Finding Just The Right Waveguide

Waveguide is still very much the transmission line of choice in a wide variety of applications, from commercial communications to military systems on land, at sea, and in the air. Waveguide transmission lines and components are also used in most deep-space applications, including on lunar programs and on the Space Shuttle.

Screen Shot 2013-09-10 at 7.50.54 AMFinding the right type of waveguide for an application, from 1 to 50 GHz, whether based on electrical or mechanical requirements, has never been easier, thanks to a unique rigid waveguide slide rule available on the website for Microwave Development Laboratories (MDL, www.mdllab.com). The slide rule can be found on a webpage entitled simply “Rigid waveguide data.”

The left-hand side of the screen provides 23 boxes containing different rigid waveguide sizes by their Electronic Industries’ Association (EIA) designations, starting from WR229 through WR10. The right-hand side of the screen shows the slide rule for all the key specifications of a selected rigid waveguide size.

But these are just the beginning of the massive amount of data that is made available for each choice of different rigid waveguide size. The slide rule offers a recommended EIA frequency range in GHz for the selected rigid waveguide size, in terms of minimum and maximum operating frequencies, but also frequency (in GHz) and wavelength (in cm) for the waveguide’s TE10 cutoff mode. In the case of the WR90 example, a recommended operating frequency range of 8.20 to 12.40 GHz is listed, with a cutoff frequency of 6.557 GHz and cutoff wavelength of 4.572 cm.

The slide rule also shows the power ratings for a selected waveguide side, with minimum power rating of 0.33 MW and maximum rating of 0.47 MW for the WR90 example. In addition, the slide rule lists some fascinating details on a selected waveguide size, based on the type of materials with which the rigid waveguide section is constructed. For example, the slide rule shows theoretical minimum and maximum attenuation for waveguide at a selected size, as a function of different materials for the waveguide, such as copper, brass, and aluminum. Attenuation levels are shown in values of dB per 100 ft. of waveguide across the operating frequency range.

On the mechanical side, the handy slide rule shows inside and output dimensions for the waveguide size selected, in terms of width, height, and even dimensional tolerances. For the WR90 waveguide, for example, it shows inside width and height of 0.900 and 0.400 in., with outside width and height of 1.000 and 0.500 in., and dimensional tolerance of ±0.004 in. The slide rule even provides a dimension for a selected waveguide’s wall thickness, a value of 0.00 in. for the WR90 example.

Specifying a waveguide product

To simplify specifying a waveguide product, the slide rule shows different flange types in terms of material selection, such as brass or aluminum, and also shows the pertinent MDL model number for the different flange choice. The slide rule changes values instantly when another waveguide size is selected, allowing users to quickly browse through different waveguide sizes and designations to find the transmission line that is suitable for their application.

In addition to the personal computer (PC) version of the rigid waveguide slide rule, the application is also available for free download from the MDL website for use on mobile devices. Admittedly, peering at the waveguide sizes and specifications on the smaller screen of a mobile device is not the same satisfying experience as browsing through MDL’s waveguide choices on the screen of a PC. But having access to the application on a mobile device may prove to be handy for in-the-field specification of high-performance rigid waveguide transmission lines.

eTools for Diverse Applications

Screen Shot 2013-09-10 at 7.56.59 AMThe rigid waveguide slide rule is just one of the handy tools available on the “tool page” of MDL’s website, at http://www.mdllab.com/tools.php. The tool page also provides easy access to a large number of computer-aided-design (CAD) drawings (by means of password access) as well as an electronic version of the firm’s 133-page catalog, with electronic pages that can be flipped with the click of a mouse button. This catalog application shows all the details of a full-sized, printed catalog, but on the convenience of a computer screen, with the capability to print out selected pages or ranges of pages as needed. The electronic catalog itself includes tools which simplify enlarging or reducing the size of displayed pages and tools which show currently viewed pages in context with previous pages and pages to come, for quick scanning when in search of a particular solution. Considering the diversity of applications for rigid waveguide, these tools can help a wide range of users find the right waveguide for their jobs and help to find them quickly.

Slide Rule app for mobile devices

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Back in May, we announced the launch of our redesigned website, http://mdllab.com. Along with visual enhancements, the site also offers a comprehensive search tool and online Slide Rule. We are excited to announce that this Slide Rule is now available for download to your mobile device!

Now available for download to iOS and Android devices, the Slide Rule mobile app enables design engineers to input their own waveguide rectangular (WR) designations to quickly perform complex conversions and determine operating parameters. By entering WR dimensions, a user can generate a range of material specifications including recommended operating frequency rate (GHz), flange type, and waveguide dimensions (in.).

Have questions about calculations or how to purchase components for your design application? Contact an MDL representative directly from the app, or tweet to us at @MDLlab.

To download the free rigid waveguide slide rule mobile app, visit our tools page.

The Wonders of Waveguide

Waveguide is a technology uniquely synonymous with high-frequency RF/microwave electronics. Described simply, it is a form of hollow conductive metal tube that carries energy from one point to another. For RF/microwave use, it handles electromagnetic (EM) energy; forms of waveguide have also been used to carry acoustical and optical energy. Waveguide can be used to fashion a wide range of RF/microwave and even millimeter-wave components, including transmission lines, couplers, power dividers, and filters.

