US3399340A

US3399340A - Transformer for high frequency currents

Info

Publication number: US3399340A
Application number: US378847A
Authority: US
Inventors: Allen F Podell
Original assignee: Adams Russell Co Inc
Current assignee: ADAMS-RUSSELL ELECTRONICS Co Inc 1380 MAIN ST WALTHAM MA 02154 ("A-R") A CORP OF
Priority date: 1964-06-29
Filing date: 1964-06-29
Publication date: 1968-08-27
Anticipated expiration: 1985-08-27

Description

A. F. PODELL TRANSFORMER FOR HIGH FREQUENCY CURRENTS Aug. 27, 1968 2 Sheets-Sheet 2 Filed June 29, 1964 INVENTOR.

l AME/v A Paa-L MMM@ United States Patent O 3,399,340 TRANSFORMER FOR HIGH FREQUENCY CURRENTS Allen F. Podell, Berkeley, Calif., assigner to Anzac Electronics, Inc., Norwalk, Conn., a corporation of Connecticut v Filed .lune 29, 1964, Ser. No. 378,847 31 Claims. (Cl. S33-33) a The present invention relates to a transformer partlcularly well adapted for impedance matching purpose and especially characterized by comparatively high power handling capacity and capability of operation at exceedingly high frequencies, in the thousand megacycle range.

Impedance matching is greatly desired, particularly 1n communication circuits and other circuits where a high deg-ree of signal fidelity is required. However, the problem of how to make an effective impedance match, particularly where the impedances differ -appreciably from one another, has long plagued the electrical art. In my copending application Ser. No. 150,697, filed Nov. 7, 1961, now Patent No. 3,262,075 and entitled, 31mpedance Matching Transformer, I disclose a particular autotransformer design which is particularly effective in these regards. It is, however, subject to the disadvantage that its power-handling capacity is limited and its fabrication on a commercial scale presents problems.

It is the prime object of the present invention to devise an impedance matching transformer capable of use at very high frequencies, capable of handling appreciable amounts of power, and capable of ready, accurate and comparatively inexpensive fabrication on a production scale.

To these ends the transformer comprises a series of two-wire networks, :the wires of each network being electromagnetically linked, the networks being connected in parallel to one another at one end of the transformer and in series with one another at the other end of the transformer. Each network, at the frequencies involved, may be considered as an electrical transmission line. Each network is electromagnetically associated with a core of high magnetic permeability. The number of networks employed is directly related to, and cont-rols, the voltage transformation ratio of the transformer. The design :of the circuitry is such, particularly in the more sophisticated embodiments here disclosed, -as to greatly minimize the number or total effective length of the cores, thereby reducing cost, reducing the power losses in the transformer, and increasing the upper frequency limits thereof. Moreover, when, as is preferred, none of the networks are wound back on themselves to define a multi-turn transformer, the frequency-handling capabilities of the overall transformer system are greatly extended, with no theoretical upper frequency limit, phase shift then being the only significant limiting factor insofar as the utility of the transformer is concerned.

The circuit arrangement is such as to permit the transformer system to be constituted by conventional and comparatively inexpensive circuit components such as concentric lines and tubular ferrite cores or, if desired, to be formed structurally in a novel manner from a unitary laminated strip comprising conductive sheets positioned `on opposite sides of an insulating dielectric layer. The embodiments of the latter type are not only easily manufactured, but are exceptionally sturdy and reliable, and greatly facilitate the achievement of proper internal electrical connections.

To the accomplishment of the above, and to such other objects as may hereinafter appear, the present invention relates to the design and construction of trans- 3,399,340 Patented Aug. 27, 1968 ICC former systems having integral turns ratios, as defined in the appended claims and as described in this specification, taken together with the accompanying drawings, in which:

FIG. l is a schematic view of one embodiment of the present invention having a 3:1 voltage transformation ratio;

FIG. 2 is a three-quarter perspective view of circuit components assembled to dene one of the networks of the embodiment of FIG. 1;

FIG. 3 is a schematic view of an embodiment similar to that of FIG. 1 but modified so as to reduce the amount of magnetically permeable core material used;

FIG. 4 is a schematic view showing an embodiment of the present invention having a 4:1 voltage transformation ratio;

FIG. 5 represents a modification of the transformer system of FIG. 4 and corresponding to the principles involved in the embodiment of FIG. 3;

FIG. 6 is a three-quarter perspective view of a unitary structural embodiment of the system of FIG. 4; and

FIG. 7 is a three-quarter perspective view of a unitary structural embodiment of the system of FIG. 5.

