A cavity for a hydrogen maser is described consisting of three parts which provide highly stable mechanical and thermal expansion characteristics for the cavity and ease of tuning. The three parts which are made of a glass ceramic material having a very small thermal expansion coefficient (1) a top plate, (2) a cylinder with three interrupted helical ramps at its bottom, and (3) a base which includes a bottom plate and three ramp lugs on which the helical ramps of the cylinder rest when the cylinder is placed on the base with the bottom plate in the cylinder. Cavity tuning is achieved by rotating the cylinder and thereby raising or lowering it on the base, which results in changing the cylinder volume by changing the distance between the bottom and top plates

Hoffman, T. E.

Levine, M. W.

Vessot, R. F. C.

English

NASA Technical Reports Server

{ (NASA-Case-HQN-10790-1) TUNfiELE CAVITY
I BESONfiTOR WITH RfiMP SHAPED SUPPORTS
Patent (Smithsonian Astrophysical
Observatory) 5 p CSCL 20E
United States Patent
Fletcher et al.
N74-11313
Unclas
00/16 22290 )
[7TT3,7717074
[45] Nov. 6, 1973
[54] TUNABLE CAVITY RESONATOR WITH
RAMP SHAPED SUPPORTS
[76] Inventors: James C. Fletcher, Administrator of
the National Aeronautics and Space
Administration with respect to an
invention of; Robert F.C. Vessot;
Thomas E. Hoffman, both of
Marblehead, Mass. 01945; Martin
W. Levine, Manchester, Mass.
[22] Filed: Mar. 20, 1972
[21] Appl. No.: 235,962
[52]
[51]
[58]
U.S. Cl 333/83 R, 333/97 R
Int. Cl HOlp 1/00, HOlp 7/06
Field of Search : 333/83 R, 83 T;
330/56,4, 4.3; 331/96; 324/95, .5 AH; 250/39
TL
[56] References Cited
UNITED STATES PATENTS
2,383,343 8/1945 Ryan 333/83 R
2,515,280 7/1950 Varian 333/83 R
2,578,429 12/1951 Karplus 331/96 X
3,386,043 5/1968 Marcatili et al 340/4.3
3,529,267 9/1970 Gunderson et al 333/83 T
FOREIGN PATENTS OR APPLICATIONS
1,020,043 2/1966 Great Britain 333/83 R
967,331 10/1950 France 333/83 R
Primary Examiner— Rudolph V. Rolinec
Assistant Examiner—Wm. H. Punter
Attorney—Monte F. Mott et al.
[57] ABSTRACT
A cavity for a hydrogen maser is disclosed consisting of
three parts which provide highly stable mechanical and
thermal expansion characteristics for the cavity and
ease of tuning. The three parts which are made of a
"glass ceramic" material having a very small thermal
expansion coefficient (a of ±£>.5X10~7 in/in/°C over
0°-389C) include 1) a top 'plate, 2) a cylinder with
three interrupted helical ramps at its bottom and 3) a
base which includes a bottom plate and three ramp lugs
on which the helical ramps of the cylinder rest when
the cylinder is placed on the base with the bottom plate
in the cylinder. Cavity tuning is achieved by rotating
the cylinder and thereby raising or lowering it on the
base, which results in changing the cylinder volume by
changing the distance between the bottom and top
plates.
8 Claims, 3 Drawing Figures
https://ntrs.nasa.gov/search.jsp?R=19740003200 2020-03-17T14:20:25+00:00Z
3,771,074
1 2
' TUNABLE CAVITY RESONATOR WITH RAMP
 DESCR.PTION OF THE PREFERRED
EMBODIMENTS
ORIGIN OF INVENTION
 The nove, features Qf ^  cavjty of ^  presem inyen_
The invention described herein was made in the per- 5 tion are shown in FIGS. 1 and 2, wherein like elements
formance of work under a NASA contract and is sub- or parts are designated by like numerals. As stated
ject to the provisions of Section 305 of the National briefly herebefore the cavity, designated by numeral
Aeronautics and Space Act of 1958, Public Law 10, consists of three basic parts. These include 1) a top
85-568 (72 Stat. 435; 42 U.S.C. 2457).
 piate 12 with several, e.g., three, integral stiffening
BACKGROUND OF THE INVENTION 10 webs 13' 2 > a hollow cy'inder 14 and 3 ) a base 16. The
cylinder 14 has a multifold, e.g., three-fold interrupted
1. Field of the Invention helical ramp or thread at its bottom. The three ramps
The present invention generally relates to a hydrogen
 are designated in FIG. 1 by numerals 18. In FIG. 2 only
