US2647951A - Microwave power divider and switch - Google Patents

Description

Aug. 4, 1953 J. F. zALEsKl MICROWAVE POWER DIVIDER AND SWITCH Filed Dec. 29, 1951 INVENTOR.

HUGE/Y5K Patented Aug. 4, 1953 UNITED STATES PATENT OFFICE- 2,647,951 MICROWAVE POWER DIVIDER AND SWITCH John F. Zaleski, Valhalla, N. Y., assignor to General Precision Laboratory poration of New York Application December 29, 1951, Serial N 0. 264,095 6 Claims. (Cl. 333-7) This invention pertains to microwave power dividers and to microwave switches.

The principal requirements for a microwave power divider include low impedance discontinuity at all power ratios and low power leakage to the cut-oil" arm in the terminal positions. DiVlsion of the input into two outputs in any ratio should be readily elfected by a single, simple and continuous adjustment. The divider should be broadband and have a voltage breakdown limit not materially lower than that for a comparable straight length of hollow guide. The design should have no critical interdependent dimensions. A microwave switch in addition to most of these requirements must have low inertia moving parts for rapid switching through a relatively small are between its terminal positions.

The microwave device of this invention has these characteristics, so that it may be applied equally well in the design of a power divider or of a switch. It is suitable for employment with the commonly used type of microwave transmission line composed of hollow rectangular guide and briefly consists of a section of rectangular hollow guide to which microwave energy can be applied, and a second similar hollow guide attached at a midpoint to the first in a T connection, its two ends serving as the two output connections. A 90 rotor and shaft provide adjustment of the output ratio when the device is used as a power divider and the shaft is operable at high speed between its extreme positions when the device is used as a microwave switch.

One object of this invention then is to provide a microwave hollow guide power divider that can also be used as a microwave switch.

Another object is to provide a microwave rectangula-r hollow guide power divider that is wideband and is eflicient in all positions of adjustment.

Still another object is to provide a microwave rectangular hollow guide switch that has only 90 motion between its two switched positions.

A further understandin of the invention may be secured from the following detailed description together with the associated drawings, in which:

Figure 1 depicts an embodiment of the invention.

Figures 2 and 3 are cross-sections of Fig. 1 taken on the planes 2-2 and 3-3 respectively.

Figure 4 is a cross-section of Fig. 1 taken on the plane 3-3 showing the rotor in its intermediate position.

Referring now to Fig. 1, a rectangular hollow microwave guide II short-circuited by a conduc- Incorporated, a cortive plate I2 at one end is arranged for excitation at the other end by microwave energy. The excitation source is schematically indicated by the microwave generator I3. Another rectangular hollow microwave guide M of similar size is joined at right angles to the guide I I, the two guides being interconnected by a rectilinear box IS, the box serving to provide space for an operating shaft I1 and its associated choke bearing I8. This construction brings the plane of the lower broad side of guide II parallel to the plane of the upper broad side of guide I4 but separated therefrom by the length of the box I 6. The guide I4 should be loaded at its two ends I9 and 2| by utilizing apparatus having impedance equal to the guide characteristic impedance to avoid refiections, in accordance with standard practice.

The junction of the guides II and I4 includes an aperture in the lower broad side of the guide II, the interior space of the box I6 and an aperture in the upper broad side of the guide I4, so that the passage provides access from the field space within the hollow guide I I to the field space within the hollow guide I4. The junction has a square cross-sectional area in the plane of the line 2-2, the length of one side being equal to the larger cross-sectional dimension A, Fig. 2, of the hollow guide. This is the maximum value that either side of the area can have although either or both sides can be smaller as will be explained later.

The distance from the end plate I2, Fig. 1, to the center line 22, Fig. 2, of the junction area is approximately A /i, Ag being the wavelength in the guide of the energy supplied to the guide II by the microwave generator I3, to produce the maximum transfer of energy from guide II to guide I 4. This distance, however, departs from the exact value of g/4 by an amount suflicient to match out the junction discontinuity.

The shaft I7, Fig. 2, bisects the area of the aperture and is journalled in two conventional choke bearings I8 and 23, although it may alternatively be journalled in the single bearing I8 and terminated near but not touching the side 24 of the square aperture.

Two conductive rods 26 and 27, positioned at right angles as respects each other are secured at one end thereof to the shaft I1 and extend normal thereto from a point midway at the transverse dimension of the wave guide I 4. These rods are made of such a length as to just clear the sides 28 and 29 of the aperture and the lower broad side 30 of the wave guide I 4 when rotated by the shaft I1.

The shaft I! acts to divide the aperture defined by the sides 24, 28, 29 and 3!, Fig. 2, into two equal orifices, each of which will support microwave transmisison in only the dominant mode. One orifice is defined by the shaft I1 and the aperture sides 24, 23 and 3i, and the other orifice is defined by the shaft i7 and the aperture sides 24, 29 and 3|.

