US 2602856 A Abstract available in Claims available in Description (OCR text may contain errors) y 8, 19512 v. H. RUMSEY POWER DISTRIBUTION SYSTEM Filed Aug. 18, 1948 ll 20 2| l5 l9 I8 I I3 7 a T 2 SMTS-SHEET l aid Io POINT l2 A+Z+V +X+ INT ll INPUT :EJ.I' I E SECTION NUMBER JUNCTION CHARACTERISTIC T'JUNCT'ON FOR FIG. 4 IDENTIFICATION IMPEDANCE as B Z 37 A 2 4|.9I as B 2 65.7! 4| a. 58.? I6 42 A 2 L 46 p B l I7 41 A g 40.23 49 B in 'sgcnou IMPEDENCE FOR COMPLETE DISTRIBUTION SYSTEM ILIE=3 VICTOR H. RUMSEY m HH o 6219 N 2 SHEETS$HEET 2 V. H. RUMSEY POWER DISTRIBUTION SYSTEM July 8, 1952 Filed Aug. 18, 1948 .ViCTOR H- RUMSEY SEHDNI NI BOlOflbNOD HBNNI'dO HlOlM hm T Om 1 Patented July 8, 1952 UNITE-D STATES PATENT OFFICE I Y Q asoassc I I I POWER DISTRIBUTION SYSTEM I Victor H. Rumsey, Columbus, Ohio, assignor to Minister of Supply in His Majesty's Government of the United Kingdom of Great Britain and Northern Ireland, London, England Application August 18, 1948, Serial No. 44,952 3 Claims. (01. 178-44) This invention relatesto electrical power distribution systems and in particular to radio frequency power distributing systems separating input electrical energy into a plurality of components of uniform phase but non-uniform power levels for deliverance into a plurality of load circuits. I In numerous applications of electrical equipment where it is desired to deliver energy from a single source to a plurality of energy operative devices some power division network is required to control the amount of power fed to each of the devices. Where this energy is of a radio frequency character many applications may require that the energy delivered to all the devices possess the same electrical phasing or differ by some multiple of 360 degrees. Such a power distribution problem may be encountered in radio antenna work where a pluralityof individual antenna elements are assembled to form an array. In this typical situation, an antenna structure having a plurality of radiator elements is employed which are excited in phase but with different amounts of power to minimize the intensity of side lobe radiation. Coaxial transmission line feeders have been commonly employed for such antenna elements but where a large number of elements are required the conventional coaxial system becomes quite complex. Additionally, the impedance matching sections required for coaxial line feeding of the various elements with different amounts ofpower are not easy to construct. j I v 1 It is therefore an object of the present invention to provide a powerdistribution systemfor supplying a plurality of; load devices with different amountsof iii-phase electrical energy froma single source: q 7 Another object of the present invention is to provide a power. distribution system of easily constructed design for delivering electrical energy from a single. source to each of a plurality of energy operative devices so that different amounts of energy may be supplied in an inphase manner to each. v ' Another object of the, present invention is to provide a radiofrequency power distribution system'for exciting a plurality of energy operative devices with in-phase energy of different amplitudes in which-a maximum percentage of the interconnecting feeder lines are operated without standing waves. . Other and further present invention will become apparent upon a careful consideration of the following detailed description and the accompanying drawings which illustrate a typlcalgembodiment of; the present invention. 1 1 1 Figure 1 shows. inschematic form a-general transmission. system '1 of delivering; electrical fenobjects and features of the; 2 ergy in selected ratios from a single source to a plurality of energy operative devices. Figure 2 shows in cross. section-a basic form of coaxial transmission line, in which the characteristic impedance thereof may be adjusted over a considerablerange by variation of the diameter of the inner conductor. Figure 3 is a graph showing, for a typical rectangular coaxial transmissionline having a strip type inner conductor, constructed in accordance with the teachings of the present invention typical impedance variations with width of the inner conductor. Figure 4 is a plan view of atypical rectangular coaxial power distribution system designed to transfer in-phase electrical energy in various amounts from a single source to a plurality of energy operative devices, showing in particular, the inner conductor. Figure 5 shows a cross section view through the rectangular transmission line of Fig. 4 as indicated by 5-5. I Figure 6 is a curve showing typical impedance variation characteristics for rectangular type coaxial lines. l In accordance with the general concepts of the present invention a' power distribution system is provided which is capablev of delivering radio frequency electrical energy from a single energy source to eacho'f a plurality of energy operative devices in such a manner that all of. the devices receive in-phase electrical energy at different, selected, power levels. A rectangular coaxial transmission section is employed in which a branched inner conductor, in the form of flat, thin paths leading from intersection points to the devices isadjusted ,inwidth at selected portions. thereof to produce required impedance matching. -The' total lengths of "the energy paths from 'thejsource to each of the devices are made equal so that the time delay of transmission from the source to each of the devices through the power distribution system of uniform impedance, typically half-wave resonant