US3264584A

US3264584A - Adjustable impedance matching transformers

Info

Publication number: US3264584A
Application number: US152534A
Authority: US
Inventors: Charles F Edwards
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1961-11-15
Filing date: 1961-11-15
Publication date: 1966-08-02
Anticipated expiration: 1983-08-02

Description

Aug. 2, 1966 c. EDWARD$ ADJUSTABLE IMPEDANCE MATCHING TRANSFORMERS Filed Nov. 15, 1961 4 Sheets-Sheet 1 FIG. IA

Z w M w I i I 4 5 7 4 W 2 a T m a E H mm ,m X .n J E E A a 2 2 a w c A ,c H 6 LP H 2 V,

A TTOR/VE V Aug. 2, 1966 C F. EDWARDS ADJUSTABLE IMPEDANCE MATCHING TRANSFORMERS Filed Nov. 15, 1961 4 Sheets-Sheet 2 m/ VEA/ TOR C. E EDWARDS A T TOR/V5 V 966 c. F. EDWARDS 3,2645% ADJUSTABLE IMPEDANCE MATCHING TRANSFORMERS Filed Nov. 15, 1961 4 Sheets-Sheet 5 nvvavroe By CFEDWARDS W daww A T TORNEV 2, 1966 c. F. EDWARDS 3,264,584

ADJUSTABLE IMPEDANCE MATCHING TRANSFORMERS Filed Nov. 15, 1961 I 4 Sheets-Sheet 4 A TTORNE V United States Patent 3,264,584 ADJUSTABLE IMPEDANCE MATCHING TRANSFORMERS Charles F. Edwards, Red Bank, N.J., assignor to Bell Telephone Laboratories, Incorporated, New York,

N.Y., a corporation of New York Filed Nov. 15, 1961, Ser. No. 152,534 14 Claims. ((11. 33333) This invention relates to electrical networks and more particularly to adjustable impedance matching transformers.

Generally, radio frequency transmission systems are composed of many separate component parts connected by a number of low-loss transmission lines. In such systems the impedance of each of the component parts is preferably made equal to the characteristic impedance of the transmission line connecting the parts. There are several reasons for matching impedances in arbitrary systems, the primary one being that maximum energy is transferred from one component to another when their impedances are matched; moreover, a matched condition eliminates reflected wave energy and minimizes the losses in the transmission line.

Typically, components of high frequency transmission systems intended to transmit or utilize wave energy are matched to the interconnecting transmission lines by means of reactive impedance matching networks. Such networks can be lengths of transmission line utilizing tuned stubs or dielectric elements. The behavior of such matching networks is substantially equivalent to the more conventional circuits used at lower frequencies.

Typically the matching network is an integrated structure which is inserted between two components to be matched or between a component and a transmission line.

For laboratory and test use it is desirable that these impedance transformers be variable, so that a simple manual adjustment enables the operator to match any two impedances. Transformers of the single, double and triple-stub variety have been used extensively for this purpose but they suffer from certain drawbacks, one of which is the fact that at least two manual adjustments must be made in order to match any two impedances.

In many instances, especially those encountered in laboratory practice, it is desirable to match impedances which are purely resistive. When using one of the prior art variable impedance transformers for this purpose, it is still necessary to make at least two manual adjustments in order to eliminate any re-act-ance introduced by the transformer itself. By a novel arrangement of reactive elements, the present invention obviates this necessity.

It is, therefore, the general object of the present invention to provide a matched coupling between networks of diverse impedances.

It is a more specific object of the present invention to provide transformers for matching purely resistive impedances and capable of being adjusted by a single manual control.

It is yet another object of the present invention to provide impedance matching transformers wherein the reactive and resistive components can be adjusted separately.

In keeping with the principles of the present invention the foregoing objects are accomplished through the use of T and 1r networks comprising adjustable reactance elements. In the high frequency embodiments of the invention, open and shorted coaxial line stubs are utilized as the network elements, whereas in the low frequency embodiments inductors and capacitors are utilized as the network elements.

