US2769145A

US2769145A - Microwave power divider

Info

Publication number: US2769145A
Application number: US241222A
Authority: US
Inventors: John F Zaleski; George R Gamertsfelder
Original assignee: General Precision Laboratory Inc
Current assignee: General Precision Laboratory Inc
Priority date: 1951-08-10
Filing date: 1951-08-10
Publication date: 1956-10-30
Anticipated expiration: 1973-10-30

Description

J. F. ZALESKI ET AL 2,769,145

MICROWAVE POWER DIVIDER Oct. 30, 1956 2 Shee ts-Sheet 1 Filed Aug. 1.0, 1951 J F. ZALESKI -r AL 2,769,145 MICROWAVE POWER DIVIDER United States Patent 2,769,145 MICROWAVE POWER DIVIDER Application August 10, 195 1, Serial No. 241,222 5 Claims. (Cl. 333-4) This invention pertains to an adjustable microwave power divider, and more specifically to a device for variably coupling a source of microwave energy to one or more branch utilization circuits while presenting a substantially constant impedance to the source. a

i In controlling large amounts of microwave energy, the need arises for continuously varying the power output of a microwave generator or other source between zero and a maximum value while maintaining constant output impedance. It is highly desirable that this should be done so as to present a constant impedance to the generator and, for convenience, should .be effected by the continuous adjustment of a simple control means. The prior conventional devices employed for low power control, that is, for outputs of less than about watts of average power or 1 kilowatt of pulse power, are not applicable, and the conventional high power attenuators that are known are:.not readily adjustable. 1

The instant invention provides a device for apportioning microwave energy in a wave guide between a plurality of output branches, some of which may comprise dissipative loads. It is easily and continuously adjustable, and causes substantially no reflection, so that voltage standing wave ratios under. 1.05 are obtainable.

The device is essentially an adjustable, constant-impedance energy divider having in general at least two microwave output branches. If desired one branch may contain an absorption load while others are connected to utilization devices constituting useful loads. Thus by variation of the adjustment of the device the output to the useful loads can be continuously varied from zero to the full capacity of the generator or source. Since the device of the instant invention is a power divider, it can not only be used for the above purpose but also can be used for adjustably dividing a quantity of input power in any desired ratio between a plurality of useful loads, with no substantial variation in the impedance of the load imposed upon the generator or source.

As will be clearer from subsequent description the socalled branch waveguides, coupling irises and other electrical equivalents, through which microwave energy is transferred from one guide to another correspond to the two conductors of circuits for currents having frequencies below the microwave range, and therefore such irises or waveguides may be considered to be the equivalent of terminal pairs in the lower frequency field.

One purpose of the instant invention is to provide an improved device for controlling the flow of microwave energy from a microwave source while at the same time presenting a constant impedance to the source.

Another purpose of the instant invention is to provide a constant impedance means for dividing a quantity of microwave energy adjustably into at le ast two portions having any selected ratio.

One embodiment of the invention chosen for purposes of illustration comprises a hollow round microwave guide having at least two rectangular coupling irises mm H Patented Oct. 30, 1956 "ice stituting output terminals in the walls of the guide connecting with respective output hollow microwave guides. The functioning of the apparatus includes the excitation within the round guide of the TE1,r mode of microwave transmission. The principles of operation basically depend upon the controlled relative rotational position of the electromagnetic field within the round guide with respect to the position of the coupling irises by which variable energy coupling is provided between the electromagnetic field in the round waveguide and the branches connected to the coupling irises. The coupling irises are disposed substantially apart around the axis of the round guide so that there are reciprocal trigonometric function relationships between the coupling of the electromagnetic field in the round guide with the respective branches. The elimination of reflections. that would cause losses and variations of impedance loading of the source is effected by conventional means, and any dummy load employed may be of any known type.

A better understanding of the invention will be obtained by reference to the detailed description and the drawings in which:

Figure 1 illustrates one form of the present invention comprising a round hollow wave guide having a shunt rectangular guide side connection and two rectangular guide end connections, one rotatable.

