US2436427A - Impedance transformer - Google Patents

Description

1948. E. L. GINZTON IMP EDANGE TRANS FORMER Filed Feb. 18, 1943 INVENTOR Edward L 615102 5021,

ATTORNEY Patented Feb. 24, 1948 UNITED STAT NT OFFI CE IMPEDANCE TRANSFORMER Edward L. Ginzton, Wantagh, N. Y., assignor-to The'Sperry Corporation, a corporation of'Delaware 23 Elaims.

The present invention relates to the art-including impedance matching and transforming devicesespecially adapted for use in systems utilizing high frequency electromagnetic energy. In transferring energy from one high frequency device to another, it is well known that the impedances of the source and load must be properly matched in order to avoid the production-of standing waves with-attendant losses and decreases in the eiiiciency and power-carrying capacity of the energy-transmitting system.

The present invention is directed toward the provision of an improved impedance transforming device whichis adapted-to-efficiently couple and match one impedance element with a second impedance element, or to transform a given impedance value into a desired value, with a minimum of adjustment and-a maximum facility and efficiency. Many types ofimpedance matching and transforming devices are known, such as those shown in tcopending application Serial No. 4:48,!392, filed June 29, 1942, in the-names of William W. Hansen et a1. However, all such devices require the use-of sliding metallic joints in order to permit adjustment-of the device for transforming an impedance value impressed at one end of the device to another value at the other end. Such sliding metallic jointsintroduce considerable complexity of construction, and increase losses due to the finite resistance ofsuch joints.

According to the present invention, an impedance transformer is provided in Whichall sliding metallic joints-in the pathof the high frequency energy flow :are entirely omitted and an easily fabricated device is produced. This is done in the present case by providing a movable section of dielectric whichacts to change the impedance characteristics of the device suitable for matching or transforming impedances, without the necessity for-sliding metallic joints.

Accordingly, it is an object of the present invention to provide an improved-impedance transformer for transforming one impedance value to another value.

It is another object of the present invention to provide an improved impedance transformer of fixed length suitable for rigid connection in a high frequency system.

It is still another object of the present invention to provide an improvedimpedance trans former having no sliding metallic conducting joints. 7

Itis a further .cbject of the present invention to provide an improvedimpedance transformer jz utilizinga movable-dielectric -mass for adjustin the characteristics-thereof.

It is still another object of the-present invention to vary the characteristics of a'transmissicn line by an adjustable dlelectricmember.

Further objects and advantages of the present invention will becomeapparent from the specification, taken in connection withthe-acccmpanydrawing wherein one embodiment of-the inventi-on is illustrated and in which 1 shows a partially cut-away perspective view of the impedance matching and/or transforming deviceof thepresent invention, and

Fig. 2 shows an impedance diagram useful in explaining the operation of the invention of The present invention provides an impedance transformer generally of the coaxial transmission line type (although othertypes of transmission lines may be used), which may be-rigidly connected inan-y coaxial transmission line system. The main bodyof the-device is provided by a housing I I which'is-shown as being of square cross-section. although it is tobe understood that any other cross-section adapted to function in the manner to be described, maybe used. This casing l i is provided witha central conductor I2 preferably concentricallyand symmetrically disposed therewithin. The casing H and conductor i2 provide a type of coaxial transmission line having a predetermined characteristicimpedance with the usual air dielectric material. This characteristic impedance may be-chosen to have a standard value, which maybe the :same as that of the concentric line usedln other portions of the system.

Connected at either end of this transmission line ii. if! is a coupling device or terminal I? comprising any usual'or conventional cylindrical coaxial transmission line terminal. Preferably the inner conductor I2 extends into and forms an integralpart of these terminals 13. and the relative dimensions of casing H lconductor l2, and terminals I3 arc -chosen to'make the characteristic impedance of the terminal sections I3 equal to that of the main portion of the device comprising casing II and conductor l2. This condition is not necessary, however, since the impedance transformer itself can compensate for any lack of matching between the terminal sections and the main body of the device. Also, if desired, a smooth transition section may be connected between theterminals I 3 and the main body 1! i to provide'a minimumofimpedance discontinuity at the aendsof the device. However,

3 these are refinements which are not necessary to the functioning of the device, although desirable.

As is clearly shown in Fig. 1, the housing II is provided with a pair of openings id at opposite sides thereof into which is inserted a movable dielectric mass or member I6. Dielectric mass l6 may be composed of any suitable dielectric material having a dielectric constant appreciably different from that of air, and is preferably chosen to have a high efficiency and low power loss at the high frequencies to be utilized. A suitable material for this dielectric is polystyrene.

