An improved system is described for cooling high power waveguides by the use of cooling ducts extending along the waveguide, which minimizes hot spots at the flanges where waveguide sections are connected together. The cooling duct extends along substantially the full length of the waveguide section, and each flange at the end of the section has a through hole with an inner end connected to the duct and an opposite end that can be aligned with a flange hole in another waveguide section. Earth flange is formed with a drainage groove in its face, between the through hole and the waveguide conduit to prevent leakage of cooling fluid into the waveguide. The ducts have narrowed sections immediately adjacent to the flanges to provide room for the installation of fasteners closely around the waveguide channel

Chen, B. C. J.

Hartop, R. W.

English

NASA Technical Reports Server

States Patent [191 [111 4,382,239 
Chem et d. [451 May 3,1983 
[54] WAVEGUIDE COOLING SYSTEM 3,633,131 1/1972 Nelson ....................... 
[76J Inventors: Alan M. Lovelace, Administrator of 
the National Aeronautics and Space 
Administration, with respect to an 
invention of Bill C. J. Chen; Robert 
W. Hartop, both of Pasadena, Calif. 
[21] Appl. No.: 259,210 
[22] Filed: Apr. 30, 1981 
[51] Int. c1.3 ............................................... HOlP 1/30 
[52] U.S. Cl. .................................. 333/248; 333/22 F; 
333/254 
[58] Field of Search ..................... 333/22 F, 229, 234, 
333/248, 254, 99 R 
[561 References Cited 
U.S. PATENT DOCUMENTS 
2,752,572 6/1956 
2,860,311 11/1958 
2,947,956 SA960 
3,030,592 4/1962 
3,212,028 10/1965 Wantuch ......................... 333/248 X 
3,241,089 3/1966 Treen .................................... 331/11 
3,369,198 2/1968 Campbell et al. ................. 333/22 F 
3,599,127 8/1971 Krijger ................................ 333/256 
3,600,709 8/1971 Ditscheld et al. .................... 333/33 
3,906,402 9/1975 Lesyk ................................ 333/22 F 
3,940,719 2/1976 Booth ................................ 333/22 F 
Primary Examiner-Paul L. Gensler 
Attorney, Agent, or Firm-Monte Mott; John R. 
Manning; Thomas Jones 
[571 ABSTRACT 
An improved system is described for cooling high 
power waveguides by the use of cooling ducts extend- 
ing along the waveguide, which minimizes hot spots at 
the flanges where waveguide sections are connected 
together. The cooling duct (24) extends along substan- 
tially the full length of the waveguide section, and each 
flange (18, 20) at the end of the section has a through 
hole (36) with an inner end connected to the duct and an 
opposite end that can be aligned with a flange hole in 
another waveguide section. Each flange (20) is formed 
with a drainage groove (60) in its face, between the 
through hole (36) and the waveguide conduit (16) to 
prevent leakage of cooling fluid into the waveguide. 
The ducts have narrowed sections (32,34) immediately 
adjacent to the flanges to provide room for the installa- 
tion of fasteners closely around the waveguide channel. 
7 Claims, 4 Drawing Figures 
https://ntrs.nasa.gov/search.jsp?R=19830018814 2020-03-22T00:43:26+00:00Z
U.S. Patent May 3, 1983 4,382,239 
20 
F I G 3  +-3 
14 
FIG4 
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4,382,239 
'I 1 
WAVEGUIDE COOLING SYSTEM 
ORIGIN OF THE INVENTION 
The invention described herein was made in the per- 
formance of work under a NASA contract and is sub- 
ject to the provisions of Section 305 of the National 
Aeronautics and Space Act of 1958, Public Law 85-568 
(72 Stat. 435; 42 USC 2457). 
BACKGROUND OF THE INVENTION 
Waveguides are often constructed by the use of nu- 
merous waveguide sections having flanges at their ends 
to facilitate their connection in series. When high power 
microwaves are to be carried, cooling ducts can be 
positioned against the sides of each waveguide sections 
to carry a cooling fluid such as water. A duct section 
can be welded to either side of each waveguide section. 
After the waveguide sections have been connected in 
series the ducts can be interconnected by hoses extend- 
ing around the flanges and connecting the ends of adja- 
cent ducts. However, it has been found that power 
breakdown or arcing, and consequent eroding of the 
waveguide still occurs near the flanges of the wave- 
guide sections. Temperature measurements have been 
made at various points along such waveguide sections, 
which show that a high temperature such as 150" C. 
may occur at the flanges of waveguide sections carrying 
microwave power at a level such as 400 kilowatts at the 
X-band (about 8 gigahertz). A system which minimized 