Figure 2 illustrates a second embodiment comprising a round hollow wave guide having a series rectangular guide rotatable side connection and two rectangular guide end connections.

Figure 3 illustrates a third embodiment of the present invention.

Referring now to Fig. 1 a rectangular hollow wave guide 11 constitutes means for introducing microwave energy to a microwave energy divider of the present invention. As regards the present invention the output end of the waveguide 11 where it connects to the disc 12 can be considered the source of microwave energy, be it a generator or a waveguide energized from a generator. The internal width and breadth of waveguides suitable for the conduction of microwave energy of any specific wave length in a particular mode are Well known in the art, and as an example, the rectangular guide. 11 and all others in the embodiments of this invention are specified as having internal width and height of 0.9 inch and 0.4 inch, respectively, suitable for the transmission of the 3.3 cm. or X-band of microwave energy. When the Wave guide 11 has these dimensions, X-band microwaves are transmitted only in the dominant TEL!) mode. It is to be understood that this invention is applicable to any length of microwave providing, of course, that the components have the appropriate dimensions for the frequencies.

The rectangular guide 11 terminates in a closely fitaperture or coupling iris in a metallic disc 12 that constitutes the end of a round hollow wave guide 13. The junction between the rectangular wave guide 11 and the round wave guide 13 is matched by suitable devices to prevent a discontinuity that wouldreflect energy back into the guide 11. A suitable matching device consists of inductive vanes, which will be described later It is well known that the dominant TE1,0 mode in a rectangular guide corresponds to the dominant mode TE1,1 of a round wave guide. By definition, the dominant mode is the one with the longest cutofi wave length. Accordingly, the dominant mode in a rectangular guide is determined and fixed relative to the inner surface of the guide by the relation of the wavelength and the dimensions of the waveguide. In a rectangular waveguide the position of the transverse electrical field of the TE1,0 mode is parallel with the direction of the narrower dimension. On the other hand, in a round waveguide all points on the inner surface with the dominant with guide 13, is rotatable. In order the guide 11 may be connected to a source of microwave energy (not shown) by a conventional flexible rectangular guide, or, alternatively, a microwave generating device, such as a klystron tube or a magnetron may be fixed to the guide 11 l0 The two rectangular wave guides 26 positioned and 27 are so apart around When this orientation exists there is pedance.

a minimum im- 30 When the junction between the guides 16 and electric field is parallel to the broad 'faces, no microwave energy enters the rectangular guide 26 and all is reflected as though the disc 28 was solid. This is the case when the relative orientation of the guide 11 and guide 26' is as depicted in Fig. 1; in order to reduce to a minimum the impedance at the coupling iris 29, 31 between the end of the guide 16 and the guide '26, the latter would have to be rotated 90 in'either direction.

between the waveguides be true, the distance A between the electrical center of the guide 27 and the end plate 28 must be one-fourth of a wave length in the guide, or

Ag T. t y a This is because it is necessary that all microwave energy arriving at the guide 26 and not accepted thereby because of the orientation thereof, and hence reflected by the end 28, must return to the guide 27 so as to be in phase with energy approaching at the same instant from the guide 11. This condition exists only when the distance is as specified or is an odd integral multiple M thereof, expressed as The energy-dividing action of the apparatus described may be more clearly understood when it is considered that the E vector of the TE1,1 mode induced in the round guides 13, 16 by the TE1,o mode of the rectangular guide 11, is along a diameter of the round guides and maybe resolved into two voltage vectors along any two mutually perpendicular directions in a plane perpendicular to the axis of the guides 13 and 16. The values of each of these vectors will be proportional to the cosine, of the angle it makes with the resultant. These vectors then will represent the proportions of voltage received by the guides 26 and 27 as the input guide 11 is rotated relative to the guide 16. The energy received by each of the guides 26 and 27 will be proportional to the squares of the respective voltages, and their sum will equal the input energy. In all cases the eifect of the variation of the impedance of the total load upon the generator, as observed from the generator, or the input end of guide 11 will be substantially zero, usually less than 1%. This is one of the salient features of this invention.