As mentioned above, a feature of the present invention is the mechanical coupling between the elements of "ice the impedance matching transformer which allows the tuning to be done with one manual adjustment. In one specific embodiment of the invention the impedance matching ratio is adjusted by varying the reactances of a plurality of coupled open-circuited and short-circuited coaxial line sections. In accordance with the principles of the present invention the react-ances are varied simultaneously and in such a manner that the reactances of two of the sections are always maintained equal to each other and the reactance of the third section is maintained equal to the negative of the other two.

In an illustrative embodiment of the invention, the mechanic-a1 means for performing this adjustment comprises a rack and pinion gear arrangement mounted on the transformer structure. In the low frequency embodiments of the invention the impedance matching ratio of the transformer is adjusted by varying either the capacitances or the inductances of the various network elements simultaneously. In these embodiments the me chanical means is easily integrated into the capacitor or inductor structure in the form of ganged capacitors and inductors.

The above mentioned and other features and objects of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings in which:

'FIGS. 1A and 1B are simplified circuit diagrams of T and 1: networks for facilitating the description of the invention;

FIGS. 2A and 2B are schematic representations of open and shorted transmission lines showing the impedances associated therewith;

FIGS. 3A, 3B, 3C, and 3D are cross-sectional views of four high frequency embodiments of the present invention;

FIG. 4 is a pictorial view, partially in cross section, of a preferred embodiment of the invention;

FIG. 5 is a pictorial view of the embodiment of FIG. 4 illustrating the mechanical ganging of the tuning controls;

FIG. 6 is a longitudinal cross-sectional view of a triple stub coaxial impedance transformer used as an aid in explaining the means by which principles of the present invention may be applied thereto;

FIG. 7A is a schematic representation of a low frequency embodiment in accordance with the principles of the present invention;

FIG. 7B is a pictorial view of a possible capacitor capable of being utilized in the embodiment of FIG. 7A; and

FIG. 8 is a schematic representation of yet another low frequency embodiment in keeping with the principles of the present invention.

Referring to the circuit of FIG. 1A, there is shown a T-network consisting of reactive elements X X and X to which there is coupled a load impedance Z The impedance Z of the circuit at terminals 1-1' is given by the equation 1 Z 1/ z. +721.) +1/1'X2 (1) By making X 1:X2, Equation 1 becomes +j XrXa and if the T is made symmetrical by making X =X then Similarly, in the 1r-network of FIG. 1B, if the reactive elements B B and B are adjusted so that the equation for the admittanceas seen across terminals 1-1' is Equations 3 and 4 are similar in form to the input im pedance and admittance of quarter-wave sections of transmission line terminated with loads Z and Y respectively. These equations are where Z and Y are the characteristic impedance and the characteristic admittance of the lines.

In other words, the networks of FIGS. 1A and,

1B, when properly adjusted, behave electrically as quarter-wave transmission line sections and enjoy the same impedance transforming properties. The important distinction between an actual quarter-wave transmission line and a so-called artificial transmission line of FIG.'1A'

or 1B is-that the characteristic impedance ofthe artificial transmission line can'be easily varied whereas the characteristic impedance of a real line can not. And even if, with some difliculty, the impedance of a real line can be varied, the range of variation is quite limited.

If, however, sections of transmission line are connected together and their, lengths proportioned in the manner to be explained in detail hereinbelow, the disadvantages peculiar to the individual transmission line when used as a quarter-wave matching section no longer exist. In accordance with the invention the several lengths of trans mission line serve, not as impedance transformers, but as reactance elements in a T or 1r network.

FIG. 2A shows an open-circuited transmission line section of length x having a characteristic impedance Z In practice, the resistive losses of a short line can be neglectedand when this is done the impedance looking into terminals 11 is a pure reactance given by:

where the phase constantfl equals 21r/7\, and A is the It viewed fromtthe wavelength in the transmission line. admittance standpoint, the susceptance B at terminals 1-1' is given by:

Z0 tan 6a:

FIG; 2B shows a section of transmission line of length.

l and characteristic impedance Z short-circuited atone of its ends. Again, if the resistive losses are neglected the impedance looking into terminals 22' is a pure re-- I actance If the lengths of the two lines are made adjustable so that the sum of their lengths x+l is'equal to M4, the reactance of the open-circuited section can be written as V, Z m

