US2709789A

US2709789A - Attenuator

Info

Publication number: US2709789A
Application number: US662464A
Authority: US
Inventors: Francis T Worrell
Original assignee: Individual
Current assignee: Individual
Priority date: 1946-04-16
Filing date: 1946-04-16
Publication date: 1955-05-31
Anticipated expiration: 1972-05-31

Description

May 31, 1955 F. 'r. WORRELL ATTENUATOR Filed April 16, 1946 INVENTOR FRANCIS T. WORRELL ATTORNEY United rates Patent ATTENUATOR Francis '1. Wort-ell, Chicago, Ill., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application April 16, 1946, Serial No. 662,464

6 Claims. (Cl. 33381) This invention relates in general to attenuators and in particular to radio frequency power attenuators.

This invention is applicable in general for attenuating electromagnetic energy and in particular for attenuating electromagnetic energy of ultra-high radio frequency.

The principal object of this invention is to provide a variable attenuator having a low insertion loss.

Other and further objects of this invention will be apparent from the following specification when taken with the accompanying drawing which is an isometric view of an embodiment of the invention.

The attenuator as shown utilizes the properties of series and parallel connected elements of wave guide transmission lines, commonly known as a Magic T. Input wave guide 10 feeds power to the magic T junction which has low loss branch wave guides 11 and 12 and output wave guide 13. Wave guides 11 and 12 from the T junction to

junctions

14 and 15 are low loss sections of wave guide and section 12 is one-quarter wave length longer than section 11. The sections of

wave guide

16 and 17 are lossy wave guides, the type used being determined by the amount of attenuation desired. A lossy wave guide section, as defined in the Bureau of Ships publication, Radar System Fundamentals, Nav- Ships 900,017, published April 1944, is a wave-guide section having a large attenuation per unit length. This attenuation is substantially greater than that of a standard wave-guide section. Reflecting

plungers

18 and 19 are arranged to move in the

lossy wave guides

16 and 17 and are coupled together by mechanical means 20 so that they can be moved equal amounts in unison by rod 21.

Plungers

18 and 19 are initially arranged so that the distance D is equal to the distance D, this then makes the distance from the T junction to plunger 19 onequarter wave length or an odd multiple of one quarter wave length longer that the distance from the T junction to plunger 18. As a result the reflected waves from the plungers will arrive back at the T junction out of phase and will thus combine to go out wave guide 13. As the plungers can be inserted as far as the

junctions

14 and 15, the minimum insertion loss is the loss incurred in having the energy travel from the T junction to

junctions

14 and 15 and back to the T junction, and as these wave guides (11 and 12) are of low-loss, the insertion loss is low. The added loss will vary directly with the distances D and D. Using lossy wave guide of known attenuation characteristics for

sections

16 and 17 the calibration data can be computed and an absolute calibration obtained.

It is not intended that this invention be limited to the details as shown as other types of transmission lines of equivalent configuration will give the same operation, and the input and output can be reversed without .afiecting the operation of the attenuator. This invention is to be limited only by the following claims.

What is claimed is:

1. An electromagnetic wave energy attenuator comprising, a magic T structure having input, output and two branch transmission lines extending from a common junction, said transmission lines being arranged where by said input line is electrically in parallel with said two branch transmission lines and said output line is electrically in series with said two branch transmission lines, each of said branch transmission lines terminating in a lossy section for dissipating electromagnetic energy therein, adjustable means in each of said lossy sections for reflecting electromagnetic energy toward said common junction, and means mechanically coupling said reflecting means in said branch arms for adjustment thereof in unison.

2. An electromagnetic wave energy attenuator comprising, a magic T structure having input, output and two branch transmission lines extending from a common junction, said transmission lines being arranged whereby said input line is electrically in parallel with said two branch transmission lines and said output line is electrically in series with said two branch transmission lines, each of said two branch transmission lines having a lossy section for dissipating electromagnetic wave energy therein, a reflecting termination within each of said lossy sec tions, the lossy section and the coacting reflecting termination of one of said two branch arms being disposed closer said common junction then the corresponding elements of the other of said two branch arms by one quarter wave length at the frequency of energy to be attenuated, and means for mechanically coupling said reflecting terminations for displacement thereof in unison through said lossy sections.

