US2428485A - Impedance matching device - Google Patents

Description

Oct. 7, 1947. P. s. CARTER IMPEDANCE MATCHING DEVICE 2 Sheets-Sheet 1 Filed June 30, 1945 BY l ATTORNEY Oct. 7, 1947. P. s. CARTER IMPEDANCE MATCHING DEV'ICE Filed June 30, 1943 2 Sheets-Sheet 2 QQ 0, W. n.

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ATTORNEY Patented Oct. 7, 1947 IIVIPEDANCE MATCHING DEVICE- Philip S. Carter, Rocky Point, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application June 30, 1943, Serial No. 492,835

8 Claims.

The present invention relates to transmission line circuits and, more particularly, to circuit elements adapted to be inserted in transmission lines for the purpose of impedance matching.

An object of the present invention is the provision of an impedance matching device which may be conveniently inserted at any desired point in a coaxial transmission line.

Another object of the present invention is the provision of an impedance matching device which may be conveniently inserted at any desired point in a coaxial transmission line utilizing a solid dielectric.

Still another object of the present invention is to facilitate the matching of a radio frequency load to a transmission line utilizing 'a solid di,`

electric between its conductors.

- A further object of the present invention is the provision of an impedance matching device utilizing series and shunt reactance elements constituted by transmission line sections.

A further object of the present invention is the improvement of the operation of radiant energy transmission systems.

Still a further object of the present invention is the provision of an impedance matching device for coaxial lines which does not require the use of slotted conductors or trombone slides.

The foregoing objects, and others which may appear from the following detailed description are attained in accordance with the principles of the present invention by providing in a single compact structure an adjustable Series reactance adapted to be connected in series in a transmission line and an adjustable shunt reactance connected across the transmission line at one end of the adjustable series reactance.

In a modification of the present invention it is contemplated providing series reactances on each side of the shunt reactance in order to avoid the necessity for reversing the circuit t match any type of load.

The present invention will be more fully understood by reference to the following detailed description, which is accompanied by a drawing in which Figure 1 illustrates, in sectional View, an embodiment of the present invention, while Figure 2 illustrates, in section, a modification of the present invention, while Figures 3 and lare curves useful in adjusting the embodiments to predetermined operating conditions.

Referring, now to Figure 1, there is shown anY embodiment of the present invention which is adapted to be inserted at any predetermined point in a :coaxial transmission line having a solid dielectric between the conductors by means of conventional coupling arrangements utilizing threaded rings I0 and 20 for connection to the outer conductor of the transmission line and central'jack connectors II and 2| adapted to contact the central conductor of the transmission line. rThe connectors II and 2| may be maintained in alignment by insulating spacers II The impedance matching device is contained Within outer cylindrical casing I3 closed at its end by conductive end plates Il! and I5. Within the outer casing I3 there is contained an inner tubular conductive member I6, conductively connected to end plate I4 at one end and bearing at its other end the jack connection H t0 which one of the central conductors of the transmission line is connected. Within the tubular member I6 there is arranged an innermost conductor in the form of an extension of jack 2| coaxially disposed with respect to tubular member I6. The extended conductor portion of 2I may, if desired, 'be conductively connected to end plate I4 of the outer casing as, for example, by plate ill), Which has another purpose to be later described, though this connection is not necessary to the operation of the invention. Between the inner surface of tubular conductor I6 and the outer surface of y elongated conductor 2| there is provided a shorting diaphragm 22 adapted to be slidably adjusted along the length of tubular conductor I6, thus connecting conductor 2| and the inner surface of conductor I6, together at any desired point. The outer surface of tubular conductor I6 is adapted to be connected to the interior of cylinder I3 at any point along the length thereof by means of an annular conductor ring II.

In Figure 1 a shunt impedance element across I!) and II is provided by the concentric line section constituted by the inner surface of cylinder I3 and the outer surface of tubular member I6. Ihe magnitude and sign of this impedance may be adjusted by moving the annular conducting ring I'I up or down along the length of tubular conductor member I6. Likewise, a series impedance element appears between the upper end of tubular conductor I6 and the extreme end of conductor member 2l Where it connects to the inner conductor of the associated transmission line. The magnitude and sign of this impedance may likewise be varied by shifting the annular conductor or diaphragm 22 along the length of interior of tubular member I6. Thus, if the effective length of either of these concentric line sections is of the order of one-quarter of the operating wavelength, an effectively iniinite impedance appears across its terminals while if the length is of the order of one-half wavelength the impedance is substantially zero. The impedance is likewise extremely low approaching Zero for zero line length. Thus as the length of either section is varied from zero to one-quarter wavelength the impedance varies from zero to infinity and is inductive while as the length .is further increased to one-half' wavelength the impedance is capacitive and varies from infinity to zero. Thus, by a combination of the variable shunt rem4 actance and the variable series reactance any given load may be conveniently matched to a given line impedance.