The rods 26' and 2'!" act selectively to interdict the orifices to microwave energy. This occurs when either rod spans either of the orifices because a rod, in so panning. the orifice, divides it into two equal spaces, enough to support the applied' microwave energy in any mode. substantially the same purpose as a solid metal shield in preventing the passage of. microwave.

energy through an orifice of'this size.

When an orifice such as that defined iii-Fig; by the shaft [1 and sides 25, 23 and 3! is left open, that is, unspanned byeither rod, the open oblong'orifice constitutes a. longitudinal slot in a broadside. of the guide ll, displaced from its longitudinal center line, it length-being equal to the dimension A and its width being less than one-half A by the amount of the radius of the shaft l1. However, the width may be made as small as desired although the coupling coefficient will decrease with the width. Such an orifice or slot has the property of radiating microwave energy out of the guide and the discontinuity which it presentsto the source can be matched out almost completely by a uitable matching device. Such a matching device is constituted by the end plate [2, which is placed at a distance from the orifice midpoint departing from g/-& by an amount sufficient to match out the impedance discontinuity.

The oblong orifice can also be considered as constituting a series opening as respects the guide H. Such a series opening couple energy to the guide if the length of the opening, which lies transversely across the guide, is greater than the outofi value of the dimension A, for the applied frequency, this cutoff dimension being approximately one-half of the wavelength in free air of the applied energy. Any impedance discontinuity presented by thisseries opening is matched by the previously mentioned departure of the spacing of the end plate l2 from a distance of )\g/4.

In operation, the generator l3-to microwave energy is the guide II. The shaft I1 is so positionedas to cause the-rods 25; and 21 to assume the positions shown in Fig. 3. The microwave energy then is coupled through the orifice defined by the shaft 11 and apertured sides 24, 2B- and. 3| to the guide 14. There-the energy is prevented from passing towardtheright as seen in' Fig. 3. by the rod 21, which interdicts the right arm IA of guide M. The microwave energy therefore passesout through only the left arm M" of the guide 14. Leakage to the right past rod 26 will not be in phase .with leakage to the right past rod 21 and therefore these two leakages will not be directly additive and will to some'extent cancel each other; Such leakage as remains is minimized by reducing the rod clearances and the net efiect is easily reduced sufficiently to provide 25 db decoupling. between the two arms of guide Hi.

When shaft l1-is rotated 90 clockwise therod 21 is. brought into: the dashed position. 32; Fig; 3, and the. rod 25- is brought into the vertical position formerly occupied by rod 2.1.. The orifice defined by the. shaft lland aperture-sides 24,

neither of which is'large' A rod of this 'characterthusserves applied from I 28 and 3|, Fig. 2, is then interdicted and microwave energy passes out the other orifice only into arm [4 of guide M.

This power divider presents a relatively low impedance discontinuity to the input arm at all positions of the shaft I1. As an example of operation at an intermediate position, Fig. 4 illustrates the power divider adjusted to divide the input power into two equal outputs, the rods 26 and 2'! being in their midpositions. The microwave energy then passes from guide H into the left arm W through'an area defined in its lesser dimension by the: perpendicular distance from therod 2'] to the edge 28 of the junction aperture.

. Theimpedan'ce of such an area exposed to microwave energy as described is in direct relation to the magnitude of this dimension, and is in this caselesathan the characteristic guide impedance. Similarly, microwave energy passes from guide l I into the'right arm l4. through. a similar area defined by thesgap between the rod 26 and the edge29 of the aperture, this area also presenting an impedance less than the characteristic guide impedance. But since these two impedances are effectively in series a presented to the source, their sum has a magnitude roughly equal to that characterizing the guide. Therefore, in this midposition, and it is found to be true also atall other positions of the rods 26 and 21, only a small impedancediscontinuity is presented to the microwave energy source.

The device can also be employed as a microwave switch, in which use the device is especially valuable because it has but one moving part, its throw is only 90, its-rotatingparts can be made tohave very low inertia, and because the impedance discontinuity during switching is minimized. In order to operate the power divider as a switch it is merely necessary to connect the shaft I! to manual or other means for moving it from one terminal position to the other, such means being schematically indicated in Fig. 2 by the crank and handle 33 Whatis claimed is:

1. A device of the class described comprising, a first rectangular hollow wave guide having. an input terminal at one end adapted to be connected to a source of microwave energy and having the other end refiectively terminated, at second similar wave guide. having. its broad sides parallel to the broad sides of said first wave guide and having two arms containing ends adapted for use as outputterminals, said second wave guide being-connected intermediate said two ends in overlapped relation to said first wave guide adjacent said other end thereof to form a T junction, means defining an aperture in the overlapped areas joining the. interior spaces of said first and second wave guides, said aperture having a length in. a. direction transverse to said second wave guide such that. the full length thereof. will-transmit. applied microwave energy while. substantially less than the. full length thereof. willprevent the transmission of such energyinany mode, a rotatableshait parallel to said first wave guide and dividing said aperture into two equal windows, anda pair of equal length rods secured normally to said shaft and normany to each other intermediate the sides of said aperture to extend into one or the other of said windows and to extend into one or the other of said arms'respectively in accordance with their positioning by said shaft, thereby controlling the impedance of said windows and arms to microwaveenergy;