4% Substituting for x,

E e l/Z tan p( \/4+ l)-=1/Z tan (1r/2,8l)

and since tan .(1r/2iA)=cot A,l.then;

hi I B Z0 cot. til

It is apparent .from Equations. 5 throughw8 that X =X and B =B These,'however,.are the requirements thatmust be met by X and X2 and B and 'B iinthe networksof FIGSylA and lBiinzorder to obtain impedancettrans-formingt action, Thus, by combin-l ing anopen and a shorted transmission line section, :the-

sum of whoselengths is a ;qu arter.wavelength, and by adding another opentor, shorted transmission, line sec-l tion as the third reactive element, ;various circuits having the desired impedance, transforming properties are'hobtained. Furthermore, if the reactance of the various sections is changed by varying ;their:lengths, the circuits are capable of providing, a wide range of impedance-ratios. FIGS.- 3A and-=3B are cross-sectionalvieWs of two:

embodiments of the invention utilizing coaxial line construction arranged in the manner of a T-network. FIG"; 3A shows a thigh-pass T-network consisting of substan-t -tially identical quarter-Wavelength inner; conducting rods 10 and 11 joined by conductor 12 which makes a;slideable contact with each along their, respective lengths;

The regions, of rods 10 and 11 below the'slideable'junc-l tion providecltby conductor lz are surrounded by. cylindrical !Olltl conductors 13 and 14, respectively. The

regions ofrods 10iand 11 above these-points are surrounded by cylindrical condu'cting sheaths 15 and '16 which, in turn; are surrounded by cylindrical outer con-= Inner conducting rods: 10 land :11 are shorted ,tozouter- V conductors l3 and -l4 byv means

ofshorting disks

19 and 20. This construction enables rods 101and 11 to move ina direction-parallel to vtheir longitudinal faxes while maintaining: contact with outer HCOHdUCtOISe 13, and 14. The dashed line connecting rods 10 andvll indicates a mecihanical connection for, moving both arodsi simultaneous y.

Input connections to the device are provided across the open ends'of outer conductor 17 and sheath'15. The

load lmpedance Z, to be transformed is connected across 1 outer conductor '18 and sheath ;16.- The input: and

output connections can, of course, be interchanged as seen from the symmetry of the device.

Returning to the terminology of FIG. 1A," it is evident that the coaxial section formed by rod 11 and sheath 16 corresponds to the reactance Xi, and the coaxial section formed by rod 10 and sheath 15 corresponds to reactantce X5. The parallel. combination of the two ,sec-

tions formediby .rods 10 and Hand outer conductors 13 and 14, respectively, corresponds to the third reactance X 7 In'operation, the impedance transforming ratio is changed when rods 10 and 11 are moved simultaneously in a direction parallel to their From the vstandpoint of symmetry,-i=t is seen that X land X3 are always equal; and since the: lengths of rods 10 and 111 are onequarter wavelength at a the operating frequency,

In FIG. 33, there is shown a lowepass T-network substantially identical to the high-pass network of FIG. 3A. In this figure like numerals have been utilized to indicate the correspondences, between the elements 201. this embodiment and that of FIG. 3A. The only substantial difference between this embodiment and the previous one is that shorting disks 19' and 20 have replaced

disks

19 and 20, respectively. The functions of the various elements and combinations of elements are substantially the same as those of FIG. 3A except that rods and 11 are now shorted to conducting sheaths 15 and 16.

In keeping with the principles of the present invention, the coaxial line sections formed by rods 10 and 11 and sheaths 15 and 16; and sheaths 15 and 16 and

outer conductors

17 and 18 are designed so that their characteristic impedances are equal. Since the coaxial sections formed by rods 10 and 11 and outer conductors 13 and 14 are in (parallel, they are :designed to have a characteristic impedance equal to twice this value.

In FIG. 3C there is shown in cross section another embodiment of the present invention intended tfor operation at high radio frequencies. This embodiment is a coaxial Ir-IlfifiWOlk arranged in the manner of a highpass filter. In this embodiment two substantially identical quarter-

wavelength conducting rods

21 and 22 are slideably connected along their lengths to conductors 30 and 31, respectively. Conductors 30 and 31, in turn, serve as the inner conductors of the input and output

coaxial line sections

34 and 35, respectively.

