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Nov, 26, 1946. ' c, B, WAT-rs, JR 2,411,564 COUPLING CIRCUIT Filed July 4. 7,1942 ‘ ' FIG 1 . ' v I I ' ‘ ‘a: 35 ,LI a?” .‘ I - z r HEGH — FREQUENCY souncs ‘ HIGH '_ FREQUENCY $0URCE HIGH ‘—— FREQUENCY SOURCE ‘—'— HIGH FREQUENCY SOURCE INVENTOR BYG-IESTER WATTS #2 I ATTORNEY Patented Nov. 26, 1946 ' -~_, I 2,411,564 ' ’ UNITEDSTATES PATENT‘ OFFICE COUPLING CIRCUIT Chester B.‘ Watts, Jr., East orange, N. _.l'., as signor to Federal Telephone and Radio Corpo ration, a corporation of Delaware Application July 4, 1942, Serial No. 449,828 9 Claims. (Cl. 178-44) 1 2 This invention relates to coupling circuits and more particularly to impedance matching trans formers for. matching dissimilar impedances of two or more networks. lengths of the two stub-lines. More particularly, the short circuited stub-line may comprise two parallel spaced apart conductors having one end thereof short circuited and the other end ‘con nected to a common junction or other point in ' Several schemes have been proposed heretofore to match dissimilar impedances such as where the load impedance of one network is either higher or lower than the characteristic imped one of the networksat which impedance match ing is desired, , Assuming that the adjustable connection has substantially the same surge im pcdance as the stub-lines, the length of the short ance of a transmission line or other network con necting the load impedance to a source of energy. 10 circuited stub-line may be chosen in the order One of the most practical schemes for‘impedance ' of a quarter wavelength should a step-up trans matching heretofore proposed is the adjustable formation be required, or in the order of a half short circuited stub-line type of transformer. Each such stub-line used, however, requires two adjustments; one being the location of the stub line with respect to either the maximum or mini wavelength should a step-down transformation be desired. If additional lengths are required 15 between the location of the transformers and mum voltage points of the transmission line, de pending upon whether step-up or step-down . } matching is desired,'and the ‘other, an adjust ment lengthwise of the stub-lineof the short circuiting conductor thereof. This type of transformer can be used with a fair degree of the points in the network to which it is to be connected, additional lengths may be added thereto in the order of a half wavelength and multiples thereof, for either quarter wave or 20 half wavelength stubs. In either a step-up or a step-down transformer, the open circuited stub-line thereof is taken sub satisfaction for impedance matching of simple stantially as a quarter wavelength and may com networks such as two transmission lines. How prise two parallel conductors arranged in spaced ever, when complex network arrangements are 25 relation with respect to the parallel conductors concerned such, for example, as when aplurality of the short circuited stub-line. I ?nd that when of loads are to be matched to a transmission line the overlap between the two lines, or the dis having a single source of high frequency energy tance provided for movement of the adjustable thereby requiring two or more stub-line trans connection, is slightly less than a quarterwave formers, it is exceedingly di?lcult to reach an 30 length, that is to say, about two-tenths of a impedance balance. This is because each stub wavelength, more or less, the maximum of the line has ‘two adjustments, and any network re reflected waves for all positions of the adjustable quiring more than one transformer will require connection occurs at substantially the end of twice the number of adjustments as there are the short circuited stub-line towhich a trans transformers, and since the adjustment of each 35 mission line or other network is connectable. transformer alters the impedance matching char The amount of overlap as well as other dimen acteristics of each of the others, it is almost a sions of the transformer may be considerably hopeless task to properly match by means of stub varied, and the relative dimensions which may line transformers a complex network system. be chosen are further described hereinafter. One of the objects of this invention, there 40 The adjustment of the'transformer is carried fore, is to provide an impedance matching trans- 7‘ out by providing a movable connection compris former having but a single adjustment. Another object of the invention is to provide an impedance matching transformer which may be readily arranged for step-up or step-down impedance matching. » Still another object of the invention is'to pro vide impedance matching transformers vfor ef ing a pair of conductors conductively connecting the corresponding conductors of the two stub lines. This adjustable connection is movable lengthwise of the stub-lines and as the short circuited end of one stub-line is varied by such adjustment, the open circuited end of the other line is likewise varied but in