collar) flanges on WR102 guide

MIL-Spec

MIL-DTL-3922 is a United States Military Standard giving detailed descriptions of choke, gasket/cover and cover flanges for rectangular waveguide. MIL_DTL-39000/3 describes flanges for double-ridge [15] waveguide, and formerly [16] [17] also for single-ridge guide.

MIL-Spec flanges have designations of the form UG-xxxx/U where the x's represent a variable-length catalogue number, not in itself containing any information about the flange. [2]

These standards are works of the U.S. government, and are freely available online from the U.S. Defense Logistics Agency.

IEC

International Electrotechnical Commission (IEC) standard IEC 60154 describes flanges for square [18] and circular waveguides, [19] as well as for what it refers to as flat, [20] medium-flat, [21] and ordinary [22] rectangular guides.

IEC flanges are identified by an alphanumeric code consisting of; the letter U, P or C for Unpressurizable [2] (plain cover), Pressurizable [2] (with a gasket groove) and Choke [2] (with both choke gasket grooves); a second letter, indicating the shape and other details of the flange and finally the IEC identifier for the waveguide. For standard rectangular waveguide the second letter is A to E, where A and C are round flanges, B is square and D and E are rectangular. So for example UBR220 is a square plain cover flange for R220 waveguide (that is, for WG20, WR42), PDR84 is a rectangular gasket flange for R84 waveguide (WG15, WR112) and CAR70 is a round choke flange for R70 waveguide (WG14, WR137).

The IEC standard is endorsed by a number of European standards organizations, such as the British Standards Institution.

EIA

The Electronic Industries Alliance (EIA) is the body that defined the WR designations for standard rectangular waveguides. EIA flanges are designated CMR (for Connector, Miniature, Rectangular waveguide [2] ) or CPR (Connector, Pressurizable, Rectangular waveguide [2] ) followed by the EIA number (WR number) for the relevant waveguide. So for example, CPR112 is a gasket flange for waveguide WR112 (WG15).

RCSC

The Radio Components Standardization Committee (RCSC) is the body that originated the WG designations for standard rectangular waveguides. It also defined standard choke and cover flanges with identifiers of the form 5985-99-xxx-xxxx where the x's represent a catalogue number, not in itself containing any information about the flange. [2]

Related Research Articles

Flange external or internal ridge, or rim which provides strength

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Coaxial cable A type of electrical cable with an inner conductor surrounded by concentric insulating layer and conducting shield

Coaxial cable, or coax is a type of electrical cable that has an inner conductor surrounded by a tubular insulating layer, surrounded by a tubular conducting shield. Many coaxial cables also have an insulating outer sheath or jacket. The term coaxial comes from the inner conductor and the outer shield sharing a geometric axis. Coaxial cable was invented by English physicist, engineer, and mathematician Oliver Heaviside, who patented the design in 1880.

BNC connector type of electronic connector

The BNC connector is a miniature quick connect/disconnect radio frequency connector used for coaxial cable. The interface specifications for the BNC and many other connectors are referenced in MIL-STD-348. It features two bayonet lugs on the female connector; mating is fully achieved with a quarter turn of the coupling nut. BNC connectors are used with miniature-to-subminiature coaxial cable in radio, television, and other radio-frequency electronic equipment, test instruments, and video signals. The BNC was commonly used for early computer networks, including ARCnet, the IBM PC Network, and the 10BASE2 variant of Ethernet. BNC connectors are made to match the characteristic impedance of cable at either 50 ohms or 75 ohms. They are usually applied for frequencies below 4 GHz and voltages below 500 volts.

N connector

The N connector is a threaded, weatherproof, medium-size RF connector used to join coaxial cables. It was one of the first connectors capable of carrying microwave-frequency signals, and was invented in the 1940s by Paul Neill of Bell Labs, after whom the connector is named.

F connector coaxial RF connector used for television and cable Internet

The F connector is a coaxial RF connector commonly used for "over the air" terrestrial television, cable television and universally for satellite television and cable modems, usually with RG-6/U cable or, in older installations, with RG-59/U cable.

SMA connector

SMA connectors are semi-precision coaxial RF connectors developed in the 1960s as a minimal connector interface for coaxial cable with a screw-type coupling mechanism. The connector has a 50 Ω impedance. SMA is designed for use from DC to 18 GHz, and is most commonly used in microwave systems, hand-held radio and mobile telephone antennas, and more recently with WiFi antenna systems and USB software-defined radio dongles. It is also commonly used in radio astronomy, particularly at higher frequencies.

