# Патент USA US2408746

код для вставкиoct. s, 1945. , « D. c. ESPLEY' '2,408,145 ' VARIABLE IMPEDANCE TRANSFORMER Filed Nov. 10, 1942 Fig’. 2. A7 Zo ....-A_.._ 8 7 ì Fig.v 3. Í \\\\\ Fig. 5. ì Mé , , 2,408,745 Patented Oct. 8, 1946 UNITED STATES PATENT OFFICE 2,408,745 VARIABLE IMPEDANCE TRANSFORMER Dennis Clark Espley, North Wembley, England, assignor to The General Electric Company Limited, London, England Application November 10, 1942, Serial No. 465,143 In Great Britain November 11, 1941 13 Claims. l This invention relates to impedance transform ers of the type in which part at least of the im pedance transformation is effected in a transmis sion line. The proposition upon which the action of such impedance transformers depends is this. Let a load impedance Z be connected to given input terminals through a transmission line or a set of transmission lines connected in series; then by a suitable choice of the length and char acteristic impedances of the line or lines, the input impedance looking into that end of the transmission line which is connected to the given input terminals can be given any assigned value Zn. When the suitable choice is made, the line or lines are said to transform Z to Zn. The object of this invention is to produce a I simple and convenient variable transformer of this type. In accordance with one form of the invention, a variable-impedance transformer of the type in ~ which part at least of the impedance transforma tion is effected in a transmission line comprises a transmission line having a first pair of termi nals adapted to have coupled thereto an imped ance of a first value and having a second pair of terminals at which it is desired that the first value of impedance be transformed by the line to a second value of impedance. The transformer includes modifying means readily slidable along ‘the transmission line in the operative condition thereof to modify the characteristic impedance of at least two substantial parts of the line which parts have positions along the line selectable by movement of the modifying means. Also in accordance with the invention, a high frequency impedance-matching device adapted for connection between and for matching at a_ given frequency a, plurality of impedances having 2 Fig. 1 is an explanatory diagram of a trasmis sion line, , Fig. 2 shows diagrammatically one embodiment of the invention, and Figs. 3, 4, 5 and 6 show diagrammatically parts of alternative embodiments, given by Way of ex ample. The principle underlying the invention will now be described with reference to Fig. 1, which shows a transmission line which, in the absence of the means for modifying its characteristic imped ance, has a characteristic impedance Zu; the wave-length of the oscillations translated by the line, where the characteristic impedance is Zo, is l. At the left hand end the line is shownin conventional manner as being terminated by the complex impedance R14-irl. The portions of the line between the sections B, C and D, E thereof are each modified so that they have character istic impedance Z1; the lengths of these sections are each A74, where i’ is .ther wave-length of the oscillations in these sections. Sections C and D are separated by a space of length l1 over which the characteristic impedance of the line is Z0. In order that the line may be matched to an im pedance Z0 at the right hand end, the impedance ZE looking into the section E towards the left must be Z0. The problem is to determine the conditions under which this condition can be ful filled by adjusting suitably'the distance l1 between the two modified parts of impedance Z1 of the line and the distance of the section B from the left-hand end of the line. The known proposition appropriate to the prob vl lem is this. » Consider two sections U and V across a uniform transmission line of characteristic im pedance Z, these sections being separated by a distance .'12 positive in the direction from U to'V. Then if ZU, Zv are the impedances looking into any values within a substantial range of magni-l 40 these sections in the direction in which :c is posi tude and phase comprises a plurality of substan tive tially parallel .conductors adapted to be connected between the impedances and having a predeter mined characteristic impedance within the afore said range between a predetermined pair of the aforesaid conductors. The device includes a plu rality of means between the conductors and indi ZV'i'jZ tall ßx Z”‘Z(Z+jzv' an ß.) ‘(1) where ß=21r/i\ and i is the wave-length of the oscillations along the line, . vidually adjustable axially therealong, each of the It is a consequence of Equation 1 that some section A can be found, distant a: from the left adjustable means 'being of such shape and mate rial as to alter the aforesaid characteristic im the impedance looking to the left is wholly real, pedance for matching the resistive components and canceling the reactance components of the aforesaid plurality of impedances over the afore said range of values. In the accompanying drawing: hand end of the line shown in Fig. 1, at which say R. It is sufficient therefore to discuss how, if at al1, the distance l between the sections A, B and the distance l1 may be adjusted so as to transform the real impedance R at A