It is obvious that if the arm 11 be fixed and the round guide 16 together with its output arms 26 and 27 be rotatable, it will be necessary in general to make connections to the arms 26 and 27 by flexible guide or equivalent means. i The output arms26 and 27 may be connected respec- 'tively to two useful respective loads, or as previously mentioned, one may be connected to a useful load, such as a transmitting antenna, while the other may be connected to a dummy load of any known type suitable for the amount of powerto be dissipated. In this case either the arm 26 or the arm 27 may be connected to the useful load, as the characteristics of the output arms 26 and 27 are quite similar.

Since operationally, the arms 26 and 27 are rsimilar,.it is obvious that the end arm 26 may be replaced by a shunt side outlet of rectangular waveguide identical to the guide 27 and located like it a distance of or odd multiple thereof, from the end plate 28, which should be solid and Without any aperture. The replacing arm would be positioned 90 mechanical degrees from the arm 27 around the round guide axis in either direction, and the description of its operation would be similar to that given for the case of the end and side outlet arms.

Referring now to Fig. 2, a round waveguide 32 is connected by means of two rotary joints 33 and 34, similar to the rotary joint 14, Fig. 1, to two

round wave guides

36 and 37 respectively, the

guides

36, 37 may be of a size suitable for the transmission of a microwave in the TE1,1 mode; for example, inch in diameter for X-band microwaves of 3.3 cm. in length. The

round guides

36 and 37 are terminated by

metal disc ends

38 and 39, to which are connected rectangular wave guides 41 and 42 of dimensions suitable for supporting the TE1,0 mode of the X-band. The broad sides of the respective guides 41 and 42 are oriented at right angles with respect to each other and are mechanically connected by any suitable means so as to be rotated together around their common axis, this connection being schematically indicated by the dashed line 43. The round guide 32 has a series side arm 44 consisting of a rectangular wave guide of a size suit- Nxg for reasons which will presently appear. Theoretically, the use of a series side arm can be made the electrical equivalent of a shunt side arm by appropriately changing the dimensions B and C.

In this embodiment the side arm 44 is adapted to serve as an input for microwave energy and the end arms 41 and 42 are adapted as output terminals. Energy entering the round guide 32 from the rectangular series side arm guide 44 divides, with one-half passing toward the guide 41 and the remainder toward the guide 42. The microwave energy in the round guides 32, 36 and 37 is transmitted by fields in the TE1,1 mode, these fields having, in a guide positioned as depicted in Fig. 2 their E vectors in the horizontal plane. The orientation of the E vectors is determined by the polarization of the rectangular input guide 44. Such fields are accepted by rectangular guides oriented like guide 42 because, as mentioned above, the dimensions of this guide are such as to support a TE1,u mode of the X-band which mode corresponds to the TE1,1 mode of the round guide. Accordingly, the guide 42 presents a minimum impedance to the microwave energy in round guide 32 of the polari zation mentioned while guide 41 presents a maximum impedance as if the round guide end 38 were solid. The distance B being equal to NXg 2 the reflected energy is returned to the location of the guide 44 at such phase as to reinforce waves travelling toward the right, so that all of the energy introduced at the guide 44 is received by the guide 42. l

By similar reasoning, it is readily seen that if the guides 41 and 42 be turned about the axis of the round guide 32 through an angle of all of the energy will be emitted from the guide 41 and none from the guide 42. Likewise, at intermediate positions of the guides 41, 42 the energy transmitted by each guide will be a function of the angle between the broad faces of the respective guides 41, 42 and the E vector in round guide 32, which vector is fixed by the position of guide 44 as described in connection with Fig. 1. In all cases the substantial constancy of the impedance of the device as reflected to the generator or input terminal 44 is of the greatest practical utility.

It is obvious that in place of either or both output terminal guides 41 and 42 there may be substituted side arm output rectangular guides, either of the shunt type 27, described in connection with Fig. 1, or of the series type identical with the input arm 44, Fig. 2. In either case the adjacent round guide ends may be solid and the distances between the ends and the respective output side arms would be i for the shunt type and i for the series type.

