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.

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