US2249963A

US2249963A - Impedance transformation means

Info

Publication number: US2249963A
Application number: US304573A
Authority: US
Inventors: Nils E Lindenblad
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1939-11-15
Filing date: 1939-11-15
Publication date: 1941-07-22
Anticipated expiration: 1958-07-22
Also published as: DE919247C

Description

N. E. LINDENBLAD 2,249,963

IMPEDANCE TRANSFORMATION MEANS Filed Nov. 15, 1939 July 22, 1941.

2 Sheets-Sheet 1 Z i" ii Z 22 INVEN TOR. N/LS E. LINDENBLAD BY M I ATTORNEY.

' July 22, 1941. BL D 2,249,963

IMPEDANCE TRANSFbRMATION MEANS Filed Nov. 15. 1939 2 Sheets-Sheet 2 6 v 22 z, .24 z, 26 1 L- -mp-J INVENTOR. N/LS E. L/NDENBLAD ATTORIYEY;

Patented July 22, 1941 IMPEDANCE TRANSFORMATION MEANS Nils E. LindenbladQ Port Jefferson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application November 15, 1939, Serial No. 304,573

16 Claims.

The present invention relates to transmission lines and, more particularly, to a method of, and means for, transforming the impedance of one transmission line to such a value that it may be directly connected to another transmission line of a different impedance.

An object of the present invention is to provide a means for matching the impedance of one transmission line to that-of another.

Still another object of the'invention is to provide a means for matching the impedance of a pair of transmission lines without introducing losses.

Still another object of the present invention is to provide a means for transforming the'impedance of a transmission line without introducing circuits of high volt ampere storage.

The present invention includes, among its features, a plurality of short sections of concentric transmission lines which are designed to be connected in series at one end and the series combination directly connected to one trans mission line. The other end of the sections are connected in parallel and connected to the other transmission line. In some instances, it may be necessary to interpose between certain of the sections and one of the transmission lines phase inverting circuits so that the resultant phase of the currents in all of the sections will be'the same at the junction point. By a structure constructed in accordance with the present invention it is possible to obtain animpedance multiplication which is the square of the number of intermediate sections employed.

Other objects, features and advantages of the present invention will appear from the following detailed description, which is accompanied by drawings in which Figures 1, 2 and 4 illustrate simplified transformation systems useful in explaining the principles of the present invention; Figure 3 illustrates a simple embodiment of the present invention whereby an impedance ratio of 4 to 1 is obtained; Figure 5 illustrates another embodiment of the invention also resulting in a 4 to 1 impedance transformation ratio; Figure 6 illustrates another embodiment of the invention in which an impedance ratio of 9 to l is obtained; while Figure '7 illustrates a modification of the form of my invenpedance of 2 to 1. The circuit shown in Figure 1 comprises a concentric transmission lineA having an inner conductor I and an outer shell 2. The inner and outer conductors of this transmission line are each connected at one end to the center conductors 3 and 4 of a pair of pushpull concentric line branches. An outer conducting sleeve 6 surrounds the end of line A for a distance equal to a quarter of the operating wavelength and is joined to the outer conductors 5 of the push-pull branches as shown.

To understand clearly the operation of the circuit, let us visualize the circuit from the lower end into which are fed currents of opposite instantaneous direction in the two push-pull branches 3 and 4, as indicated by the arrow marks. Since, in a single concentric conductor line the center conductor current and the shell current on the inner surface of the outer conductor are opposite to each other in direction but of the same magnitude, it follows that the inner conductor 4 of one branch of the push-' pull circuit should continue as the inner conductor I of the single concentric line A, while the inner conductor 3 of the other push-pull branch should continue as the shell 2 of the single line A. To prevent short-circuitingof the push-pull branch connected to the outer conductor 2 of line A, it is necessary for the shell 2 of line A at its end to present a high impedance on its outer surface to the operating frequency. If this is so, all current arriving over conductor 3 must travel over the inner surface of shell 2 of line A and none is carried by shell 5 back to the outer conductor of line 3, The necessary high impedance is obtained by making the length of shell 2 extending within sleeve 6 a quarter of a wavelength long and connecting the upper end of sleeve 6 to the outer conductor of line A. Since lines 3 and 4 are eifectively in series with respect to line A each must have a surge impedance equal to half the surge impedance of line A. An impedance transformation of 2 to 1 is therefore obtained. a