hot spots along a waveguide composed of numerous 
sections connected in series, which could be con- 
structed at low cost, and which did not significantly 
interfere with rapid connection and disconnection of 
the waveguide sections, would be on considerable use in 
high power microwave applications. 
SUMMARY OF THE INVENTION 
In accordance with one embodiment of the present 
invention, a microwave waveguide is provided which 
minimizes hot spots along the waveguide while permit- 
ting the waveguide to be easily assembled out of wave- 
guide sections. Each of the waveguide sections includes 
the usual microwave conduit with flanges at its ends 
and a cooling duct extending along its length direction. 
At least one of the flanges has a through hole that is 
spaced from the waveguide conduit, with one end of the 
hole coupled to the cooling duct and another end open- 
ing into the outer face of the flange. When flanges are 
connected in series with their waveguide conduits 
aligned, the through holes in the flanges are automati- 
cally aligned to permit the flow of cooling fluid adja- 
cent to the flange areas of the waveguide sections so as 
to cool them and minimize hot spots. 
Each of the flanges can be formed with a drainage 
groove in its outer face, with a portion of the drainage 
groove lying between the coolant-carrying through 
hole and the waveguide conduit, and with an end of the 
drainage groove extending to an edge of the flange. If 
cooling fluid leaks out of the space between the flanges 
of adjacent waveguide sections, any flow toward the 
waveguide conduit is interrupted by the drainage 
groove to prevent the cooling fluid from reachinp the 
waveguide conduit. Each cooling duct can be provided 
with a wide portion extending beside the middle of the 
microwave conduit, and narrow portions near each of 
the flanges, to provide room for installing fasteners 
immediately around the waveguide conduit while pro- 
L 
viding maximum cooling of the waveguide conduit 
where possible. 
The novel features of the invention are set forth with 
particularity in the appended claims. The invention will 
5 be best understood from the following description when 
read in conjunction with the accompanying drawings. 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a partial perspective view of a waveguide 
FIG. 2 is a partial side elevation view of the wave- 
FIG. 3 is a view taken on the line 3-3 of FIG. 2. 
FIG. 4 is a sectional view taken on the line 4-4 of 
10 constructed in accordance with the present invention. 
guide of FIG. 1. 
l5 FIG. 3. 
DESCRIPTION OF THE PREFERRED 
EMBODIMENT 
FIG. 1 illustrates a waveguide 10 formed of individ- 
2o ual waveguide sections 12 joined in series. Each wave- 
guide section includes a rectangular pipe 14 forming a 
microwave conduit 16, and a pair of flanges 18, 20 
mounted at either end of the pipe. The waveguide sec- 
tions 12 are joined together at their flanges by a group 
25 of eight fasteners 22 lying closely around the rectangu- 
lar pipe 14. The waveguide is designed to carry micro- 
waves at high power levels, and is provided with cool- 
ing ducts 24,26 at opposite sides of the rectangular pipe, 
Each of the cooling ducts such as 24 includes a wide 
portion 30 extending along most of the length of the 
waveguide section, and a pair of narrow portions 32,34 
lying near either end of the waveguide section. The 
35 narrow portions such as 34 lead directly into a through 
hole 36 formed in a flange, to pass the cooling fluid 
through the flange. As also shown in FIGS. 3 and 4, 
each flange is formed with a pair of holes 36 laterally 
spaced from either side of the waveguide conduits 16. A 
4o sealing groove 38 is formed around the through hole to 
hold an O-ring 40. 
A pair of waveguide sections can be connected to- 
gether by placing the outer faces 41 of the flanges face- 
wise against one another, with a sealing or O-ring 40 in 
45 the grooves around the holes 36, and then fastening the 
flanges together with the fasteners 22. Such a connec- 
tion simultaneously connects the microwave conduit 16 
of the waveguide sections, and the cooling fluid pas- 
sages formed by the duct 24 and flange holes 36 in each 
As shown in FIG. 2, two of the waveguide sections 
12A and 12B are modified, in that one end of each wide 
duct portion 30 thereof is sealed, and a hose coupling 50 
is provided to connect a coolant hose 52, 54 thereto, to 
55 flow cooling fluid through the system. In the prior art, 
each waveguide section was provided with only the 
wide conduit portion 30. A hose coupling such as 50 
was provided at either end of each conduit portion such 