As a further corollary, more than two outlets may be provided with the microwave energy dividing in accordance with the principles described, to the outlets in accordance with the respective orientation of the outlets with respectto the polarization of the field in the round guide. I

In Fig. 3 a TE1,1 field is excited in a inch diameter round guide 46 by the introduction through an end plate 47 of microwave energy in the TE1,0 mode from a rectangular waveguide 48, the field in the round guide 46 being rotatable through rotation of the input guide 48 and the end plate 47 relative to the, round guide 46. R- tat-ional movement between the waveguide 48 and the round guide 46 is permitted by the provision of a connecting rotary joint 49 which is similar in construction to joint 14 shown in Fig. l. A side outlet terminal in the form of rectangular guide 52 is provided. So far the power divider is similar to that described in connection with Fig. 1. However, in Fig. 3 the end output terminal 50 is of the circular cylinder guide type and consists of an absorptive load. This dummy load may be of any one of a number of known types suitable for the power required to be dissipated and in the form shown is a wood cone 51 having a resistive skin of colloidal graphite. .The apex of the cone is pointed toward the power input and is long enough to prevent the effect of 'a discontinuity that would cause reflections. Its length in any case should not be less than one and one-half times the diameter of its base.

The rectangular guide shunt side arm 52 is positioned at a convenient distance from the input end 47. Since the round guide 46 is not reflective at its loaded end 50, a reflective, quarter-wave closed stub 53 is provided to 'cause proper functioning of the side arm 52. This stub 53 is of the shunt type and is positioned on the round guide 46 in longitudinal alignment with the arm 52, on the side away from the power input guide terminal 48. The electrical distance D between the electrical center of the stub 53 and the electrical center of the arm 52 must be or an odd multiple thereof in instances, both where the shunt and series types of arms and stubs are used.

A mode transformer 55 is provided to permit all input and output branches of the complete device to remain stationary, and yet provide for the adjustable rotation of the guide 48 about the axis of the power divider to vary the orientation of the field within the guide 46 with relation to the side outlet terminal arm 52. The mode transformer 55 consists of two round guides 54 and 56 connected by a rotary joint 57 similar to that described in, connection with Fig. l. The guides 54 and 56 have an internal diameter of 1 inches and are closed by respective solid metal disc ends 58 and 59. An input branch or terminal in the form of a rectangular guide 61 connected to the guide 54 as a series side arm is positioned a distance G, equal to one-half of a TMo,1 mode wavelength and of a. TE1,1 mode wavelength in the guide from the disc end 58, and an output branch in the form of a rectangular guide 62, also connected to the guide 56 as a series side arm, is positioned a distance F equal to one-half of a TMo,1 mode (a of a TE mode wavelength) in the guide from the disc end 59. An orientation scale 63 fixed to the guide 56 is associated with a fixed index plate 64 to determine the relative position of the guide. 56 and the guide 54. The output terminal 62 is connected by a length of curved rectangular waveguide 66 to the rotatable input waveguide 48 of the power divider. 7

In the operation of this modified form the input terminal61 may be fixed to a microwave generator, or

other input equipment, and the output terminal 52 may be fixed to stationary output or utilization equipment. The part between the rotary joint 57 and the rotary joint 49 may be rotatably adjusted and its orientation is indicated by the position of the scale 63 attached to the round guide 56 in relation to the index mark 67 carried by the fixed index plate 64.

