US3086178A - Directional coupler for individually connecting each of plural inputs, without cross talk, to all of plural outputs - Google Patents

Description

Ap 1963 c. R. BOYD. JR

IDIRECTIQNAL COUPLER FOR INDIVIDUALLY CONNECTING EACH 0F PLURAL INPUTS, WITHWT CROSS TALK, TO ALL PLURAL ouwms 3 Sheets-Sheet 1 Filed June 19, 1961 SOURCE FiGJA SOURCE SOURCE I, ulnlllll l LOAD LOAD A INVENTOR R J w Y O /E B N R R O T S T E m A A B H C April 16, 1963 C. R. BOYD, JR

DIRECTIONAL COUPLER FOR INDIVIDUALLY CONNECTING EACH OF PLURAL INPUTS, WITHOUT CROSS TALK, TO ALL PLURAL OUTPUTS Filed June 9, 1961 3 Sheets-Sheet 2 FlG.5

1 Y "F V2 Y SOURCE: W I 0 T y "Y I 2Y Y SOURCE} k k 4 4| 'a''-43 2: -44 K 8 M a 6 4| SOURCE: 1 8

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INVENTOR'. CHARLES R.BOYD JR., BY

HIS ATTORNEY Aprll 16, 1963 c R. BOYD, JR 3,086,178

DIRECTIONAL COUPLER FOR INDIVIDUALLY CONNECTING EACH OF PLURAL INPUTS, WITHOUT CROSS TALK, To ALL. PLURAL OUTPUTS Filed June 9, 1961 3 Sheets-Sheet 5 Y FIGJC. SOURCE L I 23 LOAOA I2 2Y0 29 30 L IS a 30 9 5) l6 SOURCE 2\ 8 LOADB l4 29 30 8 SOURCE V 1 I I LOADC H62. INPUT OUTPUT l2 l3 l4 l5 l6 w UNBALANCED T T MODE BALANCED MODE T L l T l L X TOTAL AMPLITUDES o o u UNBALANCED MODE b BALANCED MODE FIG.4.

2e: DIFFERENTIAL PHASE ANG-LE 0 INVENTORI CHARLES R. BOYD JR.

HIS ATTORNEY.

United States Patent Ofilice 3,086,178 Patented Apr. 16, 1963 DIRECTIONAL COUPLER FOR INDIVIDUALLY CONNECTING EACH OF PLIURAL llNPUTS, WITHOUT CRGSS TALK, TO ALL 6F PLURAL OUTPUTS Charles R. Boyd, Jr., North Syracuse, N.Y., assignor to General Electric Company, a corporation of New York Filed June 9, 1961, Ser. No. 116,184 9 Claims. (Cl. 333-45) The present invention relates to wave transmission devices of the type ordinarily referred to as directional couplers and hybrid junctions.

Directional couplers are multiple port devices used to couple electrical wave energy from one or more sources to one or more loads. Their unique property in energy coupling is isolation between selected ports and arbitrary power division factors between coupled ports. The energy isolation and coupling properties are highly dependent upon the manner in which the coupled ports are terminated and optimum performance is usually restricted to a limited range of frequencies.

The essential transmission properties of the class of directional couplers related to the present invention arise from simple wave interference phenomena by which destructive cancellation occurs at mutually isolated ports and does not occur at the coupled'ports. In general, these phenomena require dimensional selections of integral quarter, one half, etc. electrical wavelengths so as to bring into play the foregoing wave combining properties. For this reason, devices of this nature find most frequent application at higher radio frequencies (usually in execess of 50' megacycles) wherein the dimensional requirements for these fractional electrical wavelengths are easily and conveniently satisfied.

Directional couplers of the general sort to which the present invention is most closely related are of the four port variety wherein each of the ports are interconnected by paths of one quarter wavelength, electrical length. Assuming that the device is properly adjusted, the device has two identical sets of mutually isolated ports; one port being isloated from one adjacent port and coupled to the remaining ports. Assuming that power is applied to one port, no energy is coupled to the isolated adjacent port, and in the event that the remaining ports are properly matched, a predetermined division of energy is made between the non-isolated ports.