For RF, microwave, and millimeter-wave applications, waveguide can be constructed of flexible and rigid conductive materials, and can be rectangular, elliptical, and circular in shape. In contrast to coaxial cables, where signals pass through the cables and electric and magnetic fields propagate through the inside and around the outside of the cables, propagating electric and magnetic fields in waveguide are confined to the space within the conductive guides, so power is not lost due to radiation as in coaxial cables. Waveguide are normally filled with air, which serves as the dielectric material for the propagation of energy, so dielectric losses are also minimal. Some transmitted power is lost as heat within the walls of the metal waveguide, but this loss is minimal compared to losses from coaxial cables, such as insertion loss and radiation loss.

The most common forms of waveguide for EM applications are rectangular waveguide, denoted by a model number such as WR62 which represents the shape and a specific guide size, double ridge rectangular waveguide, with sizes identified by the WRD letters and a number combination, such as WRD650, and circular waveguide, with sizes identified by the WRC letter prefix and a number for the relative size of the guide. Circular waveguide are often used in applications requiring rotation, such as for a rotary joint in a radar antenna, although the greater number of applications for low-loss waveguide in commercial, industrial, and military systems call for rectangular or double ridge rectangular waveguide. The use of ridges in the double ridge rectangular waveguide configuration helps boost bandwidth albeit with somewhat higher attenuation and lower power-handling capability than a comparable size of rectangular waveguide.

The lower-frequency limit, or cutoff frequency, of a waveguide component is determined by the physical dimensions of the waveguide. Signal energy below the cutoff frequency will be significantly attenuated in a short distance by a given waveguide structure. (It should be noted that the cutoff frequency of a coaxial cable refers to the other frequency direction, or its highest frequency of operation.) As the required operating frequencies for different waveguide structures increases, the dimensions of the waveguide diminish. A waveguide transmission line can propagate energy in a number of different modes, including in transverse electric (TE), transverse magnetic (TM), and transverse electromagnetic (TEM) modes. To differentiate, a waveguide operating in TE mode has no electric field in the direction of propagation; a waveguide in TM mode, has no magnetic field in the direction of propagation; and a waveguide in TEM mode has no electric or magnetic fields in the direction of propagation. For a particular waveguide component or transmission line, the dominant mode is that mode which exhibits the lowest cutoff frequency; for rectangular waveguide, this is the TE mode. Waveguide are usually designed and fabricated to support only one mode.

As an example, WRD650 is a size of double ridge rectangular waveguide with outer width and height dimensions of 0.720 x 0.421 in. Typically formed of aluminum, brass, and copper, this particular waveguide has an operating frequency range of 6.50 to 18.00 GHz. A similar rectangular waveguide size, WR62, has outside width and height dimensions of 0.702 x 0.39 in. and is usually made of copper and aluminum. It has an operating frequency range of 12.4 to 18.0 GHz. A circular waveguide size for TE-mode operation from 13.2 to 18.9 GHz, designated as WRC621D1, has an inside diameter of 1.281 in. and an outside diameter of 1.441 in. At higher, millimeter-wave frequencies, where metals tend to suffer higher losses, dielectric rod and slab waveguide are typically used to minimize signal losses.

A flexible version of rectangular waveguide, with a size designation of WR62 and typically fabricated from brass, will also provide low-loss performance from 12.4 to 18.0 GHz, although trading some electrical performance for mechanical flexibility compared to the standard WR62 waveguide. Similarly, a flexible version of WRD650 double ridge rectangular waveguide will also cover a frequency range of 6.50 to 18.00 GHz, although with different insertion loss, power-handling capability, and other characteristics than the standard double ridge rectangular waveguide for that size.

To learn more about waveguides, follow MDL on Twitter!

Reflections on IMS 2013

Our team is back from a successful exhibition at IMS 2013 in Seattle, WA.  Thanks to everyone who visited our booth throughout the show!

MDL IMS 2013We had several exciting updates to share at this year’s International Microwave Symposium including our newly redesigned website and Road to IMS sponsorship.  Visitors to booth 1430 could interact with our sales team, get their road maps stamped for chances to win prizes, and take a quiz about MDL history and products.  Didn’t have a chance to take the quiz at the show?  There’s still time to enter for a chance to win an iPad Mini.

Visitors to the booth could view several product offerings from MDL including high frequency waveguide and coaxial rotary joints, both single channel and dual channel.  IMS attendees were particularly interested in the broadband coaxial single channel rotary joint from MDL as well as all cast waveguide components.

The International Microwave Symposium is an exciting opportunity to share new technologies, connect with industry professionals, and catch up with old friends.  Thanks for making IMS 2013 a success.  See you next year in Tampa, FL!

For more MDL news and updates, connect with us on Twitter, LinkedIN and here on our blog.

Welcome to the MDL Lab Blog

Thanks for joining the MDL Lab community! Here we’ll cover the waveguide and microwave technologies that are impacting our industry. Take a tour around our newly redesigned website, and visit us on Twitter and LinkedIN.

ImageFrom military radar systems to satellite communications, this blog will discuss the unique challenges engineers face within the microwave and RF fields. We will also examine current and emerging applications that rely upon waveguide technology including UAVs and advanced medical equipment.

Looking for resources to help you design your next project? Check out our new Slide Rule app to input your own data and find configurations quickly and easily. Have questions? Speak with an experienced MDL engineering representative in real time.

Visit our new interactive catalogue with enhanced search features to find MDL products and custom designs in just a few clicks.

Have a question or suggestion for a future blog? Share it with us in our Comments section. Stay connected to MDL here on our blog, and on Twitter and LinkedIN!