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Waveguide sizes

WAVEGUIDE SIZES for MICROWAVE AMATEUR RADIO

Retangular Waveguide

Preface by Dick Knadle, K2RIW, enriched by SW3ORA

The calculated absolute minimum cut-off frequencies are where the WG loss goes to almost infinity, as you approach that frequency, from the high side. WG is the world's best high pass filter. The added data is shown inside a parenthesis.

The calculation assumes that the guide has the exact inside dimension of the WG number. Also, if you double the parenthesis (cut-off) frequency, you will know the absolute maximum WG frequency; above that frequency the next higher mode is possible to propagate. Naturally, the calculated absolute max or min frequencies include no guard band; but with care, we amateurs should be able to use frequencies that are almost at these numbers, in a pinch.

The low freq min occurs when the guide max dimension is 1/2 wavelength or greater (TE10 mode possible). The next higher mode, in rectangular guide, occurs when either the max guide dimension approaches 1.0 wavelength or greater (TE20 mode possible) or the guide min dimension approaches 1/2 wavelength or greater (TE01 mode possible). "Flat Guide" (less than half height guide) is useful to suppress the TE01 mode or to form a lower impedance match.

Also, I feel that we shouldn't be too afraid of the next higher mode. In wide bandwidth commercial/military operations it is troublesome because the dual mode signals can beat against each other and create insertion loss ripple versus swept frequencies (the defferent modes have different propagation constants). However, we usually use the WG at a fixed frequency where we can tune the system for optimum response of the dual modes. The net benefit is considerably lower WG loss when "oversized" WG is being used.

Double ridged WG uses the extra capacitance of the ridges to both lower the cut-off frequency (for the same max guide dimension) and to increase the WG bandwidth. Therefore, in a pinch, we could add ridge material to a short piece of WG as a way of using it at lower frequencies. Even placing a piece of low loss dielectric material down the center of a WG can have this effect.

There are also circular waveguides. The advantages of round WG are: lower loss than rectangular (of the same dimension); it supports circular polarization; and we can buy it at a Home Depot Store. The disadvantage is round WG has a smaller frequency range between the max and min frequencies. But, since we usually use only a fixed frequency, that usually is no problem. Also, round WG types often make a superior feed horn for illuminating a dish.

 

Background by Tom Williams, WA1MBA:

One of the definitions of a waveguide is that it is a transmission line with only one conductor. It is possible to construct waveguides with two conductors, but such systems will support modes other than waveguide modes of transmission. Free space transmission is TEM, or Transverse Electro-Magentic. This is also the type of propogation supported in multiple conductor transmission lines such as coaxial and twin-lead. Waveguides do not normally support TEM, but instead support TE and TM modes. There are many modes, and they are numbered with two digits (actually, two numbers, and some very high mode numbers are used in some applications where very high power has to be transmitted). Some mode numbers don't exist in some types of waveguides. As Dick mentioned, the most common rectangular mode is TE10, which is a fairly low loss mode and which is easily launched and permits waveguide twists and bends with very predictable results.

There are loads of waveguide sizes. And it is possible to use some waveguide sizes on ham bands that are outside of the normal operating frequency. The easiest way to tell a waveguide size is to bring along a ruler or a caliper when you go to a hamfest. I cut out an index card with the widths of the waveguide that I am interested in and jam it into the waveguide to decide what size/frequency it is.

The wide dimension of the inside of rectangular waveguide in hundredths of an inch is the WR designator. e.g. WR650 is 6.50 inches wide, WR90 is 0.90 inches wide, WR75 is 0.75 inches wide, WR5 (sometimes called WR05) is .05 in. The actual size of each waveguide is up to a few thousandths of an inch from this, so the WR-size is rounded to the nearest hundredth of an inch. With a few exceptions, waveguide is about half as high as it is wide. Sometimes you run into waveguide with ridges in the middle. These were developed for military use where very wide bandwidth is needed. The figures below do not apply to that kind of waveguide.

WR90 is probably the most commonly used waveguide for the 10.368 GHz band. Because waveguide can be used below the design frequency but above the cutoff, WR62 and WR75 can also be used on 10.368 GHz. WR62 might not look terribly close to cutoff for this band (cutoff around 9.52 GHz). Even so, some users of it have reported loss when sharp WR62 waveguide bends are in the line. Note that WR112 is still not "moding" (see K2RIW's discussion above) so it is OK for 10.368 GHz as well! That's a lot of waveguide that can be used for one of the most popular microwave bands - WR62, WR75, WR90 and WR112. If you don't mind a dB (in some cases under 1/2 dB) loss, you can use different sizes in one run. Experimenting will tell you how well a particular type of waveguide will work in your application.