The directional couplers are designed for a given powor division factor and retain a directional property-en isolated portso long as the load impedances match the coupled ports. They retain this property largely independent of impedance conditions at the isolated port, and are reciprocal in the sense that input and output functions may be reversed. The hybrid junction, which provides equal power division between the coupled ports, is one member of the directional coupler class.

It is an object of the present invention to provide a novel multiple port directional coupler performing the same functions listed above in devices having more than four ports.

It is another object of the present invention to provide a novel multiple port directional coupler wherein electrical wave energy may be distributed in controlled fashion between 3,4 or more load devices.

It is a further object of the present invention to provide a novel directional coupler wherein electrical wave energy may be combined coherently from three, four or more sources.

It is an additional object of the present invention to provide a new and improved six port hybrid.

It is still another object of the present invention to provide anew and improved eight port hybrid.

It is another object of the present invention to provide a novel multiple port directional coupler having more than four ports wherein additional operation bandwidth is achieved.

These and other objects are achieved in accordance with the present invention by a parallel path transmission device recurrently loaded by a plurality of regularly spaced star connections. The transmission device is provided with three or more such parallel paths and at least two star connections, one occurring at the input to the device and one occurring at the output of the device. The dimensions of these paths and of the branches of the star connections are so proportioned as to give a susceptive loading of one sign to waves propagated in the device in the unbalanced mode and of the other sign to waves propagated in the device in the balanced mode. In this manner a controlled differential phase angle will occur as the two modes are propagated down the device leading to a difference a resultant wave intensities at the outputs of the device.

In accordance with a specific embodiment of the invention, a three transmission path device is disclosed having an electrical length of one quarter wavelength and a pair of Y connections whose branches are of one eighth wavelength, electrical length. The characteristic admittances of the transmission elements and of the branches of the Y connections are then selected with respect to the characteristic admittance of the external transmission lines so that the vectorial representations of these three quantities form a closed right triangle. Under these conditions, perfect directional coupling may be achieved. If the characteristic admittance of the transmission elements is set equal to twice the characteristic admittance of the external transmission lines and the characteristic admittance of the branches of the Y set equal to 3 times the external transmission line characteristic admittance, the device becomes a hybrid junction providing equal threeway power division.

In accordance with a further specific aspect of the invention, a novel eight port hybrid junction is described utilizing three star connections interconnecting four transmission lines. Upon an appropriate selection of characteristic admittances, an equal energy distribution among the four output ports is obtained.

The foregoing devices may be used for coherent energy combination by utilizing coherent properly phased energy sources.

The features of the invention which are believed to be novel are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description when taken in connection with the drawings, wherein:

FEGURES 1A and 1B are structural drawings of a six port directional coupler embodying the invention;

FIGURE 10 is a schematic circuit representation of the first embodiment;

FIGURE 2 is a collection of vectorial diagrams representative of wave propagation within the first embodiment;

FIGURE 3 is an equivalent circuit representation of the first embodiment suitable for mathematical analysis;

FIGURE 4 is a graphical representation of the admittance parameters of the transmission line elements of the first embodiment; and

FIGURE 5 is a schematic representation of a second embodiment of the present invention.

A six port hybrid embodying the invention will now be described with reference to FIGURES 1A, 1B and 1C. The six port hybrid illustrated in FIGURE 1A is seen to comprise a circular disk shaped member 11 having on its upper surface three symmetrically placed coaxial line fittings or ports: 12, 13 and 14-, respectively. On the under surface of the disk shaped member 11, three additional coaxial fittings or ports (not shown in FIGURE 1A) are arranged immediately beneath each of the ports on the upper surface. The fittings illustrated are adapted to accommodate standard military coaxial connectors.

