US2646551A - Wave guide variable attenuator - Google Patents

Description

7 July 21, 1953 s. ROBERTS 2,646,551

WAVE GUIDE VARIABLE ATTENUATOR Filed Feb. 25. 1944 IN VEN TOR.

SHEPARD ROBER TS BY WM 94-11 XH- vrne of insulating material.

Patented July 21, 1953 V 7 2,646,551 J l Y WAVE cums v aIABLEnTTENUA'roR Shepard Roberts, Cambridge, Mass, assignor, by

'mesneassignments, to the United 'States of- America as represented by 'the Secretary of .War

nim iqeti n FebruaryZS, 1944, Serial ndszasss' fTClaims. (o1. sea-+3 1) @This invention relates to a guide control and particularly to a variable attenuator foruse in wave guides. v r

The principal object ofthe invention is to prof vide a simple, inexpensive and readily adjustable small strip dimension the maximum intensity electric vector.

Attenuation is btained by itioningthe sistance' stripwithin the guide space so that the attenuator of this character whereinfthere is 1 little or no reflection of the guided waves. I l ,I, In the accompanying drawing, Fig; 1 is a part.- ly cut-away perspective view of the invention;

and Fig. 2 is a modification.

The attenuator is shown as embodied ma) rectangular metallic Wave guide portion 5, Fig. l,, which is constructed the. usual'mannerand with the usual ratio'of larger side to shorter. side and dimensions determined by transmitted frequency. If desired, the attenuator may-"be applied to a circular wave guide having a mode of wave propagation where the maximum intensity electric vector lies in a diametral plane. An elongated strip of resistance material 6 is disposed within theguide portion, end 1 of said strip being fixed to a shorter guide side by fastening means such as bolt 8.

Thus the anchored end is at a region of said guide where the electric vector has its minimum intensity. Strip 6 may be comv posed of some insulating material such as Bakelite with one side thereof coated with a layer of carbonaceous material to provide a desired resistance characteristic. The free end of the strip movable part, constitutes aneffect'ive portion" which may be moved from a position of-minimum electric field intensity. (r'ight j up against the guide wall) to a' position of maximum field intensity (substantially in the center-of the space provides visual indication of strip position, al-

is tapered as shown at 9, the longitudinal length of the taper being at least a half wave length of the transmitted wave.

A micrometer or similar adjusting device I0 is fixed to the exterior of the waveguide portion and positioned in relation to the free end of strip 6. The guide portion is suitably apertured to received positioning pin ll of the micrometer.

enclosed-by the guide walls) The, micrometer though a simple screw control or other means may be used'if desired.

The modification of Fig. z'shows an attenuator embodied in a rectangular waveguide portion 20 constructed and dimensioned in the risualmanner. A- narrow centrallydisposedlongitudinal aperture 2| is provided in the larger guide side. This aperture is along the line of intersection of the wave guide wall and plane of maximum electric field'intensity. A circular guide may have a similar construction. The attenuator comprises an elongated supporting metallic member 22, which is suitably connected to the apertured guide side as by hinge 23. A thin sheet of resistance material 24 depends from supporting member 22 and registers with aperture 2|. The resistance sheet is wide at its central region and tapers or curves at least half a wave length to each end asshown. The center width of sheet 24 substantially correspondsto the width of a shorter guide side so that the element may terminate just short of its opposite guide side when moved 7 to its maximum position within the guide. Ele- This pin'bears on the surface of strip 6 near its free end and causes said strip to bend away from theguide side into the space within the guide in accordance with micrometer adjustment. The pin ispreferably of small diameter and may be A recovery spring 15 of ments of hinge 23 may fit rather tightly so that friction will retain the pivoted attenuator in any predetermined position.

1 It'will be seen that the invention provides a readily variable attenuator for use with wave guides. .The device has been found to cause little or no appreciable wave reflection. Having thus described the invention, what I claim as new and desire to-secure by Letters Patent is: r

1. An attenuator for use. in a wave guide in which high frequency electric waves are progagated comprising a wave guide portion having a,

modeof propagation in which the maximumintensity electric vector lies in a fiat plane symmetrically through and longitudinal of said guide portion, a thin, fiat resistance member carried by said guide at a region where the electric vector is substantially zero, and lying generally in a plane parallel to that of the maximum intensity electric vector, and means for moving at least part of said member in a direction generally perpendicular to the maximum intensity electric is parallel to the plane of 3 vector from a region of minimum field intensity to a region of maximum field intensity.

2. The structure of claim 1 wherein said member has a tapered end along the line of wave propagation with the taper portion at least half a wave length in the full attenuation position.

3. An attenuator for use in -agwave 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 sym v metrically through and longitudinal of said'guide portion, a thin, fiat resistance member mounted;

on said guide to lie in the maximum intensity" electric vector plane, said guide being: slottedttog clear said member and means for moving said. member from the exterior of meanders the irrterior thereof for varying the attenuation; where a V in said member is pivotally mounted at one end thereof. with/the member having the general shape of a segment of a circle.

a 4, lncomhination, a hollow wave guide ri eali to vary the ntensity of waves transrr'li-tteditv r ethrough, said means. comprising a flexiblejdiele ctric, member attached to the inner wall or sai guide, and means arrangedexternally of said guide and connected withfsaid memmer through a wall of said-guide variably. .to'adjustsaid'mem her in positions extending from the'wall of said: guide toward the center thereof graually along the lengthof a portion offthe guide, said dielec trie member carrying thereon resistance mate rial .to absorb the energy or said wave.

5. In combination, a dielectric wave guide along which a high'frequency wave s propagated comprising a hollow rectangular pipe having" walls of conductive material and attenuating means for said wave comprising, a thin strip of resistive material extending longitudinally along the inner surface of one of said walls, said strip having its endpresented to a wave traveling gated strip having a conductive surface layer 'on at least one'sidethereof with a resistance substantially. greater than that of said guide surface,

said strip being positioned within said guide and extending lengthwise thereof with said side substan ally parallel tq the electric field of said wer on said strip being secured to a wall of said guide with the strip extending away from said point in angular relation to said wall. 7'. In a high frequency system, a hollow tubular guideforan'electro magnetic wave, said guide having a conductive inner surface and a rectangular transverse section with a pair of wide walls and ja pair'of narrow walls, and an elongated strip having a conductive surface layer on at i least one sidethereon with a resistance substantially greater than that of said guide surface, said strip being positionedwithin said guide and extending lengthwise thereof with said side substanti-ally perpendiculartosaid "wide walls; a point onsaidstrip" beingsec'ured to one of said narrow walls with the strip extending away from said point in angular relationv to said, one narrow wall. v v I p ROBERTS. References Cited in theme of this patent UNITED STATES; PATENTS

Images