into the impedance Zo at E. Applying Equation 1 to the 2,408,745 3 4 region Íbetween sections A and B, the impedance at B looking to the left is given by R-i-ÍZU Zn’i‘jR tall tan might vary continuously along the line; but no advantage is known in this suggestionLastly there might be more than two modified h sections. By this means the range of the ratio of’ transformation corresponding to a given 7c can be increased, but the difficulty of adjustment to give a desired ratio increases also. For when Applying Equation l to the region between sec tions B and C, the impedance at C looking to the left is given by Z2 20:27; there are only two modiñed sections, two variables l and Z1 have to be adjusted; the adjustment has to be made by double trial and error, ‘ke the adjustment of a bridge to balance for both A. C. and D. C. This is feasible, but the adjustment would be very laborious with (say) three modl ñed sections and three variables. (3) Applying Equation 1 to the region between sec tions C and D, the impedance at D looking to the left is given by Zeri-.izo tall ßli Finally for ZE ZDIZWOMZC tan et Those skilled in the art will realise how the characteristic impedance of the line may be modi ñed at adjustable places. One method is to pr=2-~ vide blocks, slidable along the line, and of a ma terial having a permittivity whose ratio to the (4) __ZÍ Z,.ZD <5) Putting ZE==Zu, eliminating ZB, Zo and ZD from (2), (3), (4), (5), and writing lc=Zn2/Z12 perrnittivity of the medium intervening between the conductors on the unmodified part of the line is K, and substantially different from 1. Then, if the dielectric fills all the space occupied by the oscillating ñeld 7c=K. Suitable materials are known for which K=2.5 relative to air; hence if there are two blocks, each 7\’/4 long, the ratio (6) of transformation can be varied over a range (2.5) 4 to l, i. e. about 40 to l. Equating real parts and imaginary parts, In the embodiment shown in Fig. 2 the line is 30 concentric and the modifying means are dielec tric blocks. I and 2 are inner and outer members of a concentric line, which has the characteristic (ZO- kilt) (R- k2Z0) In order that the desired transformer ratio may be possible, l and Z1 must be real, and the right- ., hand sides of both (7) and (8) must be posi tive; that is to say (Zu-ICZR) and (R~lc2Zo) must the load impedance connected to one end of the line. 5 and E are similar blocks, each made of the material known commercially as Distrene, which be of the same sign, which implies has a dielectric constant K relative to air of about 2.5. The length of each is A74 where A’ is the 40 'wave-length of the oscillations in the block; if Accordingly the values of R that can be transformed to Zo by an appropriate choice of l and l1 cover a range, geometrically centered upon Zo, of hr4 to 1. There is a corresponding range of A is the wave-length in the absence of the block, the length is A/‘iKlá Each block is slidable along the line by means of threaded pins 1 projecting through slits in the member 2 at opposite ends possible values of R1+7`X1. of a diameter. When they are adjusted, the blocks are then clamped in place by means of nuts â on The invention is not confined to the use of a uniform transmission line or to the modification of it in the manner assumed in the foregoing argument. A completely general theory would be impedance Z0 in the absence of the blocks. The rectangle marked Z indicates diagrammatically the threaded pins 1. If the ratio of the internal diameter of the member 2 to the diameter of the member l is 3.5 to 1, Z0 will be 75 ohms and any load resist ance between 12 and 470 ohms can be transformed to '75 ohms when the ‘blocks 5 and 8 have the length and composition last described. Other methods of modifying the characteristic .. impedance of the line at adjustable places are shown in Figs. 3 to 6. Fig. 3 shows a metal sleeve 9 slidable along the inside of the outer conductor of a concentric line and Fig. 4 shows a metal sleeve I0 slidable along the outside of the inner con 60 ductor of a similar line, IDA denoting a shifting very complicated and would be of little or no value A in practice. Accordingly only a _few other ways of modifying the line will be mentioned specifical~ ly. If the modified sections of the line were again two in number and each of the same char acteristic impedance, but each of length x78, the range of values of R that could be trans~ formed to Zn would be k2 to 1. Again if the modi~ fied sections were each of length i’/4, but had diiîerent characteristic impedances Z1 and Z2, then the said range would be k12lc22 to l, where and locking member of insulating material. Again `the lengths of the two modified sections need not be equal. Again the line in the absence of the modifying means need not be uniform; it may be modified permanently at certain places, so as tu have a different characteristic impedance at these places; these places may lie between two movable modified sections or outside both of them. In particular a modified section having a length 10W/2, where A" is the wave-length in the sec~ tion and n is an integer, may obviously be intro duced anywhere along the line without substan~ tially modifying the foregoing theory. Indeed the characteristic impedance of