Figure 2 shows a modification of the form of construction shown in Figure 1 wherein the outer shell 5 of the push-pull concentric line is continued through sleeve 6 as a single piece with a notch cut out of one side in order to enablethe connection of the conductors of line A thereto. The operation of this figure is otherwise as described with reference to Figure 1. Figure 3 shows how Figure 2 may be modified in order to connect the two balanced concentric lines 3 and 4 to a single transmission line B for impedance shell 3|. 'shell'2 of transmission line A. The current in the matching. A phase shifting loop I is connected in series with one of the balanced lines, conductor 3, in the figure, said loop I having a length equal to a half the length of the operating wave. Therefore, at the point of connection of conductor 9 of transmission line B the current in ly connected to branches 3 and 4 in parallel it.

must have an impedance equal to half that of each of the branches or Z/2. Thus, it will be seen we have an impedance transformation of 4 to 1.

By involving another aspect of the present in-- vention it is possible to connect a first transmission line to another line by bringing a conductor from the first line through the inside of the inner conductor and connecting it to the inside of the outer conductor of the other line as well as a conductor from the outside of the outer conductor and connecting it to the inner conductor. In order to prevent short-circuiting of the first line each of the conductor connections should be a quarter of the length of the operating wave from the end of the other line where the inner conductor is bonded to the shell. I have shown in Figure 4 how this principle of connection may be employed. Since the voltage required in the two branches containing conductors 3 and 4 are of opposite phase, I use the U- shaped phase reversal circuit as described with reference to Figure 3. Each branch 3, 4 of the U circuit then contains a current I. The center conductor currents and the corresponding shell currents in the two branches add up in the common line A which they feed, as illustrated by the arrows. It will be noted that the inner conductor 3 of one branch is connected to the inside of the outer shell 2 while the inner conductor 4 of the other branch is connected to the outside of the inner conductor 1. The outer shell of the branch containing conductor 3 is, for convenience, in this figure shown as a continuation of the centercondu'ctor I of transmission line A.

The voltage at the termination of thecommon line A is equal to that of each branch line 3 and 4. The impedance of the common line A thus has to be half of the impedance of the branch lines. This figure simply represents an exampleof one principle of my invention since the impedance' of common line A is the same as that of common line B and is shown and described to 'make what follows more clearly understood. This example shown in Figure 4 shows two ways of adding currents and transmission lines at the same voltage. The branch lines 3 and 4 can be considered as added into transmission line A or as into transmission line B.

In Figure 5 I show how the individual branch lines 3 and 4 may have their currents added in series. The current in the common line A is the same as in the branches but the voltage is doubled. It should be noted that branch line 3 enters the transmission line A as a quarter wave The inner conductor 3 connects to the shell 5 of the left-hand branch then continues along the conductor passing through the aperture in wall 5| and becomes the center conductor current in conductor 4. The center conductor current of 3 continues as a shell current of transmission line A. The shell section 3| within the casing l and 2 is then an intermediary point at which the voltage appearing in conductor 3 is connected. in series with that appearing in conductor 4. Due to the quarter wave length of shell 3! current is prevented from flowing along its outside surface. Since the current in line A thus must be equal to the current in each of the branches 3 and 4 and since the voltage is the sum of the voltages, the impedance of line A must be twice that of either of the branch lines.

It should also be noted that the currents in the branch lines are in phase requiring no phase reversal. They may be connected directly in parallel at their lower end and connected to

conductors

8 and 3 of transmission line B as shown. Thus, the total circuit from B to A of Figure 5 represents an impedance transformation of 4 to 1 with a system which is matched throughout.