The embodiment of FIG. l discloses a transformer system having a voltage transformation of 3 and impedance matching ratio of 9. It comprises three networks generally designated 2, 4 and 6, each comprising a pair of electromagnetically linked conductors 8 and 10, the conductors 8 and 10 of each network being identified by a subscript corresponding to the network. Thus

conductors

82 and 102 are the conductors for the network 2, and conductors 84 and 10., comprises the network 4, and

conductors

86 and 106 comprise the network 6. The conductors 8 and 10 of each network are schematically shown in FIG. 1 as being parallel to one another, this being the preferred arrangement of the conductors, but that specific relationship is not essential to the functioning of the disclosed systems. Each of the networks 2, 4 are preferably identical to one another, and are so designed as individually to have an input impedance Z0 which is one-third of one of the impedances to which the transformer system is to be matched. The external 3Z0 impedance is connected across the right hand end of the system as shown in FIG. 1.

For purposes of explanation, it may be assumed that the left hand end of the system of FIG. 1 is the input end and the right hand end is the output end, although it will be appreciated that the designations of the opposite ends as input and output respectively are purely arbitrary, and may be reversed. As the terms input and output are here used, the transformer system is considered as a voltage step-up transformer, the generalized input voltage being V and the generalized output voltage being nV.

At the input end of the system of FIG. 1, the networks 2, 4 and 6 are connected in parallel with one another. Thus, if

points

12 and 14 be considered the input terminals of the system, the input terminal 14 may be connected to ground or any other source of reference potential, while the input terminal 12 is connected as indicated at 16, 18, 20 and 22, to the left hand ends of

conductors

82, 84 and 86 respectively. The left hand ends of the

conductors

102, 104 and 106 are connected to one another and to ground as indicated at 24, 26 and 28. Thus the networks 2, 4 and 6 are connected in parallel at their left hand or input ends.

The

terminals

30 and 32 are the output terminals of the transformer system. The terminal 32 is connected to ground and to the right hand end of conductor 106. The terminal 30 is connected to the right hand end of the conductor 82. The right hand ends of

conductors

102 and 84 are connected as indicated at 34, and the right hand ends of the

conductors

104 and 86 are connected as indicated at 36. Consequently it will be seen that the networks 2, 4 and 6 are connected in series with one another at their right hand or output ends.

Although the connections to and between the conductors of networks 2, 4 and 6 at their ends are shown as discrete leads, this is by way of illustration only, and the actual electrical length of those connections should be minimized, and preferably should be zero, or as close thereto as possible.

The networks 2 and 4 are each electromagnetically associated with cores of high magnetic permeability, such as ferrite material, the cores functioning in part to increase the power-handling capacity of a transformer system of given size. Since such cores are comparatively expensive, and also constitute a source of power loss or attenuation within the transformer system, it is desirable to minimize the total effective core length-the amount of core material employed-consistent with power-handling requirements. The design of the systems of the present invention is particularly salutary in this regard. Thus, as illustrated in FIG. 1, the network 2 is electromagnetically associated with a pair of

cores

38 and 40 `(or a single core having the combined effective length of the cores 38 and 40), the network 4 has associated therewith only a single unit core 42, and the network 6 has no core associated therewith. The thus-disclosed corenetwork relationships represents the minimal number of unit core lengths to be used with the system of FIG. l as that system is specifically disclosed, minimization of the total effective core length being desirable for the reasons set forth above. More cores could be associated with one or more of the networks 2, 4 and 6 if desired, but with an increase in cost and, it is believed, no significant increase, and possibly a decrease, in efficiency and effectiveness of operation.