Rods

21 and 22 are surrounded by

outer conductors

23 and 24 over that portion of their lengths below the points of connection with conductors 30 and 31. The regions of

rods

21 and 22 lying above these points extend into two

cylindrical cavities

25 and 26, respectively, which have been fiormed in a solid conducting element 27.

Element 27, which is proportioned so that its length is equal to one-quarter wavelength at the operating frequency, is, in turn, surrounded by an outer conductor 28 and conductively attached thereto by end-plate 29. The coaxial input and output sections as well as

outer conductors

23, 24, and 28 are oonductively joined so as to provide a

shield surrounding rods

21 and 22 and conductors 30 and 31.

Shorting

disks

32 and 33 are attached to the lower end points of

rods

21 and 22, respectively, so that each rod is slideably shorted to its corresponding

outer condoctor

23 and 24. Again, for the sake of clarity, the means for positioning and holding conductors 30 and 31 have not been shown but can comprise any of the lowloss dielectric beads or spacers known in the art.

In the terminology set forth in connection with FIG. 1B, the coaxial section formed by nod 22 and outer conduotor 24 corresponds to the susceptance B The coaxial section formed by rod 21 and outer conductor 23 corresponds to susceptance B and the series combination of the coaxial sections formed by rod 21 and cavity 25 and rod 22 and cavity 26 corresponds to the third susceptance B Again, it is obvious from the symmetry of the structure that B and B are always equal; and since the lengths of

rods

21 and 22 are one-quarter wavelength at the operating frequency, B =B In FIG. 3D, there is shown another embodiment of the present invention substantially identical to that of FIG. 30, wherein the numbering of the elements has been carried over from the corresponding elements of that embodiment. This embodiment i a low-pass Ir-network wherein the shorting disks 32' and 33' have replaced

disks

32 and 33 so that

rods

21 and 22 are slideably shorted to the inner conducting surfiace of

cylindrical cavities

25 and 26, respectively.

In operation,

rods

21 and 22 in both embodiments 3C and 3D are moved simultaneously along their longitudinal axes. The mechanical means for operating this portion is not shown but merely indicated by the dashed line.

In the embodiments of FIGS. 3C and 3D the coaxial line sections formed by

rods

21 and 22 inside

outer conductors

23 and 24 are designed to have a given characteristic impedance, and since the coaxial sections formed by

rods

21 and 22 inside

cavities

25 and 26 are in series, these sections are designed to have a characteristic impedance of one-half this value. As mentioned above, the coaxial line section formed by element 27 and outer conductor 28 is one-quarter Wavelength long; therefore, it has no effect on the other coaxial sections and its characteristic impedance is not critical.

In FIG. 4 there is shown, partially in cross section, a refinement of the present invention derived from the embodiment of FIG. 3C. This embodiment consists of hollow,

cylindrical conductors

40 and 41 of substantially equal cross-sectional dimensions oriented so that their ends are in close proximity and their axes colinear. A conducting rod 42 extends along this common axis through conductor 41 and into conductor 40.

Rod 42 is conductively insulated from conductor 40 by dielectric disk 43 which allows longitudinal motion of rod 42 relative to conductor 40'. Rod 42 is joined to inner conductor 44 of coaxial transmission line section 45 by means of a spring contact 46. Contact 46 is located in the region between

conductors

40 and 41. The nature of contact 46 is such that it allows rod 42 to move longitudinally while maintaining electrical contact with inner conductor 44.

Cylindrical conductor 40 is conductively connected to inner conductor 47 of coaxial line transmission section 48 at its end nearest conductor 41. Connection 49 is a rigid one and allows no relative motion between

conductors

40 and 47.

Conductor 40, which surrounds a portion of rod 42, is, in turn, surrounded by a cylindrical outer conductor 50. Conductor 50 extends the entire length of conductor 40 and is joined to conductor 41 and the outer conductors of

transmission line sections

45 and 48. In this

manner conductors

41 and 50 and the outer conductors of

transmission line sections

45 and 48 form a continuous surface.