As illustrated in the drawing 1A, three sources are shown connected to the upper ports; source A to port 12, source B to port 13, and source C to port 14-. On the under surface; load A is connected to port 15, load B to port 16, and load C to port 17. As will be explained in greater detail below, the foregoing six port hybrid junction has the property that when any one of the sources are energized with energy of proper frequency and each load port is properly terminated, all of the energy will be equally distributed between the load connected ports 15, 16 and 17 and essentially none reflected back to the source connected ports. Furthermore, irrespective of source impedance, the members of the source connected ports are then mutually isolated, so that all energy is forwardly coupled to the loads.

As best seen in FIGURES 1A and 113, a preferred embodiment of the six port hybrid uses strip transmission line techniques in its internal connections. The internal strip transmission line conductors are illustrated in the exploded view of FIGURE 1B. They may be seen to consist of a pair of similarly shaped fiat conductive members 18 and 19. The members 18 and 19 are three branched, of roughly Y-shape in that they each have three arms radiating from a common center of hub 31. They are assembled in the housing 11 in mutually parallel means with like parts face to face. The hybrid housing 11 is formed of three members including the principal frame member 29 and an upper cover plate 21 and lower cover plate 22. The principal frame member 20 is a circular disk-like member having a relatively thin central web portion with a thickened peripheral flange portion. The flange is provided with ledges 23 and 24 on its upper and lower surfaces for accommodating respectively the upper cover plate 21 and the lower cover plate 22, which are fastened thereto by screws or other suitable means. It may be seen that when the upper and lower cover plates are fastened to the principal frame member 21), two 150- lated and similarly disk-shaped chambers are defined in the hybrid junction.

The upper Y-shaped conductor 18 is installed within the upper chamber and the conductor 19 within the lower chamber. The conductor members 18 and 19 are each supported equi-distantly from the upper and lower walls of their respective chambers by a pair of insulating dielectric spacers 25. Additional positioning of the conductor members is provided by the electrical connections made to the individual arms.

Considering now the electrical connections: each arm is bent inwardly twice so that each arm resembles a half portion of an S. This configuration tends to reduce the diameter of the device, and is for dimensional convenience. At the remote ends of each of the arms a connection 26 is made between the upper and lower conductive members 18 and 19. These connections are made by a cylindrical conductive member 26 passing through suitable apertures provided in the central web of frame member 20 and the two innermost spacers 25. The members 26 are then fastened to the extremities of the respective arms by pins and/ or other suitable means.

The external electrical connections are made at the outer bends 27 of the individual arms. As illustrated in FIGURE 1A, it may be seen that the external conductors of the three source connected coaxial line fittings 12, 13 and 14 are fastened to the upper cover plate 21. Similarly, the external conductors of the three load connected coaxial line fittings are connected to the lower cover plate 22. These coaxial fittings are arranged symmetrically upon the respective cover plates and aligned with the conductor members 18 and 19 such that their central coaxial conductors 28 are in facing alignment with the outer bends 27. The central coaxial conductors 23 which pass down through the plane of the cover plate and an outer insulating spacer 25, are then fastened to these bends 27 by pinning and/ or other suitable means.

The electrical paths of the hybrid are shown best in the schematic diagram 1C. They are seen to comprise three transmission elements 29 directly connecting source ports to load ports with a three branch Y connection element at each end of the transmission elements. The branches of this Y connection element bear reference numerals 311. In accordance with the invention, the transmission elements 29 are each of one quarter wavelength, electrical length while the branches 30 are of one eighth wavelength, electrical length. Assuming that all of the entrance ports 12 through 17 are of an admittance Y the characteristic admittance of the transmission elements 29 should be 2Y while the characteristic admittances of the Y branches should be /3Y if equal power distribution is desired. The reasons for these selections will be established below.