The specific electrical and structural design of the networks 2, 4 and 6 and of the cores 38-42 will vary depending upon the specific electrical problem presented. Insofar as the networks 2, 4 and I6 are concerned, they should be designed so that each of them has an input impedance of Z0, each of them being substantially identical to the other, the electrical transmission lines which are preferably defined by the networks 2, 4 and 6 at the frequencies involved should be smooth, and the electrical connections between them should be carefully made so as to eliminate undesired reflections.

The current, voltage, and impedance conditions at various points in the system of FIG. 1 are shown on FIG. l, the currents being indicated by arrows and their magnitude being represented by integral multiples of the unit current the voltages being indicated either by the numeral (representing reference potential) or by integral multiples of the unit voltage amount V, and the impedances being indicated in terms of the system output impedance 3Z0. Thus it will be seen that the system of FIG. 1 steps up an input voltage V to an output voltage of 3V, effectively matches an input impedance of ZO/ 3 to an output impedance of 3Z0, and makes a corresponding current reduction from an input current of 3l' to an output current of i. Each unit length of cores 38-42 is effective to permit a change in voltage by an amount V from one end thereof to the other.

The networks 2, 4 and 6 specifically disclosed in FIG. 1 are all of the single-turn variety, extending in a substantially straight line through the cores 38-42 and not wound back upon themselves. This is particularly desirable in the case of very high frequency operation, since the use of multiple-turn windings inherently limits the maximum frequency which can be employed. However, where maximum frequency requirements are not too rigorous, and where spatial and power-handling requirements are severe, networks 2, 4 and 6 defining multi-turn windings could be employed.

FIG. 2 is a semi-pictorial representation of a typical network such as the network 2, the

conductors

82 and 102 being defined by the inner and outer conductors respectively of a conventional concentric transmission line, that line passing snugly through the axial aperture of a core 38 having a length equal to, and therefore being the substantial equivalent of, the combined cores 38 to 40 of FIG. 1.

In a circuit designed in accordance with the teachings 0f FIG. 1 and having n networks and a corresponding voltage transformation of n, the number of cores employed for the first network 2, speaking in terms of total unit core length, is (n-l), the second network 4 will have (n-2) cores, the third network 6 will have (n-3) cores, and the total number of cores wiU be n(n-1)/2. (The unit length will be determined in a given instance, as explained above, by the power-handling requirement for which the system is designed.)

This amount of core material can be further reduced by designing the circuit as shown in FIG. 3. In essence FIG. 3 represents the same circuit as FIG. l, ybut with certain sections of the system being common to more than one network. Thus the network 6 comprises a section 6A and a section 6B. Section 6B is connected to the

networks

2, 4 and 6A. The network 4 comprises

sections

4A and 4B, each of the same length, the left hand end of the section 4B being connected to the network 6 at the dividing point 56 between network sections 6A. and 6B. The network 2 comprises a single section 2A having the same effective length as the section 4A and connected at its left hand end to the network 4 at the dividing point 54 between the

sections

4A and 4B. Thus, reading from left to right, network 6 comprises

sections

6A and 6B, network 4 comprises

sections

4A, 4B and 6B, and network 2 comprises

sections

2A, 4B and 6B. Stated otherwise, section 6B is common to all three networks and section 4B is common to networks 2 and 4. With this circuit arrangement a core 38A of single unit length is electromagnetically associated with the section 2A and a core 42A of single unit length is electromagnetically associated with the section 4B, the core 42A thus functioning, in effect, both as the core 42 in the network 4 of FIG. 1 and as the core 40 in the network 2 of FIG. l, the core 42A thus being common to networks 2 and 4. Considering the network 6A in FIG. 3, it, like the network 6 in FIG. 1, will have an input impedance of Z0, and the overall system impedance at the left hand end of the network 6, that is, 6B, will be Z0/3. The left hand end of the network defined by the

sections

4A and 4B, namely 4B, will have an input .impedance of Z0/2, and the left hand end of the network section 2A will have an input impedance of Z0. The right hand ends of all three networks 2, 4 and 6 will have an input impedance of Z0. With this arrangement it will be seen that the total unit core length is two-thirds that required in the embodiment of FIG. l, and may be generally represented by the formula (rr-l), where n is the transformation ratio of the system. For purposes of explanation, and in order to facilitate comparison with FIG. 1, the voltage, current and impedance conditions at various points on the system of FIG. 3, are shown on the drawing in a manner similar to that employed in FIG. 1.