Conductors

40 and 50 are conductively shorted by annular shorting ring 51. Ring 51 is attached to cylinder 52 which extends past the ends of

conductors

40 and 50 and enables the position of the short provided by ring 51 to be adjusted.

Rod 42 is shorted to conductor 41 by means of annular shorting ring 53 which is attached by means of rods 54 to another ring 55 lying outside the end of conductor 41. Set-screw 56 is provided in ring 55 in order to clamp the two

rings

53 and 55 in position on rod 42. Thus, ring 53 can be moved with respect to rod 42 and conductor 41 or with respect to conductor 41 only.

The lengths of the three coaxial sections which make up the impedance transformer in the present embodiment have been designated l l and Length 1 is that of the shorted coaxial section formed by conductor 41 and rod 42 extending from spring contact 46 to shorting ring 53. Length 1 is that of the open-ended coaxial section formed by conductor 40 and rod 42 between contact 46 and the end of rod 42. And length 1 is that of the shorted coaxial section formed by outer conductor 50 and conductor 40 between junction 49 and shorting ring 51. In keeping with the principles of the present invention, the three coaxial sections referred to are proportioned so that they all have the same characteristic impedance Z In operation, 1 and 1 are made equal by adjusting the position of shorting ring 51 or 53. This adjustment is easily made if cylinder 52 and either of rods 54 has first been calibrated and the lengths marked thereon. After this preliminary adjustment rod 42 is adjusted so that the length l +l is electrically equal to one-quarter wavelength at the operating frequency. This adjustment is fiacilitated by observing the impedance at input section 48 when the output section 45 is terminated with a purely resistive impedance. When the length l +Z is properly adjusted the impedance seen at the input of the device has no imaginary component.

In order to operate the device as an adjustable impedance matching transformer, it'is' necessaryito vary The other requirement that l +l equal one-quarter vwave-- the lengths so that l and are always equal.

length is metif the shorting ring 5 3 is clamped in place. on rod .42 by means of set-screw 56 after its initial adjustment.

FIG. 5 illustrates the mechanical means utilized in adjusting the transformer of FIG. 4. Like numerals have been employed to designate like elements in the two figures. A dual rack and pinion

arrangement comprising racks

60 and 62 and pinion gear 64- is mounted on thedevice as shown. RackGOJisattached to cylinder 52' by means of end plate 61. Similarly, rack62 is attached to ring 55 by means of plate 63. The two racks are engaged by pinion gear 64 which is manually It is therefore seen that the range of impedance transformation'can be quite large, depending on the range.

over which l l and 1 can be varied.

It is understood that the mechanical means shown in FIG. 5 is for the purpose of illustration only and that many other mechanical gauging arrangements can be utilized in practicing the invention.

The principles of the present invention may also be applied to the prior art device known as the triple-stub tuner. FIG. 6 shows a simplified cross-sectional view of such a device. The triple-stub tuner of F'IG.-6 comprises a main coaxial transmission line section 70with three associated coaxial line stubs'71, 72, and 73,-ar ranged alongthe length thereof. In general, the longitudinal spacing between consecutive stubs is one-quarter wavelength at the operating frequency. The positions of the shorting rings within

stubs

71, 72, and 73 are adjustable by means of

cylinders

74, 75, and 76, which may or may not be of conducting material.

The lengths of the input, intermediate, and output stubs have been designated l l and I respectively, in order to explain the operation of the device of FIG. 6 modifie'd by the principles of the present invention. In order to enable the triple-stub tuner to couple a network. of one purely resistive impedance of a given value to that of another purely resistive impedance the following pro- .15 adjusted :by knob 65. The Whole assembly consisting.

cedure should be followed. First, the lengths l and I are maintained substantially equal.

For this purpose 1

cylinders

74 and 76 are rigidly joined by member 77 which allows lengths l and 1 to be change-d only simultaneously so that 1 always equals 1 Secondly, the lengths l +l (and l +l are made equal to one-quarter wavelength.

The second requirement is met by gauging cylinder .75' '65 This arrangement similar to that .of FIGS. Such a mechanism. can be easily constructed by a skilled mechanic and is not illustrated in FIG. 6.

