# RE: [SI-LIST] : Chassis hole opening and frequencies

From: Jian Zheng ([email protected])
Date: Mon Jan 10 2000 - 14:29:43 PST

Hi, Everybody:

The radiation vs. frequency for chassis hole opening is very interesting. In
my opinion, the radiation is normally related to the actual situation.
However, we can use some typical case study to see the radiation level for
the holes. In the following, I use our high performance IE3D electromagnetic
simulator to simulate a circular hole fed by a microstrip line. The
radiation level vs. frequency data is attached. Hopefully, it might be

When the diameter over the wavelength is about 0.45 or the diameter
(D/Lambda) is about 45% of the wavelength, we can see a resonance with
majority of the power radiated. When the (D/Lambda)is below 10%, the
radiation will be less than 1% of the input power. When the (D/Lambda) is
below 1%, the radiation will be about 0.01% of the input power.

----------------------------------------------------------------------------
Jian-X. Zheng, Ph.D
Zeland Software, Inc., 39676 Mission Blvd., Fremont, CA 94539, U.S.A.
Tel: 510-797-8109, Fax: 510-797-8241, Web: http://www.zeland.com
----------------------------------------------------------------------------
---------------------------------------------------
An circular hole with diameter of 1 inch fed by
a microstrip line.

---------------------------------------------------
(GHz) (%) Power (%) Power (%)