FIGS. 4 and 5 are similar to FIGS. 1 and 3 respectively except that they show systems having a voltage transformation ratio of 4, which therefore utilize four networks. The same reference numerals are employed in FIGS. 4 and 5 as in FIGS. 1 and 3 for corresponding parts, the fourth network being designated 7, the

sections

7A and 7B thereof in FIG. 5 having a length relationship of 3:1, the core associated with the network 6 in FIG. 4 being of single unit length and being designated 43, the additional cores associated with the networks 2 and 4 in FIG. 4 being designated 40-1 and 42-1 respectively, the core associated with the section 6B of the f' network 6 in FIG. 5 being designated 43A, and the dividing point between the

sections

7A and 7B being designated 58.

It will be noted that in the embodiments of FIGS. 3 and 5 the same volts per turn are applied to all of the cores, and that a similar relationship exists in the embodiments of FIGS. 1 and 4 insofar as each unit length of core is concerned.

The transformer systems above described can all be constructed of comparatively conventional circuit components such as wires, concentric lines, and the like. The electrical design of the transformer systems are also very well adapted to be formed conveniently, inexpensively and reliably into a novel substantially unitary physical structure which is not only structurally strong and electrically reliable, but which in addition inherently assures the attainment of proper electrical connection between the ends of the networks. FIGS. 6 and 7 illustrate such embodiments, the structureof FIG. 6 corresponding to the transformer system of FIG. 4 and the structure of FIG. 7 corresponding to the system of FIG. 5. In both instances the transformer, apart from the cores, is formed from an elongated body generally designated 44 and comprising a pair of conductive layers 8X and 10X disposed on opposite sides of an intermediate insulating layer 46, the layers 8x and 10X and the layer 46 being laminated to one another to define a unitary structure. In the embodiment of FIG. 6 the body 44 is slit longitudinally along a major portion of its length, thereby dividing the body 44 into four longitudinally extending sections designated 2X, 4x, 6x and 7X, each of the sections being of the same length and so designed as to exhibit an input impedance Z between the conductive layers 8X and 10X thereon. These sections 2x--7X are separated from one another, the material of which the various layers of the body 44 is formed permitting such distortion, and cores are then applied to each of the sections as appropriate. Thus cores 38X, 40X and 40--1X are slid over section 2X, cores 42X and 42-1X are slid over the section 4X and core 43X is slipped over the section 6X, thereby corresponding to the location of the cores on their respective networks in FIG. 4. (As has been explained previously, the three cores 38X, 40X and 40-1X could, for example, be substituted for by a single core having a length equal to the combined length of those three cores.) Thereafter the free ends of the sections 2-7x are twisted 90 degrees so that the conductive layers 8x on each section are uppermost and the conductive layers 10X on each section are lowermost. Next the lower conductive layer 10X on the section 2x is placed against the upper conductive layer 8x on the section 4X, the lower conductive layer 10x on the section 4x is placed against the upper conductive layer 8X on the section 6X, and so on, and the contacting conductive layers are physically and electrically secured to one another in any appropriate manner, as by soldering, welding or brazing. Appropriate external electrical input connections are made to the conductive layers 8x and 10X at the left hand end of the body 44 as viewed in FIG. 6, and appropriate external output connections are made to the exposed upper conductive layer 8x and lower conductive layer 10x on the sections 2X and 7x respectively. It will be seen that the network defined by this structure is the same as that of FIG. 4, this similarity being emphasized by the use, in FIG. 6, of the same reference numerals as are used in FIG. 4, distinguished, however, by the subscript x.