So far, the various embodiments of the present invention have only been described with regard to operation wherein one purely resistive impedance is transformed i into another purely resistive impedance of a dilferent I 811- value; For most laboratory purposes this is the :only casethat is encountered. If,ghowever, it is desirable to adjust the'reactivewomponent of an .impedance so as.

to eliminate it ,in the transformed impedance or; totintroduce a reactive component, a furtherstepgcan be, taken.

If it is desired to adjust :the .reactive'component independentlyofthe resistive component, a simple matchresistiveand reactivecontrols can be tolerated, this: adjustment can be made without employing a separate stub. In this case, the; real-'or-resistive component can;be adjusted using the-inventiomas -de'scribed=hereinabove and then by disengaging theaganging mechanism andadjusting 1 separately to.the desired ,value of reactance.

The original T and 1r-networks 0f FIGS. 1A and 13 can be exploited to provide variable impedance transformers for lowerfrequencies. FIGSJ7A and 8 are schematic diagrams ,oftwo embodiments of the present invention employing lumped parameter: circuit elements. FIG 7A is a T-networktuseful in the. .low. megacycle regions; It consists of ganged capacitors-C C and C and inductor L as the constituent reactive elements: of 1 thestransforment, The input ofthe transformer'is at ter- 'minals v1-1 andthe output is: terminatedby load'im- I pedance R..

Returning to the terminology developed ;in association with FIG. :1A, in FIG. 7A:

C decreases,-then .C +C is maintainedconstantand Equation" 12 is satisfied. The impedanceofthe trans- I former of FIG;:7A, looking into terminals1-1'=is, from Equations 3 and 12:.

FIG. .7B is asimplified.pictoriajtillustration of a variable capacitor for use inthe embodiment of FIG. 7A..

The capacitor consists of shafti80aon which there is mounted rotor plates 84, :85, :and 86.; Stator plates 81,

82, and 83 are located .onei-ther side of each of the rotor. plates 84, 85, and 86;.respectively. Inthis manner. rotor plate 84 and stator plates 81 form a capacitor 0 plates 82 and 85form capacitor C and plates 86 and 83 form capacitor C The. position of stator plates 82 are physical degrees from the position of p1ates=81*and 83.

Therefore, the capacitance of C 'decreases. as that of C and C increases and. if the physical dimensions and:

spacing ofeach set of plates are equal,C '|-C is always constant and C is always equal ,to (3 The present in-: :vention-should not be deemed limitedby'the capacitor 9 shown in FIG. 7B, since it is included for purposes of illustration only.

FIG. 8 is a schematic representation of another lowfrequency embodiment of the present invention. The lowpass T-network of FIG. 8 is similar to the high pass T of FIG. 7A except that inductances L L and L have replaced C C and C and capacitor C has replaced inductor L. The requirements in this transformer are that L equal L and L +L or L +L be constant. If identical tapped inductors are used it is readily seen that the above relationships can be satisfied.

In all cases it is understood that the abovedescribed arrangements are illustrative of a small number of the many specific embodiments which could represent an application of the principle of the invention. Other arrangements, including variable impedance transformers utilizing transmission lines other than the coaxial type can readily be devised in accordance with these principles by those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. In combination, a plurality of variable reactances, means for connecting a first variable reactance X between a first terminal and a first common junction, means for connecting a second variable reactance X between said first common junction and a second common junction, means for connecting a third variable reactance X between said first common junction and a second terminal where X =X X input means connected between said first terminal and said second common junction, output means connected between said second terminal and said second common junction, and a single means for adjusting all of said reactances simultaneously while maintaining the relations X '=X =X 2. The combination according to claim 1 wherein said first and third variable reactances are variable capacitors and said second variable reactance is a parallel combination of an inductor and a variable capacitor.

3. The combination according to claim 1 wherein said first and third variable reactances are variable inductors and said second variable reactance is a series combination of a capacitor and a variable inductor.

4. The combination according to claim 1 wherein said first and third variable reactances are open-circuited transmission line stubs and said second variable reactance is at least one short-circuited transmission line stub.

5. The combination according to claim 1 wherein said first and third variable reactances are short-circuited transmission line stubs and said second variable reactance is at least one open-circuited transmission line stub.

