US2766430A - Microwave power divider - Google Patents

Description

J. Fl ZALESKI Oct. 9, 1956 MICROWAVE POWER DIVIDER Filed April 2, 1955 United States Patent Ofiice 2,766,430 iatented Oct. 9, 1956 2,766,430 MICROWAVE POWER DIVIDER John F. Zaleski, Thornwood, N Y., assignor to General Precision Laboratory Incorporated, a corporation of New York Application April 2, 1953, Serial No. 346,330

6 Claims, (Cl. 333-7) This invention relates to adjustable microwave power dividers and attenuators, which are wide band, have constant impedance and high breakdown potential.

The problem of attenuating large amounts of microwave pulsed power presents problems not met in controlling electricity at lower frequencies. It has not been found simple to attenuate large powers without encountering spark-over and serious changes of the impedance presented to the source of power.

One of the methods of microwave attenuation involves the use of an adjustable power divider and this method is employed in the instant invention to provide a device having constant input impedance, wide band operation, and a high spark-over potential.

The instant invention is based upon the properties of that form of the microwave hybrid junction known as the magic tee. It also depends upon the properties of a round hollow microwave guide. This type of guide is combined with rectangular hollow guide to form a magic tee having two collinear arms made of round guide and series and shunt arms of rectangular guide, the assembly constituted by these four arms being rotatable relative to the fixed input and output waveguides. The microwave power is introduced to the round guide, setting up a TE1,1 non-symmetrical field therein. The rectangular guide arms comprise a series or E arm and a shunt or H arm and are rotatably positioned so that they may either intercept all of the energy permitting none to pass, or may intercept none and permit all to pass, or may be intermediately positioned to intercept some, permitting the remainder to pass.

If the series arm and shunt arm are terminated in nonreflecting dissipative elements all energy taken out of the round guide by them is dissipated in heat, and whatever energy is not removed by the series and shunt arms may be utilized at an exit further along in the round guide. The amount of energy available at this exit is thus easily controlled by rotation of the rotatable guide section comprising the hybrid juction. With proper termination and impedance matching of the several arms, no change of impedance is reflected to the source as the attenuator is adjusted. The device is only slightly frequency sensitive, and the power carrying capacity is nearly as high as that of a straight length of hollow guide of the same size.

One purpose of this invention is to provide a simple microwave divider for dividing a quantity of microwave energy into three parts, the ratio of one part to the other two being adjustable in any proportion, and these two parts being equal.

Another purpose of this invention is to provide a simple and improved microwave power attenuator.

A furtherunderstanding qf this invention may be secured from the detailed description and the associated drawings, in which:

Figure 1 is an isometric representation of an embodiment of the invention.

Figures 2 and 3 illustrate field modes which may be set up in the guide junction of Figure 1.

Referring now to Fig. 1, a round conductive hollow pipe 11 suitable for transmission of microwave energy is so excited as to transmit microwave energy in the TE1,1 mode. Any microwave frequency at which round and rectangular hollow guides can be used may be employed as, for example the x-band frequency of 10,000 megacycles, and in this example the round guide 11 has a suitable diameter for this frequency. It may be conveniently excited by microwave energy introduced by a rectangular guide 12 connected to round guide 11 through a guide transformer or, as shown, through an end plate 13 with a suitable coupling iris such as the inductive iris 14 in the end of the rectangular guide. Any equivalent means of matching the rectangular guide impedance to that of the round guide may of course be employed. When the rectangular guide carries microwave energy in the TE1,0 mode, the TE1,1 mode is excited in the round guide, and microwave energy is transmitted through the round guide in that mode.

The other end of the round guide is arranged in any convenient way for the utilization of energy passing through it. For example, as there are several advantages in the use of rectangular guide for microwave transmission, a transition torectangular guide may be made by any convenient means as, for example by the same means used at the input end. A flat end plate 16 is used to terminate the round guide and carries a rectangular hollow guide 17 with the direction of its shorter cross sectional dimension parallel to the direction of the shorter cross sectional dimension of input guide 12. The guide 17 is appropriately impedance matched by any means, for example'by an iris 18. In addition, the guide 17 is terminated in its own characteristic impedance to prevent refiection of energy.

1 At an intermediate cross sectional plane of the round guide 11 two side arms 19 and 21 made of rectangular hollow guide are attached at right angles to the round guide. One arm 19 has its longer cross sectional dimension in the plane of the round guide cross section and therefore constitutes a series or. E side arm. The other arm 21 has its longer cross sectional dimension parallel to the axis of the round guide and therefore constitutes a shunt or H side arm. The two side arms are spaced circumferentially apart on the round guide. These series and shunt side arms together with the round guide thus form a magic tee with the collinear arms consisting of round guide sections and the series and shunt arms of rectangular guide sections. This magic tee behaves I ike a magic tee made entirely of rectangular guide provided that the field mode in the round guide is TE1,1 and further provided that this mode is so oriented as to excite the maximum amount of energy in the TE1,1) mode in the rectangular side arms. The usual provisions as to internal matching should be observed to avoid reflections. This may be done by the use of buttons, rods, septums or irises at the junction, one simple way being to insert irises in the side arms as indicated at 22 and 23.

The portion 11A of the round guide 11 containing through rectangular guide 12- excites the TE1,1 mode in round guide 11. This field mode is as depicted in the proper direction to excite the TE1,0 mode in both side arms 19 and 21, and all of the energy divides into two equal parts and passes out of these arms, the field relationships being indicated in Fig. 2. Since the series arm 19 extends in the direction of the E-vector of the field, represented by the lines in the round guide, it has maximum voltage coupling to the interior of the round guide and is excited to the maximum. Also the shunt arm 21, extending perpendicularly in the E-vector direction, has maximum current coupling and excitation. Since all of the energy is taken by the side arms, no energy passes them and there is no output from the end guide 17.

