US2991434A - Wave guides for propagation of high frequency wave energy - Google Patents

Description

y 1961 J. M. LAMB 2,991,434

WAVE GUIDES FOR PROPAGATION OF HIGH FREQUENCY WAVE ENERGY Original Filed May 51, 1947 INVENTOR, 2,. m

Aaewr United States Patent 2 Claims. (Cl. 333-95) This invention relates to improvements in flexible wave guides for the propagation of high frequency wave energy and in the art of producing flexible wave guides from flat stock. The invention is directed particularly to flexible wave guides suitable for making connection between rigid wave guides or other elements of an ultra high frequency transmission line.

The present application is a continuation of my copending application, Serial No. 257,581, filed November 21, 1951, now abandoned, which in turn is a division of my application, Serial No. 751,561, filed May 31, 1947, now Patent No. 2,600,169, issued June 10, 1952.

Known flexible wave guides consist of rectangular metal tubes having corrugated side walls, the flexibility being imparted to the tube by bending permitted in the walls of the corrugations. One guide of this type is made by winding a formed metal strip helically over a rectangular arbor, then suitably engaging adjacent edges of the strip to form a seam on the outside or inside of the corrugation. In guides of this description, mechanical difliculties are encountered in the attachment of fittings thereto by reason of the configuration of the helix at the plane where cut-ofiis effected. A non-symmetrical terminating surface results and this irregularity creates objectionable mechanical characteristics. An added disadvantage of the helical wound flexible wave guide resides in the electrical losses from the resistance and surface discontinuity of the seam, where the adjacent convolutions are interengaged to form the continuous tube.

In another form of flexible wave guide, corrugations are formed in a seamless rectangular tube by expanding the tube transversely at spaced locations along its axis. Basic seamless tubes for this formof wave guide must be fabricated of metal with a high percentage of elongation in order to permit the stretch necessary to corrugation depth which provides flexibility without distortion of the rectangular configuration; and this is a limitation which becomes more acute as the physical dimensions of the wave guide increase. With the trend to use of higher power for long range applications flexible seamless types of wave guides are not available; and correspondingly large wave guides having long dimensions of from six to twenty-one inches are required to meet these increasing requirements.

A further disadvantage of the seamless type of flexible wave guide, and particularly of utilizing extremes of elongation in metals of which flexible guides are normally made, is the tendency to minute cracking of the stretched side walls at location of non-uniformity of the tube. While failures of this kind may not present problems at atmospheric pressure, they do preclude eflicient pressurizing of the guide in accordance with practices in the ultra high frequency art.

Some flexible corrugated wave guides are fabricated by re-forming a rectangular, extruded, seamless tube as, for example, the one disclosed in US. Patent No. 2,563,- 578, issued August 7, 1951, to Candee. To make a guide of this nature, a tube of appropriate rectangular dimension is first produced then annularly corrugated step by step by stretching the side walls and radius corners to ICE meet the desired configuration. This process is limited to relatively small wave guides the tubing for which does not exceed the size of known extruders and sizes which are within the limits of the stretching of material to meet the required corrugation depth which provides the flexibility. Brass is a conventional material for waveguides and, while wave guides are currently used in sizes of the range of 11.5 inches deep by 23 inches across, the units of diameter'for known seamless-drawn tubing of cuprous alloys is in the range of 8-10 inches. Likewise, to meet the required flexibility, the stretching requirement of the cuprous alloy for larger wave guides made from seamless tubing is far beyond the 50% limit of elongation for themost ductile cuprous alloys. While the annular corrugations of the Candee wave guide are superior to the helical corrugations of earlier flexible units, these limitations, in the face of ever increasing sizes, are detrimental to the overall utility of such a seamless product.

To overcome difiiculties of this kind, I provide an improved flexible guide formed from a relatively thin, wide, continuous flat strip which is corrugated, folded and seamed to rectangular shape, the corrugations being disposed in theside walls at right angles to the longitudinal axis of the guide. In the use of this construction, it is possible to take advantage of the desirable flexing characteristics of a guide having'corrugated side walls and at the same time to retain the superior construction outlined above which is free from a helical configuration and which may be obtained within the physical units of stand ard commercial materials and using readily available rolled stock sizes. I locate the seam of my flexible guide at the centerof the broad inner face because at thatlo cation the current travels parallel to the seam and electrical losses are therefore negligible. The construction of the seam is such that there is a minimum of surface discontinuity on the inside, the lap of material being offset outwardly of the guide. Customary electroplatiug and molding techniques are' followed during the assembly of the guide with its fittings to produce a finished assembly which may be readily installed in an ultra high frequency transmission line. Y I t In the use of this construction it is also possible to take advantage of the commercial availability of wide thin sheets of metal such as are accurately rolled for manufacturing and building'construction'to make guides which are beyond the size range possible for seamless tube construction and without the objectionable helical configuration with its extensive helical seam. Corrugation depths may be produced to practically any limit within the limits of elongation of preferred copper alloys.