3. An electromagnetic wave energy attenuator comprising a magic T structure formed of input, output and two branch recangular wave guides mutually coupled at and extending from a common junction, said wave guides being arranged whereby said input wave guide is electrically in parallel with said two branch wave guides and said output wave guide is electrically in series with said two branch wave guides, a first lossy wave guide section for dissipating electromagnetic wave energy disposed in the first of said two branch wave guides at a first distance from said common junction, a second lossy wave guide section for dissipating electromagnetic wave energy disposed in the second of said two branch Wave guides at a second distance greater than said first distance by one quarter wave length measured at the frequency of energy to be attenuated, a first reflecting termination adjustable within said first lossy wave guide section for reflecting energy toward said common junction, a second reflecting termination adjustable within said second lossy wave guide section for reflecting energy toward said common junction, mechanical means joining said first and second reflecting terminations for displacement in unison through said lossy wave guide sections, said second reflecting termination being disposed a distance from said common junction greater than the distance of said first reflecting termination from said common junction by one quarter wave length measured at the frequency of energy to be attenuated.

4. An electromagnetic wave energy attenuator comprising, in combination, a magic T wave guide assembly having an input arm, a pair of H-plane side arms in parallel therewith and an output E-plane arm in series with said side arms, said arms extending from a common junction, said H-plane side arms differing in length by one-quarter wave length of the frequency of the electromagnetic energy being coupled to said assembly, a section of lossy wave guide terminating each of said H-plane side arms and shorting plungers axially displaceable within said lossy wave guide sections for adjusting the effective lengths thereof and for reflecting incident electromagnetic energy back towards said common junction, said plungers being interconnected to move in unison thereby to maintain said elfectivc lengths equal during their adjustment.

5. An electromagnetic wave energy attenuator comprising, in combination, a magic T wave guide assembly having input, output and two branch arms extending from a common junction, said arms being arranged whereby said input arm is electrically in parallel with said two branch arms and said output arm is electrically in series with said two branch arms, said branch arms difiering in length by one-quarter wave length of the electromagnetic energy being propagated within said assembly, a section of lossy wave guide coupled to the end of each of said branch arms, and means for adjusting the eliective lengths of said lossy sections while maintaining equality thcrebetween, said last-mentioned means consisting of interconnected shorting plungers disposed within said 'lossy wave guide sections and adapted to move axially in unison to provide short-circuited terminations for said lossy wave guide sections whereby electromagnetic energy coupled to said input arm and subdivided between said two branch arms is equally attenuated by said lossy wave guide sections and reflected back toward said common junction by said shorting plungers appearing thereat as equal amplitude signals in phase opposition.

6. An electromagnetic wave energy attenuator comprising a magic T wave guide assembly having input, output and two branch arms extending from a common junction, said arms being arranged whereby said input arm is electrically in parallel with said two branch arms and said output arm is electrically in series with said two branch arms, said branch arms differing in length by one-quarter wave length of the electromagnetic energy being propagated in the assembly, a section of lossy wave guide connected to the end of each of said branch arms, shorting plunger disposed within each of said lossy wave guide sections for determining the effective length of these sections and for reflecting incident electromagnetic energy back towards said common junction, said shorting plungers being located at equal distances from the ends of said branch arms and being mechanically interconnected to move in unison whereby electromagnetic energy initially coupled to said input arm and subdivided between said branch arms is equally attenuated by said lossy wave guide sections and reflected by said shorting lungers thereby to reappear at said common junction as equal amplitude, out-of-phase signal components for coupling into said output arm.

eferences Cited in the file of this patent UNITED STATES PATENTS 2,088,749 King Aug. 3, 1937 2,106,763 Southworth F b. 1, 1938 2,197,123 King Apr. 16, 1940 2,438,914 Hansen Apr. 6, 1948 2,498,548 Howard Feb. 21, 1950 2,510,016 Fernsler May 30, 1950 2,564,030 Purcell Aug. 14, 1951 2,593,120 Dicke Apr. 15, 1952