When the round guide section 11A is rotated in either direction by 90, as indicated in Fig. 3, the attitudes of both side arms become such relative to the TE1,1 field in the round guide 11A as to prevent any energy entering either side arm. The microwave energy accordingly passes through the round guide unhindered and all of it leaves the round guide through the end rectangular guide 17.

At intermediate positions of the rotatable section 11A, lesser amounts of energy are abstracted by the side arms 19 and 21, the remainder in each case passing out guide 17. In each case the amount of energy abstracted by the side arms is equally divided between them.

A useful application of this invention in which no flexible arm connections are required is in the control of microwave power by attenuation without change of impedance reflected to the source. In this application the arms 19 and 21 are terminated in resistive powerabsorbing loads. These may be of the wedge type as indicated at 27 and 28, and may be made compact and integral with the side arms. The wedges 27 and 28 may be made of finely divided iron in an insulating solid matrix, commonly known as polyiron. In the position shown with input at 12, all energy passes into the side arms and is absorbed, while none reaches the output arm 17. In the position at 90 to that shown all energy reaches 17 and none is absorbed, while in intermediate positions intermediate amounts of energy reach the output guide 17.

In place of employing the guide 17 as the single outlet arm of the attenuator this arm may be terminated in a resistive non-reflective load and two useful loads may be placed to terminate the arms 19 and 21, instead of the dissipative loads 27 and 28.

What is claimed is:

1. A device of the class described comprising, a round hollow microwave guide suitable for transmission of microwave energy at a selected frequency in the TE1,1 mode having a specific voltage vector direction, a portion of said round hollow microwave guide constituting the two collinear arms of a magic tee hybrid junction extending in either direction from a selected point in the common axis thereof, and two rectangular guide side arms extending mutually at right angles from said round hollow microwave guide orthogonally at said selected point, one said side arm being a series arm and the other said side arm being a shunt arm, and means for adjustably efiecting rotation of the two said side arms in concert relative to said specific voltage vector direction.

2. A device of the class described comprising, a round hollow microwave guide suitable for transmission of microwave energy at a selected frequency in the TE1,1 mode, means for exciting the TE1,1 mode of field transmission of microwave energy having a selected voltage vector direction in said round hollow microwave guide, a portion of said round hollow microwave guide constituting on either side of a selected point in the axis thereof the two collinear arms of a magic tee hybrid junction, two rectangular guides constituting the two side arms of said magic tee hybrid junction extending mutually at right angles from said round hollow microwave guide orthogonally at said selected point in the axis, one said side arm being a series arm and the other said side arm being a shunt arm, and means for adjustably rotating said side arms in concert about said axis to any angular position within relative to said selected voltage vector direction, whereby the amount of energy abstracted equally by said side arms from said round guide is varied between zero and the full amount of the input energy.

3. A device of the class described comprising, a round hollow microwave guide suitable for transmission of microwave energy at a selected frequency in the TE1,1 mode, a portion of said round hollow guide constituting on either side of a selected point in its axis the first and second collinear arms of a magic tee hybrid junction, a rectangular hollow input guide suitable for transmitting microwave energy at said selected frequency in the TEm mode, means for coupling said rectangular hollow input guide coaxially to one end of the first collinear arm of said round hollow microwave guide, two rectangular hollow guides suitable for transmitting microwave energy at said selected frequency in the TE1,0 mode, said two guides being joined to said round guide at said selected point, said two rectangular guides being perpendicular to said axis and perpendicular to each other and constituting two magic tee side arms, one said side arm being oriented at the juncture as a series arm and the other said side arm as a shunt arm, and means for adjustably rotating said side arms in concert about said axis and the longitudinal axis of said rectangular input guide to any angular position of said series arm within 90' of the direction of the lesser cross sectional dimension of said rectangular hollow input guide.

4. A device of the class described in accordance with claim 3 including means for deriving microwave energy from said second collinear arm.

5. A microwave power divider comprising, a round hollow microwave guide suitable for transmission of microwave energy at a selected frequency in the TEl,1 mode, said round guide constituting on either side of a selected point in its axis the first and second collinear arms of a magic tee, a rectangular hollow input guide suitable for transmitting microwave energy at said selected frequency in the TE1,0 mode, means for coupling said input guide coaxially to the distal end of said first collinear arm, a rectangular hollow output guide suitable for transmitting microwave energy at said selected frequency in the TE1,0 mode, means for coupling said output guide coaxially to the distal end of said second collinear arm, with the shorter cross sectional dimension thereof parallel to the shorter cross sectional dimension of said input guide, two rectangular hollow guide side arms suitable for transmitting microwave energy at said selected frequency in the TEi,o mode, said side arms being joined to said round guide at said selected point in its axis and perpendicular thereto and to each other, one said side arm being oriented as a series arm and the other said side arm being oriented as a shunt arm, and a pair of rotatable joints in the round guide on either side of said selected point in the axis whereby the two side arms and associated round guide section may be rotated around said axis between a position in which the series arm is parallel to the direction of the shorter cross-sectional dimension of said input guide to a position in which the shunt arm is parallel to said dimension.

6. A device of the class described in accordance with claim 5 in which each of said rectangular side arms is terminated in a resistive non-reflective load.

References Cited in the file of this patent UNITED STATES PATENTS 2,526,383 Meier Oct. 17, 1950 2,584,399 Preston Feb. 5, 1952 2,603,710 Bowen July 15, 1952 2,606,248 Dicke Aug. 5, 1952 2,634,331 Honda Apr. 7, 1933 FOREIGN PATENTS 635,760 Great Britain Apr. 19, 1950

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