AC power plugs and sockets connect electric equipment to the alternating current (AC) power supply in buildings and at other sites. Electrical plugs and sockets differ from one another in voltage and current rating, shape, size, and connector type. Different standard systems of plugs and sockets are used around the world.

IEC 60309 Standard for industrial and multi-phase sockets in Europe

IEC 60309 is an international standard from the International Electrotechnical Commission (IEC) for "plugs, socket-outlets and couplers for industrial purposes". The maximum voltage allowed by the standard is 1000 V DC or AC; the maximum current, 800 A; and the maximum frequency, 500 Hz. The ambient temperature range is −25 °C to 40 °C.

Horn antenna

A horn antenna or microwave horn is an antenna that consists of a flaring metal waveguide shaped like a horn to direct radio waves in a beam. Horns are widely used as antennas at UHF and microwave frequencies, above 300 MHz. They are used as feed antennas for larger antenna structures such as parabolic antennas, as standard calibration antennas to measure the gain of other antennas, and as directive antennas for such devices as radar guns, automatic door openers, and microwave radiometers. Their advantages are moderate directivity, low standing wave ratio (SWR), broad bandwidth, and simple construction and adjustment.

A vacuum flange is a flange at the end of a tube used to connect vacuum chambers, tubing and vacuum pumps to each other. Vacuum flanges are used for scientific and industrial applications to allow various pieces of equipment to interact via physical connections and for vacuum maintenance, monitoring, and manipulation from outside a vacuum's chamber. Several flange standards exist with differences in ultimate attainable pressure, size, and ease of attachment.

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EIA RF Connectors are used to connect two items of high power radio frequency rigid or semi-rigid (flexline) coaxial transmission line. Typically these are only required in very high power transmitting installations where the feedline diameters may be several inches. One side of the connection is denoted as a male connection, or bullet, while the other side is denoted as the female connection, or cup. The EIA under the Electronic Components Industry Association, are responsible for a number of standard imperial connector sizes.

U.S. Military connector specifications

Electrical or fiber-optic connectors used by U.S. Department of Defense were originally developed in the 1930s for severe aeronautical and tactical service applications, and the Type "AN" (Army-Navy) series set the standard for modern military circular connectors. These connectors, and their evolutionary derivatives, are often called Military Standard, "MIL-STD", or (informally) "MIL-SPEC" or sometimes "MS" connectors. They are now used in aerospace, industrial, marine, and even automotive commercial applications.

Waveguide filter electronic filter that is constructed with waveguide technology

A waveguide filter is an electronic filter that is constructed with waveguide technology. Waveguides are hollow metal tubes inside which an electromagnetic wave may be transmitted. Filters are devices used to allow signals at some frequencies to pass, while others are rejected. Filters are a basic component of electronic engineering designs and have numerous applications. These include selection of signals and limitation of noise. Waveguide filters are most useful in the microwave band of frequencies, where they are a convenient size and have low loss. Examples of microwave filter use are found in satellite communications, telephone networks, and television broadcasting.

Waffle-iron filter

A waffle-iron filter is a type of waveguide filter used at microwave frequencies for signal filtering. It is a variation of the corrugated-waveguide filter but with longitudinal slots cut through the corrugations resulting in an internal structure that has the appearance of a waffle-iron.

Cam and groove

A cam and groove coupling, also called a camlock fitting, is a form of hose coupling. This kind of coupling is popular because it is a simple and reliable means of connecting and disconnecting hoses quickly and without tools.

Planar transmission line Transmission lines with flat ribbon-like conducting or dielectric lines

Planar transmission lines are transmission lines with conductors, or in some cases dielectric (insulating) strips, that are flat, ribbon-shaped lines. They are used to interconnect components on printed circuits and integrated circuits working at microwave frequencies because the planar type fits in well with the manufacturing methods for these components. Transmission lines are more than simply interconnections. With simple interconnections, the propagation of the electromagnetic wave along the wire is fast enough to be considered instantaneous, and the voltages at each end of the wire can be considered identical. If the wire is longer than a large fraction of a wavelength, these assumptions are no longer true and transmission line theory must be used instead. With transmission lines, the geometry of the line is precisely controlled so that its electrical behaviour is highly predictable. At lower frequencies, these considerations are only necessary for the cables connecting different pieces of equipment, but at microwave frequencies the distance at which transmission line theory becomes necessary is measured in millimetres. Hence, transmission lines are needed within circuits.

ASME is a non-profit organization that continues to develop and maintains nearly 600 codes and standards in a wide range of disciplines. Some of which includes the Boiler and Pressure Vessel Code (BPVC), Elevators and Escalators, Piping and Pipelines, Bioprocessing Equipment (BPE), Nuclear Facility Applications (NQA), Process Performance Test Codes (PTC), and Valves, Flanges, Fittings and Gaskets (B16).