maser and, more particularly, to an improved cavity
 two of the ramps are shown. The base 16 which is
therefor. 15 shown resting on a metal disc 19 includes the bottom
2. Description of the Prior Art
 plate 20 of the cavity and a plurality, e.g., three ramp
Atomic hydrogen masers have been developed and
 lugs 22, which engage the cylinder's interrupted ramps
described in the literature. These masers have have i8. The base is strengthened by stiffening webs 24.
proven to be useful both as spectroscopic tools and as
 In practice the cylinder 14 rests on the base with the
frequency standards. As is appreciated by those famil- 20 ,ugs 22 engaging the ramps 18> so that the bottom plate
iar with the art the accuracy and stability of the output
 20 is imide the cylinderj and the top plate 12 is piaced
frequency of such a maser greatly depends on the sta-
 at the top of the cyiinder. Thus the volume of the cavity
bility of various critical elements, particularly the me-
 jg defined b ^ cyiinder's inner diameter and the dis-
chanical and thermal stability of the maser's cavity. In
 tance between the and bottom |ates Cavit tuni
addition, the tuning of the latter ,s very critical for an 25 .g ^ ise, achieved by rotating the cylinder
accurate and stable output frequency Although to date
 and thefeb raisi Qf ,owerin it Qn the base which •„
various cavity structures have been des.gned none has
 tum contj,s ^ d«gtancc of {h* ,ate ffom the bot.
adequately solved the stringent stability and tuning re-
 tom , whkh .g fixed| connected and is a rt of
^
ulrements
-
 3Q the base.
OBJECTS AND SUMMARY OF THE INVENTION The material from which the top plate 12, the cylin-
,. . i_- . r u • • der 14 and the base 16 are manufactured is chosen onIt is a primary object of the present invention to pro- ... . . .... , . . .... . . ..... .
.. " j •: j •» the basis of its mechanical and thermal stability charac-
vide an improved hydrogen maser cavity. . . . . . .-• .. ,, '.. ,A »u u- . Au »• . • - . . - -j tenstics. At present materials are available which ex-Another object of the present invention is to provide .... „  , . , . . . .... .
a hydrogen maser cavity which exhibits superior me- ** hibit excellent mechanical and thermal stability charac-
chanical and thermal stability characteristics. tenstlcs' These matenals are generally known in the art
A further object of the present invention is to provide as Sla?s ceramics. So™e of these materlals have a
an improved hydrogen maser cavity which is easily and thfmal expansion coefficient, known as a, with |a|
precisely tunable, and which exhibits superior mechan- < °,5 X 1<H in in/in/°C over a temperature jange of
ical and thermal stability characteristics «> °°-38°C- Thus they are particularly adapted for fabri-
These and other objects of the invention are achieved Catin6 the cavlty's Parts' In one embod.ment actually
by providing a three-part cavity structure made of a reduced to Practice a material sold bv Owens-Illinois
material which exhibits extremely low thermal expan- and known "» CER-VIT C-l 01 was used with excellent
sion and superior mechanical stability characteristics. results- This malenal is mentioned herein merely to re-
The three parts of the cavity include 1) a top plate, 2) 45 cite one lVPe of material which may be used, rather
a cylinder with a plurality of interrupted helical ramps than to limit the invention thereto,
or threads at its bottom, and 3) a base which contains In practice the cavity is supported and secured within
the bottom plate of the cavity and a plurality of ramp a metallic hold-down cylinder 25, shown in FIG. 3. Cyl-
lugs, which engage the cylinder's interrupted helical inder 25 is fastened at the bottom to the disc 19. A
threads. The number of ramp lugs is the same as the 50 Belleville spring assembly 26 is used to provide uniform
number of the interrupted helical ramps. Cavity tuning downward pressure at the outer circumference of the