0.1 0.847457627 99.98743639 0.012563605
0.2 1.694915254 99.98204281 0.017957194
0.3 2.542372881 99.9771613 0.022838696
0.4 3.389830508 99.91070394 0.089296057
0.5 4.237288136 99.85147719 0.148522811
0.6 5.084745763 99.79785426 0.202145739
0.7 5.93220339 99.74492886 0.255071139
0.8 6.779661017 99.68868267 0.311317326
0.9 7.627118644 99.62636566 0.37363434
1 8.474576271 99.55616357 0.443836427
1.1 9.322033898 99.47681211 0.52318789
1.2 10.16949153 99.38730139 0.612698615
1.3 11.01694915 99.28664475 0.713355253
1.4 11.86440678 99.17369006 0.826309941
1.5 12.71186441 99.04692775 0.953072247
1.6 13.55932203 98.90427608 1.095723915
1.7 14.40677966 98.74282029 1.257179714
1.8 15.25423729 98.55842513 1.441574867
1.9 16.10169492 98.34520312 1.654796883
2 16.94915254 98.09470091 1.905299088
2.1 17.79661017 97.79463108 2.205368916
2.2 18.6440678 97.42692423 2.57307577
2.3 19.49152542 96.96455519 3.035444806
2.4 20.33898305 96.36646408 3.633535917
2.5 21.18644068 95.5693294 4.4306706
2.6 22.03389831 94.47457813 5.525421865
2.7 22.88135593 92.92957494 7.070425064
2.8 23.72881356 90.70711506 9.292884941
2.9 24.57627119 87.50930637 12.49069363
3 25.42372881 83.08439355 16.91560645
3.1 26.27118644 77.62210501 22.37789499
3.2 27.11864407 72.33352302 27.66647698
3.3 27.96610169 69.12411248 30.87588752
3.4 28.81355932 68.77678973 31.22321027
3.5 29.66101695 70.27708991 29.72291009
3.6 30.50847458 72.22616117 27.77383883
3.7 31.3559322 73.81638443 26.18361557
3.8 32.20338983 74.7651442 25.2348558
3.9 33.05084746 75.02379615 24.97620385
4 33.89830508 74.60496898 25.39503102
4.1 34.74576271 73.51329938 26.48670062
4.2 35.59322034 71.72347827 28.27652173
4.3 36.44067797 69.17619677 30.82380323
4.4 37.28813559 65.78226547 34.21773453
4.5 38.13559322 61.43513283 38.56486717
4.6 38.98305085 56.03818528 43.96181472
4.7 39.83050847 49.55739017 50.44260983
4.8 40.6779661 42.10930782 57.89069218
4.9 41.52542373 34.07864555 65.92135445
5 42.37288136 26.21539124 73.78460876
5.1 43.22033898 19.59967837 80.40032163
5.2 44.06779661 15.36437499 84.63562501
5.3 44.91525424 14.23669111 85.76330889
5.4 45.76271186 16.20230669 83.79769331
5.5 46.61016949 20.56636559 79.43363441
5.6 47.45762712 26.33263504 73.66736496
5.7 48.30508475 32.5865053 67.4134947
5.8 49.15254237 38.6829154 61.3170846
5.9 50.00000000 44.25423683 55.74576317
6 50.84745763 49.13671002 50.86328998
6.1 51.69491525 53.28860863 46.71139137
6.2 52.54237288 56.72857311 43.27142689
6.3 53.38983051 59.4966059 40.5033941
6.4 54.23728814 61.63162047 38.36837953
6.5 55.08474576 63.15898919 36.84101081
6.6 55.93220339 64.08326226 35.91673774
6.7 56.77966102 64.38309959 35.61690041
6.8 57.62711864 64.00681298 35.99318702
6.9 58.47457627 62.86804988 37.13195012
7 59.3220339 60.84246326 39.15753674
7.1 60.16949153 57.76837398 42.23162602
7.2 61.01694915 53.4580922 46.5419078
7.3 61.86440678 47.73254271 52.26745729
7.4 62.71186441 40.49806753 59.50193247
7.5 63.55932203 31.88238292 68.11761708
7.6 64.40677966 22.41463142 77.58536858