antenna elements. In atypical installation it was desired to provide the energy operative devices with in-phase electrical energy in different amounts, with currents of 2.34, 3.65, 5.85, and 7.9 amperes, respectively going to the devices at points ll, l2, l3, and M. A branched or T-junction type feeder system as shown schematically in Fig. 1 can provide such a current distribution when impedance elements are placed in the feederlines leading therefrom to the energy operative devices; 7 r For the transmission'of radio frequency energy where the physical spacing of adjacent points ll-IZ, l2--l3, etc. is a large portion of a wavelength, such as a half-wave length or some multiple thereof, the impedance elements may conveniently comprise sections of transmission line such as the parallel wire onthe' coaxial type. Also in such radio frequency transmission lines it is desirable to operate certain lines connectin to the impedance elements in a matched impedance terminated condition to reduce standing waves along them and increase transmission efficiency. A further requirement for such a feeder system is that of bandwidth. In many applications it is desirable that thefeeder system be capable of operating withoutretuning and with minimum impedance mismatching'occurring over a wide frequency range, typically percent of the mid frequency. '1. "I To satisfy these "requirements the impedance elements and the complete feeder system mustbe of adesign permitting exact calculation. Additionally' the entire feedersystem must be of an overall design which lends itself readily to mass production techniques. In-phase deliverance of energy to each of the points ll, '12, 'l3,andjl4 (Fig. '1) is insured by arbitrarily making the lengths of energy travel to each point the same. Each T-junction (numbered [5, I6, and I1) is preceded with impedance transformer line sections designed to make the ratio'of the' conductances at each T-junction equal to the required power division at the T-junction. Besides maintaining this condition over the frequency band, it is desirable that the impedance transformers also make the input impedance to each T-junction equal to the impedance of the energy operative devices I], [2, etc., so that similar design procedure can be applied to all T-junctions. 1 j j' 1 To simplify design and construction it may be desirable to make a section of transmission line between point ill and section A1 equal to the impedance '(ZL) of the load located at point II. This impedance is also identified as (Z0). With a series arranged double quarter wave transformer or transmission line section such as shown in Figure 2 having characteristic impedances of (AiXand' (Bi) theimp'eda'nce (Zn) ofthe load de'vice'located at point I I can be trans-, formed to another constant resistance (R1) at the input in accordance with the formula Similarly the impedance of'thedevi'ce at point l2 (also (Zn) in the typical-case) can be transformed by a double quarter wave transformer having impedances (A2) and (132) into a second constant resistance (R2) at the input in accordance with R?" (A2)? To deliver (P) times as much power to point 'I I as to point l2 the following condition must then be satisfied. The input impedance of the T-junction is then which, as previously mentioned, is preferably made equal toth'e impedance (ZL) of either of the loading devices placed at points I I and [2. The characteristic impedances of the line sections (A1, A2, B1 and B2) may then be calculated according to the formulas Under certain conditions single quarter wave transformers may be substituted for the double quarter wave transformers. Where the desired impedance transformation is small, that is where the impedance is between 1.5 and 0.667 times the value of the desired impedance, such a single quarter wave matching section is adequate. With reference to Figure 2, when the impedance of the load (ZL) placed at point H is within the range of 1.5 to 0.667 times the impedance (R1) desired at the input end of (B1) the two quarter sections (A1, B1) may be replaced by a single quarter wave matching section. For this condition (A1) will be made equal to- (Z0) and Equation 1 will not be applied. The impedance of the section (131) will then be calculated in accordance with Equation 7. The preferable feeder system of this type, both from the electrical and mechanical standpoints, is one which uses the smallest relative range of characteristic impedances for-these quarter wave transformer sections. Although the foregoing equations and methods of calculation are entirely correct, a somewhatsmaller relative range of characteristic impedances may be obtained by making the input impedance (Z'r) of the T-junction somewhat lower than (Zn), typically not less than (0.66'IZ1.) and then employing an additional single quarter wave matching transformer (B3) at the input of the T-Junction to convert the impedance back to the desired value (21.) for a subsequent T-Ju'nction; For this modified calculation the input impedance (Zr) from Equation 4 would be less than (21.) The characteristic impedances of the line sections (A1, A2, B1 and Ba) would then be calculated according to the revisedequations: The value of the compensating section (B3) can then be calculated from the equation for a conventional quarter wave matching equation. To illustrate the method of application of the above principles and calculation methods, reference is again had to the typical schematic of Fig. 1, in which it is desired that the points II and [2 be one wavelength apart in air and that