References

  1. 1 2 3 4 5 Harvey, A. F. (July 1955). "Standard waveguides and couplings for microwave equipment". Proceedings of the IEE - Part B: Radio and Electronic Engineering. 102 (4): 493–499. doi:10.1049/pi-b-1.1955.0095.
  2. 1 2 3 4 5 6 7 8 Brady, M. Michael (July 1965). "Rectangular Waveguide Flange Nomenclature (Correspondence)". IEEE Transactions on Microwave Theory and Techniques. 13 (4): 469–471. doi:10.1109/tmtt.1965.1126031. ISSN   0018-9480.
  3. 1 2 3 4 5 6 Bagad, Vilas S. (2007). Microwave and Radar Engineering. Technical Publications Pune. ISBN   81-8431-121-4.
  4. Richard Feynman; Robert Leighton; Matthew Sands. "24 Waveguides". The Feynman Lectures on Physics. 2. Addison-Wesley. ISBN   0-201-02117-X.
  5. 1 2 U.S. Department of Defense (8 January 2010), MIL-DTL-3922/59F: Flanges, Waveguide (Choke) (Square, 4 Hole) (PDF)[for WG:15,16,17,18,20,22—WR:112,90,75,62,42,28]
  6. 1 2 U.S. Department of Defense (27 May 2008), MIL-DTL-3922/60C: Flanges, Waveguide (Choke) (Round, 6 Hole) (PDF)[for WG14—WR137]
  7. 1 2 U.S. Department of Defense (8 January 2010), MIL-DTL-3922/61E: Flanges, Waveguide (Choke) (Round, 8 Hole) (PDF)[for WG10—WR284]
  8. 1 2 U.S. Department of Defense (8 January 2010), MIL-DTL-3922/62D: Flanges, Waveguide (Choke) (Round, 8 Hole (2 Holes Centered Horizontally, 2 Holes Centered Vertically)) (PDF)[for WG12—WR187]
  9. 1 2 U.S. Department of Defense (3 February 1975), MIL-F-3922/69: Flanges, Waveguide (Choke) (Square, 4 Hole) (PDF)[for WG19—WR51 and WR102]
  10. 1 2 Andrew Goldstein (9 May 1995), Norman Ramsey, an oral history conducted in 1995, IEEE History Center, New Brunswick, NJ, USA
  11. John Bryant (20 June 1991), Norman F. Ramsey, an oral history conducted in 1991, IEEE History Center, New Brunswick, NJ, USA
  12. "Winfield W. Salisbury - Writings and History". Southwest Museum of Engineering, Communications and Computation.
  13. 1 2 3 Baden Fuller, A. J. (1969). Microwaves (1 ed.). Pergamon Press. ISBN   0-08-006616-X.
  14. Davis, Joseph R. (2001). Copper and copper alloys. ASM International. ISBN   0-87170-726-8.
  15. U.S. Department of Defense (20 January 2009), MIL-F-39000/3C: Flanges, Waveguide, Double Ridge, Socket Mount (Bandwidth Ratio 2.4:1) (PDF)
  16. U.S. Department of Defense (2 July 2003), MIL-F-39000/1B Notice 2: Flanges, Waveguide, Single Ridge, Socket Mount (Bandwidth Ratio 2.4:1) (Cancellation Notice) (PDF)
  17. U.S. Department of Defense (2 July 2003), MIL-F-39000/2B Notice 2: Flanges, Waveguide, Single Ridge, Socket Mount (Bandwidth Ratio 3.6:1) (Cancellation Notice) (PDF)
  18. IEC (1974-01-01), IEC 60154-7 Flanges for Waveguides Part 7: Relevant specifications for flanges for square waveguides (1 ed.)[Flange type K]
  19. IEC (1969-01-01), IEC 60154-4 Flanges for Waveguides Part 4: Relevant specifications for flanges for circular waveguides (1 ed.)[Flange type J]
  20. IEC (1982-01-01), IEC 60154-3 Flanges for Waveguides Part 3: Relevant specifications for flanges for flat rectangular waveguides (2 ed.)[Flange type G]
  21. IEC (1983-01-01), IEC 60154-6 Flanges for Waveguides Part 6: Relevant specifications for flanges for medium flat rectangular waveguides (1 ed.)[Flange types L, N]
  22. IEC (1980-01-01), IEC 60154-2 Flanges for Waveguides Part 2: Relevant specifications for flanges for ordinary rectangular waveguides (2 ed.)[Flange types A, B, C, D, E]