From the above it may be seen that the electrical path length from the port connected bend 27 of the upper conductive member 13 measured to the outer end of its arm, and then down through the member 26 to the port connected bend on the lower conductive member 19 is one quarter wavelength (FIGURE 1B) and has a characteristic admittance of 2Y This and the other two similar paths correspond to segments 29 of FIGURE 1C. Similarly, the path from the port connected bend 27 to the hub 31 of the Ys has an electrical path length of one eighth wave length and a characteristic admittance of /3Y (FIGURE 1B). This and the other two similar paths correspond to branches 30 of FIGURE 1C. (The external ports 12, 13, 14, 15, 16 and 17 have a characteristic admittance Y A moments retrospection will now clarify the purposes and potential effects of the foregoing path length selections. It may be seen that source A is linked to each of sources B and C by transverse path lengths (through branches 30-) of one quarter wavelength, electrical length, and to load A through a longitudinal path (through transmission element 29) of one quarter wavelength. As to source A; source B, source C, and load A are adjacent. Source A is linked to load B and load C by no path requiring less than one half wavelength, electrical length, and all direct paths are of that length. Accordingly, load B and load C are non-adjacent to source A. It may be observed that as between adjacent ports; two alternative connective path lengths exist: waves may travel directly one quarter wavelength or waves may go the long way around in a path having a total electrical wavelength of three quarters wavelength. Since the difference in electrical path length is one half wavelength, this effect may be used to provide cancellation and thus isolation as between adjacent ports. As between non-adjacent ports, essentially all paths are of one half wavelength, and accordingly cancellation does not occur. The non-adjacent ports are thus coupled. It should be apparent that this isolation and coupling resemble the properties of the traditional four port hybrid junction, and this resemblance extends to both single source and multiple source excitation. The practical attainment of isolation, and coupling factors is achieved in devices having the foregoing electrical wavelengths through control of the admittances of the hybrid elements and careful matching to externally connected loads.

One may now observe that applicants novel six port junction has bilateral symmetry as viewed from input and output considerations as well as symmetry between the individual members of the three port set on each face of the junction. Thus if parameters can be selected so as to provide equal output power distribution for power supplied to any one input port, then equal output power distributions are assured for power supplied to any input port. The symmetry as between the ports on one side of the junction also implies that superposition techniques may be used in establishing the correct values for the electrical properties of the branches (30) of the Ys and of the transmission elements (29), (FIGURE 1C).

Using the superposition technique, a traveling wave incident on port 12 may be considered to be a linear superposition of two traveling wave modes simultaneously incident on ports 12,, 13 and 14. At port 12 the individual wave amplitudes associated with each mode reinforce to produce a substantial resultant while at ports 13 and 14 the individual wave amplitudes cancel to produce a zero resultant. One mode of excitation, usually designated the unbalanced mode, is characterized by components of equal phase and amplitude at each of the input ports. A second mode of excitation usually designated the balanced mode is characterized by equal phases and amplitudes for two components, and an opposite phase and double amplitude for the third component. Assuming excitation of port 12, the double amplitude component is associated with that port, and has the same phase as the unbalanced mode component associated with that port. These relationships are illustrated in FIG- URE 2. If one makes a vector addition of the components of the respective modes, one arrives at the total input amplitudes indicated in FGURE 2 (verifying an equivalence to an original traveling Wave applied to port 12 of three units assumed amplitude).

One may now deduce the conditions which bring about equal power distribution as between the output ports 15, 16 and 17, assuming that the output ports 15, 16 and 1? are non-reflectively terminated. It may readily be appreciated that differences in the loading effects of the Ys as between the unbalanced mode and the balanced mode will introduce some difierential phase shift between these modes as they propagate between the input ports 12, '13 and 14 and the output ports 15, 16 and 17. The solution of the problem requires one first to find the desired differential phase shift to achieve the desired power distribution, after which one determines the electrical junction parameters required to produce this phase shift.

