US2863128A - Waveguide tuner - Google Patents

Description

Dec. 2, 1958 HQc. GlLcHRlsT ET AL 2,863,128

WAVEGUIDE TUNER Filed sept. 19, 195e y.. E f3- gl. 5

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N WW@ WAVEGUIDE TUNER Harry C. Gilchrist, Pleasantville, and John F. Zaleski,

Valhalla, N. Y., assignors to General Precision Laboratory Incorporated, a corporation of New York Application September 19, 1956, Serial No. 610,863

2 Claims. (Cl. S33-98) This invention relates to devices for matching irnpedance discontinuities in waveguides.

Waveguides are widely used for the transmission of energy at microwave frequencies and so long as the waveguide maintains the same dimensions and contains no bends, junctions, loads, or the like, the energy can be transmitted without reflection. Practical circuits, of course, nearly always include one or more of such discontinuities which will cause reection and power loss unless some provision is made for compensating for their presence.

One widely used technique for eliminating reflections caused by a discontinuity is the use of a rod or screw inserted into the waveguide parallel to the lines of electric force. Such an arrangement introduces an additional reflection which can be made equal in amplitude but opposite in phase so as to cancel the reflection caused by the discontinuity. If the screw is inserted through a longitudinal slot in the face of the waveguide, the phase of the added rellection may be adjusted by varying the longitudinal position of the screw while the magnitude may be adjusted by varying the amount by which the screw is inserted. A number of tuners of this class have been constructed in the past, but have been subject to the disadvantage that two adjustments are required to match a discontinuity. To overcome this disadvantage, the use of a large asymmetrically placed screw having a projection on one side beyond the end has been proposed. While this arrangement requires but a single adjustment, it is subject to the disadvantage that the voltage standing wave ratio observed in tuning a mismatch is a complicated function of the insertion.` This is because the reflection caused by the body of the screw remains fixed phase while that caused by the projection varies, and also because the projection moves transversely as well as longitudinally.

It is an object of the present invention to provide a simple waveguide tuner for compensating for impedance discontinuities.

Another object is to provide a waveguide tuner having a single control for varying both the magnitude and phase of the susceptance.

Briefly stated, one embodiment of the invention comprises a thin rod inserted into the waveguide through a longitudinal slot on the centerline. The amount of insertion is varied by rotating a cam which bears on the end of the rod. As the cam rotates, it, together with the rod, is moved longitudinally by the action of a lead screw.

For a clearer understanding of the invention reference may be made to the following detailed description and the accompanying drawing in which:

Figure l is an isomeric view of a preferred embodiment of the invention;

Figure 2 is a fragmentary cross sectional view taken on the line 2-2 of Figure l; and

Figure 3 is a cross sectional view taken on the line 3-3 of Figure l.

Referring first to Fig. 1, there is shown a rectangular States Patent() M 2,863,128 latented Dec. 2, 1958 waveguide section 11 supported by two upstanding end pieces 12 and 13 which may also serve as flanges for connecting the device to other microwave components. Mounted on top of the waveguide section 11, on one broad side thereof, is a block 14 of rectangular cross section slightly narrower than the waveguide and extending the full length between the end pieces 12 and 13. Block 14 is fastened securely to the waveguide 11, as by soldering or brazing, so as to make the waveguide 11 and the block 14 effectively one piece. A narrow slot 15 is cut through the block 14 and the waveguide 11 on the center line and at least one-half a guide wavelength long. A carriage comprising two upstanding frame portions 16 and 17 with a bottom portion 18 integral therewith is arranged to slide longitudinally along the top of the block 14 and the waveguide 11. Two plates 19 and 21 are fastened to the carriage and help to guide it along the block 14 and waveguide 11. A machine screw 22 is fastened at its ends to the end pieces 12 and 13 and is positioned directly above the slot 15 and parallel thereto.