The specific diameters of the guides 54 and 56 are such as to support both the TMo,1 mode and the TE1,1 of propagation of microwave energy one in resonance and the other in anti-resonance therein. The introduction of microwave energy in the TE1,o mode through the rectangular guide 61 to the round guide 54 tends to cause both modes TE1,1 and TMo,1 to be established in the round guide 54 and 56. However, because the distance Gis 2 of TMo,1 mode and TE1,1 mode (resonant to TMo,1 and anti-resonant to TE1,1), the TE1,1 mode may be said to be tuned out, and its elimination leaves the mode TMo,1 as the sole means of propagation of all of the input energy without reflection through the guides 54 and 56 to the rectangular output'guide 62 where the transformation to the TE1,1) mode recurs without harmful reflection because of the termination of the round guide 56 by the end plate 59 at the particular distance F from the longitudinal center of the rectangular guide 62. The TMo,1 mode solely existing in the round guides 54 and 56 is symmetrical about the axis of the guides, so that the relative axial rotation of the guides 54 and 56 causes no change whatever in the phase or orientation of the microwave energy entering the branch or terminal 62. This energy is de livered to the terminal 48 without substantial loss or reflection regardless of its angular position. The angular position of the terminal 48 does determine, however, the orientation of the TE1,1 mode in the round guide 46 and therefore determines the division of energy between the output arm 52 and the dummy load 51, in exactly the way that field orientation determines energy division in the'embodirnent described in connection with Fig. 1.

As a result, the mode transformer 55 provides the means for carrying out the purposes of this invention yet obviates the necessity for employing flexible guides or other adjustable coupling attachments to the input and output end terminals. The impedance of the load on the generator (or other source) remains constant for all orientations of the rotatable portion of the device, a fact of the greatest utility.

It is obvious that the mode transformer 55 of Fig. 3 can be applied to any input or output microwave terminal connection in the end of a round guide that may be required in any of the embodiments of this invention. It is also obvious that the side arm and end arm input and output terminal connections and all other components described may be associated in a great many combinations, but in most cases each of such components and each of their interrelations should preferably be as have been herein described in connection with the embodiments of the invention.

Within the broad aspects of the present invention the rectangular guides, may be considered as polarizing irises and it will be clearly understood by those skilled in the art that the rectangular guides could be replaced by other intenconnecting waveguides or coaxial lines so long as they are capable of transmitting the desired frequencies. The important thing is that either the interconnecting device or the coupling device be capable of polarizing or of being sensitive to electric fields of a definite polarization. Also the mode transformer 55 interposed between the input 61 and output terminal 52 in Fig. 3 may be considered merely illustrative of a component for transmitting or carrying circularly polarized microwave energy at the desired frequency.

Any of the rectangular guide input and output arms or terminals described in the example can be replaced by any other well-known device by which the TE1,1 mode can be induced in a round guide, or which can be excited by the TE1,1 mode in a round guide while being sensitive to the orientation of the electric field thereof. Common examples of such well-known devices include an antenna or probe extending a suitable distance into the side wall of a round guide, and a side or end aperture of generally elongated shape. Any of such devices may be employed so as to be electrically the equivalent of the described rectangular wave guide input and output arms. Each of the side arms and other branch guides by which the microwave energy is transmitted corresponds effectively to the two conductors of an electrical circuit for frequencies below the microwave region. Accordingly, for convenience, the word terminal is used in such sense in the appended claims and in the specification.

What is claimed is:

1. A microwave power controlling device comprising a waveguide section capable of supporting independently at orthogonal positions in said section only the dominant TEu non-circular mode of wave transmission at a given frequency, said section having an impedance discontinuity for reflecting wave energy in at least one plane of polarization, input means for establishing incident wave energy in said non-circular mode in said section with the transverse electric vector at a selected plane of polarization, a plurality of output means connected to said section at position orthogonally related electrically around the axis of said section, at least one of said output means being connected at an in-phase position for incident and reflected wave energy, said output means being connected to said section through respective oblong polarizing coupling apertures having their planes of polarization orthogonally related, the major axes of said apertures being of such dimension as to support only the dominant TEio mode corresponding to the TE11 mode in said section, the minor axes of said apertures being of such dimension as not to support a dominant mode corresponding to the TEro mode in said section and means for changing the plane of polarization of the incident wave relative to said polarizing output coupling apertures.