As shown in the drawing, dielectric mass I6 is adapted to be moved transversely of the housing H by means of a suitable screw l1 threaded into a member l8 which is prevented from transverse mot on by means of guide flanges l9. Accordingly. rotation of knob 2| will produce a transverse displa ement of dielectric mass l 6. Dielectric mass 16 is also adapted to be moved axially of t e dev ce by means of a knob 23 and a screw 22 which is also threaded into member IB. Accordingly. by rotation of knob 23, dielectric mass it is axially displaced along the device, guided by flanges l9. Dielectric mass l6 may be formed in a number of different shapes but is preferably chosen to have a wedge-shape, such as shown in the figure, straddling the inner conductor l2 of the device.

It will be seen that in this manner rotation of knob 2! will insert an adiustable length of dielectric between inner conductor 12 and the outer housing I I. As is well known a change in dielectric material in'a coaxial transmission line produces a chan e in the characteristic impedance of the line. Adjustment of knob 2| therefore will produce a section of coaxial transmission line at the center of the device, having adjustable length and with a characteristic impedance differing from that of the rest of the line. At the same time, adjustment of knob 23 will displace the relative position of this difierent-characteristic-impedance coaxial line section along the device. Thus knob 2| adjusts the axial extent of the dielectric, or the distance separating the left airfilled line section from the right air-filled line section, while knob 23 adjusts the position of the dielectric, and thus increases one of the air-filled end section while decreasing the other equally. These two adjustments, as will be seen, provide all the adjustments necessary to transform an impedance value impressed at one end of the device to another value at the other end.

Although dielectric mass iii is shown in the form of a right triangular wedge, many other forms can be utilized, the only necessary condition being that the axially-extending dimension of the dielectric mass is variable along the transverse direction so that varying lengths of dielectric can be effectively inserted into the device by rotation of knob 2!. Another shape for dielectric member [6 which is well adapted for use isan isoceles triangular shape having its axis of symmetry perpendicular to the central conductor l2.

Referring to Fig. 2, there is shown an impedance diagram whose coordinate axes represent, respectively, resistance and reactance. On this diagram, the point Z1 represents the characteristic impedance of the coaxial line i l. l2 when the dielectric mass i6 is entirely Withdrawn. and point Z2 represents the characteristic impedance of the coaxial lineat the position of dielectric mass 46 when the dielectric mass 16 is inserted. In view of the fact that the dielectric constant 9f dielectric mass I6 is greater than that of air, it will be seen that the characteristic impedance value Z2 must be less than Z1.

If now an impedance element of arbitrary impedance value is connected to one end, say the left end, of the device, it may be required to match this impedance value or transform it to the characteristic impedance Z1 of the line section II, l2. This situation may arise, for example, where the entire apparatus to the right of the device of the present invention is already suitably matched in impedance to that of line ll, 12.

Let the arbitrary impedance element have an impedance value represented by the point Z, and let it be connected to the left end of the device of Fig. 1. Generally, this impedance value will have both resistive and reactive components, as shown by the illustrated position of Z. As the position of dielectric mass [6 is moved axially of the device by means of knob 23, the impedance value at the left edge of dielectric mass I6, seen looking toward the arbitrary impedance element of impedance value Z, will vary with motion of the dielectric mass 16 along an arc of the circle of the diagram passing through point Z. This circle is formed as one of the bipolar coordinate circles having the point Z1 as the pole thereof. A more complete discussion of the use of such bipolar coordinate circles is given in the abovementioned U. S. application Serial No. 448,992, and in the book Microwave Transmission by J. C. Slater, at pages 29-40. Briefly, it may be stated that for each half wavelength of transmission line of characteristic impedance Z1 inserted between the arbitrary impedance Z and the point of observation, the transformed impedance value at the point of observation will make one rotation about the circle passing through the impedance value Z. For less than a half wavelength of line thus inserted, the impedance value will be transformed by an amount corresponding to a smaller arc of this circle. Accordingly, by making the opening l4 in casing II at least one-half wavelength long, the transformed impedance value at the leading edge of the dielectric mass Hi can he made to assume any value on the circle passing through point Z.

