US 3010082 A
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NOV. 21, 1961 H. T. BUDENBOM 3,010,082
HYBRID RING NETWORK Filed July 25. 1952 m." w n-4.21 a
/N l/E N 7 0/? H 7'. BUDENBOM A 770/? NE V United States Patent 3,010,082 HYBRID RING NETWORK Horace T. Budenbom, Short Hills, N.J., assignor to Bell Telephone Laboratories, Incorporated, New York, N.Y., a corporation of New York Filed July 25, 1952, Ser. No. 300,909 13 Claims. (Cl. 333-9) This invention relates to wave transmission networks and more particularly to hybrid ring networks.
The object of the invention is to improve the impedance match at certain arms of a five-arm hybrid ring.
A more specific object is to make the input impedances equal at all arms of a five-arm hybrid ring without incurring an appreciable loss of power.
A five-arm hybrid ring may be designed to have certain desirable conjugate relationships which may be utilized, for example, in branching arrangements or in networks for obtaining the complex sum of and difference between two coherent input voltages or powers. Rings of this type are disclosed, for example, in the paper by W. A. Tyrrell entitled Hybrid Circuits for Microwaves, published in the Proceedings of the I.R.E. for November 1947, and in my copending United States patent application Serial No. 52,856, filed October 5, 1942, now Patent No. 2,7 84,381 issued March 5, 1957. In one embodiment, such a ring comprises a closed transmission loop having an effective length of wavelengths A at a selected design frequency f and five transmission branches or arms connected in series with the loop at successive points thereon spaced apart by M4 at the frequency For reference, these arms may be designated one to five, with a spacing of M2 between the first and the fifth. The loop and the arms may be constituted by a wave guide, a coaxial cable, or some other suitable type of transmission line. If all of the arms have the same characteristic impedance Z each is terminated in an impedance Z and the loop has a characteristic impedance equal to Z /VZ there will be a good impedance match with the loop for the third arm, but a considerable mismatch for the other arms. In practice, this mismatch has been found to be of the order of three decibels, which is undesirably large for some applications, especially if high power transmission is involved.
In accordance with the present invention, this mismatch is greatly reduced, without substantial power loss, by adding a sixth series arm of characteristic impedance Z connected to the loop at a point midway between the first and the filfth arms, iteratively terminating the added arm, and providing an auxiliary transmission path between the third arm and the sixth arm. The addition of this sixth terminated arm only, without the auxiliary path, will provide an impedance match at the first, second, fourth, and fifth arms, but a considerable fraction of the input power will be lost by dissipation in its termination. The function of the auxiliary path is to prevent this loss of power. In one embodiment, the third and the sixth arms are connected by an auxiliary path extending across the loop and having an electrical length equal to )\/4. If a wave guide of the hollow-pipe type is used, it may be necessary to include dielectric material within the guide to provide the required electrical length. In a second embodiment, the auxiliary path includes a directional coupler connecting the third and the sixth arms.
The nature of the invention and its various objects, features, and advantages will appear more fully in the following detailed description of typical embodiments illustrated in the accompanying drawing, of which FIG. 1 is a perspective View, partly cut away, of one embodiment of a hybrid ring network in accordance with the invention; and
FIG. 2 is a similar view the invention.
The hybrid ring network shown in FIG. 1 comprises a section of transmission line 10 formed into a loop or ring and provided with six equally spaced transmission branches or arms, numbered consecutively 1 to 6, and an auxiliary transmission path 7. As shown, the ring and the branches are made of hollow-pipe wave guide of oblong cross section, adapted to transmit electromagnetic waves having an smaller transverse dimension, as indicated by the arrow 11 in the branch '4. It and branches may also be constituted by coaxial cable or some other suitable type of transmission line. In the ring 10, the smaller transverse dimension of the guide is parallel with the plane of the ring. The branches are connected to the ring 10 in the electric plane; that is, they branch from a wider side of the ring and the smaller transverse dimension of each branch is parallel with the plane of the ring. This corresponds to a series electrical connection. The ring 10 has a mean circumference equal to wavelengths A within the guide at a selected design frequency f and, therefore, the branches 1 to 6 have a spacing around the ring of A/ 4 between centers. Each of the branches has the same characteristic impedance Z of another embodiment of The wave guide forming the ring 10 has a characteristicimpedance equal to Z /x/f. The branch 6 is terminated in an impedance Z which may, for example, be provided by inserting a block 12 of dissipative material, preferably tapered at its inner end, as shown, to prevent reflection.