The problem of finding the desired differential phase shift between modes to achieve equality of output waves may be solved trigonometrically. If one assumes that the balanced mode, as it appears at the output terminals 1'5, 16 and 17, is delayed a reference amount, then one may treat the delay of the unbalanced mode as a variable. Assuming lossless conditions and symmetry in the junction, the output vectors of the unbalanced mode are all of unitary length and of the same phase. At ports 15, 16 and 17 the output vectors of the balanced mode are respectively 2 units at 0; '1 unit at 180, and 1 unit at 180 (FIGURE 2). Using the law of cosines (c'-=a +b -2ab cos 2) and initially solving for the angle g5, while eliminating c from the two initial equations respectively for the ports 15, '16 or 17, one finds that the unbalanced mode vectors should be at 120. Solving for c one finds that the resultant vectors at all output ports are units 65 length. Though equal in amplitude, the resultants are not all of the same phase. The phases at ports 16 and 17 are alike but differ from that at port by 120 as illustrated in FIGURE 2.

The determination of values for the admittances of the junction elements to bring about a 120 phase differential will now be considered. The selected modes greatly simplify the treatment of this problem. Assuming perfect unbalanced propagation, no current will pass through the Ys since there is no potential difference between the tails.

elements 29. However, charging current will enter the branches 30, though not crossing the center 31 of the Y. In eflect, the branches will appear to be open-circuited at the center of the Y, and will present a capacitive susceptance of +jY at their junctions to the transmission line, as illustrated in the first equivalent circuit of FIG- URE 3. This notation is selected to imply that the arms 30 are of a characteristic admittance Y and are of an equivalent one eighth wavelength, open-circuited shunt elements. The transmission line elements 29 are represented by a one quarter wavelength transmission line of admittance Ygg, With the lower conductor being essentially the ground path realized in the housing structures. The equivalent circuit may now be solved by standard transmission line techniques.

The rationale for the second equivalent circuit of FIGURE 3 is similar, though difierent in supporting de- In balanced mode propagation, with a double amplitude wave on one line, and unit amplitude waves on the other two lines; the impedance to the hub of the Y from the one line is twice that from the hub to the two lines having equal potentials. As a result, the hub assumes a zero potential, implying an equivalence to a shorted termination. The branches 29 are accordingly represented as -jYo1, implying as before a characteristic admittance Y but denoting an equivalent eighth wavelength shorted termination. This equivalent circuit may now be solved by standard transmission line techniques.

The output voltage V of the unbalanced equivalent circuit may be related to the input voltage V by the following expression:

1+1 where 1 is the reflection coefiicient attributable to the output termination of the transmission elements 29, transformed to the input, and 3L is the electrical length in radians of the elements 29. Since flL=II/ 2; Expression 1 becomes:

. 1 I V1 -11 V m 2 From transmission line theory,

Where Y is the admittance at the input of transmission element 29, and Y is the characteristic admittance of element 29. Assuming a quarter wave line:

Y'OZ2 Y T Y0+JY01 (4) where Y is the output load admittance, and "Y is the admittance of the branch 30'.

From Expressions 2, 3 and 4 we find:

the angle of the total load admittance Y -j- 'Y By controlling the Y admittance one has an elegant way to achieve a desired differential phase angle.

Since the total desired differential phase angle is the totfl load admittance must have an angle of 60.

Stated mathematically:

In order to achieve a match to the transmission line, the input admittance (Y of the junction must equal the characteristic admittance (Y of the external transmission line. The input admittance of the junction is the sum of the transformed load admittance and the admittance of the input connected Y:

where Y is now re-defined to the transformed load admittance as defined in Expression 4 for unbalanced mode propagation as well as its conjugate applicable to balanced mode propagation. Similarly, the admittance of the input Y is stated with equal generality for both modes.

For matching conditions, then:

Y =Y ijY Eliminating Y from Expressions 4 and 9:

1 YOIlIJYOl Y0 iJYOI Expression l0 involves two complex conjugates. Solving for Y,,;, we find:

Thus We have determined the required relationship between each of the admittances Y ou and Y for matching conditions. (Equal power distribution is implied if relation 7 is obeyed.) One may observe that these admittances may be represented by a right triangle, as illustrated in FIGURE 4.