the inverse relation. fective impedance matching of a single or plural It follows, therefore, that the overall effective load and/or a single or plural source of high 50 length. of the two stub-lines always remains the ‘frequency energy- ' same regardless of the position‘ of the adjustable The above and other objects of this invention ‘ i connection. When the connection is moved to I accomplish by combining a short circuited stub ward ‘the short circuited end of, the one stub, the line and an ‘open circuited stub-line conductively impedance correction is increased and when the connected together by an adjustable connection connection is moved toward the open end of the ‘so as to vary in inverse relation the e?'ective .otherstub, the impedance correction is reduced. 2,411,564 3 Since only one adjustment is required by my improved impedance matching transformer, it is not only highly satisfactory in matching two dis similar impedances but may also be used in con junction with a plurality of loads for connection to a common source of high frequency current. Thus, when a plurality of impedance lines or loads are to be’connected to a common trans mission line, a separate impedance transformer 24 of the conductors 20 and 2! are connected through the connecting line H2, £5 to the com mon junction 33, 3|. The open circuited stub line of the transformer It! comprises two parallel spaced apart conductors 25 and 25, the ends 21 and 28 of which are adapted to be connected to the lines 8' ands of the load I. In some instal lations the- co'nductors 25 and 25 may comprise extensions of the transmission line 8, 9. The two stub-lines may overlap in spaced re may be provided for each of the loads and since 10 lation for about two-tenths of a wavelength, more only one adjustment is required for each trans or less. This overlapping relationship depends on former, it is a relatively simple matter to adjust the impedance characteristics of the adjustable the two or more transformers to reach an im connection between the two lines and also the pedance balance at the common junction. The impedance matching transformer of this 15 length of the distance C. When these relations are properly chosen the operating results of the invention is also of particular use for matching a plurality of sources of energy to a single or a plurality of loads. The transformer connection combined stub-lines provides maximum voltage points at the ends 23, ‘.24 and at points a half wavelength and multiples of half wavelengths therefrom along the line Ill, l5. 20 plished by a step-down transformer arrange The adjustment of the impedance matching ment wherein the short-circuited stub-line characteristics of the transformer is effected by thereof is chosen in the order of a half wave a movable bracket 35 having two suitably ar length. In this arrangement the amplitude of ranged conductors 36 and 31, the conductor 36 the standing waves produced by the transformer provides a reduction in the impedances at the 25 providing conductive connection. between the to a plurality of sources of energy may be accom transformer connection looking in the direction of the load, a minimum wave point occurring at the end of the half wavelength line to which the sources of energy are connected. conductors 20 and 25 of the two stub-lines and the conductor 31 providing conductive connec tion between the conductors 2i and 26. The lo cation of this conductive connection between the If more than one load is applied to the trans 30 two lines may be described as dividing the ef fective lengths of the lines between parts A and mission line, then, in addition to the step-down B. The distance A is the distance between the transformer just described, a step-up trans conductors of the bracket 35 and the open end former will be required for each such additional of the open circuited stub-line and the distance load. Thus, the plural sources of impedance lines B is the distance from the conductors of the may be matched by a single transmission line bracket 35 to the short circuiting bar 22 of the and the impedance thereof again matched to a short circuited stub-line. As the bracket 35 is plurality of loads. moved either to the right or left, the distances For a better understanding of the invention, A and B will be varied in inverse relation. That reference may be had to the following detailed is to say, when the bracket 35 is moved toward description to be read in conjunction with the the short circuited conductor 22, the distance B accompanying drawing, in which, will be diminished and the distance A will be Fig. 1 is a schematic illustration of the step up transformer of my invention applied to a transmission system coupling a plurality of loads to a single source of high frequency cur rent; and Fig. 2 shows an impedance matching trans former of my invention of the step-down type coupling a single load to a plurality of sources of high frequency current. Referring to Fig. 1 of the drawing, I have shown tWo sources of high frequency