US2600466A

US2600466A - Wave guide attenuator

Info

Publication number: US2600466A
Application number: US486013A
Authority: US
Inventors: Arnold E Bowen
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1943-05-07
Filing date: 1943-05-07
Publication date: 1952-06-17
Anticipated expiration: 1969-06-17
Also published as: NL71519C

Description

June 17, 1952 BOWEN 2,600,466

WAVE GUIDE ATTENUATOR Filed May 7, 1945 //v VENTOR- A. E. BOWEN I?" BY? Arrouzv Patented June 17, 1952 UNITED STATES PATENT WlAVE GUIDE ATTENUATOR Arnold E. Bowen, Red Bank, N. J., assignor to. Bell TelephoneLaboratories, Incorporated, New York, N. Y., av corporation of New York Application May 7, 1943, Serial No. 486,013

21 Claims. 1

This invention relates to wave transmission network and more particularly to an attenuator for guided electromagnetic waves.

An object of the invention is to attenuate guided electromagnetic waves.

Another object is to provide a wave guide attenuator which may be continuously varied from zero to any chosen upper limit of attentuation.

In transmission systems employing an airfilled metallic pipe as a guide for electromagnetic waves it is often desired to introduce a known amount of attenuation. It is convenient to be able to vary the attenuation continuously from zero to the required upper limit.

The present invention provides a wave guide attenuator which is continuously variable from zero to any desired maximum value. The attenuator comprises a section of metallic pipe wave guide within which is longitudinally positioned a resistive septum. To make the attenuatorv variable, means are provided for moving the septum sidewise and thereby varying the separation between the septum and a side of the waveguide. In the embodiment disclosed the guide is of rectangular cross-section and the septum is parallel to a side of the section.

The nature of the invention will be more fully understood from the following detaileddescription and by reference to the accompanying draw,- ings in which:

Fig. 1 is a perspective vview of a wave guide attenuator in accordance with the invention;

Fig. 2 is a plan view, partly in section, of the attenuator of Fig. 1; and

Fig. 3 is. a perspective view of theresistive septum used in the attenuator shown in Figs. 1 and 2.

As shown in perspective in Fig. 1 and in plan in Fig. 2, the attenuator comprises a section of metallic pipe wave guide I of rectangular cross-section, a resistive septum 2 positioned within the section I substantially parallel to the shorter dimensioned side 3 of the section I and means for moving the septum 2 either toward or away from the side 3. Each end of the section I is provided with a flange 4 for connecting the attenuator to an adjacent section ofwave guide. The flange 4 may be provided with aligning pins 5 which fit into holes such as 6 in a flange on the end of the adjacent section of, guide. They section I is made of a metal or an alloy having good electrical conductivity such, for example, as brass, and is preferably plated on the inside with precious metal such, for example, as silver or platinum.

The septum 2 is moved by means of a rod I to the inner endof which the septum 2 is fastened by a screw 8 which passes through a cen tral hole in-the-septum2 and screwsinto a tapped hole in the end of the rod I. The rod1= and the screw 8 are madeof suitable insulating material such, for example, as hard rubber. The rod? 1 slides in a hole 9-in the lower block I0 and: passes through a hole II in the side 3 ofthe guide section I. The rod I is actuated by means of the rack I2-, which is fastenedto the rod I, and the pinion'gear I3. The pinion I3-.is on the lower end of a shaft I4 which passes through a hole in the upper block I5. and is held in. place by the pronged member l6 which is fastened at one end to the top of the block I5 andat the other end fits into an annular groove-in the shaft; I4. The upper-block I5'is fastened to the lower block III by the screws I1 and the entire assembly is securely attached to the side 3 of the section. I.

The dial I8 and knob I9: are fastened tothe upper end of the shaft I4 by the setscrew20-and a pointer orindex 2|, fastened tothe section I; is provided for reading the calibration on the dial I8, as shown at 22. The calibration 22 may conveniently be made directly in decibels.

As shown more clearly in the perspective view of Fig. 3, the septum 2- consists of a plate of suitable insulating materialsuch, for example, as phenol fibre, coated on the face toward the side 3 with one or more layers of resistive material 23. The resistive material may, forexample, be a mixture of finely divided graphite and-a suit.- able binder, sprayed onto the side ofrthe septum 2 in one or more coats. The endsofrthe septum 2 are preferably specially. shapedto reduce. the reflection effects when the section lis inserted into the wave guide system. Asv shown at 24 and 25 in Fig. 3, this special shaping mayxtake the form of' arectangular notch, the optimum depth and-width of whicharebest determined by trial. Other forms of special shaping may, however, be used. In order to minimize. the variation inattenuation with frequency the central'hole' 26 in the septum 2 may be extended on each side in the longitudinal direction, as shown at 21 and 28. The optimum dimensions for these extensions are also best found by trial.