6. An adjustable impedance matching transformer comprising, in combination, a plurality of variable reactances, means for connecting a first variable reactance X between a first terminal and a common junction, means for connecting a second variable reactance X between said first terminal and a second terminal, means for connecting a third variable reactance X between said second terminal and said common junction where X =X X input means connected between said first terminal and said common junction, output means connected between said second terminal and said common junction, and a single means for adjusting all of said reactances simultaneously while maintaining the relations X =X X 7. The combination according to claim 6 wherein said first and third variable reactances are open-circuited transmission line stubs and said second variable reactance is at least one open-circuited transmission line stub.

8. The combination according to claim 6 wherein said first and third variable reactances are short-circuited transmission line stubs and said second variable reactance is at least one open-circuited transmission line stub.

9. A variable impedance transformer including, in combination, a plurality of sections of coaxial transmission line all having the same characteristic impedance, and connected as follows: a first section of coaxial transmission line comprising a hollow inner conductive cylinder and a surrounding outer conductive cylinder; second and third sections of coaxial transmission line, each having an inner conductor and a surrounding outer conductor, and each having one end thereof abutting upon one end of said first line; adjustable means for conductively terminating the other end of said first line located at a distance 1 from said one end; the outer conductors of said second and third lines making conductive contact with the outer cylinder of said first line; means for connecting the inner conductor of said second line to the inner cylinder of said first line at said one end; a fourth section of coaxial transmission line having an inner conductor and a surrounding outer conductor colinearly aligned with said first line with the outer conductors thereof in conductive contact; the inner conductor of said fourth line extending past the inner conductor of said third line and making slidable contact therewith and further extending into said hollow inner cylinder a distance past said slidable contact and forming therewith a fifth section of coaxial transmission line; adjustable means for conductively terminating said fourth line at a distance I, from said slidable contact; means for simultaneously varying said distances l and 1 while maintaining the relationships l =l and l +l equal to a constant; and input and output means connected to the other ends of said second and third lines respectively.

10. An adjustable impedance matching transformer arranged in the manner of a high-pass T-network comprising a pair of parallel conducting rods, means for conductively connecting said rods at corresponding points intermediate the ends thereof, a first pair of hollow cylindrical conductors coaxial to and surrounding a portion of each of said rods and extending from said points past one pair of corresponding ends of said rods, a second pair of hollow cylindrical conductors coaxial to and surrounding a portion of each of said rods and extending from said points past the other corresponding ends of said rods, said first and second pairs of cylindrical conductors being conductively insulated from each other, a third pair of hollow cylindrical conductors coaxial to and surrounding said second pair of cylindrical conductors over the entire lengths thereof, said first and third pairs of cylindrical conductors being conductively connected, a single mechanical means for simultaneously varying the position of said points along the lengths of said rods, input means connected between one of said second pair of cylindrical conductors and the corresponding conductor of said third pair of cylindrical conductors, output means connected between the other of said second pair of cylindrical conductors and the corresponding conductor of said third pair of cylindrical conductors, and means for conductively connecting corresponding ends of said rods to adjacent points on the respective conductors of said first pair of cylindrical conductors.

11. An adjustable impedance matching transformer arranged in the manner of a low-pass T-network comprising a pair of parallel conducting rods, means for conductively connecting said rods at corresponding points intermediate the ends thereof, a first pair of hollow cylindrical conductors coaxial to and surrounding a portion of each of said rods and extending from said points past one pair of corresponding ends of said rods, a second pair of hollow cylindrical conductors coaxial to and surrounding a portion of each of said rods and extending from said points past the other corresponding ends of said rods, said first and second pairs of cylindrical conductors being conductively insulated from each other, a third pair of hollow cylindrical conductors coaxial to and surrounding said second pair of cylindrical conductors over the entire lengths thereof, said first and third pairs of cylindrical conductors being conductively connected, a single mechanical means for simultaneously varying the position of said points along the lengths of said rods, input means connected between one of said second pair of cylindrical conductors and the corresponding conductor of said third pair of cylindrical conductors, output means connected between the other of said second pair of cylindrical con-. ductors and the corresponding conductor of said third pair of cylindrical conductors, and means for conductively connectingcorresponding ends of said rods to adjacent points on the respective conductors ofv said second pair of cylindrical conductors.

