US2596458A - Wave guide stub - Google Patents

Description

y 1952 J. F. ZALESKI 2,596,458

WAVE GUIDE STUB Filed April 23, 1949 2 SHEETS-SHEET l Zmnentor JOHN F. ZALESKI attorney May 13, 1952 J z s 2,596,458

WAVE GUIDE STUB Filed April 23, 1949 2 SHEETS SHEET 2 Gttorneg Patented May 13, 1952 WAVE GUIDE STUB John F. Zaleski, Queens Village, N. Y., assignor to General Precision Laboratory Incorporated, a corporation of New York Application April 23, 1949, Serial No. 89,267

2 Claims. (01. 178-44) This invention relates to a tunable wave guide stub and particularly to an improved device for introducing variable reactance into microwave circuits.

Circuits for microwave energy employ transmission lines which are uniquely different from those used in lower frequency circuits, and which in general consist of hollow wave guides, coaxial transmission lines or dielectric rods. Inductive and capacitive devices for use with such lines also bear little resemblance to those employed at lower frequencies.

One such device commonly used for continuous adjustments of impedance from a low positive reactance value through infinity to a low negative reactance value consists of a short length of rectangular hollow wave guide short-circuited at one end by a movable plunger and open at the other end for attachment to microwave guide in either series or shunt connection. 7

This form of device is designed for use with rectangular hollow wave guide and when connected into a broad side of such a guide to form a series arm its reactance is presented to the guide as series reactance, while if connected into a narrow side to form a shunt arm its reactance is in shunt with that of the guide. While such a tunable stub has been the best variable reactance means heretofore available and has been widely used it suifers from the faults of mechanical complexity and cost. The slidable plug must be precisely made and should incorporate quarter-wave or half -wave trap slots to prevent escape of microwave energy around its edges. Likewise these devices have sliding contacts which are disadvantageous.

The instant invention provides a tunable stub which substitutes for the sliding end plug an adjustable fin of thin sheet material projecting through a longitudinal slot into the interior of the guide. It thus substitutes for the intricate and costly sliding plunger a simply made and easily operated fin of sheet material, greatly simplifying the design and facilitating its employment.

The exact nature of the invention will be more readily understood from the following detailed description when considered with the attached drawing in which:

Figure 1 illustrates one form of the invention applied to a series stub.

Figure 2 illustrates a similar to a shunt stub.

Figure 3 is a side view of a modified form of the invention.

device as applied Figure 4 is a plan view of the modification of Figure 3.

In Figure 1 a section of hollow rectangular wave guide II is closed at one end by a solid conductive plate I2 soldered or brazed to the guide. At the other end l3 the guide is fastened into an opening in a broad side of another section of guide l4 so that the first section is a series arm of the second section. This second section I4 represents any wave guide or microwave equipment through which microwave energy may fiow and which may require for any purpose a tunable wave guide stub attached as :a series arm.

The stub section II is provided with a slot l8 cut in the center line of one of its broad faces and in which is variably positioned a fin is com-- posed of metal or a good dielectric, the former being preferable as the effects produced thereby are somewhat more pronounced. The fin I9 is hinged to the stub section I l by means of a hinge pin 2| which passes through one end of the fin and the cooperating arms ll and 42 of a bracket 43 fastened to the stub section. This rotation of the fin about its pivot point 2| varies the depth of insertion of the fin in the stub section.

To facilitate this adjustment an adjusting screw 22 and compression spring 23 cooperate with an extension 45 on the fin l9 in such fashion that the fin may be moved in either direction without lost motion. To this end the screw 22 is in threaded engagement with a leg 44 of the bracket 43 and has its end bearing on the upper edge of the extension 46 of the fin [9 while the spring 23 is positioned between the upper surface of the stub section II and the under edge of the extension 46. Rotation of the adjusting screw in one direction thus causes the fin l9 to be rotated in a counterclockwise direction against the force of the spring 23 and increases the depth of insertion of the fin I9 in the stub section II. Rotation of the adjusting screw in the other direction, however, permits the spring 23 to rotate the fin Is in the opposite direction and results in a reduced depth of penetration of the stub H by the fin 19.

The fin may be shaped as illustrated, that is, constituting a segment of a circle, or it may be of any other desired shape so long as the shape chosen is such that variation in depth of insertion produces a gradual change in the area of the fin which is contained in the stub section I I.

If desired the slot l8 may be provided with coamings in the form of one-quarter wave or one-half wave traps to prevent radiation thereby as more fully illustrated and described in the V copending application Serial No. 86,293, dated April 8, 1949, of John F. Zaleski, now Patent No. 2,591,329 issued April 1, 1952.

Fig. 2 illustrates the closed-end guide stub ll of Fig. 1 attached as a shunt arm to a narrow side of another section of wave guide 11 which, like the guide M of Fig. 1, represents any wave guide or microwave equipment through which rnicrowave energy may flow and which may resize of rectangular hollow guide chosen are trans mitted through'the guide section I4. With the fin Hiremoved entirely from the interior of the guide, the sign and amount of the reactance which the stub -H offers in series with the guide M at the stub opening 13- depends entirely upon the magnitude of its length L. This reactance has-avalue'ofinfinity when L equals one-quarter wavelength in-the-guideor any odd integral multiple thereof, andis zero ifL is'one-half wavelength or any multiple of it. Between these values 'the reactance offe'red ranges through all inductive and capacitive values. For instance, when L is between and AM, where A is the wavelength in the guide, or in general between where N is any integer, thereactance is inductive and rangesf rom zero to infinity. For lengths between %/\g and. or in general from 75 H 2 'th'ereactanc'e is capacitiveand'ranges from in- 'finity to zero. I