To form a network corresponding to that of FIG. from a laminated body 44 of the type under discussion, that body is provided with longitudinally extending slits separating the body into a plurality of separated longitudinally extending sections. Slits 48, 50 and 52, equally laterally spaced from one another but of progressively increasing length, divide the body 44, at its right hand end or output end, into sections ZAy, 4Ay, 6Ay and 7Ay. The sections 2Ay and 4Ay meet at point 545., defining the end of slit 4S, and to the left of point 54 section 4By is defined, separated from section 6Ay and of a width equal to the combined widths of sections 21Ay and 4Ay. At point 565 defining the end of slot 50, section 4By meets section 6Ay, section 6By extending to the left thereof separated from section 7Ay and of a width corresponding to the combined widths of sections 4By and 6Ay. At point 585 defining the end of slot 52, the section 6By meets the section 7Ay, the area to the left of point 58 constituting the total width of the body 44. A core 43Ay is placed around the section 6By, the core 42Ay is placed around the section 4By and the core 38Ay is placed around the section 2Ay, each of the cores preferably having the same length but having different diameters in order to accommodate the different thicknesses of network sections which they surround. The free ends of the sections 2Ay--7Ay are twisted and brought into electrical and physical engagement with one another in the same manner as has been described in connection with the embodiment of FIG. 6, the lower conductive layers 10y on each of the sections being engaged and connected with the upper conductive layers Sy on the sections immediately therebelow, the conductive layer 10y on the section ZAy and the conductive layer Sy on the section 7Ay being exposed at the upper and lower surfaces of the thusproduced stack respectively for appropriate electrical connection to external output circuitry. The cores 43Ay, 42Ay and 38Ay may be sequentially slid over the appropriate body sections before the free ends of those sections are secured to one another, or the cores may be formed in a plurality of pieces which may be secured in place around the appropriate network sections after the free ends of those sections have been secured to one another. The similarity between the structural embodiment of FIG. 7 and the schematic of FIG. 5 is emphasized by the use in FIG. 7 of the same reference numerals as in FIG. 5, distinguished, however, by the subscript y.

The structures of FIGS. 6 and 7 are sturdy and reliable, may be very readily manufactured and assembled, are easily incorporated into the structure of associated equipment, and inherently assure the proper electrical characteristics of the various networks and the proper connection of those networks in parallel at one end and in series at the other end.

By using the teachings of the present invention impedance-matching transformers may be designed and built which are exceptionally effective for impedance-matching purposes, or for other transformer applications, where exceedingly high frequencies on the order of several thousand megacycles per second are involved. The devices of the present invention are particularly useful where significant amounts of power must be handled, but the utility of the teachings of the present invention is not necessarily limited to such applications. The size of the magnetically permeable cores associated with each of the networks forming a part of the transformer systems of the present invention will depend in part upon the power to be handled, the greater the power the larger the cores required, but even with cores of one inch unit length frequencies on the order of 1000 megocycles per second can be handled effectively. When cores of 1A unit length are employed the frequency limit for effective operation goes up to 5000 megacycles per second. As has been shown in FIGS. 6 and 7, the transformer design lends itself to structural embodiments characterized by reliability and inexpensiveness. The overall circuit design, particularly in its more sophisticated aspects as shown in FIGS. 4 and 5, but also in its more basic aspects as shown in FIGS. 1 and 3, minimize the number of cores required to perfor-m the appropriate electrical functions, thus appreciably minimizing expense and reducing electrical losses.

While only a limited number of specific embodiments are here disclosed, it will be appreciated that many variations may Ibe made therein, all within the scope of the instant invention as defined in the following claims.

I claim:

1. A transformer having a transformer ratio of n, where n is an integer greater than one, comprising a pair of input terminals, a pair of output terminals, n networks each comprising first and second electromagnetically linked conductors, the first conductors of each network being connected at one end to one input terminal, the second conductors of each network being connected at said one end to the other input terminal, the first conductor of said first network being connected at its other end to one output terminal, the second conductor of each network and the first conductor of the next network being connected at their other ends to one another, and the second conductor of said last network being connected at each of its ends to a reference potential, said other input terminal and the other output terminal being connected to said reference potential, at least all of said networks other than said last network being electromagnetically associated with a core of high magnetic permeability each of said networks comprising essentially single turn networks.