The amount of attenuation introduced by the attenuator depends primarily upon the length, width and thickness of the-resistive coating" 23 and the distance between the septum 2 and the side 3 of the section I. When the septum 2 is in contact with the side 3 the attenuation is substantially zero. As the septum 2 is moved away from the side 3 the attenuation increases in accordance with a smooth curve until a maximum is reached when the septum 2 has moved half-way or less across the section I. The desired attenuation is obtained by turning the knob l9 which rotates the pinion gear [3 and, acting through the rack 12, pushes the rod 1 either in or out and thus determines the separation between the side 3 and the septum 2, which is fastened to the end of the rod 1. A maximum attenuation of as high as 40 decibels has been obtained with a variable attenuator of the type disclosed herein.

What is claimed is:

1. An attenuator comprising a section of metallic pipe wave guide and a resistive septum longitudinally positioned within said section and spaced from a side of said section, the ends of said septum being notched.

2. An attenuator in accordance with claim 1 in which the ends of said septum have rectangular notches.

3. An attenuator comprising a section of metallic pipe wave guide of rectangular cross-section and a resistive septum positioned within said section substantially parallel to, but separated from, a side of said section, the ends of said septum being notched.

4. An attenuator in accordance with claim 3 in which the ends of said septum have rectangular notches.

5. A variable attenuator comprising a section of metallic pipe wave guide, a resistive septum longitudinally positioned within said section and means for moving said septum laterally.

6. An attenuator in accordance with claim 5 in which the ends of said septum are notched.

7. An attenuator in accordance with claim 5 in which said septum comprises a Plate 0f insulating material coated on a major face with re sistive material.

8. A variable attenuator comprising a section of metallic pipe wave guide of rectangular crosssection, a resistive septum positioned within said section substantially parallel to a side of said section and means for moving said septum laterally.

9. An attenuator in accordance with claim 8 in which said septum comprises a plate of insulating material coated on a major face with resistive material.

10. An attenuator in accordance with claim 8 in which said section has unequal cross-sectional dimensions and said septum. is substantially parallel to a side of said section having the shorter width dimension.

11. An attenuator in accordance with claim 8 in which said means permit moving said septum to a position of substantially zero attenuation.

12. An attenuator in accordance with claim 8 in which said means permit moving said septum from a position of substantially zero attenuation to a position of maximum attenuation.

13. An attenuator for use in a wave guide in which high frequency electric waves are propagated comprising a wave guide portion having a mode of propagation in which the maximum intensity electric vector lies in a flat plane symmetrically through and longitudinal of said guide portion, a thin, flat resistance member carried by said guide section andhaving an effective portion thereof lying in a plane parallel to the maxi- 4 mum intensity electric vector and means for moving said effective portion from a region of minimum electric field intensity to a region of maximum electric field intensity whereby a continuously variable degree of attenuation may be provided.

14. An attenuator in accordance with claim 5 in which one end of said septum is specially shaped to reduce reflection.

15. An attenuator in accordance with claim 8 in which one end of said septum is specially shaped to reduce reflection.

16. A variable attenuator comprising a section of metallic pipe wave guide, a resistive septum longitudinally positioned within said section and means for moving said septum laterally, in which the ends of said septum are specially shaped to reduce reflection.

17. A variable attenuator comprising a section of metallic pipe wave guide of rectangular crosssection, a resistive septum positioned within said section substantially parallel to a side of said section and means for moving said septum laterally, in which the ends of said septum are specially shaped to reduce reflection.

18. A variable attenuator comprising a section of metallic pipe wave guide of rectangular crosssection, a resistive septum positioned within said section substantially parallel to a side of said section and means for moving said septum laterally, in which said means permit moving said septum from a position adjacent to a side of said section to a position approximately half-way across said section.

19. An attenuator for a rectangular wave guide comprising a relatively thin plate of dielectric material carrying on at least one broad face thereof a loss-producing coating, said plate being mounted within said guide with its plan parallel with the electric field in said wave guide, and means at one end of said plate for matching the input impedance of said attenuator to the characteristic impedance of said wave guide.

20. An attenuator comprising a section of metallic pipe wave conductor, an elongated dielectric carrier longitudinally positioned within said section, a coating of resistive material on the main section of said carrier, and at least one end portion of said carrier having a resistive coating of a different resistance value per unit length of the carrier than the coating on said main section to reduce wave reflection in said conductor.

21. An attenuator comprising a section of metallic pipe wave conductor, an elongated dielectric carrier longitudinally positioned within said section, a coating of resistive material on th main section of said carrier, and at least one end portion of said carrier having a resistive coating specially shaped to reduce wave reflection in said conductor.

ARNOLD E. BOWEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,151,157 Schelkunofi Mar. 21, 1939 2,207,845 Wolfi July 1 6, 1940