the conductor shown schematically be in polystyrene or other suitable insulating material. Since the values of (A1. B1, A: and B2) will always be greater than (21.) it is well to choose a low value of (ZL),typically- 33.58 ohms. Since the loads at points II and I2 constitute definite known values a logical T-junctio'n about which to start calculations is junction [5. It is desirable as previously stated that point I2 receive more power than point ll, therefore, the line section between points l8 and I9 is established as (A1), that between [9 and I as (131), that between 20 and 2| as (A2), that between 2| and i5 as (B2), and finally that from l5 to 22 as the compensating section (B3). The sections between points [2 and '18 and between points H and 20 are length matching sections tocompensate for the difference of wavelength in air and in polystyrene. As a starting point the line sections (A1) and Bi) may be assigned values equal to (ZL), no impedance transformation being effected, (A2) and (B2) are then calculated to give characteristic impedance values of 41.91 and 65.71 respectively. The value'for (B3) then necessary to reproduce an impedance of 33.58 ohms at point 22 is 28.3 ohms. In a similar manner calculation is extended to the next T-junction, point [6. In assigning the quarter wave matching symbols it is again necessary to determine which point receives more power, 22 or I3. Point 22 receives more power therefore the symbol (A1) is affixed-to the line section between 22 and 23, the symbol (B1) to the line section between 23 and I6, (A2) to the section between 24 and 25, (B2) to the section between 25 and i5, (B3) to the section between it and 26. The connecting section between points [3 and 24 is of the load impedance (ZL). Figure 3 shows the tabulated results of the calculations for the entire feeder system with load currents as previously set forth. Numbers corresponding to those employed in Fig. 4 are shown also. From these figures it is seen that the characteristic impedance of the various matching sections varies only over the range of 28.3 to 65.71 ohms, a range which may easily be obtained with a transmission line system constructed according to the teachings of the present invention. The construction of so many matching sections in a conventional type line structure such as a parallel wire or a circular coaxial type is quite time consuming and requires a high degree of mechanical skill for assembly and hence is usually considered impractical. In accordance with the teachings of the present invention a feeder system of simple mechanical structure and of a type permitting great ease of construction is provided. A typical feeder structure constructed to fulfil the impedance requirements of Fig. 3 is shown in partially cut-away form in Figure 4. A rectangular type conductor assembly is employed, similar in certain respects to a coaxial line having conductors of rectangular cross-section. The inner conductor is a flat, thin strip of highly conductive material which may be cut or stamped to the shape shown in the cut-away portion of Figure 4. This inner conductor is sandwiched between two flat strips of insulating material of suitable thickness and dielectric characteristics for the frequencies and voltages to be experienced. An eilicient insulating material for many systems would be polystyrene. About this insulated conductor assembly is placed a box-type outer conductor to give strength and protection as well as form a portion of the electrical energy path. To illustrate this construction more fully, reference is now had also to Fig. 5 which is a cross section view of the entire feeder in the plane indicated by 5+5 in Fig. 4. "The ends of theinner conductor are indicated by numeral 21. The flat slabs of insulating material bear the numerals 28. Numerals 29 and 30 indicate two sections of the outer conductor, which may be riveted or bolted together by appropriate members 3|, 32. An energy operative device (antenna) is indicated by numeral 33. An input terminal for connection to energy source I0 is indicated by numeral 34. V The inner conductor as shown in Figs. 4 and 5 may be cut or stamped from a sheet of material in one simple operation. Typically the conductive sheet used may be of copper having a thickness of 0.005 inch and each insulating slab used may be 0.156 inch thick. It is seen. that a single strip of the inner conductor will cooperate with the outer conductor to act as an unbalanced line, in a manner similar to that of a conventional round coaxial line. It is possible to vary the characteristic impedance of this unbalanced line by varying the width of the inner conductor. The characteristic impedance of a typical transmission line of this type was determined experimentally as a function of the width of the inner conductor and is shown graphically in Figure 6. It is therefore possible simply to vary the width of the inner conductor over the range of 0.1 to 0.5 inch to obtain the characteristic impedances desired for the various sections for the typical system previou'sly calculated. The entire system is then cut and assembled to physically resemble the schematic Figure 1 to produce the device of Figure 4 with smoothly rounded corners and junction points in the innerconductor, the length of the various matching and connecting sections required being measured along the electrical center line in traversing the corners and junctions. The matching sections are numbered in accordance with the tabulation of Fig. 3, and the length compensating sections 50,5l, 52, 53, 5!. of (ZL) impedance have been added. It is desirable that coupling between adjacent parallel sections of the inner conductor be negligible otherwise some energy transfer may occur to upset the impedance matching. In determin-" ing the magnitude of this coupling, the space between the parallel sides of the outer conductor (in the narrow dimension) is treated as a waveguide below cut-off. The conductor would excite this waveguide in the TEM mode, for which the cut-off wavelength is equal to twice the spacing between the parallel conductors, multiplied by the dielectric constant of the insulation. This produces an attenuation of approximately db per inch spacing between conductors showing that the strips can be placed quite close together without serious coupling. From the foregoing it is apparent that considerable modification of the features of the present invention is possible and while the device herein described and the form of apparatus for the operation thereof constitutes a preferred embodiment of the invention, it is to be understood that the invention is not limited to this precise device and form of apparatus and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims. What is claimed is: 1. A power distribution system for delivering electrical energy in selected ratios from a source to a plurality of energy operative devices, comprising; an outer conductor sheath of rectangular cross section having at least the long dimension surfaces of the cross-section comprising conductive material, a pair of flat insulating members substantially equal in width to the long cross-sectional dimension of the sheath placed within the sheath, and a strip type inner conductor placed between the insulating members, said inner conductor comprising a sheet of conductive material cut in a branched manner having junction points in number one less than the number of energy operative devices, each of said junction points having a single energy input path and dual energy output paths, with first quarter wave impedance transforming inner conductor portions of selected widths in the output paths defining progressively lower impedance portions going towards said energy operative devices in proximity to each junction to control the ratio of power delivered to the two energy output paths and with a second quarter wave impedance transforming inner conductor portion of selected width in the input path in proximity to the junction to convert the impedance of the junction to a selected input impedance. 2. A power distribution system for delivering electrical energy in selected ratios from a source to each of a plurality of energy operative devices, comprising; a branched and flat inner conductor structure, a pair of flat insulating members enclosing the inner conductor, a sheath type outer conductor enclosing the inner conductor and insulating members, said inner conductor comprising a sheet of conductive material cut in a branched manner having junction points in number one less than the number of energy operative devices, each of said junction points having a single energy input path and dual energy output paths, with first quarter wave impedance transforming inner conductor portions of selected widths in the output paths in proximity to the junction to control the ratio of power delivered to the two energy output paths defining progressively lower impedance portions going towards said energy operative devices and with a second quarter wave impedance transforming inner conductor portion of selected width in the input path in proximity to each junction to convert the impedance of the junction to a selected input impedance. 3.A power distribution system for delivering electrical energy in selected ratios from a source to a pluralityof energy operative devices, comprising; an outer. conductor sheath of rectangular cross-section having at least the long dimension surfaces of the cross-section comprising conductive material, a pair or flat insulating members substantially equal in width to the long cross-sectional dimension of the sheath placed within the sheath, and a strip type inner conductor placed between the insulating members, said inner conductor comprising a sheet of conductive materialcut in a branched manner having junction points in number one less than the number of energy operative devices, each of said junction points having a single energy input path and dual energy output paths leading to the energy operative devices, said inner conductor additionally having quarter wave impedance transforming portions of selected widths in the output paths defining progressively lower impedance portions going towards said energy operative devices in proximity to each junction point to control the ratio of power delivered to the two energy output paths, said inner conductor additionally having quarter wave impedance transforming portions of selected width in the energy input path thereto to adjust the input impedance thereof, said inner conductor including additionally time delay means in the output paths controlling the time phasing of the energy delivered to each output energy path. VICTOR H. RUMSEY. REFERENCES CITED The following references are of record in the file of this patent: UNITED STATES PATENTS Number Name Date 2,241,616 Roosenstein May 13, 1941 2,283,620 Alford May 19, .1942 2,465,843 Brown Mar. 29, 1949 2,502,359 Wheeler Mar. 28, 1950 2,508,030 Karns May 16, 1950 FOREIGN PATENTS Number Country Date 592,119 Great 'Britain Sept. 9, 1947 Patent Citations
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