There are various sources for waveguide dimensions and frequency ranges, including ARRL and RSGB manuals on microwaves & UHF.The cutoff frequencies are usually a little below 0.8 times the low frequency of the standard range. Two sources were used for cutoff information. The first is a practical guide, the last is a theoretical cutoff. The smallest flaw can increase the frequency of cutoff.

Another interesting parameter is loss. There are various formulae floating around, and they do not produce the same results. The "Wave Guide Handbook" is a half-century old, and various physics/electomagentic books provide formulae that disagree with all published values from the waveguide manufacturers. The best hint I have heard regarding these differences is that the math does not take into account surface imperfections on the order of skin depth. Because skin depth gets very very small at EHF, the difference between calculated and measured loss in the smaller waveguides becomes significant. Fortunately, some manufacturers measure actual waveguide rather than publish theoretical data. So, for now, I have used a manufacturer's set of data for millimeter wave (EHF) waveguides, and refer the reader to the Andrew page for the DC bands (WR42 and larger).  Eventually, I will fill in the loss values for the low frequency waveguide in this table. The next table has been edited by SW3ORA, with more updated data.

 

 

EIA designation
(Standard US)
and /RG number

RCSC Designation
(Standard UK)

Band

Inside Dimensions
inches

Inside Dimensions A mm Inside Dimensions B mm

Outside Dimensions
inches (typ)

Standard Freq Range, GHz

Low Cutoff Freq GHz,
Source #1, (Source #2)

High Limit Freq GHz

Loss per foot
Low end - High end
of waveguide band

Power Handling
Low to High freq
MW=Megawatts, kW=Kilowatts

WR2300

WG 00

 

  23.000, 11.500

  584.200   292.100  0.32 to 0.49

0.257

0.513

   

WR2100

WG 0

 

21.000, 10.500

533.400 266.700  0.35 to 0.53

0.281

0.562

   

WR1800

WG 1

 

18.000, 9.000

457.200 228.600  0.41 to 0.625

0.328

0.656

   

WR1500

WG 2

 

15.000, 7.500

381.000 190.500  0.49 to 0.75

0.393

0.787

   

WR1150

WG 3

 

11.500, 5.750

292.100 146.050  0.64 to 0.96

0.513

1.026

   

WR975

WG 4

 

9.750, 4.875

247.650 123.825  0.75 to 1.12

0.605

1.211

   

WR770

WG 5

 

7.700, 3.850

195.580 97.790  0.96 to 1.45

0.766

1.533

   
WR650 /RG69 WG 6   6.50, 3.25 165.100 82.550 6.66, 3.41 1.12 to 1.70 ? (0.91)

1.816

   
WR510 WG 7   5.10, 2.55 129.540 64.770  1.45 to 2.20 1.157

2.314

   
WR430 /RG104 WG 8   4.30, 2.15 109.220 54.610 4.46, 2.31 1.70 to 2.60 ? (1.37)

2.745

   
WR340 WG 9A   3.40, 1.70 86.360 43.180 3.56, 1.86 2.10 to 3.00 ? (1.6)

3.471

   
WR284 /RG48 WG 10   2.84, 1.34 72.136 34.036 3.00, 1.50 2.60 to 3.95 ? (2.08)

4.156

  2.2 - 3.2 MW
WR229 WG11A   2.29, 1.145 58.166 29.083 2.418, 1.273 3.30 to 4.90 ? (2.58)

5.154

  1.6 - 2.2 MW
WR187 /RG49 WG12   1.872, 0.872 47.549 22.149 2.000, 1.000 3.95 to 5.85 ? (3.16)

6.305

  1.4 - 2.0 MW
WR159 WG13   1.590, 0.795 40.386 20.193 1.718, 0.923 4.90 to 7.05 ? (3.71)

7.423

  0.79 - 1.0 MW
WR137 /RG50 WG14   1.372, 0.622 34.849 15.799 1.500, 0.750 5.85 to 8.20 ? (4.31)

8.603

  560 - 710 kW
WR112 /RG51 WG15  1.122, 0.497 28.499 12.624 1.250, 0.625 7.05 to 10.00 ? (5.27)

10.519

  350 - 460 kW
WR90 /RG52 WG16 X 0.900, 0.400 22.860 10.160 1.000, 0.500 8.20 to 12.4 ? (6.56)

13.114

  200 - 290 kW
WR75 WG17   0.750, 0.375 19.050 9.525 0.850, 0.475 10.0 to 15.0 ? (7.87)

15.737

  170 - 230 kW
WR62 /RG91 WG18 Ku 0.622, 0.311 15.799 7.899 0.702, 0.391 12.4 to 18.0 9.50 (9.52)

18.976

  120 - 160 kW
WR51 WG19   0.510, 0.255 12.954 6.477 0.590, 0.335 15.0 to 22.0 ? (11.57)

23.143

  80 - 107 kW
WR42 /RG53 WG20 K 0.420, 0.170 10.668 4.318 0.500, 0.250 18.0 to 26.5 14.08 (14.05)

