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September 26, 2016

## RectangularWaveguideDimensions

Our other info on waveguide can be found on these pages:

Waveguide primer (main waveguide page)

Waveguide mathematics

Waveguide construction

Waveguide loss calculation

Waveguide Components (on everything RF)

For June 2016: We deleted the waveguide table that existed on this page since the beinging of Microwaves101, because it was not as comprehensive as Uli's list (which is a pdf document in the link below).  We've also added a new section on manufacturing tolerances.

Here's two contributions from Spinner GmbH, on waveguide cross sections (including ordinary, reduced height, circular and double-ridged) and waveguide flange dimensions, both in pdf documents. These are the most comprehensive lists on the world-wide web.  Thanks, Uli and Simone!

-          TD-00036 Issue K: CROSS REFERENCE FOR HOLLOW METALLIC WAVEGUIDES                    “Uli’s Waveguide List”

-          TD-00077 Issue C: FLANGES FOR ORDINARY RECTANGULAR WAVEGUIDES                        “Simone’s Flange List”  (Revised November 2015)

Both of these and our original waveguide table (we consider it obsolete) are also available in our download area

The inner cross-section of a standard rectangular waveguide has a 2:1 aspect ratio in most cases (not exactly true for WR-90 and there are plenty of other exceptions). That is, the broad wall is twice the dimension of the narrow wall, or very nearly so. Rectangular waveguides support E-M waves only over a certain frequency band, depending on the cross-sectional dimensions. The bigger the size of the waveguide, the lower the lower the working frequency of the waveguide. Waveguides are specified in WR numbers. WR stands for "rectangular waveguide" except the military long ago decided that all adjectives must follow nouns for some reason.

### Waveguide dimension rule of thumb

How do you know what WR number of a waveguide is, just by looking at it? The number, in most cases, is simply the dimension of the the inside broad wall in mils, divided by 10. Thus the waveguide depicted below is WR-62 (if you look closely at the caliper it indicates 620 mils), which is used in Ku-band.

## Effects of manufacturing tolerances

A good reference on this topic is "Mismatch caused by Waveguide Tolerances, Corner Radii and Flange Misalignment", by A. R. Kerr at NRAO, revised January 2011, 2010.  Using EM tools, the author provides a comprehensive study that will save you a lot of time. Cases include a and b wall dimensional tolerances, corner radii, linear flange misalignments in both axes, and angular misalignment. Say you wanted 40 dB return loss or better, from any one of these effects.  Here's advice we gleaned from this resource:

• Tolerance on the linear dimensions should be 0.5%
• Corner radii should be less than 10% of the broad wall dimension
• Linear misalignment should be less than 3%
• Rotation should be less than 6 degrees

We can't comment on how combinations of tolerance add up, except that reducing misalignment is exactly why alignment pins are used in flanges.

This is an over simplification of the data reported.  We will post the entire paper as soon as we get permission from the author.  Meanwhile, If you want a copy of the report, just google the title...

Author: Unknown Editor