current 5, 5’ having two transmission lines 6, ‘I and 6’, 1' to which a plurality of loads Ll‘, L2 and L3 are adapted to be coupled by transformers If], ll and i2, respectively. Each load such as Ll may be connected by means of a transmission line 8, 9, which preferably is matched to the load, to the increased proportionally. Conversely, when the bracket 35 is adjusted in a direction toward the open end of the open circuited stub-line, the dis tance A will be decreased and the distance B will be increased, the overall effective length of the two stub-lines (that is, A plus B) will always re main the same. It will, therefore, be clear that the adjustments of my impedance matching transformer may be made without changing the overall effective length of the coupling. As an illustrative example of the relative di mensions of av transformer constructed in ac cordance with my invention, the dimensions in the following table are those of a transformer which I caused to be constructed and which was successfully operated at 110‘ megacycles. The dimensions in the table are given with respect to transformer IE3. Where it is desirable to have a common junction to the transmission ‘line 6, ‘I at 60 the parts shown in the transformer ill, Fig. 1. a distance'from the transformer, a connecting Dimensions of transformers for 110 mc. line such as M, l5 may be provided in the order of a half wave or a multiple thereof between the Diameter of conductors 20, 2|, 25 and transformer and the common junction. The 26 __________________________ "inches" transformers l0 and 12 are shown connected by 65 Space X between conductors of each stub lines each a wavelength long and the transformer line ________________________ __inches__ H is shown connected by a line a half wavelength Space Y between conductors of overlap— long. ping lines _______ __'_ _________ "inches" Since each of the transformers In, H and I2 is identical to the other, a detailed description of 70 Bars 36 and 31 are rectangular__,___do____ one will sui?ce. Referring to the transformer ID, the stub-line thereof comprises a pair of parallel conductors 20 and 21 connected together at one end by a short circuiting conductor 22. The ends 23 and 75 Length of bars 36 and 31 ________ __-do____ Space between bars 36 and 31 ____ __do____ 3/3 13/16 1% 3A6}; 21/2 2/32 Overlap of lines (A-l-B) ____wavelength__ 0.2 Length of distance C _________ __'___do____ 0.05 9,41 15 5.64 5 The tworectangularbars referred to ‘in the table are. mounted on a'plate made; ofta composi tion of mica and a phenol‘condensation product known as “Micalex..f" The; sides: of‘ the bars; are provided‘ with arcuate grooves ' to“ accommodate the conductors of the stub-lines with which the bars have sliding contact. ' ' 6 bracket '55. The open circuited stub-line 54 is curved like the portion 5| and‘arranged in spaced opposed relation thereto. The lengths A’, B’, and C’ correspond to the lengths A, B and C of the form shown in Fig. 1. ' By adding to the short circuited stub-line 52 a quarter wavelength of line 53, the minimum voltage point of the line Will occur substantially at the junction point 45 and this relationship While I have found the. foregoing dimensional relations of the transformer to operate satisfac tory at 110 megacycles, I wish it understood that 10 renders the operation of the transformer as an the invention, isrnotzrestricted to these dimen sional proportions but-that: they may bezconsid erably varied ‘depending; apparently upon. vari ance of the impedance, of: certain of" the parts thereof. For example, a variation‘in the im pedance of the movable bracket 35 may require a different dimensional relation; between. the lengths A, B on the one hand and C onthe other impedance step-down transformation between the plural'sources of energy and the single load L4. If desired, an additional length or lengths of line in the order of a half wavelength or multiple 15 thereof may be inserted between the line section 53 and junction points 45. ' From the foregoing, it will be clear that a plu rality of sources of energy may be coupled to a hand. Also, the overall distance A. plus B. plus C plurality of loads. In other" words, the loads Ll, may be greater than a quarter wavelength. It 20 L2, and L3 may be substituted for the load L4 by will be understood, therefore, that the dimensions using the same transformer arrangement as il given for the llil-megacycle transformer are se lustrated in Fig.v 1 to the right of the junction lected for purposes of illustration only and- that points 30, 3|. Such a system will then have a they may be varieddepending upon the wavee plurality of sources of energy having a common length and thestructural shapes and‘ arrange junction such as 45, a step-down transformer ments of‘ the parts thereof. such as 50 coupled in a transmission line between The transformer It as above described may be ' the junction 45 and the load junction 30, 3| to adjusted by moving the bracket. 