It has beenffou'nd th t when a fin such asfin 7 E9 in Fig. 1 is inserted longitudinally into a broad side of a hollow rectangular wave guide, micro- Waves passing through the guide are retarded, and the amount-of retardation is representative of both the depth of insertion and the length of the inserted portion of the fin. 'If the insertion guide stub such as stub II in Figs. 1 and 2, the electrical length of the stub is increased as the fin is lowered into the guide, for theretardation produced by the fin is equivalent to a phase lag and the effect is electrically similar to the effect produced by increasing the physical length L of the stub. This permits adjustment of the stub by means of the fin to have any value whatever of reactance. For instance, if the length L is chosen to be and the fin is made large enough to be capable of producing at maximum insertion a retardation of at least 180, then the electrical length of the stub may be varied by means of the fin from a length of when the-fin is out of the guide to an electrical length of )\g when the fin is inserted'to its maximum permissible depth. As before described these lengths offer at the open mouth I3 of the stub all possible values of reactance ranging from zero through all inductive values to infinity, then from infiity throughall capacitive-values tozero. These values are interposed in series withthe guide section I 4 in Fig. 1. r

In Fig. 2 exactly the same description applies except that the reactance values are a'p'plied at the open mouth in of the stub l-l inshunt with the'imp'edance of the guide ll.

In Fig. 3 is-illustrated asecond'form of tunable stub which may, like the first ror'm, be connected to a waveguide carrying microwaves as either'a' V series arm as shown in Fig. 1 or a shunt-arm as be made at the longitudinal ce'nteriline or ingeneral in a region of maximum electric field and in a direction parallel to the lines of electric field intensity, the effect will be most pronounced and will be unaccompanied by any appreciable loss of energy.

The ends of the inserted portion of he Tin-are tapered to prevent impedance discontinuities and accompanying loss of energy. The leng'th'ol the fin is made of the order of six or seven wavelengths and' its maximum depth of insertionis limited only by high voltage breakdown or shortcircuiting of the guide. Under these conditions a retardation ofmicrowave energy of over 180 electrical degreesis easily attainable.

It is notable that the retardingactionof the fin on microwaves passing by itis doubly effective: microwaves-entering from the guide M are retarded as they passthe fin and after reflection fromthe closed'end I'2 areretarded a. second. time as they return towardthe-guide t4.

y means of a fin such as described in a waveshown in Fig. 2. In Fig. 3 the connection as a series arm is chosen for illustration. The stub 25 is connected to the waveguide it through which microwaves are transmitted. The end 3| .of' the stub 26 may be either closed oropen since in this form of the invention little of any microwave" energy will reach the end. The stub contains two longitudinal slots, one in the center line of each broad face, and each is protected by twocoamings forming wave traps 32 and 3'3 such as described in the copending application mentioned'supra. These wave traps produce high im- .pedance at the slots for microwave energy attempting to escape therefrom.

.Afin 29 in the shape of a 'stri'pbf sheet material is hinged by a screw 21 to two bosses'lii-ZB, more clearly shown in Fig. 4. The screw issupplied with a nut 31 so that when tightened it clampsthe bosses 28 against the fin 29-andp'reve'nts'it from turning. By loosenin'g the nut the finmay be moved into and clamped at a'ny'p'osi tion'suc'hia's the one shown in'Fig. 3 by full lines "orthat'shown by the 'dashedoutline 34. In these two positions shown and at any intermediate position the edge 36 of the fin near the guide section 24 serves as a short-circuiting post across the'guide, the effective position'of .theshort cir- 'cuit being near the'p'oint 38 where the finpasse's fin effect. This phase-retardation is accom-' plished without the production of any impedance discontinuity because of the oblique position of the edge 36 in the guide.

The lines of intersection of the plane of the fin with the planes of the broad faces of the guide are high impedance regions because of the action of the trap coamings, so that microwave energy is prevented from passing between the fin and the guide faces even when high potential is present.

Although rectangular hollow wave guide is used as an example in the embodiment of this invention, any other type of microwave guide can be employed instead, for use with an adjustable fin, as is more fully explained in the copending application mentioned supra.

In Figs. 1 and 2 a screw is employed for adjusting the fin and in Fig. 3 a clamping hinge is used. However any other convenient method for adjustment of the position of insertion of the fin maybe employed instead.

What is claimed is:

1. A microwave tunable wave guide stub comprising, a rectangular wave guide section provided with longitudinal opposed openings in each of the broad faces thereof, a fin of sheet metallic conductive material pivoted at one end to the external face of said wave guide section at a point adjacent one end of one of said longitudinal openings, said fin extending through said openings and across the narrow dimension of said wave guide section, means for adjusting the angular position of said fin about said pivot, said fin being so shaped and the limits of angular adjustment being such that in any position of adjustment the area of the fin contained within the wave guide section increases gradually from one end.

2. A microwave tunable wave guide stub comprising, a wave guide section provided with longitudinal opposed openings in the periphery thereof, a fin of sheet metallic conductive material pivoted at one end to the external face of said wave guide section at a point adjacent one end of one of said longitudinal openings, said fin extending through said opening and across said wave guide section, means for adjusting the angular position of said fin about said pivot, said fin being so shaped and the limits of angular adjustment being such that in any position of adjustment the area of the fin contained within the Wave guide section increases gradually from one end.

JOHN F. ZALESKI.

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

UNITED STATES PATENTS Number Name Date 2,427,098 Keizer Sept. 9, 1947 2,433,368 Johnson Dec. 30, 1947 2,457,695 Liskow Dec. 28, 1948 FOREIGN PATENTS Number Country Date 591,369 Great Britain Aug. 15, 1947 OTHER REFERENCES Microwave Transmission Circuits," edited by George F. Ragan, Radiation Laboratory Series, Vol. 9, first edition, published by McGraw-Hill. copyright May 21, 1948.

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