is achieved by rotating the cylinder and thereby raising *°P Plate 12. The tension of the spring assembly is set
or lowering it on the base which results in changing the by means of adjusting screws 28 and a force distribut-
volume of the cylinder between the top and bottom »ng ring 29 so that thermal movement of the cylinder
plates. 25 relative to that of the cavity material does not cause
The novel features of the invention are set forth with any appreciable change in the compressive force on the
particularity in the appended claims. The invention will top plate 12 of the cavity. In FIG. 3 the entire assembly
best be understood from the following description is shown supported within a bell jar 30 is also secured
when read in conjunction with the accompanying draw- . to the bottom disc 19.
ings. Although particular embodiments of the invention
have been described and illustrated herein, it is recog-
BRIEF DESCRIPTION OF THE DRAWINGS
 nized that modiflcations and variations may readily
FIG. 1 is an isometric view of the novel cavity of the occur to those skilled in the art and consequently it is
present invention; ,, intended that the claims be interpreted to cover such
FIG. 2 is a side view of parts of the cavity; and modifications and equivalents.
FIG. 3 is a side cross-sectional view of the assembled What is claimed is:
cavity and the manner in which it is employed. 1. In a tunable cavity the arrangement comprising:
3,771,074
3 4
 - . . .
a hollow cylinder having first and second opposite her is of a material which has a thermal coefficient of
ends; expansion definable as a which is not more than
a top plate closing said first end; and ±0.5X10~7 in/in/°C over a preselected temperature
a base member including a bottom plate insertable in range.
said cylinder through said second end and support 5 4. The arrangement as recited in claim 1 wherein n
means for engaging the cylinder at said second end js not less than 3.
so that the distance between said top and bottom
 s> The arrangement as recited in claim 4 wherein
plates varies as said cylinder is rotated about its
 each of said ramps is helically shaped,
longitudinal axis while the cylinder is supported
 6 The arrangernent as recited in claim 4 wherein
and engaged by said support means, said support 10 each of said top plate, said cylinder and said base mem-
means comprising n ramp lugs extending upwardly
 feer .g of a materia, whkh has a therma, coefficient of
from said base member, n being an integer and
 rion definable M „ which is not more than
said cylinder forms n interrupted ramps at said sec- ^5xlQ-, in/in/oc over a preselected temperature
ondend, with each interrupted ramp resting on one K K
of said lugs whereby as said cylinder is rotated in 15 ra"^e', ... , . , ,. ,
a first direction the cylinder is lowered on the base 7" The arrangement as recited ,n claim 5 further m-
and is raised therefrom when the cylinder is rotated cludin8 means for providing a uniform compresswe
in a second direction opposite said first direction, force to *e outer circumference of said top plate,
to thereby control the distance between said top 8- The arrangement as recited in claim 7 wherein
and bottom plates, within said cylinder. 20 each of said toP Plate' said cy|inder and said base mem-
2. The arrangement as recited in claim 1 further in- ber is of a material which has a thermal coefficient of
eluding means for providing a uniform compressive expansion definable as a which is not more than
force to the outer circumference of said top plate. ±0.5X1 (Tr in/in/°C over a preselected temperature
3. The arrangement as recited in claim 1 wherein range.
each of said top plate, said cylinder and said base mem- 25 * * * * *
30
35
40
45
50
55
60
65.
PATENTEDNOY 61973 3,771,074
SHEET 1 OF 2
F I G .
12
18
F I G . 2
PATENTED NOV 61973 3.771.074
SHEET 2 OF 2
FIG. 3
25-
30'
14
k\\ \\X\\1\ \X\V \ \X\ \ \ \K\ \ \ \X\
22 19 18 22 20


Tunable cavity resonator with ramp shaped supports

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