The transformed impedance value at the right end of dielectric mass IE will be displaced from the first transformed impedance value along an arc of a similar bipolar coordinate circle having the point Z2 as the pole thereof, the amount of such displacement depending on the axial length of dielectric mass I6 interposed between conductors II and I2. A number of such bipolar coordinate circles are shown in the drawing for each of the two poles Z1 and Z2. By adjusting the axial position of the dielectric mass I6, therefore, the impedance value at the left edge of dielectric mass l6 can be transformed to a value Z which lies on the bipolar coordinate circle ZZ1 having pole Zz. Therefore, by adjusting the knob 2| to adjust the effective length of the transmission line section having the dielectric therein, the impedance value Z at the left edge of the dielectric mass It can be transformed into the impedance value Z1, as is required. Since this impedance value at the right edge of the dielectric mass 16 is the same as the characteristic impedance Z1 of the line H, l2 and of the terminal l3 (under the condition where the terminal has the same characteristic impedance as the main line section H, l2) it will be seen that the arbitrary impedance value Z has been suitably transformed into the value Z1 at the right hand of the device, and if the sysannih late I' I.,. I2. and'the length of: transmission line formed by terminal l3: transformsthis impedancevaluei-ntothe required-"impedance value Z at the-right of terminal [3 which matches the system'tothe right: Thus; bysuitably'adjusting'the axial position of dielectric mass t6; the impedance-value Z impressed to the left terminal of the device could be transformed into an impedance value Z" at the left edge of the dielectric mass l6; This impedance: value 'Z" isthen transformed to" an impedance value 2' at'theright ed'ge' of the dielectric mass" l6'by 'adjustingscrew 2|", and the' furtherv section of concentric line H, l21t'o the rlghtof 'di'electriemass I6 will then transform this impedance value Z' into the required impedancel value Z. Thus the impedance value-Z istransformed into. another'impedance valuez. Although the above description has stated that: the leading edge-or. left edge ofrdiclectric mass lfiiwas. perpendicular to the axial dimension. of

the. device; it is to be notedthatthis need not- Rather, the dielectric mass may be -made isosceles triangular or maybehe made strictly thus.

made to have any desired contour; without changing the qualitative correctness of the explanation: given above. A changein the'contour will merely change. the relationship between. an

angular displacement of, knob 21 andits efiect:

upon impedance-matching: By suitable choice of this contouncptimum facility in adjustment. may be derived.

Also;.the impedance element of valueZ tober transformed: need not: be connected to: the left' end of the device; as-assumed abovefor; purposes of illustration, but maybe connected at either end. Accordingly, I have shown. an improvedform of" impedance; transformer which: does" not;

need. any sliding: metallic contacts: and: which is: adaptedto easily: and simply transform one impedance value i-ntora. second impedance value;

Asmany: changesz couldibe' made in the above construction" and many apparently widely different embodimentsof this: invention could-ber'made withoutdepartingfrom the scopev thereof,. it is intended that all-matter contained'in the above description-or shown in'the accompanying drawingsshall be I interpreted as illustrative and not in a limiting-isense:

WhatI' is claimed'ist 1. An; impedance: matching transformer com' prising section of coaxial transmission-- line adapted to-be'connected" between the circuits to be matched in impedance, a dielectric mass of contour variable in a direction along the axis'of said" line and adapt'ecl'to be inserted between in her and: outer conductors ofsaid line; means for adjusting said dielectric mass transverselywith respect to said'line section-whereby an adjustable length of said dielectric mass appears between said conductors; and meansfor adjusting the positionofsaiddielectric mass along said linesec--- ticn, whereby said circuits may be matched in impedance: by adjusting: the; longitudinal-1f and;

transverse positions of. said: dielectric massa.

2; impedance: matching:- transformer: coma prising: a1.v section: of coaxial transmission line.- adapted towbe connected. between two circuits. to be matched in impedance; means .for inserting an: adjustable length of dielectric material between; the inner andouter conductors of'said line, and" means for adjusting the; position of; a predetermined length of said: dielectric material. along:

saidline whereby: said circuits may be matched in impedance by adjusting the inserted length:

and posi-tion of" said dielectric material;

3; An impedance matching transformer comprising a: section-off transmission line having an. impedance element ofarbitrary impedance value. connected ati'onez endthereof, and means forv producing an arbitrary desired impedance valuemeasured at the other end of said section, said; last-named means comprising means icr insert- .ing an-adj'ustable length of dielectric material" in said line section; and means for adjusting the position of a predetermined length of said di el'ectricmaterial 'along sai'd'line section, whereby said desired imp edance value may :beobtained' 'by' adjusting the inserted: lengthand position of said" dielectric material';

a; An impedance matching transformer comprising a section o-f transmission line adapted to have acircuit" element: of arbitrary impedance value connected atone end: thereof, and means for producing an arbitrary-desired impedance value measured'at the-other end-of said section, said last-named means comprising: a dielectric mass: of: contour variable in a direction along said line section, and means for inserting said" mass in saidline section intermediate the endsthereof and for adjusting the transverse position of said mass with re-spect'to said line section; wherebythe length ofdielectric mass between said conduct'orsmay be adjusted to pro-- duce said desired impedance value.