Considering the problem of power division with somewhat greater generality, it may be demonstrated by geometrical considerations similar to those used in constructing FIGURE 2 that the relative power coupling (K) from an input port to a non-adjacent or auxiliary output port is as follows:

K=g(lcos20) 12 where 0 is the angle defined in FIGURE 4, and 9 is the square of the number of transmission elements (29). In this expression one should treat the angle 0 as the independent variable. If one desires equal power coupling in a system having three output ports, one would assign to K the value of A, from which a solution of Expression 12 would indicate that the angle 20 is equal to 120 as previously determined. If one desires non-equal power distribution, i.e. a value of K differing from /3, then a value for 0 would be determined by that selection. One would then construct a new right triangle similar to that illustrated in FIGURE 4 to determine the desired values for Y and Y dictated by the pre-selection of 0. When compatible values for Y and Y have been selected, matching occurs and the power transfer to the various loads is reflection free.

The embodiment of the invention illustrated in FIG- URES 1A, 1B and 1C is adapted to provide eificient power division (and the other functions characteristic of a hybrid junction and directional coupler) to signals of a restricted frequency range. The center frequency of this range is that for which the various physical lengths in the junction yield the indicated electrical length It is well-known that devices of this nature function over a band of frequencies extending above and below the design center frequency. Should the occasion arise that a greater bandwidth is desired than is readily obtained by a single section device as illustrated in 1A, 1B and 1C, then one may cascade a succession of these sections making up the aggregate differential phase shift in equal (or unequal if desired) increments in the individual sections. The admittances of the transmission elements 29 and of the initial and final Y branches (30) will in the equal case remain the same as for a single section unit making up the indicated portion of the total differential phase shift. The admittances of the intermediate Y branches in this same case will assume a value of twice the admittance of the terminating Y branches.

The arrangement so far described is that of a six port directional coupler. However, the basic principles are readily generalized to junctions having three, four and more transmission elements, coupled at the indicated intervals by star connections. When three and four transmission elements are employed, one may achieve equal power division between each of the output ports. Where greater numbers are involved, the directly coupled output port must be favored by a greater fraction of the total energy than the auxiliary line ports. Expression 12 when solved for 0 may be more generally stated as:

where M is the number of parallel transmission elements.

The bracketed quantity being a cosine may never exceed unity in magnitude:

This expression defines the maximum design power coupling factor (K) to auxiliary ports as restricted by the total number of lines (M).

An eight port device is illustrated in schematic form in FIGURE 5. The hybrid junction is seen to comprise four transmission elements 41 all of one half wavelength and the three 4-arm one eighth wavelength star connections. The star connections are arranged respectively at the beginning, the middle, and end of the transmission elements 41 and bear respectively the numerals 42, 43 and 44. The eight port hybrid junction is then suitably energized by sources A, B, C and D shown coupled to the junctions of the transmission elements 41 with the star connections 42. The loads A, B, C and D are likewise coupled to the remote ends of the transmission elements 41 to which the star connections 44 are joined.

Assuming that one desires to achieve equal power distribution between the loads A, B, C and D of FIGURE 5, one may determine 0 by an equation similar to Expression 12 except for the substitution of the number 16 (M for the number 9. Having determined 0 one may then proceed to determine the relationship between the admittances of the elements 41 and the star connections 42, 43 and 44. In order to achieve 4-way equality in the power distribution, two sections are required, with e.g., each section producing a differential phase angle of 45, and the admittances of the terminating star connections (42 and 44) should then be equal to the admittance of the external transmission lines (Y while the admittance (Y of the transmission elements 41 would be VEY The admittance of the intermediate star connection 43 would be 2Y In the embodiment discussed in FIGURE 5, one may also use additional numbers of sections so as to increase the bandwidth of the junction by reducing the differential phase shift achieved in each individual section. One must also employ the Expression l2 involving 0 and K, and may employ the triangle admittance relationship of FIGURE 4 to achieve matching conditions in providing non-equal reflection free power distribution to the output ports.