the modified line Since such sleeves will decrease the ratio of the inner diameter of the outer conductor to the outer diameter of the inner conductor, the characteris tic impedance will be decreased. Fig. 5 shows a parallel line lA, 2A having a metal sleeve I l slid able on one conductor, and Fig. 6 shows a similar line having a dielectric block l2 slidable on both conductors. I claim: l. A variable impedance transformer of the type in which part at least of the impedance trans formation is effected in a transmission line com prising, a transmission line having a first pair of terminals adapted to have coupled thereto an 2,408,745 5 impedance of a first yvalue and having a second a first pair of terminals adapted to have _coupled pair of terminals at which it is desired that said first value of impedance be transformed by said line to a second value of impedance, and modify ingmeansreadily slidable along said transmis thereto an impedance of a first value and hav ing a second pair of terminals at which it is de sired that; said first value of impedance be trans formed by said line to a second value of im sion line in the operative condition thereof to pedance, two modifying elements disposed with modify the characteristic impedance of at least in the outer conductor of said line for modifying two substantial parts of >said line which parts have positions along said line selectable by move the characteristic impedance of two substan tial parts of said line, and means extending out of said outer conductor for independently vary ing the positions of said elements along said line. ment of said modifying means. 2. A variable impedance transformer of the type in which part at least of the impedance transformation is effected in a transmission line comprising, a transmission line having 'a first pair of terminals adapted to have coupled there 7. A high-frequency impedance-matching de vice adapted for connection between and for matching at a given frequency a plurality of im pedances having any values within a substan tial range of magnitude and phase comprising, a to an impedance of a first value and having a Second pair of terminals at which it is desired that said first value of impedance be transformed by said line to a second value of impedance, and plurality of substantially parallel conductors adapted to be connected between said impedances and having a predetermined characteristic im pedance within said range between a predeter mined pair of said conductors, and a plurality of blocks separately slidable along said line and of ‘ a permittivity different from that of the medium intervening between the conductors along the un means between said conductors and individually modified part of the line, said blocks constituting modifying means whereby the characteristic im adjustable axially therealong, each of said ad justable means being of such shape and materials pedance of at least two substantial parts of said ‘f’ as to alter said characteristic impedance for line may be modified. matching the resistive components and cancel ling the reactance components of said plurality 3. A variable impedance transformer of the type in which part at least of the impedance of impedances over said range of Values. transformation is effected in a transmission line comprising, atransmission line having a first pair 1‘ of ‘terminals adapted to have coupled thereto an impedance of a first value and having a second pair of terminals at which it is desired that said 8. A high-frequency impedance-matching de vice adapted for connection between and for matching at a given frequency a plurality of im pedances having any values within a substantial range of magnitude and phase comprising, a plu first value of impedance be transformed by said line to a second value of impedance, and metal rality of substantially parallel conductors adapt ed to Fbe connected between said impedances and sleeves slidable along at least one of the con ductors constituting said transmission line, said sleevesconstituting modifying means whereby the characteristic impedance of at least two su‘b stantial parts of said line may be modified. 4. A variable impedance transformer of the 6 comprising, a concentric transmission line having having a predetermined characteristic impedance fl d means being of such shape and material as to type in which part at least of the impedance modify said characteristic impedance over at least one limited distance along said conductors for matching the resistive components and cancelling the reactance components of said plurality of im transformation is effected in a transmission line comprising, a transmission line having a first pair of terminals adapted to have coupled there- i to an impedance of a first value and having a second pair of terminals at which it is desired that said first Value of impedance be transformed by said line to a second value of impedance, and two blocks separately slidable along said line and of a permittivity different from that of the medi um intervening between the conductors along the unmodified part of the line, the length of each of said blocks being one-quarter of the wave length, in a modified part of the line, of the os cillations in connection with which the trans former is adapted to be used. 5. A variable impedance transformer of the type in which part at least of the impedance transformation is effected in a transmission line comprising, a transmission line having a first pair of terminals adapted to have coupled there pedances over said range of values. 