as 30 of a waveguide section. Short hoses were utilized 
60 to interconnect the conduit portions such as 30 of adja- 
cent waveguide sections, with each short hose extend- 
ing around the joined flanges of the waveguide sections. 
This not only required many more parts and steps in the 
joining of waveguide sections, but also resulted in hot 
65 spots near the flanges, to which the cooling ducts did 
not directly extend. It was thought that by separating 
the cooling connections from the waveguide conduit 
connections, greater reliability could be achieved in 
3o to carry water or other cooling fluid. 
50 waveguide section. 
4,382,239 
3 4 
each connection. However, the high temperatures at levels of only 330 kilowatts before serious cold plasma 
the ends of the waveguide sections leads to cold plasma arcing occurred. At the same power levels, the maxi- 
arcing and consequent erosion of the waveguides, mum temperature along the walls of the waveguide 
which has limited the power levels that could be trans- conduits 16, which occur at the ends of the waveguide 
mitted through the waveguides. 5 sections, were found to be reduced from 105" C. to 35" 
In the present waveguide, the mechanical connection C. 
Of the microwave conduits 16 and of the cooling pas- Thus, the invention provides a cooled high power 
sages at the holes 36, are made at the Same time when microwave waveguide, which reduces hot spots along 
the flanges of a pair of waveguide sections are joined, the waveguide that can limit its power carrying capac- 
and yet these two conduits or passages are maintained 10 ity, while also facilitating the connection of waveguide 
reliably separate from one another. The flange faces 41 sections to set UP to waveguide. This can be accom- 
are ground flat and engage one another facewise, SO plished by utilizing a through hole in the flanges of the 
there is substantially no gap at the faces 14E of the waveguide sections at locations spaced from the wave- 
Pipes l4 that form the waveguide. The guide conduit and extending the cooling ducts up to the 
sealing of the K d a n t  passage 39 is made by way ofthe l5 flanges, so that cooling fluid flows up to and through 
elastomeric sealing rings 40 which do not interfere with the flange portions of the waveguide sections. Leakage 
face-to-face contact of the flanges. In order to avoid of cooling fluid where the flanges of adjacent wave- 
waveguide conduit, a drainage groove 60 is formed in 20 drainage groove in the flange face, with a portion of the 
damage to the waveguide pipe l4 if an O-ring 40 fai1% so 
that water under pressure might be forced into the 
each flange' Each drainage groove 6Q extends between 
guide sections are joined, can be avoided by utilizing an 
O-ring in a groove around the hole, and by providing a 
drainage groove lying directly between the coolant-car- the end of the waveguide conduit 16 and the hole 36 in rying hole and the waveguide, and with another portion 
would first have to enter the groove 16. The groove 16 25 ing duct along each waveguide section, can include a 
also extends to the extreme edge of the flange, so any wide portion extending along most of the length of the cooling fluid will be drained into the environment to 
avoid the buildup of fluid pressure in the groove. Each waveguide section, and a narrower portion immediately 
groove can be formed by merely milling a straight adjacent to each flange to avoid interference with the 
groove the width of the flange face, to lie be- 3o installation of fasteners that join the flanges of different 
tween the waveguide conduit 16 and the flange hole 36. waveguide sections together, but with the narrow duct 
the flange, so that if any 
the 
fluid leak Out Of 
fluid passage towards the waveguide 16? it 
ofthe drainage groove extending to the extreme edge of 
the flange to drain fluid into the environment. The cool- 
The narrower cooling duct portions such as 34 which portion deep enough to flow fluid the 
extend up to the flanges such as 20, are utilized to pro- 
vide room for the installation of fasteners 22 close to the *lthough particular embodiments Of the invention 
waveguide conduit 16 so as to securely join the flanges 35 have been described and illustrated herein, it is recog- 
without any significant gap between the waveguide nized that modifications and variations may readily 
pipe ends 1 4 ~ .  It may be noted that each duct portion occur to those skilled in the art and consequently, it is 
could be formed of a C-section together with a side of intended that the claims be interpreted to cover such 
the waveguide pipe, although this would result in con- modifications and 