The invention will be best understood by consideration of the drawing forming a part of this specification in which,

FIGURE 1 is a fragmentary longitudinal elevation view showing the guide of my invention in assembly with a wave guide end fitting, partially cut away for clarity;

FIGURE 2 is an end elevation view of the guide assembly of FIGURE 1 taken from the left hand end;

FIGURE 3 is a developed view of a strip of material as is used in producing the wave guide of my invention, after corrugating but before interfolding to rectangular form; and

FIGURE 4 is an end view of the guide of my invention after the rectangular forming operations on the blank of FIGURE 3.

Referring to the drawings, FIGURE 1 shows a flexible wave guide assembly 25 consisting of a flexible metal inner core 28 of rectangular transverse configuration which forms the wave guide proper of the assembly. Flange fitting 29, illustrating a typical termination, is secured over the end of the guide as by soldering at 34 and the external guide surface adjacent fitting 29 is covered with flexible molded layers of rubber or synthetic rubber 26, which serves as a mechanical protection and as a stabilizing member of the assembly. It will be understood that terminal fittings are employed at both ends of the guide and that various other types of fittings than as illustrated may be for termination, depending upon the requirements of the circuit.

The guide inner core 28 is constructed with corrugations or undulations in its side walls in order to permit a limited degree of flexing. This flexing may take place in one of two planes with respect to the longitudinal axis of the guide, either of the long dimension or the short dimension. The corrugation depth and shape may vary, a suitable guide being constructed by forming the corrugations so that they are somewhat rectangular as shown in the drawing. The metal from which the guide is constructed is usually brass in the rangeof thickness of from three to thirty-five-thousandths of an inch, although the particular material used, tl 1e size and specific shape of the corrugations may be varied.

The corrugations of the inner core 28 are disposed at right angles to the longitudinal axis of the guide and in the construction of such a guide I first form a flat, elongated blank 35 of a desired length, as illustrated in FIG- URE 3, having transverse corrugations 32 rolled or otherwise established therein. Advantageous methods of producing such corrugations are by progressive stamping operations utilizing a punch and die set or, an alternative method could be pursued using mated, opposed rolls, each of the rollers having a corrugated periphery, and by passing the flat strip between such rolls.

When the blank has been corrugated as in FIGURE 3, it may then be formed as the rectangular tube or inner core 28, as in the end view of FIGURE 4. Rectangular forming may be accomplished by first producing right angle bends in the blank normal to the corrugations at the location of the corners of the tube and thereafter lapping and soldering or brazing the seam as shown at 36 in FIGURE 4, with the lap offset outwardly thereby making for a minimum of internal surface discontinuity. Furthermore, the seam may be discontinuously soldered or brazed longitudinally of the formed tube suflicient only to hold the tube in firm rectangular shape, and permit molding of the rubber covering 26; in which case a limited amount of twisting is available in the finished guide. A butt joint may be substituted for the lap joint 36, however, I have found that the lap seam provides an accurate product with minimum tooling.

I locate the seam, as hereinbefore indicated, at the center of a broad inner face of the guide since, at that location, there is a null point in the high frequency current pattern by reason of the fact that the current travels axially of the guide, hence there is a minimum of loss from the seam as compared with known guides. having helical seams peripherally disposed where the current must travel across each seam.

It will be noted by further observing FIGURE 2, that there is regularity of the undulation at the entrance to the guide and, while undulations are present, theseare of a uniform pattern suitable to transmission of ultra high frequency current.

Having thus described my invention, 1 claim:

1. A flexible wave guide constructed in the form of a rectangular, longitudinally seamed tube and adapted, to the propagation therethrough of ultra high frequency wave energy, the side walls of the tube being formed of a continuous series of uniformly spaced corrugations arranged transversely with respect to the longitudinaltube axis, the seam of the tube being electrically closed throughout its length, but structurally discontinuously closed and located centrally of a broad inner face where ultra high frequency current traveling in the tube is, parallel thereto, whereby electrical losses in propagation are efficiently curtailed.

2. A flexible waveguide assembly constructed, in part, in theform of a rectangular, longitudinally seamed metal tube adapted to the propagation therethrough of ultra high frequency wave energy, the side walls of thetube being formed of a continuous series of uniformly spaced corrugations arranged transversely with respect to the longitudinal tube axis, the seam of the tube being, electrically closed, but discontinuously mechanically closed throughout its length and waveguide terminal fittings secured at the ends of the tube.

References Cited in the file of this patent UNITED STATES PATENTS 341,019 Kent May 4, 1886 343,024 Gordon et a1. June 1, 1886 1,811,678 Smith June 23, 1931 2,006,925 Klemp July 2, 1935 2,115,441 Black Apr. 26,. 1938 2,156,934 Barrett May 2, 1939 2,358,960 Cleve Sept. 26, 1944 2,441,081 Perry May 4, 1948 2,563,578 Candee Aug. 7, 1951 I UHMR no I.

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