In Figure 6 I have shown a system by means of'which a total impedance transformation of 9 to 1 may be accomplished by using three branches connected in parallel to transmission line B and in series to transmission line A. As will be seen from an inspection of the drawings, each of the

branches

22, 24 and 23 are surrounded by a shell 28 a distance equal to a quarter of the operating wavelength and connected at its lower end to the outer conductors of the branches. These intermediate shells, therefore, have a very high impedance on their outside to currents of the operating frequency. The current in the center conductor 23 of the first branch becomes the shell current for the middle branch and the current of the center conductor 25 of the center branch becomes the shell current of the right-hand branch. Neither the current in conductor 23 which flows to the shell 24 of the center branch and the current in conductor 25 which flows to the shell 26 of the right branch can go to the outside of the respective shell due to the high impedance of the quarter wave section surrounding the shell but must go on the inside and become the shell current as already stated. The shell current of the left-hand branch becomes the center conductor current of the main line A while the center conductor current of the right-hand branch becomes the shell current of the main line A. Since the three branches 22, 24 and 26 are connected in series and are in phase relationship, the impedance of each of these branches should be one-third of the impedance of the line A. At their lower ends each of the branches are connected in parallel and connected to the center conductor 9 and shell 8 of transmission line B. The impedance of transmission line B will thus have to be onethird of the impedance of each of the intermediate sections. The transformation ratio, therefore, becomes 9 to 1 between transmission line A and transmission line B.

In Figure 7 I have shown a modification of the form shown in Figure 6 which is particularly significant in that the parallel and series branches are so arranged that the transformation takes place as the waves travel along the system. The construction of this modification may in some cases be mechanically preferable to the previous modification. In this modification transmission line A is composed of an outer shell 12 and an inner conductor H). The inner conductor I0 is carried throughout the length of the transformation section and is connected to the inner conductor [9 of transmission line B. The lower portion of conductor I0 is surrounded by a shell H which forms with conductor I!) one of the intermediate matching sections. Shell It is surrounded by another shell l3 thus forming a second transformation section in which shell H acts as the center conductor and shell I3 as the outer conductor. The upper end of shell II is connected to the upper end of conductor 2 of transmission line 13. Due to the quarter wavelength of shell II from its end to its point of connection with shell l3 the current from conductor 20 must flow on the inner surface of shell ll. Likewise, in the upper portion of the figure shell l3 becomes the inner conductor of a transformation section in which the shell I2 of line A forms the outer conductor. The end of conductor 2| is connected to the upper end of shell l3. The current from 2! is compelled to flow on the inner surface of shell 13 as described with reference to shell I! above. The impedance of line section 20 is so adjusted that the current at the junction of 2D and I9 divides one-third to conductor I0 and two-thirds to conductor 20. Likewise, the impedance of section 2| is so adjusted that the current 2! at the junction of 20 and 2| divides equally.

Regardless of the path each portion of current takes as it is divided, at the points where the current-s are brought together they are again in phase, since the total path lengths are equal. I

The three portions of current added in series to feed transmission line A result in a voltage of 3E and a total current of i as compared to the voltage E and current 3i in transmission line B. A 9 to l impedance transformation is therefore obtained.

The fundamental principle underlying all of these circuits is that a center conductor current in one line may be made the shell current in another line. If the current paths are so arranged that no gaps are presented either to the center conductor current or the shell current the system operates to produce an impedance transformation without any accompanying voltampere storage.

Throughout this application, wherever I have spoken of lengths of transmission line as being equal to a quarter of the length of the operating wave. it should be distinctly understood that if it is desired any odd multiple of that length may be used. A single quarter wavelength has been referred to since it is not only simple language but also results in a more compact structure.