siderably more welding and the greater possibility of 40 
leakage out of a failed weld. As shown in FIG. 3, the 
flange 20 has eight fastener holes 70, of which two 70a, 
70b on either side of the waveguide conduit lie close to 
the narrow conduit portion 34. However, the narrow 
conduit portion 34 is still wider than the hole 36 so that 45 
all of the conduit portion 34 can be positioned in align- 
ment with the hole 36. 
Cooling of the end portion of the waveguide pipe 14 
is enhanced by several factors. In addition to the cool- 
ing resulting from cooling fluid such as water flowing 50 
through the hole 36 (FIG, 4), cooling of the end portion 
of the waveguide section is enhanced by the water 
flowing directly along the inside face 72 of the flange, at 
the flange face region 74 lying between the waveguide 
conduit 16 and the through hole 36. This results from 55 
constructing the narrower duct portion 34 with consid- 
erable depth D to extend from close to the pipe 14 to a 
position across the flange hole 36. Of course, there is 
also cooling along the length of the narrow conduit 
portion 34 where it is against the waveguide pipe 14. 
A waveguide 10 of the type described herein has been 
constructed and tested at power levels of up to 600 
kilowatts, at X-band (near 8 gigahertz), the power level 
being limited by the microwave source rather than the 
waveguide power-carrying capacity. Prior art wave- 65 
guides of the same construction, but with coolant ducts 
extending only partially along each section and con- 
nected together by hoses, could be utilized at power 
inside face Of the flange. 
We 
A microwave 
a waveguide section which includes a conduit pipe 
forming a microwave conduit and having a pair of 
pipe ends, a flange mounted at either end of the 
Pipe, and walls forming a duct extending 
along the length direction of said conduit and lying 
beside said conduit pipe; 
at least one of said flanges having a through hole 
therein laterally spaced from said conduit and hav- 
ing one hole end coupled to said cooling duct. 
2. The waveguide d e ~ r i b e d  in claim 1 wherein: 
said one flange has a drainage groove formed on the 
flange face which is opposite said duct, said groove 
lying between said hole and said microwave con- 
duit, and said groove extending to an edge of the 
flange, whereby to drain away cooling fluid so it 
does not reach said waveguide conduit. 
comprising: 
3. The waveguide described in claim 1 wherein: 
said one flange has a plurality of fastener holes spaced 
about said conduit pipe for receiving fasteners to 
attach to a flange of another waveguide section; 
and 
said duct has a wide portion extending beside the 
middle of the conduit pipe, and a narrower portion 
adjacent to said flange, whereby to provide room 
for installing fasteners and to also provide maxi- 
mum cooling of the end of the conduit pipe. 
4. The waveguide described in claim 1 wherein: 
60 
4,382,239 
5 
said cooling duct has an end portion of greater depth 
than said through hole, said duct end portion ex- 
tending up to said flange, to flow cooling fluid 
along a flange portion lying between said through 5 
hole and said microwave conduit. 
5. A microwave waveguide, comprising: 
a plurality of waveguide sections, each section having 
walls forming a microwave conduit, a flange at 1o 
each end of each of said conduits, and a cooling 
duct extending along the length direction of each 
conduit up to either flange; 
each flange having a pair of holes, said holes lying at 
and spaced from either side of said microwave 
conduit, and each hole having an inner hole end in 
communication with one of said cooling conduits 
and an outer hole end at the outer face of the flange 
15 
20 
6 
which lies opposite the cooling duct of the same 
waveguide section; 
said waveguide sections joined in series, with the 
conduits and flange holes of adjacent waveguide 
sections in alignment, and with at least one flange 
of each adjacent pair of flanges forming a groove 
around a flange hole, and including an O-ring in the 
groove. 
6. The waveguide described in claim 5 wherein: 
at least one flange of each adjacent pair of flanges 
forms a drainage groove lying between the aligned 
holes of the flanges and the aligned ends of the 
microwave conduits. 
7. The waveguide described in claim 5 wherein: 
an end of each duct which extends up to a flange has 
sufficient depth to flow cooling fluid along a por- 
tion of a face of the flange which lies between the 
microwave conduit and said flange hole. * * * * *  
25 
30 
35 
45 
50 
55 


Waveguide cooling system

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