The hybrid ring just described may, for example, be used to obtain the sum of and ditference between two coherent voltages of frequency f. If the voltages are applied to the arms 2 and 4, a voltage proportional to their complex sum will appear at the arm 3, and a voltage proportional .to their complex difference will appear at the arm 1 and also at the arm 5. However, if the input voltages deviate from the frequency f, the output voltages at the arms 1 and 5 will be oppositely phased and mayv a sort of. first-orderbe combined differentially to provide cancellation of frequency sensitivity, thus increasing the useful frequency band of the network. Even without the auxiliary path 7, if the arms 1 to 6 are all iteratively terminated there will be an impedance match with the ring 10 at each of the branching points, but a considerable part of the input power will be dissipated in the termination 12 of the arm 6.
This power loss is substantially eliminated by connecting the arms 3 and 6 through an auxiliary path 7 extending across the ring 10. As shown, the path 7 is a series-connected, hollow-pipe wave guide having an effective electrical length of )\/4. The required electrical length may be obtained by placingwithin the guide 7 a properly dimensioned core 13 of suitable dielectric material, if necessary. The characteristic impedance of the path 7 is so chosen that the input voltage arriving thereover at the arm 6 will be substantially equal to the voltage arriving at the arm 6 via the ring 10. Due to the half-wave difference between the length of the path 7 and the half-perimeter of the ring 10, these voltages will be 1r radians out of phase with each other and, since they are equal, will tend to cancel, leaving substantially no net voltage on the arm 6. Therefore, only a negligible electric field parallel to the is to be understood that the ring iteratively terminated in a dissipative block 16, corresponding to the termination 12 in FIG. 1. The auxiliary path connecting the arms 3 and 6 is provided by the coupling apertures 19 and 20 which extend through the adjacent walls of the portions 17 and 18. The apertures 19 and 20 are of equal area and are spaced apart a distance equal to 7\/4 at the frequency f to constitute a directional coupler of the type disclosed in greater detail, for example, in United States Patent No. 2,562,281, to W. W. Mumford, issued July 31, 1951. The desired compensating voltage is obtained from the arm 3 by means of a directional coupler so that no impedance irregularities will be introduced into the arm.
In order to prevent loss of input power by dissipation in the termination 16, it is required that the voltage efiective thereon derived from the arm 3 shall be equal in magnitude to, but 1r radians out of phase with, the voltage at that point derived from the ring 15 by the arm 6, so that these two voltages will cancel each other. This is substantially accomplished by so choosing the areas of the apertures 19* and 20 that these voltages are equal, andby making the length of the arm 6 such that the voltages'will be 1r radians out of phase.
It is to' be understood that the above-described arrangements are illustrative of the application of the principles of the invention. Numerous other arrangements may be devised by those skilled in the art without departing from the spirit and scope of the invention. For example, the transmission line may be of a different type than wave guide, the length of the ring can be other than 3M2, and some or all of the arms can be connected to the ring in shunt instead of in series. Explicit rules to be followed in making these latter modifications are given in the Tyrrell paper and in my copending application cited above.
What is claimed is:
1'. A network comprising a closed transmission loop having an effective length of wavelengths at a selected design frequency, six transmission branches connected in series with said loop at equally spaced points thereon, a matching termination for one of said branches, and means for substantially preventing the dissipation of power in said termination comprising an auxiliary transmission path connecting said one branch and the branch opposite th re o.
2. A network in accordance with claim 1 in which said auxiliary path extends across said loop.
3. A network in accordance with claim 2 in which said auxiliary path has a length equal to a quarter wavelength at said frequency.
4. A network in accordance with claim 2 in which said auxiliary path is constituted by a wave guide and said wave guide has a core of dielectric material.
5. A network in accordance with claim 1 in which said auxiliary path includes a directional coupler.
6. A network in accordance with claim 1 in which said one branch has a" portion lying alongside a portion of said opposite branch, and said auxiliary path includes a directional coupler coupling said portions.
7. A network in accordance with claim 6 in which said directional coupler includes two apertures of equal area extending through adjacent walls of said portions.
8. A network in accordance with claim 7 in which said apertures are spaced apart a distance equal to a quarter wavelength at said frequency.
9. A network in accordance with claim 1 in which said loop is constituted by a wave guide.
10. A network in accordance with claim 9 in which said wave guide is oblong in cross section and the smaller transverse dimension of said guide is parallel with the plane of said loop.
11. A network in accordance with claim 1 in which each of said branches has a characteristic impedance Z and said loop has a characteristic impedance equal to Z /2.
12. A network in accordance with claim 1 in which said termination is constituted by a block of dissipative material.
13. A network in accordance with claim 12 in which said block is tapered at its inner end.
References Cited in the file of this patent UNITED STATES PATENTS Ring Mar. 31, 19 53
Citations de brevets