5'; An impedance matching transformer comprising a section of hollow-conductor transmission' line having a predetermined characteristic impedance when containing only air and adapted to have an element of arbitrary impedance v value connected'at one end thereof; and means for producing an arbitrary desired impedance valuemeasured'at the other end of said section,

said last named means comprising a dielectric mass having'avarying dimension parallel to saidline section wherebythe axial extent of theporti'on of'line; whose characteristic impedance is affected by the dielectric mass, is a function of said'varying dimension; said varying dimension extending ior a: substantial portion of the axial 1 extentof said dielectric mass, said dielectric mass being positioned inter-mediate the ends of' said hollow conductor transmission line witha preselected -'value of said dimension interposed within said transmission line, and means for adjusting the-position of= saiddielectric' mass along said section; whereby said desired impedance may be produced;

6: An impedance transformer comprising a section of hollow-conductor transmission line having a predetermined characteristic imped ance, said transmission line section being adapted to b'e connect'ed'atoneendto-a device having a first-impedance value and at the other end to a device having'a second impedance value; a dielectric mass in said line section and intermediate said devices, said dielectric mass having avari'abl'e dimension parallel to said line section whereby the axial extent of the portion of line section, whose characteristic impedance is affected by the dielectric mass, is a function of said varying dimension, said varying dimension extending for a substantial portion of the axial extent of said dielectric mass, and means for adjusting the position of said dielectric mass with respect to the conductors of said line to match said two impedance values connected to the ends of said line section.

7. An impedance matching transformer comprising a transmission line section of a first characteristic impedance adapted to be connected between a pair of devices having impedances to be matched, means for modifying a portion of said section to form thereof a transmission line portion having a different characteristic impedance from said first characteristic impedance, means for adjusting the length of said portion, and means for adjusting the position of said portion along said section, whereby said two impedances may be matched by adjustment of said adjusting means.

8. An impedance transformer comprising a first air-filled transmission line section having a predetermined characteristic impedance, a sec ond air-filled transmission line section having the same characteristic impedance as said first line section, a third line section intermediate said first and second sections and having dielectric means therein defining the axial extremes of said third line section, said dielectric means being adjustable to vary the separation of said axial extremes and thereby varying the axial length of said third line section, said dielectric means being also axially adjustable for altering the axial position of said third line section relative to said first and second sections.

9. An impedance transformer comprising a transmission line having a hollow conductor, dielectric means intermediate the ends thereof and having a pair of boundary surfaces separated along the axis of said conductor, at least parts of said surfaces being within said hollow conductor, said dielectric means being adjustable to vary the axial separation of the boundary surfaces within said hollow conductor and also being adjustable to simultaneously move the boundary surfaces within said hollow conductor axially of said line and in the'same direction, whereby by adjustment of the separation and position of the boundary surfaces within said hollow conductor an impedance value presented at one end of said line may be transformed to an arbitrary desired value at the other end.

10. An impedance transformer comprising a transmission line section having at both ends a predetermined characteristic impedance, di: electric means for modifying a portion of said section to form a transmission line portion intermediate said ends having a different characteristic impedance, and means for adjusting the position 'of said portion within said section, whereby a device of given impedance Value connected to one end of said section may produce a desired impedance value at the other end of said section.

'll. An impedance transformercomprising a transmission line section having a predetermined characteristic impedance, dielectric means for modifying a portion of said sectionto form a transmission line portion having a different characteristic impedance, and means for adjusting the length of said portion, whereby an arbitrary impedance value appearing at one end of said first section may be transformed to a desired impedance value at the other end of said first section.

12. An impedance transformer comprising a section of transmission line of predetermined characteristic impedance interposed in cascade relation along further sections of transmission line of different characteristic impedance, means for adjusting the length of said first-named section, and means for adjusting the positioning of said first-named section with respect to said further sections, whereby an arbitrary impedance value appearing at one end of said further sections may be transformed to a desired impedance value at the other end of said further sections.