2. A transformer having a transformer ratio of n, where n is an integer greater than one, comprising a pair of input terminals, a pair of output terminals, n networks each comprising first and second electromagnetically linked conductors, the first conductors of each network being connected at one end to one input terminal, the second conductors of each network being connected at said one end to the other input terminal, the first conductor of said iirst network being connected at its other end to one output terminal, the second conductor of each network and the first conductor of the next network being connected at their other ends to one another, and the second conductor of said last network being connected at each of its ends to a reference potential, said other input terminal and said other output terminal being connected to said reference potential, said first network being electromagnetically associated with a core of high magnetic permeability having an effective unit length of n-1, said second network being electromagnetically associated with a core of high magnetic permeability having an effective unit length of n-2, and so on.

3. The transformer of claim 2, in which the last nth of the last network is common to its network and all of the preceding networks, the next to the last nth of the next to the last network is common to its network and all of the preceding networks, and so on; the first nth of said rst network, the second nth of said second network, and so on, but not necessarily including the last nth -of the last network, each being electromagnetically associated with a core of high magnetic permeability having an effective unit length of l, whereby the core associated with each network after the first network is common to its network and to each preceding network.

4. The transformer of claim 3, in which each of said networks has a characteristic input impedance of Z0, said transformer having an input impedance of Zo/n and an output impedance of nZO.

5. The transformer of claim 3, in which each of said networks comprises an essentially single turn network having a characteristic input impedance of Z0, said transformer having an input impedance of ZU/n and an output impedance of nZU.

6. The transformer of claim 3, in which said networks comprise essentially single turn networks.

7. The transformer of claim 2, in which each of said networks has a characteristic input impedance of Z0, said transformer having an input impedance of Zn/n and an output impedance of nZo.

8. The transformer of claim 2, in which said networks comprise essentially single turn networks.

9. The transformer of claim 8, in which each of said networks has a characteristic input impedance of Z0, said transformer having an input impedance of Zo/n and an output impedance of nZ.

10. A transformer having a transformer ratio of n, where n is an integer greater than one, comprising n networks each comprising first and second electromagnetically linked conductors, said networks `being connected in parallel to one another at one end and in series with one another at the other end of said transformer, said first network being electromagnetically associated with a core of high -magnetic permeability having an effective unit length of n- 1, said second network being electromagnetically associated with a core of high magnetic permeability having an effective length of n-2, and so on.

11. The transformer of claim 10, in which said networks comprise essentially single turn networks.

12. The transformer of claim 11, in which each of said networks has a characteristic input impedance of ZD, said transformer having an input impedance of Zo/n and an output impedance of nZo.

13. The transformer of claim 10, in which each of said networks has a characteristic input impedance of Z0, said transformer having -an input impedance of ZO/n and an output impedance of nZO.

14. The transformer of claim 10, in which the last nth of the last network is common to its network and all of the preceding networks, the next to the last nth of the next to the last network is common to its network and all of the preceding networks, and so on; the first nth of said first network, the second nth of said second network, and so on, but not necessarily including the last nth of the last network, each being electromagnetically associated with a core of high magnetic permeability having an effective unit length of l, whereby the core associated with each network after the first network is common to its network and to each preceding network.

15. The transformer of claim 14, in which said networks comprise essentially single turn networks.

16. The transformer of claim 14, in which each of said networks has a characteristic input impedance 0f Z0, said transformer having an input impedance of Zo/n and an output impedance of nZo.

17. The transformer of claim 14, in which each of said networks comprises an essentially single turn network having a characteristic input impedance of Z0, said transformer having an input impedance of Zo/n and an output impedance of nZU.