9. A high-frequency impedance-matching de vice adapted for connection between and for matching at a given frequency a plurality of im pedances having any values within a substan tial range of magnitude and phase comprising, a hollow outer conductor and an inner conductor substantially coaxial therewith to- provide a trans mission line having a predetermined characteris tic impedance within said range and adapt ed to be connected between said impedances, and a plurality of means between said conductors and individually adjustable axially therealong, it) to an impedance of a first value and having a second pair of terminals at which it is desired that said first value of impedance be transformed v: by said line to a second value of impedance, and two metal sleeves slidable along at least one of the conductors constituting said line, the length of each of said sleeves being one-quarter or the wave-length, in a modified part of the line, of “' the oscillations in connection with which the transformer is adapted to be used. 6. A variable impedance transformer of the type in which part at least of the impedance transformation is effected in a transmission line within said range between a predetermined pair of said conductors, and a plurality of means be tween said conductors and individually adjust able axially therealong, each of said adjustable each of said adjustable means being of such shape and material as to alter said characteristic im pedance for matching the resistive components and cancelling the reactance components of said plurality of impedances over said range of values. l0. A high-frequency impedance-matching de vice adapted for connection between and for matching at a given frequency a plurality of im pedances having any values within a substantial range of magnitude and phase comprising, a hol low outer conductor and an inner conductor sub stantially coaxial therewith to provide a transmis sion line having a predetermined characteristic impedance within said range and adapted to be connected between said impedances, and a plural ity of independently axially adjustable means be 7 2,408,745 tween said conductors surrounding and substan' tially coaxial with said inner conductor, each of said adjustable means being of such shape and material as to alter said characteristic impedance for matching the resistive components and cancel ling the reactance components of said plurality of impedances over said range of values. l1. A high-frequency impedance-matching de vice adapted for connection between and for matching at a given frequency a plurality of im~ pedances having any values within a substantial range of magnitude and phase comprising, a plu rality of substantially parallel conductors adapt ed to be connected between said impedances and having a predetermined characteristic impedance within said range between a predetermined pair of said conductors, and a plurality of conductive annular means between said conductors and in dividually adjustable axially therealong, each cf said adjustable means being effective to alter said characteristic impedance over a limited distance along said conductors for matching the resistive components and cancelling the reactance com ponents of said plurality of impedances over said range of values. 12. A high-frequency impedance-matching de vice adapted for connection between and for matching at a given frequency a plurality of iin pedances having any values within a substantial range of magnitude and phase comprising, a hol~ low outer conductor and a cylindrical inner con 30 ductor substantially coaxial therewith to provide a transmission line having a predetermined char~ actertistic impedance within said range and adapted to be connected between said impedances, and a plurality of cylindrical conductive means between said conductors and individually adjusta ble axially therealong, each of said adjustable means being of such shape and material as to alter said characteristic impedance for matching the resistive components and cancelling the reactance components of said plurality of impedances over said range of values. 13. A high-frequency impedance-matching de vice adapted for connection between and for matching at a given frequency a plurality ol’ impedances having any values within a substantial range of magnitude and phase comprising, a plurality of substantially parallel conductors adapted to be connected between said imped ances and having a predetermined characteristic impedance within said range between a predeter mined pair of said conductors, and a plurality 0I dielectric elements between said conductors and individually adjustable axially therealong, each of said elements being of such shape and having such a dielectric constant as to alter said char acteristic impedance for matching the resistive components and cancelling the reactance com ponents of said plurality of impedances over said range of values. DENNIS CLARK ESPLEY.

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