While I have particularly shown and described several modifications of my invention, it is to be prises coupling a plurality of short sections of transmission lines in a series relationship to one of said lines and in a parallel relationship to the other of said lines, the number of said sections being equal to the square root of the transformation ratio required.

3. In a circuit including a pair of transmission lines of difierent impedance, mean; for

transforming the impedance of one line to a value equal to that of the other comprising a plurality of short sections of transmission lines, said sections being connected in a series relationship to one of said lines and in a parallel relationship to the other of said lines.

4. In a circuit including a pair of transmission lines of different impedance, the impedance of one line being N times that of the other, means for transforming the impedance of one line to a value equal to that of the other comprising an integral number N of short sections of transmission lines, said sections being connected in a series relationship to said one transmission line and in a parallel relationship to said other transmission line.

5. In combination, a first concentric transmission line having an inner conductor and an outer shell, said shell and conductor being connected together at one end, a second and a third concentric transmission line each having one end extending into the said end of said first transmission line a distance equal to a quarter of the length of the operating wave, the outer shell of said second line forming an extension of the inner conductor of said first line, the inner conductor of said third line being connected to the shell of said first line, the inner conductor of said second line being connected to the shell of said third line whereby said second and third lines are efiectively connected in series across the conductors of said first line.

6. In combination, a first concentric transmission line having an inner conductor and an outer shell, said shell and conductor being connected together at one end, a second and a third con-centric transmission line each having one end extending into the said end of said first transmission line a distance equal to a quarter of the length of the operating wave, the outer shell of said second line forming an extension of the inner conductor of said first line, the inner conductor of said third line being connected to the shell of said first line, the inner conductor of said second line being connected to the shell of said third line whereby said second and third lines are efiectively connected in series across the conductors of saidfirst line, means for connecting said second and third lines in parallel at their ends.

7. In combination, a first concentric transmission line having an inner conductor and an outer shell, said shell and conductor being connected together at one end, a second and a third concentric transmission line each having one end extending into thesaid end 'of said first transmission line a distance equal to an odd multiple, including unity, of a quarter of the length of the operating wave, the outer shell of said second line forming an extension of the inner conductor of said first line, the inner conductor of said third line being connected to the shell of said first line, the inner conductor of said second line being connected to the shell of said third line whereby said second and third lines are effectively connected in series across the conductors of said first line.

8. In combination, a first concentric transmission line having an inner conductor and an outer shell, said shell and conductor being connected together at one end, a second and a third concentric transmission line eachhaving one end extending into the said end of said first transmission line a distance equal to an odd multiple, including unity, of a quarter of the length of the operating Wave, the outer shell of said second line forming an extension of the inner conductor of said first line, the inner conductor of said third line being connected to the shell of said first line, the inner conductor of said second line being connected to the shell of said third line whereby said second and third lines are effectively connected in series across the conductors of said first line, means for connecting said second and third lines in parallel at their other ends.

9; In combination, a first and a second transmission line each having an inner conductor and an outer shell, a plurality of short sections of concentric transmission lines connected in series at one end and to said first transmission line, means surrounding said ends for preventing current from flowing on the outside of the shells of said short sections, said sections being connected in parallel to said second line at their other ends.

10. In combination, a first and a second transmission line each having an inner conductor and an outer shell, a plurality of short sections of concentric transmission lines connected in series to said. first transmission line, means surrounding said ends for preventing current from flowing on the outside of the shells of said short sections, said sections being connected in parallel to said second line. i

11. An impedance transformer comprising a high impedance section of transmission line having an outer shell and an inner conductor, a second shell surrounding said inner conductor extending within said outer shell a distance equal to one quarter of the length of the operating wave and connected thereto, a third shell extending within said second shell a distance equal to onequarter of the length of the operating wave and also surrounding said inner conductor and connected to said second shell at the end thereof, a low impedance section of transmission line having an outer shell and an inner conductor, means connecting the outer shells of said first mentioned and last mentioned sections of transmission line together, and means for connecting the inner conductor of said last section of transmission line to the inner conductor of said first section of transmission line and to the inner ends of each of said second and third shells.