35 so as to effect which a plurality of loads such as Ll, L2 and L3 the desired wave re?ections and therefore vary are coupled by step-up transformers I0, I l and I2. the amplitude of the standing waves in the stub While two forms of the transformer and two line to correct the difference between the im applications thereof are shown and described, it pedance of the load LI and the source of energy is recognized that many variations of the two supplied by the transmission line‘ 6, T. For a _ forms together with many applications thereof plurality of loads such as Ll, L2, and L3','indi are possible without departing from the inven vidual impedance matching transformers are pro tion. It will be understood, therefore, that the vided for the loads and these transformers may forms herein illustrated and described'are to be be adjusted by moving the bracket 35‘ of each to regarded as illustrative of the invention only and such a position that the combined impedances" of not as restricting the appended claims. ' the three parallel loads will balance with ‘the What I claim is: characteristic impedance of the transmission line 40 1. An impedance matching transformer for 6, ‘I. Should, for example, each of the loads L1, connecting together two networks of dissimilar L2 and L3 be 500 ohms and the characteristic impedances to selectively control the amount of impedance of the transmission line be 500 ohms, energy transferred between said networks while the parallel loads each should have the appear maintaining; the impedance matching, compris ance of 1500 ohms. This may. be effected by 45 ing a short circuited stub-line conductively asso pro-per adjustment of the brackets 35. of the trans ciatable with one of said‘ networks, an open cir formers Iii, H and I2. Should the loads Ll, L2 cuited stub-line conductively associatable with and L3 be dissimilar, the adjustments of the the other of said networks, said stub lines being transformers l9, Hand [2 will then be‘ corre positioned in overlapping spaced relationship, the spondingly different, depending, of course, upon ' conductors of said stub lines being disposed to de the particular impedance of the load associated ?ne the corners of a rectangle lying in a plane with each transformen g _ perpendicular to the stub lines with the conduc In the form shown in Fig. 2 of the drawing, a tors of each stub line lying in adjacent corners of plurality of sources of high frequency current 40 said rectangle, means conductively connecting and M are shown connected through suitably the stub-lines together, and said means being matched transmission lines 42 and 43 to a com movable to vary in inverse relation the effective . ' mon junction 45 to which a load L4, which may be an antenna, is connected‘ by a transmission-line 46, which preferably is matched to the load L4, and an impedance matching transformer 50 of an 60 impedance step-down type. ‘ The transformer 50 may be arranged for re ciprocatable adjustment as shown in Fig. 1 or the adjustment feature may be effected in any ‘other suitable manner. In Fig. 2, I have chosen to show the transformer 50 with a rotatable bracket 55. lengths of the two stub-lines. ‘ 2. An impedance matching transformer for connecting together two networks of dissimilar impedance to selectively control the amount of energy transferred between said networkswhile maintaining the impedance matching, compris ing a short circuited stub-line conductively as sociatable with one of said networks, an open circuited stub-line conductively associatable with the other of said networks, the two lines being disposed in overlapping spaced relationship for The short circuited stub-line 52 has a bracket en gaging portion 5! thereof curved in the form of an a distance approaching but not equalling a quar arc of a circle about .2 wavelength long. This ter wavelength, means conductively connecting curved portion is connected by a portion C" the 70 said lines together, and said means being mov length of which may be varied from about 0.05 able lengthwise of said sections to vary in inverse to about 0.25 wavelength more or less depend relation the effective lengths of the two lines. ing upon the differences, if any, in the surge 3. An impedance matching transformer for impedance of the conductors of the stub-lines connecting together two networks of dissimilar and the conductors of the adjustable connecting " impedance comprising a short circuited stub-line, 12,411,664 7 an open circuited stub-line conductively asso ciatable with one of said networks, the stub-lines being disposed in overlapping spaced relation ship. a line a quarter wavelength connecting the short circuited stub to the other of said net— works, means conductively connecting the stub lines together, and said means being movalle 8 thereof oonnectable to the other of said networks, the sections being in spaced apart, parallel rela tion for a portion of a quarter wavelength so that the four conductors form the corners of a rectangle lying in a plane perpendicular to the axis of the sections, with the