The embodiments so far described have employed transmission elements of one quarter wavelength, electrical length and Y or star connection members whose branches are of one eighth wavelength, electrical length. It should be recognized that other integral multiples of these lengths may be substituted. One may for instance use transmission elements of a number of odd quarter wavelengths: fii, etc. To preserve the fundamental natureof the hybrid, however, it is essential that between adjacent input and output ports the direct path should differ electrically from the indirect path by 180 so as to achieve isolation. Similarly, the Y or star branches may be of a number of odd eighth wavelength, electrical lengths: /s, /8, /8, /8 and Here also the principal requisite is that the individual Y or star branches should appear as inductive loading to waves propagating in one mode and capacitive loading to waves propagating in the other mode.

In multiple section devices, one may use techniques analogous to those used in cascaded filter design to achieve an overall match for a maximum bandwidth. In this pursuit, one may use successive non-identical filter sections.

In using single section devices, or multiple section devices having like sections, the vectorial representations of the admittances should form closed right triangles with the arm admittances being the hypotenuse of the triangle. One may represent this relationship in geometrical terms:

The invent-ion has so far been described with principal emphasis on power sub-division. The technique may be used to provide a coherent breakdown of energy into three or four separate transmission paths. One may cascade a number of the foregoing elements in a tree so as to achieve breakdown into a greater number of paths.

Turning to the matter of power combination, it should be recognized that the invention also provides a method for power source combination. Since the hybrid junction so far described is perfectly bilateral, it may be appreciated that if all ports of one set are driven with energy of equal amplitudes, but Whose phase is properly selected (egg. to correspond to that indicated for the output ports A, B and C of FIGURE 2), one may achieve a linear combination of the power from each of the sources at one of the ports of the other set. One may also efiiciently link together power sources having unequal power outputs, providing of course that the phase relationships and admittances of the junction are suitably selected by resort to the principles herein disclosed. The invention thus may be seen to be of unique advantage in the coherent combination or division of high frequency electrical energy by numbers greater than two.

While the described embodiment has been executed in strip transmission line geometry, the invention may also be executed with transmission lines of all varieties including square and circular waveguides, coaxial lines, twin lines, etc. The principal theoretical limitation is that the lines should each have a uniquely defined phase velocity.

While particular embodiments of the invention have been described, it is intended that the scope of the invention should not be limited thereto, but should rather be as defined by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A directional coupler for operation with waves of specified frequency and having a set of M input ports and a set of M output ports adapted for coupling to external transmission lines of predetermined characteristic admittance comprising a plurality (M) of electrically parallel transmission lines each interconnecting an input port to a corresponding output port and having equal 10 electrical lengths of odd integral quarter wavelengths; a first star connection interconnecting each of said transmission lines at one end and a second star connection interconnecting each of said transmission lines at the other end, the branches of said star connections having an electrical length of an odd integral eighth wavelength;

said transmission lines and said branches having characteristic admittances chosen so that the input set of ports is matched when the output set is properly terminated by connection to an external line of said predetermined characteristic admittance.

2. The structure set forth in claim 1 wherein the quantity M is three.

3. The structure set forth in claim 2 wherein the characteristic admittance of the transmission lines equals 2Y and the characteristic admittance of the branches equals /3Y Y being the characteristic admittance of the external transmission line.