28.102

0.26 - 0.20 dB 43 - 58 kW one source
WR34 WG21  0.340, 0.170 8.636 4.318  22.0 to 33.0 22.0

34.714

  
WR28 /RG96 WG22 Ka 0.280, 0.140 7.112 3.556 0.360, 0.220 26.5 to 40.0 21.08 (21.08)

42.153

0.44 - 0.30 dB 96 - 146 kW
WR22 /RG97 WG23 Q 0.224, 0.112 5.690 2.845 0.304, 0.192 33.0 to 50.0 26.34 (26.82)

52.691

0.62 - 0.42 dB 64 - 97 kW
WR19 WG24 U 0.188, 0.094 4.775 2.388 0.268, 0.174 40.0 to 60.0 31.36 (31.06, 30.69)

62.781

0.77 - 0.54 dB 48 - 70 kW
WR15 /RG98 WG 25 V 0.148, 0.074 3.759 1.880 0.228, 0.154 50.0 to 75.0 39.87 (39.90, 39.34)

79.749

0.10 - 0.80 dB 30 - 40 kW
WR12 /RG99 WG 26 E 0.122, 0.061 3.099 1.549 0.202, 0.141 60.0 to 90.0 48.35 (48.40, 49.18)

96.745

1.8 - 1.0 dB ? kW
WR10 WG 27 W 0.100, 0.050 2.540 1.270 0.180, 0.130 75.0 to 110.0 59.01 (58.85)

118.029

2.0 - 1.4 dB 14 - 25 kW
WR8 WG 28 F 0.080, 0.040 2.032 1.016 0.160, 0.120 90.0 to 140.0 73.77 (73.84)

147.536

3.0 - 2.0 dB 8.8 - 13 kW
WR6 WG ? D 0.065, 0.0325    0.145, 0.112 110 to 170 90.79 (90.48, 84.31)   3.8 - 3.0 dB 5.9 - 9.3 kW
WR5 WG 30 G 0.0510, 0.0255 1.295 0.648 0.131, 0.105 140 to 220 115.7 (118.03)

231.428

6.1 - 3.8 dB 3.7 - 6.1 kW
WR4 WG 31  0.043, 0.022 1.092 0.546  170 to 260 137.242

274.485

  
WR3 WG 32 Y 0.034, 0.0170 0.864 0.432 0.114, 0.097 220 to 325 196.71 (196.71)

347.143

10.0 - 7.0 dB 1.9 - 2.6 kW

WR-2.8

 

 

  0.711 0.356

 

265 to 400

211

 

 

 

WR-2.2

 

 

  0.559 0.279

 

330 to 500

268

 

 

 

WR-1.9

 

 

  0.483 0.241

 

400 to 600

311

 

 

 

WR-1.5

 

 

  0.381 0.191

 

500 to 750

393

 

 

 

WR-1.2

 

 

  0.305 0.152

 

600 to 900

492

 

 

 

WR-1.0

 

 

  0.254 0.127

 

750 to 1100

590

 

 

 

WR-0.65

 

 

  0.165 0.083

 

1.1-1.7 THz

 

 

 

 

 

 

Wave American Flang

North American EIA Standard Flanges

Waveguide Eupropean Flang

European IEC Standard Flanges

Most common rectangular waveguide flange types

Waveguide Calculator

If you would like to calculate a waveguide loss or cutoff frqeuency for a particular size of rectangular waveguide and frequency press here and fill in the values. It includes loss below cutoff. Accuracy of a model depends on many things, and this one provides inaccuracies right around cutoff of about 5%. Also, it does not account for surface roughness above 20GHz, and so for above cutoff conditions, loss values calculated in that range are less than what you would expect from an actual piece of waveguide.

This page is based on equations from engineering texts which I first put into a spreadsheet, and then gave to Paul ND2X who skillfully fashioned them into this JavaScript calculator. Have fun!!


Circular (cylinderical) Waveguide

 

Cicrular cross section waveguide is the same and different from rectangular. First of all, it is the same in that both are waveguides. However, the rules for modes are different, depending only on diameter. Launches can also be tricky. Furhtermore, circular modes support two orthogonal signals, so two polarizations can be kept separated over a length waveguide. This can be very helpful in commercial, radar and military systems where two polarizations can enter a circular feed and be separated for two way communications, cross polarization information extraction, or some other bizzare effect. Also, circular waveguide, when run at very high modes, much like a high mode rectangular guide, can support very high power without arcing. Also, circular waveguide, when operating in the TMXX mode can have surprizingly low loss.

Quite often, manufacturers of circular waveguide will publish several frequency ranges of operation. Below there are some pdf files that contain circular waveguide data.

Circular Waveguide Sizes A
Circular Waveguide Sizes B

 
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