US2942204A

US2942204A - Microwave noise source

Info

Publication number: US2942204A
Application number: US719640A
Authority: US
Inventors: Poulter Howard Charles
Original assignee: Hewlett Packard Co
Current assignee: HP Inc
Priority date: 1958-03-06
Filing date: 1958-03-06
Publication date: 1960-06-21
Anticipated expiration: 1977-06-21

Description

June 21, 1960 H. c. POULTER 2,942,204

' MICROWAVE NOISE SOURCE Filed March 6, 1958 3 INVENTOR.

H. C. POULTER ATTORNEY making'such noise sources.

2,942,204] I MICROWAVE NOISE SOURCE U t e Sees P ren Howard Charles Poulter, Palo AIto CaIiL, assignor to Hewlett-Packard Company, Palo'Alto; Califi, a corporation of California r Filed Mar. 6, 1958, Ser. Nit-719,640

3 Claims. (Cl. 2331-78) This invention relates to broad band microwave noise I sources.

angle with the longitudinal axis on the waveguide. One

practical drawback of thisdevice is that unless the gaseous discharge tube is centered, within very close tlerances, with respect to the longitudinal axis of the waveguide, the presence of the tube in the waveguide introduces large impedance mismatches when the tube is in' its unfired condition. These large mismatches occur over narrow-frequency bands. Very close centering of the tube, however, does not turn out to be a practical way of The elongated gas tubes commerciallyavailable are seldom exactly straight, and break easily when a very small clearance is provided between the glass envelope of the tube and the walls of the shield.

It is an object of the present invention to provide a broad-band microwave noise source of the type described above which does not introduce these large mismatches,

when the gas tube is in its unfired condition, and which is easier and cheaper to manufacture as it does not require close centering tolerances.

In accordance with the'illustr'ated embodiment of this e 2 j 23.

Pipe sections

21 and 23 are joined or welded to the waveguide 13 and extend from the apertures 25 and 27 through' which the tube 11 passes through

waveguide walls

29 and 31 respectively. Gaseous discharge through the tube 11 may be initiated byme'ans of conventional circuit shown in the drawing and comprising voltage sources 33, coil 35, ballast resistance 37 and

switches

39 and 41.

In accordance with the illustrated embodiment of this invention the large impedance mismatches which are caused by the presence, in the waveguide 13, of the tube 11 in its unfired condition, are avoided by

cutting slots

43 and 45 in the cavity defined by the waveguide 13 and the

hollow pipe sections

21 and 23. The slots, which are preferably two in number, should be located between the planes 47 and 49. Planes 47 and 49 are planes perpendicular to the longitudinal axis of the waveguide 13 within which the gas discharge tube 11 is positioned inside "the waveguide 13. The

slots

43 and 45 are narrow, and centered with respect to a plane common to the longitudinal axis of the waveguide 13 and of the tube 11, and positioned at least in part in the

hollow pipe sections

21 and 23. The

slots

43 and 45 are preferablyloaded with lossy material 51 such as powdered iron held together by a binder, and may be covered on the outside by conducting

shields

53 and 55 to prevent leakage from the waveguide 13.

The microwave noise source in accordance with the present invention does not introduce these large narrowband mismatches when the gas tube 11 is in its unfired condition. Its use yields more accurate noise figure measurements than noise sources of the prior art.

I claim: 7

l. A microwave noise generator comprising a hollow waveguide, an elongated gas discharge tube inserted within said waveguide and having its longitudinal axis inclined at an angle with respect to the longitudinal axis of said waveguide and extending outside of said waveguide, an electrode near each end of said discharge tube for producing a discharge therein, hollow pipe sections for shielding the outside portions of said discharge tube, said yhollow pipe sections being joined to said waveguide invention this object is accomplished by providing the walls of the cavity defined by the waveguide andthe hollow pipes sections with at least one longitudinal slot located where the gas discharge tube is within the waveguide, this slot being preferably loaded with lossy material.

Other and incidental objects of this invention will be apparent to those skilled in the art from a reading of the following specification and an inspection of the accompanyingdrawing in which:

around two apertures therein, and at least one longitudinal slot in the walls of the cavity defined by said waveguide and said hollow pipe sections, said slot being located between the planes perpendicular to the longitu dinal axis of the waveguide within which the gas discharge tube is inside the Waveguide and centered with Figure 1 is a longitudinal cross-sectional view of an' charge tube 11 is inserted through a rectangular wave-.

guide 13. The waveguide 13 is dimensioned to propagate over a prescribed frequency range onlythe dominant mode. The tube 11 may be similar to a conventional fluorescent lamp, with the fluorescent wall coating omitted. Thus the tube 11 has a glass envelope 15 and 1 two

electrodes

17 and 19 near each end of the tube 11 for producing the discharge through the tube. The longitudinal axis of the tube 11 is inclined at an angle of approximately nine degrees with respect to the longitudinal axis of the waveguide 13. The portions of the tube 11 which are positioned outside the waveguide 13 are shielded by means of two hollow pipe sections 21 and.

respect to a plane common to the longitudinal axes of the waveguide and of the gaseous discharge device, and positioned at least in part in said hollow pipe section, and lossy material positioned in said slot to load the same.

2. A microwave noise generator comprising a hollow waveguide, an elongated gas discharge tube inserted within said waveguide and having its longitudinal axis inclined at an angle with respect to the longitudinal axis of said waveguide and extending outside of said waveguide, an electrode near each end of said discharge tube for producing a discharge therein, hollow pipe sections for shielding the outside portions of said discharge tube, said hollow pipe sections being joined to said waveguide around two apertures therein, and at least one longitudinal slot in the walls of the cavity defined by said waveguide and said hollow pipe sections, said slot being located between the planes perpendicular to the longitudinal axis of the waveguide within which the gas discharge tube is inside the waveguide and centered with respect to a plane common to the longitudinal axes of the waveguide and of the gaseous discharge device, and lossy material to load said slot.

3. A microwave noise generator comprising a hollow waveguide, an elongated gas discharge tube inserted within said waveguide and having its longitudinal axis in said hollow pipe sections, said slots being located between 10 the planes perpendicular to the longitudinal axis of the waveguide within which thegas discharge tube is inside the waveguide, centered with respect to a plane common to the longitudinal axes of the waveguide, and of the gaseous discharge device, and positioned at least in part in said hollow pipe sections, and lossy material positioned in said slots to load the same.

References Cited in the file of this patent UNITED STAT ES PATENTS 2,485,030 7 Bradley 061. 18, 1949 2,71 ,192 Johnson Aug. 23, 1955 2,766,431-. Barker Oct. 9, 1956 FOREIGN PATENTS" 1 760,386 a Great Britain OCL 31, 1956