12. An impedance transformer comprising a high impedance section of transmission line having an outer shell and an inner conductor, a second shell surrounding said inner conductor extending within said outer shell a distance equal to one quarter of the length of the operating wave and-connected thereto, a third shell extending within said second shell a distance equal to a quarter of the length of the operating wave and also surrounding said inner conductor and connected to said second shell at the end thereof, a low impedance section of transmission line having an outer-shell and an inner conductor, means connecting the outer shells of said first mentioned and last mentioned sections of transmission line together, and means for connecting the inner conductor of said last section of transmission line to the inner conductor of said first section of transmission line and to the inner ends of each of said second and third shells, said last mentioned means being so arranged that the current in said last mentioned line is divided equally.

13. An impedance transformer comprising a high impedance section of transmission line having an outer shell and an inner conductor, a second shell surrounding said inner conductor extending within said outer shell a distance equal to a quarter of the length of the operating wave and connected thereto, a third shell extending within said second shell a distance equal to a quarter of the length of the operating wave and also surrounding said inner conductor and connected to said second shell at the end thereof, a low impedance section of transmission line having an outer shell and an inner conductor, means connecting the outer shells of said first mentioned and last mentioned sections of transmission line together, and means for connecting the inner conductor of said last section of transmission line to the inner conductor of said first section of transmission line and to the inner ends of each of said second and third shells, said last mentioned means being so arranged that the current in said last mentioned line is divided equally between said first inner conductor and said second and third shells.

14. An impedance transformer comprising a high impedance section of transmission line having an outer shell and an inner conductor, a second shell surrounding said inner conductor extending within said outer shell a distance equal to a quarter of the length of the operating wave and connected thereto, a third shell extending within said second shell a distance equal to a quarter of the length of the operating wave and also surrounding said inner conductor and connected to said second shell at the end thereof, a low impedance section of transmission line having an outer shell and an inner conductor, means connecting the outer shells of said first mentioned and last mentioned sections of transmission line together, and means for connecting the inner conductor of said last section of transmission line to the inner conductor of said first section of transmission line and to the inner ends of each of said second and third shells, said last mentioned means being so arranged that the current in said last mentioned line is divided equally between said first inner conductor and said second and third shells, said last mentioned means being so arranged that the lengths of current path from said second line to said first line are equal.

15. An impedance transformer comprising a high impedance section of transmission line having an outer shell and an inner conductor, a second shell surrounding said inner conductor extending within said outer shell a distance equal to an odd multiple, including unity, of a quarter of the length of the operating wave and connected thereto, a third shell extending within said second shell a distance equal to an odd multiple, including unity, of a quarter of the length of the operating wave and also surrounding said inner conductor and connected to said second shell at the end thereof, a low impedance section of transmission line having an outer shell and an inner conductor, means connecting the outer shells of said first mentioned and last mentioned sections of transmission line together, and means for connecting the inner conductor of said last section of transmission line to the inner con-- ductor of said first section of transmission line and to the inner ends of each of said second and third shells.

16. An impedance transformer comprising a high impedance section of transmission line having an outer shell and an inner conductor, a second shell surrounding said inner conductor extending within said outer shell a distance equal to an odd multiple, including unity, of a quarter of the length of the operating wave and connected thereto, a third shell extending within said second shell a distance equal to an odd multiple, including unity, of a quarter of the length of the operating Wave and also surrounding said inner conductor and connected to said second shell at the end thereof, a low impedance section of transmission line having an outer shell and an inner conductor, means connecting the 10 outer shells of said first mentioned and last mentioned sections of transmission line together, and means for connecting the inner conductor of said last section of transmission line to the inner conductor of said first section of transmission line and to the inner ends of each of said second and third shells, said last mentioned means being so arranged that the current in said last mentioned line is divided equally between said first inner conductor and said second and third shells.

NILS E. LINDENIBLAD.