2. A device of the class described comprising, a first rectangular hollow guide having an input terminal at one end adapted to be connected to a source of microwave energy, a second similar wave guide having its broad sides parallel to the broad sides of said first wave guide and having two arms containing ends adapted for use as output terminals, said second wave guide being connected intermediate said two ends in overlapped relation to said first wave guide to form a T junction, means defining a rectangular aperture in the overlapped areas joining the interior spaces of said first and second wave guides, said aperture having a length in a direc tion transverse to said second wave guide such that the full length thereof will transmit applied microwave energy while substantially less than the full length thereof will prevent the transmission or such energy in any mode, a transverse metal plate terminating the other end of said first wave guide parallel to the center plane of said aperture and at a distance therefrom approximately equal to an odd quarter of the wavelength of said energy in the guide, a rotatable conductive shaft parallel to said first wave guide and dividing said aperture into two equal windows, a pair of equal length conductive rods secured normally to said shaft and to each other and lying in said center plane, means for rotating said shaft into one position to extend one said rod into one of said Windows and the other said rod into the interior space of said two arms, and into one other position to extend the other said rod into the other of said windows and the one said rod into the interior space of said two arms, thereby controlling the admittance of said windows and said arms to microwave energy.

3. A device of the class described in accordance with claim 2 in which said rectangular aperture has maximum length and width equal to the greater internal cross sectional dimension of the guide and in which the limiting minimum dimension of said rectangular aperture parallel to said first guide is equal to one-half of the wavelength of said applied microwave energy in free space.

4. A device of the class described in accordance with claim 2 in which said connection between the first and second guides comprises a short rectangular hollow guide separating the first and second guides by its length and the walls thereof supporting said shaft.

5. A microwave power divider comprising, a first rectangular hollow guide having an input terminal at one end adapted to be connected to a source of microwave energy, a second similar wave guide having its broad sides parallel to the broad sides of said first wave guide and having two arms containing ends adapted for use as output terminals, said second wave guide being connected intermediate said two ends in overlapped relation to said first wave guide to form a T junction, means defining a rectangular aperture in the overlapped areas coupling the interior spaces of said first and second wave guides, said aperture having a length in a direction transverse to said second wave guide such that the full length thereof will transmit applied microwave energy while substantially less than the full length thereof will prevent the transmission of such energy in any mode, a transverse metal plate terminating the other end of said first wave guide parallel to the center plane of said aperture and at a distance therefrom approximately equal to an odd quarter of the wavelength of said energy in the guide, a rotatable conductive shaft continuously and selectively adjustable said rectangular aperture dividing it into two equal windows, and a pair of equal length conductive rods secured normally to said shaft and to each other and lying in said center plane each rod movable with said shaft partly to bisect a respective said window thereby partially interdicting said windows to microwave energy and concomitantly partially interdicting said arms.

6. A microwave switch comprising, a first rectangular hollow guide having an input terminal at one end adapted to be connected to a source of microwave energy, a second similar wave guide having broad sides parallel to the broad sides of said first wave guide and having two arms containing ends adapted for use as output terminals, said second wave guide being connected intermediate said two ends in overlapped relation to said first wave guide to form a T junction, means defining a rectangular aperture in the overlapped areas coupling the guides, said aperture having a length in a direction transverse to said second wave guide such that the full length thereof will transmit applied microwave energy while substantially less than the full length thereof will prevent the transmission of such energy in any mode, a transverse metal plate terminating the other end of said first wave guide parallel to the center plane of said aperture and at a distance therefrom approximately equal to an odd quarter of the Wavelength of said energy in the guide, a rotatable conductive switch shaft having two terminal positions spaced ninety degrees apart said shaft being parallel to said first wave guide and lying across said rectangular aperture dividing it into two equal windows, first and second conductive rods of equal length secured normally to said shaft and normally to each other in said center plane, in one terminal position of said shaft said first rod being positioned to bisect one of said windows and said second rod spanning said second guide and in the other terminal position of said shaft said second rod being positioned to bisect the other of said windows and said first rod spanning said second guide whereby one or the other of said arms is interdicted to microwave energy.

JOHN F. ZALESKI.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,396,044 Fox Mar. 5, 1946 2,573,746 Watson et a1 Nov. 6, 1951 2,602,859 Moreno July 8, 1952 OTHER REFERENCES Microwave Transmission Circuits edited by Ragan, vol. 9 of the Radiation Laboratory Series, published by McGraw-Hill, May 21, 1948-Page 536, Copy in Div. 69.

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