12. An adjustable impedance matching transformerarranged in,the manner of a high-pass ar-network comprising a pair of parallel conducting rods, means for cone dnctively connecting the inner conductors of a pair of coaxial transmission line sections to said rods at corresponding points intermediate the ends thereof, a first pair .of hollow cylindrical conductors coaxial to and surroundmeans connectedto one of said coaxial transmission line 1 sections and output means connected to the other of said coaxial transmission line sections, a single mechanical means for simultaneously varying the position of said.

points along the lengths of said rods, and means for condnctively connecting corresponding ends of said rods to adjacent points on said first pair of cylindrical conductors.

13. An adjustable impedance matching transformer arranged in the manner of a low-pass 1r-network comprising a pair of parallel conducting rods, means for conductivelyconnecting the inner conductors of a pair of-coaxial transmission line sections to said rods at corresponding points vintermediate the ends thereof, a first pair of hollow cylindrical conductors coaxial to and surrounding a portion of each of said rods and extending from said points past one pair of corresponding ends of said rods, the other corresponding endsl ofasaid,rods-extendingyinto a pair of cylindrical cavities formed in a solid cylindrical conductor, a thirdhollow cylindrical. conductor coaxial to and surrounding said solid cylindrical conductor over the entire length thereof; said third hollow cylindrical icon-f ductorbeing conductively connected to said solid cylindrical conductor,- to said first pair: of hollow-cylindrical conductors, and .to the outer conductors of, said pair of coaxial transmission line sections, input means connected ,to one of said coaxial t'ran'smission'line sections'and out; put-means; connected to the other of said coaxial transmission line sections, a single mechanical means :for, simul taneously varying the position of .said vpoints along the lengths of said rods, and means forconductively connecting corresponding, ends of said rods to adjacent points on the inner surface of said=cylindricalzcavities.

14. A triple-stub coaxial line, :tuner comprising, in

combination, a maincoaxial linesection, fir'st,;second,

and third 'short-circuited stubs connected :in shunt with said mainsection along the-length thereof and spaced one-quater wavelength apart, said stubs having efiective electrical lengths equal to 1 I and l respectiv'ely, a single mechanical means foriadjusting all'of said lengths,

simultaneously while; maintaining the relations 1 :1 and r 'l +l =constant; r

References Cited :by the Examiner UNITED STATES PATENTS 1 2,284,529, 5/1942 Mason 3334-33 2,373,233 4/1945 Dow 33333 2,390,839 12/1945 Klingaman 33333 2,404,279 7/1946 DOW 333 -33 2,419,985 5/1947 Brown 33333 2,422,160' 6/1947 Woodward 333-33 2,428,272 9/1947 Evans 333-73 2,428,485 10/1947 Carter 333-33 2,438,912 4/1948' Hansen 333-33 HERMAN KARI; SAALBACH,Primary Examiner.

C. BARAFF, Assistant Examiner.

Claims

1. IN COMBINATION, A PLURALITY OF VARIABLE REACTANCES, MEANS FOR CONNECTING A FIRST VARIABLE REACTANCE X1 BETWEEN A FIRST TERMINAL AND A FIRST COMMON JUNCTION, MEANS FOR CONNECTING A SECOND VARIABLE REACTANCE X2 BETWEEN AND FIRST COMMON JUNCTION AND A SECOND JUNCTION, MEANS FOR CONNECTING A THIRD VARIABLE REACTANCE X3 BETWEEN SAID FIRST COMMON JUNCTION AND A SECOND TERMINAL WHERE X1=X3=-X2, INPUT MEANS CONNECTED BETWEEN SAID FIRST TERMINAL AND SAID SECOND COMMON JUNCTION, OUTPUT MEANS CONNECTED BETWEEN SAID SECOND TERMINAL AND SAID SECOND COMMON JUNCTION, AND A SINGLE MEANS FOR ADJUSTING ALL OF SAID REACTANCES SIMULTANEOSULY WHILE MAINTAINING THE RELATION X1=X3=-X2.