As best shown in Fig. 2, a sleeve 23 surrounds a portion of the screw 22 and has corresponding threads on the inside thereof. One end of this sleeve 23 is fastened to an adjusting nut 24 so that rotation of the nut turns the sleeve and moves both the sleeve and the nut along the axis of the screw 22. The sleeve 225i passes completely through the frame portion 16 and part way through the frame portion 17 and rotates freely within these portions. A cam 25 is placed between the frame portions 16 and 17 and is fastened to the sleeve 23 by means of a set screw 26 as shown in Fig. 3. lt can be seen that rotation of the nut 24 will cause the cam 25 to rotate and will also cause the entire assembly including nut 24, the cam 25, the sleeve 23 and the entire carriage to move longitudinally.

Referring now to Fig. 3, there is shown a conductive or nonconductive rod 27 which projects through the slot 15 in the block 14 and the waveguide 11. The rod 27 makes a close fit in passing through a hole in the bottom portion 18ct the carriage and the upper end of the rod is fastened to a plate 28. The plate 2S and with it the rod 27 are urged upwardly by two springs 31 and 32 which bear against the bottom of the plate and are seated in holes passing through the bottom portion 18 of the carriage and the two plates 19 and 21. The cam 25 bears against the upper portion of the plate 28 holding it in position against the urging of the springs 31 and 32. It can be seen that rotation of the cam 25 will adjust the amount by which the rod 27 is inserted into the interior of the waveguide 11 and the dimensions are selected so that this insertion varies from zero to onequarter of a wavelength.

Since the slot 15 is located on the centered line of one broad face of the guide 11 and since the guide is normally used to propagate the dominant TEM, mode very little powerwill escape through the slot. Power is prevented from leaking through the slot in the vicinity of the rod by making the distance from the inner wall of the waveguide to the top of the block 14 equal to one-quarter of a guide wave length and by a choke comprising an annular recess 33, one-quarter of a guide wavelength long, formed inV the bottom portion 18 of the carriage.

The apparatus is used to compensate for a discontinuity in a waveguide transmission band by inserting the device into the path by means of the end pieces 11 and 13. The nut 24 is turned until the best voltage standing wave ratio is obserbed. Rotation of the nut 24 rotates the cam 25 thereby adjusting the amount of the insertion of the rod 27. Since the insertion can be` varied from zero to a quarter of a wavelength reflections of any magnitude can be compensated for within one-half a revolution of the nut 24. The phase of the reflection may be adjusted by continued rotation of the nut 24 to place the rod 27 at any longitudinal point within a half guide wavelength. Thus, the entire adjustment for both magnitudeV and phase is accomplished with but a single control. Of course, not every magnitude of insertion of ythe rod 27 can be secured continuously within this haltv wavelength distance but only at many distances separated by one-half the pitch -of the screw 22. By using a screw with a line thread this limitation is minimized and as a practical matter is not important.

A speciic embodiment has been described for illustrative purposes only and many modifications will occur to those skilled in the art. It is therefore desired that the invention be limited only by vthe true scope of the appended claims.

What is claimed is:

l. A tuner comprising a section of waveguide having a longitudinal slot in the wall, a carriage slidable along the outer wall, a conductive rod mounted on said carriage in alignment with said slot, a cam -mounted on said carriage and cooperating with said rod for varying the amount by which said rod projects through said slot into the interior of said waveguide, and screw and nut means for simultaneously actuating said cam and sliding said carriage along said waveguide.

2. A waveguide tuner comprising a section of a rectangular waveguide having a slot along the center line of one broad side, a carriage on said broad side and slidable lengthwise of said waveguide section, a conductive rod mounted on said carriage in alignment with said slot, spring means on said carriage urging said rod away from said waveguide section7 a lead screw mounted above said broad face and parallel to the axis of said waveguide section, a cam freely rotatable about said lead screw and mounted between two upstanding frame portions of said carriage for inserting said rod into said waveguide against the urging of said spring, a sleeve threaded onto said lead screw and connected to said cam and an adjusting nut secured to said sleeve, whereby rotation of said nut rotates said cam, adjusts the insertion of said rod and slides said carriage along said waveguide.

References `Cited in the tile of this patent UNI-TED STATES PATENTS 2,496,837 Woodyard Feb. 7, 1950 ,2,578,249 Johnson Dec. l1, 1951 2,705,307 Nyswander Mar. 29, 1955

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