13. An impedance matching transformer for coupling a source of high-frequency energy to a load, comprising-a transmission line having two conductors, means for connecting said line at one end to said source, means for connecting said line at the other end to said load, means for inserting an adjustable length of dielectric material between the conductors of said line, and means for adjusting the position of a, predetermined length of said dielectric material along said line, whereby said source and said load are efliciently matched. 1

14. An impedance matching transformer for coupling an alternating-current source to a load, comprising a transmission line section having two conductors adapted to be connected between said source and said load, a dielectric mass of contour variable in a direction along said line section, means for inserting said mass between the conductors of said line intermediate said source and said load and for adjusting the transverse position of said mass with respect to said line section, whereby the length of said dielectric mass between said conductors may be adjusted to match said source and said load.

15. An impedance matching transformer for termination by a load of a finite impedance value adapted to be supplied from a source having a second impedance value, comprising a section of transmission line having two conductors, means for connecting said line at one end to-said load, means for connecting said line at the other end to said source, a dielectric mass of adjustable effective electrical length positioned between the conductors of said line section intermediate said load and said source, and means for adjusting the position of a predetermined value of the effective electrical length of said dielectric mass along said section, whereby said impedance values may be matched by said adjustment.

16. Apparatus for presenting a predetermined input impedance value when terminated by a load of finite impedance value, comprising a section of transmission line having two conductors, means for connecting said conductors at one end to said load, a, dielectric mass between said conductors, and means for adjusting the length and position of said dielectric mass between said conductors to vary said input impedance value.

1'7. An impedance transformer for presenting a predetermined input impedance value to an alternating current source when terminated in a load of finite impedance value, comprising a section of transmission line having two conductors, means for connecting said transmission line section at one end to said load, and a dielectric mass of adjustable electrical length variably positioned between said conductors intermediate the ends of said line for adjusting the input impedance value of said line by adjustment of the electrical length and position of said mass.

18. An impedance transformer for presenting a predetermined input impedance value to an alternating current source when terminated in a load of finite impedance value, comprising atransmission device of a fixed overall length in cluding three cascade-connected variable length transmission line sections, wherein a first of said sections for connection to said load has a first characteristic impedance, the second of said sections connected to said first section has a second characteristic impedance, and the third of said sections connected to said second section and providing the input terminal of said device has a characteristic impedance equal to said first characteristic impedance. I

19. High frequency apparatus comprising a transmission line section having coaxial outer and inner conductors, said outer conductor having an opening formed in the sidewall thereof, a low-conductive element, and means for adjust ably inserting said element through said opening into the transmission line section, said means providing adjustment of at least a portion of said element transversely of said line for a distance greater than that separating said conductors.

20. High frequency apparatus comprising a transmission line having coaxial and spaced inner and outer conductors and having a predetermined characteristic impedance, said outer conductor having an opening therein, an element in said opening and adapted to change said predetermined characteristic impedance upon insertion between said conductors, and means conpled to said element for providing adjustment of at least a portion of said element through the region adjacent said inner conductor and for a distance longer than the distance between said conductors.

21. High frequency energy transmission apparatus comprising a section or coaxial transmission line including an axially slotted outer conductive member and a coaxial inner conductive member, and a dielectric body of variable axial contour adjustably supported within said slot for transverse movement with respect to said inner and outer conductive members.

22. High frequency energy transmission apparatus comprising a section of coaxial transmission line including an outer conductive member and an inner conductive member; said outer member being axially slotted over fa predetermined portion thereof, a dielectric body of variable axial contour, and means adj ustably supporting said dielectric body within 'said slot for transverse and axial movement with respect to said inner and outer conductive members.

23. High frequency energy transmisison apparatus comprising a, section of coaxial transmission line including an axially-slotted outer conductive member and a coaxial inner conductive member, a wedge-shaped dielectric body having a continuously variable dimension parallel'to-the axis of said coaxial line section and a recess extending perpendicularly to said axis for receiving the inner conductive member when said dielectric body. is inserted within said transmission line "section, and means adjustably supporting said dielectric body within, said trans- .mission line section for transverse and axial movement with respect to said inner and outer conductivemembers, whereby a predetermined desired axial length of dielectric body may be selectively positioned relative to the ends of said line section in accordance with adjustment of said supporting means.

EDWARD L. GINZTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,927,393 Darbord Sept. 19, 1933 2,125,597 White et al. Aug. 2, 1938 2,127,408 Kaar Aug. 16, 1938 2,157,855 Koch May 9, 1939 2,192,494 Goddard Mar. 5, 1940 2,297,266 Vieweger Sept. 29, 1942 2,297,516 Walter Sept 29, 1942 2,373,233 Dow et a1 Apr. 10, 1945 2,408,745 Espley Oct. 8, 1946

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