conductors of each section being disposed in adjacent corners of the rectangle so formed, means including a pair of lengthwise of said lines to vary in inverse rela conductors conductively connecting the corre tion the lengths of the two lines. sponding conductors of said sections, and said 10 4. An impedance matching transformer for means being movable lengthwise of said sections connecting together two networks of 'rnilar to vary the points of conduction between the cor impedance to selectively control-the amount of responding conductors of said sections. energy transferred between said networks while "7. A step-up impedance matching transformer maintaining the impedance matching, compris for connecting together two networks of dissimilar 15 ing a two-conductor section having one end impedance comprising a two-conductor section thereof short circuited and the other end con in the order of at least a quarter wavelength hav nectable to one of said networks, a second two ing one end thereof short circuited and the other conductor section having one end open circuited end connectable to one of said networks, a second and the other end thereof connectable to the other two-conductor section having one end open cir of said networks, the sections being in spaced cuited and the other end thereof connectable to apart, parallel relation for at least a portion of the other of said networks, the sections being in their lengths with the conductors being dis spaced apart, parallel relation for about two posed to de?ne a rectangle in a plane perpendicu tenths wavelength, and means including a pair lar to the axis of the conductors and with the conductors about one twentieth wavelength conductors of each section lying in adjacent 25 of conductively connecting the corresponding con corn rs of the rectangle so formed, means includ ductors of said sections, and said means being ing a pair of conductors conductively connecting movable lengthwise of said sections to vary the the corresponding conductors of said sections, points of conduction between the corresponding said means being movable lengthwise of said sections to vary the impedance matching chare _ acteristics thereof while maintaining substan tially constant the combined overall e?ective lengths of the sections. 5. A step-up impedance matching transformer for connecting together two networks of dissimilar impedance to selectively control the amount of energy transferred between said networks while maintaining the impedance matching, compris ing a two-conductor section in the order of a quar ter wavelength or odd multiple thereof having one end thereof short circuited and the other end connectable to one of said networks, a second two-conductor section in the order of a quarter wavelength having one end open circuited and the other end thereof connectable to the other of said networks, the sections being in spaced apart, parallel relation for a portion but not all of their lengths, means including a pair of conductors con ductively connecting the corresponding conduc torsof said sections, and said means being mov able lengthwise of said sections to vary the points of conduction between the corresponding conduc tors of said sections. 6. A step-down impedance matching trans former for connecting together two networks of dissimilar impedance comprising a two-conduc tor section in the order of a half wavelength or multiple thereof having one end thereof short cir cuited and the other end connectable to one of said networks, a second two-conductor section having one end open circuited and the other end conductors of said sections. 8. In an electrical transmission system having a plurality of sources of high frequency energy, a transmission line and a load therefor; the com bination therewith of a step-down impedance matching transformer to connect said transmis sion line to the common junction of said two sources of energy, said transformer comprising a two-conductor section connected at one end there of to said junction and having the other end thereof short circuited, a second two-conductor section connected at one end thereof to said load and having the other end thereof open circuited, means including a pair of conductors conduc tively connecting the corresponding conductors _ of said sections, and said means being movable lengthwise of said sections. 9, In an electrical transmission system having a, plurality of sources of high frequency energy, a plurality of loads and a transmission line to connect the loads to the common junction of said sources; the combination therewith of a step down impedance matching transformer between said line and said junction and a step-up imped ance matching transformer for each of said loads, each of the step-down and step-up transformers comprising a short circuited stub-line, an open circuited stub-line, means conductively connect ing together said lines, said means being movable to vary in inverse relation the effective lengths of the two stub-lines. CHESTER B. WATTS, J R.