4. The structure set forth in claim 1 wherein the design power coupling factor (K) to non-corresponding ports is selected to be less than or equal to 4/M 5. A directional coupler for operation with waves of specified frequency and having a set of M input ports and a set of M output ports adapted for coupling to external lines of predetermined characteristic admittance comprising N iteratively connected sections; each section having a plurality (M) of electrically parallel transmission lines each forming a segment of a path directly interconnecting an input port to a corresponding output port and each having equal electrical lengths of odd integral quarter wavelengths; star connections interconnecting each of said transmission lines at each end of the directional coupler and at the sectional boundaries, the branches of said stars each having equal electrical lengths of an odd eighth wavelength; said transmission lines and said branches having characteristic :adrnittances chosen so that the input set of ports is matched when the output set is properly terminated by connection to an external line of said predetermined characteristic admittance.

6. A directional coupler for operation with waves of specified frequency and having a set of M input ports and a set of M output ports adapted for coupling to external lines of predetermined characteristic admittance comprising N iteratively connected sections; each section having a plurality (M) of electrically parallel transmission lines each forming a segment of a path directly interconnecting an input port to a corresponding output port and each having equal electrical lengths of odd integral quarter wavelengths; star connections interconnecting each of said transmission lines at each end of the directional coupler and at the sectional boundaries, the branches of said stars each having equal electrical lengths of an odd eighth wavelength; and wherein the vectorial representation of the characteristic admittance (Y of said external transmission lines, the characteristic admittance (Y of the transmission lines, the characteristic admittance (Y of the branches of the initial and final star connections form a closed right triangle of hypotenuse Yo c i. A directional coupler as set forth in claim 6 wherein the vectorial representation of the characteristic admittance Y the characteristic admittance Y and one half the characteristic admittance of the branches of the intermediate star connections form a closed right triangle.

8. A directional coupler as set forth in claim 7 wherein the quantity M equals 4, the quantity N equals 2, and wherein the characteristic admittance of the parallel transmission lines equals x/i Y the characteristic admittance of the branches of the intial and final star connections and one half the characteristic admittance of the interparallel path, said device being capable of propagating References Cited in the file of this patent Waves in a balanced and unbalanced mode and the rem current loading comprising a plurality of spaced star con- UNIIED STATES PATENTS nections, said connections having arms, each ending on ,61 ,170 Marie Oct. 14, 1952 one of sa1d paths, an electrical length selected to giYe 5 OTHER REFERENCES susceptive loading of one sign to Waves propagated in the device in the unbalanced mode and of the other sign Tang? Alternatlng Current Clrcults, 211d May to Waves propagated in the balanced mode. 1951, page 313 relied upon.

Claims (1)

1. A DIRECTIONAL COUPLER FOR OPERATION WITH WAVES OF SPECIFIED FREQUENCY AND HAVING A SET OF M INPUT PORTS AND A SET OF M OUTPUT PORTS ADAPTED FOR COUPLING TO EXTERNAL TRANSMISSION LINES OF PREDETERMINED CHARACTERISTIC ADMITTANCE COMPRISING A PLURALITY (M) OF ELECTRICALLY PARALLEL TRANSMISSION LINES EACH INTERCONNECTING AN INPUT PORT TO A CORRESPONDING OUTPUT PORT AND HAVING EQUAL ELECTRICAL LENGTHS OF ODD INTEGRAL QUARTER WAVELENGTHS; A FIRST STAR CONNECTION INTERCONNECTING EACH OF SAID TRANSMISSION LINES AT ONE END AND A SECOND STAR CONNECTION INTERCONNECTING EACH OF SAID TRANSMISSION LINES AT THE OTHER END, THE BRANCHES OF SAID STAR CONNECTIONS HAVING AN ELECTRICAL LENGTH OF AN ODD INTEGRAL EIGHTH WAVELENGTH; SAID TRANSMISSION LINES AND SAID BRANCHES HAVING CHARACTERISTIC ADMITTANCES CHOSEN SO THAT THE INPUT SET OF PORTS IS MATCHED WHEN THE OUTPUT SET IS PROPERLY TERMINATED BY CONNECTION TO AN EXTERNAL LINE OF SAID PREDETERMINED CHARACTERISTIC ADMITTANCE.

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