18. A transformer having a transformer ratio of n, where n is an integer greater than one, comprising an elongated body of insulating material with separated conductive coatings on opposite sides thereof, said body being divided along a part of its length into n longitudinally extending sections separated from one another, at least all but one of said sections being electromagnetically associated with a core of high magnetic permeability, the free ends of said sections overlying one another with the conductive coatings carried -by said sections facing and in operative electrical connection with conductive coatings carried lby adjacent sections.

19. The transformer of claim 18, in which each of said sections is of substantially the same length.

20. The transformer of claim 18, in which each of said sections is of substantially the same length, said core electromagnetically associated with the first of said sections having an effective unit length of n-l, said core electromagnetically associated with the second of said sections having an effective unit length of n-2, and so on.

21. The transformer of claim 18, in which said core electromagnetically associated with the first of said sections has an effective unit length of n-l, said core electromagnetically associated `with the second of said sections has an effective unit length of n-2, and so on.

22. The transformer of claim 18, in which said sections are of progressively increasing length, each section meeting the next section at a point intermediate the length of said next section.

23. The transformer ofclaim 18, in which said sections are of progressively increasing length, each section meeting the next section at a point intermediate the length 0f said next section, said core electromagnetically associated with said first section being associated only with said first section, said core elect-romagnetically associated with said second section being associated 'with that portion of said second section between the point Where said first section meets said second section and the point Where said second section meets said third section, and

so on.

24. The transformer of claim 18, in which said sec tions are of -progressively increasing length, each section meeting the next section at a point intermediate the length of said next section, said core electromagnetically associated with said first section being associated only with said first section, said core electromagnetically associated with said second section being associated with that portion of said second Section between the point Where said first section meets said second section and the point where said second section meet said third section, and s0 on, each of said cores having substantially the same effective length.

25. A transformer 4having a transformer ratio of n, 'where n is 'an integer :greater than one, comprising an elongated body of insulating material with separated conductive coatings on opposite sides thereof, said body being divided along a part only of its length into n longitudinally extending sections separated from one another, at least all but one of said sections respectively passing through ring-like cores of high magnetic permeability, the free ends of said sections overlying one another with the conductive coatings carried by said sections facing and in operative electrical connection with conductive coatings carried by adjacent sections.

Z6. The transformer of claim 18, in which each of said sections is of substantially the same length.

27. The transformer of claim 18, in which each of said sections is of substantially the same length, said core electromagnetically associated with the first of said sections having an effective unit length of n-l, said core electromagnetically associated with the second of said sections having an effective unit length of n-2, and so 28. The transformer of claim 18, in which said core electromagnetically associated with the first of said sections has an effective unit length of n-l, said core electromagnetically associated Iwith the second of said sections has an effective unit length of n-Z, and so on.

29. The transformer of claim 18, in which said sections -are of progressively increasing length, each section meeting the next section at a point intermediate the length of said next section.

30. The transformer of claim 18, in which said sections are of progressively increasing length, each section meeting the next section at a -point intermediate the length of said next section, said core electromagnetically associated with said first section being `associated only with said first section, said core electromagnetically associated with said second section being associated -with that portion of said second section between the point where said first section meets said second section and the point where said second section meets said third section, and

so on.

31. The transformer of claim 18, in which said sections are of progressively increasing length, each section meeting the next section ata point intermediate the length of said next section, said core electromagnetically associated with said first section being -associated only with said rst section, said core electromagnetically associated with said second section being associated with that portion of said second section between the point Where said first section meets said second section and the point where said second section meets said third section, and so on, each of said cores having substantially the same effective length.

References Cited UNITED STATES PATENTS ELI LIEBERMAN, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. 3,399,340 August 27, 1960 Allen C. Podell It. is certified thn .irol appears in the above identified patent and "het sr'iri .:Lte'fxz Patent are hereby corrected as In the heading to the printed specification, lines 4 to 6, "assignor to Anzac Electronics, Inc., Norwalk, Conn. a corporation of Connecticut" should read assgnor to Adams- Russell Co. Inc. a corporation of Massachusetts Signed and sealed this 17th day of February 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents WILLIAM SCHUYLER, JR.