2. A microwave power controlling device comprising a hollow waveguide section capable of supporting independently at orthogonal positions in said section only the dominant TEu non-circular mode of wave transmission at a given frequency, said section having one end terminated in an impedance for reflecting wave energy in at least one plane, input means for establishing incident wave energy in said non-circular mode in said section with the transverse electric vector at a selected plane of polarization, a first output means connected to said terminated end of said round section, a second output means connected to the side of said first section at an in-phase position for incident and reflected wave energy reflected from said terminated end of said section, said output means being connected to said section through respective oblong polarizing coupling apertures orthogonally related electrically about the axis of said section, the major axes of said apertures being of such dimension as to support only the dominant TE1o mode corresponding to the TE11 mode in said section, the minor axes of said apertures being of such dimension as not to support a dominant mode corresponding to the TEio mode in said section and means for changing the plane of polarization of the incident wave relative to said polarizing output coupling apertures.

3. An adjustable microwave power controlling device comprising a round hollow waveguide section having such internal diameter as to support only the TEii mode of wave transmission at a given frequency, a polarizing oblong input guide rotatably attached in coaxial relation to one end of said round section, the other end of said round section having terminating means: for reflecting wave energy in at least one plane, a first hollow polarizing oblong output arm coupled in coaxial relation to the other end of said round section at a fixed orientation therewith to accept microwave energy in a plane of polarization orthogonal to that reflected by said terminating means, a second hollow oblong polarizing output arm connected to the side of said round guide at an in-phase position along the axis of said round section with its plane of polarization orthogonally related about the axis of said round section to the plane of polarization of said first output arm, the major axes of said oblong guides being of such dimension as to support only the dominant TEIO mode corresponding to the TEM mode in said round section, the minor axes of said arms being of such dimension as not to support a dominant mode corresponding to the TE10 mode in said section and means for rotating said input arm about its axis whereby the wave energy entering said round section through said oblong input arm will be divided between said output arms as functions of the angular position of E vector in said round section with respect to the respective planes of polarization of the respective output arms.

4. An adjustable microwave power controlling device comprising a round hollow waveguide section having such internal diameter as to support only the TE11 mode of wave transmission at a given frequency, said section having its ends terminated in impedances for reflecting wave energy in respective orthogonal planes, an input arm fixed to one side of said section and coupled through a polarizing aperture, a plurality of output means connected to said round section through respective rotatably adjustable walls having polarizing coupling apertures, :said output arms being connected to said round section at in-phase positions spaced along the axis of said round section, the major axes of said apertures being of such dimension as to support only the TEm mode corresponding to the TEii mode in said section, the minor axes of said apertures being of such dimension as not to support the dominant mode in said section, means connecting said rotatably adjustable walls for rotating them in unison about the axis of said round guide while maintaining the major axes of said output apertures in a relatively fixed orthogonal relation, whereby the wave energy in the TE11 mode in said round section will be divided between said output arms as respective functions of the position of the E vector in said round section with respect to the respective planes of polarization of the TE1o mode in the respective output arms without substantially affecting the total impedance at said input arm.

5. An adjustable microwave power controlling device comprising a round hollow waveguide section having such internal diameter as to support only the TEu mode of wave transmission at a given frequency, said section being terminated in an impedance for reflecting wave energy in one plane, a rectangular input arm and a plurality of rectangular output arms connected to said round section, said input arm being fixed to the side of said round section with its axis perpendicular to the axis of said round section, the broad walls of said input arm being perpendicular to the axis of said round section, the broad walls of said output arms being parallel to the axis of said round section and perpendicular to each other, said output arms being rotatably connected to the opposite ends of said round section, means for simultaneously rotating said output arms in unison about the axis of said round guide while maintaining their orthogonal relation to each other, said output arms being connected to said round section at in-phase positions along the axis of said round section whereby wave energy in said round section will be divided between said output arms as functions of the respective References Cited in the file of this patent UNITED STATES PATENTS 2,129,712 Southworth Sept. 13, 1938 Regan:

12 Bowen Oct. 7, 1941 Ring Aug. 12, 1947 Fox Mar. 23, 1948 Dicke Aug. 5, 1952 OTHER REFERENCES Microwave Transmission Circuits, vol. 9,

M. I. T. Rad. Lab. Series, published by McGraw-H-ill, pages 368-69. Copy in Patent Office Library.