7.7 65.25423729 13.15045711 86.84954289
7.8 66.10169492 5.550231827 94.44976817
7.9 66.94915254 0.991988371 99.00801163
8 67.79661017 0.148823662 99.85117634
8.1 68.6440678 2.723288757 97.27671124
8.2 69.49152542 7.73701929 92.26298071
8.3 70.33898305 14.05767491 85.94232509
8.4 71.18644068 20.77065494 79.22934506
8.5 72.03389831 27.29030242 72.70969758
8.6 72.88135593 33.31127306 66.68872694
8.7 73.72881356 38.71498138 61.28501862
8.8 74.57627119 43.48878477 56.51121523
8.9 75.42372881 47.67178607 52.32821393
9 76.27118644 51.32310805 48.67689195
9.1 77.11864407 54.50505072 45.49494928
9.2 77.96610169 57.27491007 42.72508993
9.3 78.81355932 59.68146679 40.31853321
9.4 79.66101695 61.76374268 38.23625732
9.5 80.50847458 63.55073202 36.44926798
9.6 81.3559322 65.06136748 34.93863252
9.7 82.20338983 66.30432219 33.69567781
9.8 83.05084746 67.27740048 32.72259952
9.9 83.89830508 67.96633404 32.03366596
10 84.74576271 68.34279463 31.65720537
10.1 85.59322034 68.36150076 31.63849924
10.2 86.44067797 67.95625674 32.04374326
10.3 87.28813559 67.03503671 32.96496329
10.4 88.13559322 65.47459258 34.52540742
10.5 88.98305085 63.11624333 36.88375667
10.6 89.83050847 59.76672668 40.23327332
10.7 90.6779661 55.21215786 44.78784214
10.8 91.52542373 49.25908116 50.74091884
10.9 92.37288136 41.82122372 58.17877628
11 93.22033898 33.06180885 66.93819115
11.1 94.06779661 23.55765428 76.44234572
11.2 94.91525424 14.36625735 85.63374265
11.3 95.76271186 6.827929962 93.17207004
11.4 96.61016949 2.079816524 97.92018348
11.5 97.45762712 0.571319502 99.4286805
11.6 98.30508475 1.957123776 98.04287622
11.7 99.15254237 5.400627406 94.59937259
11.8 100.0000000 9.985026152 90.01497385
11.9 100.8474576 14.97272224 85.02727776
12 101.6949153 19.87544381 80.12455619
12.1 102.5423729 24.41679356 75.58320644
12.2 103.3898305 28.46516573 71.53483427
12.3 104.2372881 31.97494787 68.02505213
12.4 105.0847458 34.94560407 65.05439593
12.5 105.9322034 37.39639753 62.60360247
12.6 106.779661 39.35190405 60.64809595
12.7 107.6271186 40.83417933 59.16582067
12.8 108.4745763 41.85873258 58.14126742
12.9 109.3220339 42.43259857 57.56740143
13 110.1694915 42.55357988 57.44642012
13.1 111.0169492 42.21021767 57.78978233
13.2 111.8644068 41.38244686 58.61755314
13.3 112.7118644 40.04317521 59.95682479
13.4 113.559322 38.16138023 61.83861977
13.5 114.4067797 35.70761968 64.29238032
13.6 115.2542373 32.66320242 67.33679758
13.7 116.1016949 29.03429417 70.96570583
13.8 116.9491525 24.87156139 75.12843861
13.9 117.7966102 20.29373299 79.70626701
14 118.6440678 15.50907268 84.49092732
14.1 119.4915254 10.82272943 89.17727057
14.2 120.3389831 6.614227765 93.38577224
14.3 121.1864407 3.275200492 96.72479951
14.4 122.0338983 1.117439057 98.88256094
14.5 122.8813559 0.286611957 99.71338804
14.6 123.7288136 0.724654041 99.27534596
14.7 124.5762712 2.199753797 97.8002462
14.8 125.4237288 4.384130769 95.61586923
14.9 126.2711864 6.938976976 93.06102302
15 127.1186441 9.574792127 90.42520787

> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]]On Behalf Of LATOURRETTE,JEFF
> (HP-SanJose,ex1)
> Sent: Monday, January 10, 2000 12:14 PM
> To: '[email protected]'
> Subject: RE: [SI-LIST] : Chassis hole opening and frequencies
>
>
> Doug & Chris:
>
> I agree with Ray's 1/10th wavelength and have even heard 1/20th
> recommended.
> Remember that on your 1/4 wave example that the 1/4 wave frequency is the
> most efficient which will radiate, but certainly other frequencies both
> higher and lower can and will radiate from that line. The same
> is true for
> apertures sizes in a chassis. It is true, however that you can achieve
> cut-off by having sigificant depth in your aperture so that it resembles a
> waveguide. The amount of attenuation to signals below the cutoff
> frequency
> is directly proportional to the length of the waveguide structure. I've
> captured some of this in an Application note, AN 1166: [18pp/195KB (Pub.
> 3/99)] "Minimizing Radiated Emissions of High-Speed Data Communications
>
> http://www.semiconductor.agilent.com/fiber/fiberapps.html
>
> Also, Make sure meshes used actually make conductive contact at its own
> cross points, as well as on its edges to the chassis. Some
> cheaper screens
> are weaved wires without electrical contact. Some use two mesh
> screens and
> for extra high performance use an extruded mesh structure with
> depth (like a
> honeycomb) in place of a screen.
>
>
> Regards,
>
> Jeff La Tourrette
> SJ Applications Manager
> Agilent Technologies Fiber-Optics Components
> 370 West Trimble Rd. M/S 90TH
> San Jose, CA 95131
> Voice: 408 435-4083 FAX: 408 435-4915
>
>
> -----Original Message-----
> From: Ray Waugh [mailto:[email protected]]
> Sent: Monday, January 10, 2000 11:09 AM
> To: [email protected]
> Subject: RE: [SI-LIST] : Chassis hole opening and frequencies
>
>
> Doug...
>
> Have you ever seen a parabolic dish antenna which uses a mesh (instead
> of a solid metal surface)? It lets the wind and rain through. As a
> rule of thumb, keep the holes in the mesh under a tenth wavelength in
> dimension.
>
> I'd suggest doing as the RF instrument people do -- cut a hole in your
> chassis large enough for your fan, and mount a mesh over it. To avoid
> having the mesh act as a RF radiator, make certain that it is
> continuously attached to the rim of the chassis.
>
> You could probably build and test a dummy chassis quicker than you could
> do a proper analysis.
>
> Ray
> ------------------------------------------------------
> Raymond W. Waugh - WSD Diode Applications
> E-mail: [email protected]
>
> USPS : Agilent Technologies
> Wireless Semiconductor Division
> 39201 Cherry Street, MS NK20
> Newark, California 94560
> ------------------------------------------------------
>
> -----Original Message-----
> From: Chris Padilla [mailto:[email protected]]
> Sent: Thursday, December 30, 1999 1:39 PM
> To: [email protected]
> Subject: Re: [SI-LIST] : Chassis hole opening and frequencies
>
>
> Doug,
>
> In antenna theory, a microstrip (for example) that is fed (by an ideal
> infinite rise-time source) in one end and
>
> (a) shorted at the other end will radiate at the frequency that
> corresponds
> to a quarter wavelength
>
> (b) open at the other end will radiate at the frequency that corresponds
> to a half wavelength
>
> So if our microstrip is 12 cm long and it is shorted at one end, we
> should
> be able to radiate 625 MHz pretty well. If you imagine your ideal
> source
> is in the hole of the chassis and connected across the longest dimension
> of the hole, we have the same thing set up in (a) above. Our source is
> referenced to ground and the short is, effectively, ground, too. Does
> this
> make any sense???
>
> So my long-winded answer is a "quarter wavelength of the longest
> dimension
> that defines the hole."
>
> This should get you very much in the ballpark.
>
> WARNING::DEVIATION FROM QUESTION::WARNING---------------**************
>
> Now the next question is: What if I have 2 or 3 or a whole matrix of
> holes
> (air holes for cooling for instance) in my chassis. How will THAT
>
> I can indirectly answer that question as follows:
>
> We can get SE (shield effectiveness) from:
> 20*log(wavelength/2*max_length)
>
> where max_length is the maximum dimension of the slot or aperture.
>
> So the SE of a 100 mil opening at 5 GHz is 21.45 dB-->watch units!
>
> Mulitple apertures reduce the shielding effectiveness. Lets call it
> MA_n.
>
> The amount of reduction depends on (1) the spacing between the
> apertures,
> (2) the frequency, and (3) the number of apertures. When apertures of
> equal
> size are placed close together (less than a half wavelength), the
> reduction
> in shielding effectiveness is approximately proportional to the square
> root
> of the number of apertures n:
>
> MA_n= -10*log(n)
>
> So now our total shielding effectiveness, SE_tot = SE + MA_n
>
> Example: 4 100 mils holes at 5 GHz provides a reduction in shielding of
> 6 dB
> if the holes are less than a half wavelength or 1.18 inches apart.
>
> So now our SE = 21.45 + (-6) = 15.45 dB at 5 GHz.
>
> I know, I know, it is more than you wanted to know.
>
>
> ----->Chris
>
> At 09:45 AM, you wrote:
> >As I recall, there is a relationship between a hole in a chassis and the
> >frequencies that can pass through that opening. I recall that
> the longest
> >dimension of the hole defines the wavelength, or quarter wavelength, or
> >something, of the lowest frequency than can conveniently enter or escape
> >through the opening.
> >
> >Can anyone give me the correct relationship?
> >
> >Thanks.
> >
> >And Happy New Year to All...........
> >
> >Doug Brooks
> >and all of us here at UltraCAD
> >
> >
> >
> >
> >
> >.
> >************************************************************
> >See our updated message re in-house seminars on our web page
> >.
> >Doug Brooks, President [email protected]
> >
> >
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> >
> >
>
>
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