In Figure l I have shown a preferred method of adjusting the position of conducting ring I1 which includes a threaded sleeve I8 carriedon translational motion along the outer surface of cylinder I3. The translational motion isv pro'- vided by a nut 26 engaged in the threads of sleeve I8', the nutbeing supported for rotational moye-l ment only on anv outer supporting sleeve I9 by means of' a bearing ring 25 which isl preferably knurled on its outer surface for convenience in rotating. An edge of the member 25 may be suitable graduated' to indicatefra'ctions of a turn whileA axial graduations may be provided along the outer surface of tube I3 in order to provide a means for duplicating or reproducing thel posi.. tioning of the interior conducting ring I'T, as desired. The-ring IT is compelled `to move alongV the length of cylinder I3 as threaded sleeve I81i's moved by the screws 21, passing through elongated -slots 28 in the cylinder I3'. The screws also preventring I'I from rotating as ring 25i's turned. In order ,to provid'efgoodcontact be tween ring I1' and the outer surfaceotubular;

member` IS a'springfarrangement 29'fmay be--pro'-` vided-within an annulargroove on the-inner surface of ring IT.. It is preferred' that the spring arrangement be arranged like that shownV in Patent #2,280,728; granted' April 21, 1942,' t0 Streib on application #305.871, led November 24, 1939, though othery arrangementsl forrobtaining good electrical connection between they ring' and cylinder may be used if' desired. A- somewhat similar arrangement is provided for movingthe shorting member 22 `along the lengthV of'conductor 2I within the interior of tube I6. In this case, however, the inner tubular member 2| ha-sy elongated slots 38 alongr its length and a'threaded` screw 32 is carried within its hollow interior. On the threaded screw is carried a nut 3|V which is coupled to ring 22 by means of screws'2'l passing through ring 22 and into nut4 3I. Screw 32 has at its lower end an adjusting .knob 33 by mean-s of'rwhich' screw'3 2 isrotated. Some means are provided" to prevent longitudinal motion of the screw 32; This means may includeY a recess within plate 40 which engages a ring 4IV secured. to-screw-32x Ihusy ring 4I' bears against either endy plate I4 orl plate 4U; depending upon the direction of rotation ofthe screws; An adjusting knob 3-3 may be providedV with indicating means for convenience in' readjusting -thei position of shorting ring 22' to any-predetermined position.

"I'hev modification of the present invention shown inl Figure 2 is, in its lower portion, exactly as describedwith reference to Figure 1k and the same reference characters have been employed.` However, the outer casing I3 is extended upwardly adifstanceequal to a half wavelength andltheinn'er' conducto-r-v I'Iis also extended upwardlyi withinthewcasing I3`as1an extension I6'vr connected Vto the `end'wall IfEPatAitsupper end'.

In this modification themember Il, which engages the central conductor of the transmission line, is continued on as an extended conductor 42, extending inside of tubular conductor IE and connected to the interior of tubular member IIS' by means of an adjustable shorting ring 22.

The position of shorting ring 22 along the interior ofi tubular rmember I6 is adjusted;` by an adjusting knob 33" operating feedl screw 32' in the same way as adjusting knob 33 in the modi- `i'lcation of Figure 1 and, likewise, in the lower portion ofFigure 2. Y

Shorting ring I1 connects the inner surface of, outer shell |13 and the outer surface of tubular A member 161 in the-same way as ring I1 connects shell I3 and-tubular member I6. Since the impedance of. the. line section formed by shell I3l and tubular member IS is in shunt with that formed by' shell I3 and tubular member I6, it is preferable that the length of this section be adjusted to one-quarter of the V'operating wavelength and all matching operations carried out; by adi justingonly ring jI'I. Therefore, ringITI' may-v be;y permanently -Xed vinronez locationl orxit `may; bez arranged to be moved b-y inserting threaded rods through@ apertures Y5I] in. endvplatef I5' and'screwi-v ingthem'into threadedholes 54. Afterrfthe proper:v adjustment is attainedthe rods may be removed.

It will bei seenv that the modification vof* Figure. 2 may beinserted in .avconcentric line,rthe1shunt. reactance adjusted to. the required value. and; either knob 33' or knobv 33 adjusted to; ,interposd a series reactance of the desired values on..either' sidevofV theV shunt reactancey withoutyrequiri'ng the.- reversal. Aoi the structure, or; if desired.. soma'.

series reactancemay be. inserted'. on; each side.`4 of the shunt reactance..

The impedance; matching deviceasf Aso.. far described may be adjustedv .inf practice :by-trialiand, error. to,- determinefthe properv settings for minii.

mum reflectionon `,the lines or vtheucurves ofligaV ures 3 and4'ma-y-besused if desired. Thefcurves present in graphical. form the results of compu'- tations as to the quantities-tofberad'dedto aline.

Y tomatch-af given load.V Y

line'formed by conductor 2l and member IIimayrA be determined for any ratio by curveY 6I' while'.` the length of the outer short line uformed by'shell Il: andv member Iii-may be determined l'from curve; 1

The second combination is shown by the :dotted curves 62 and 12. Thus the dotted curve `62gives the lengthfof the innerseries line vwhile dotted curve 'I2 gives the-length ofthe outer shuntrline' for the required impedance. The` same curves; hold wheny ther load resistanceis lower. than the surge impedance of the line if the circuit is re-` versedzand we use the resistance looking ,towardv the'gerlerator` as the load resistance.V

When the equivalent7 load presented by the transmission line at the device andlooking 'to-'v ward the load is a pure resistance there' is no preference as to which pair of thetwo combinations arerused. However, in general the equivL alent load at the devicewill have "a reactive com'` ponent and in such circumstances the combination requiring the minimum addition of shunt susceptance is preferred since by choosing this combination the losses in the device are minimized. In the general case it is desirable to consider the quantities which must be added to the load to match the line. It simpliiies matters if we consider the equivalent load of the line at the device looking toward the load as a parallel circuit of conductance g1 and susceptance Y1. If the susceptance is positive the combination using series inductance is preferred since the susceptance of the equivalent load is then made to serve as part of the required shunt admittance.

Figure 4 displays the ratios of series reactance X to line impedance Zo and shunt susceptance b to line admittance Yo plotted against the ratio of load conductance g1 to line admittance Yo when the conductance looking toward the load is less than the surge admittance of the line. When the conductance component of the load admittance is greater than the surge impedance of the line the same curves hold true if in place of the admittance looking toward the load we use the admittance looking toward the generator. The equivalent admittance of the line at the device may easily be determined by sliding meter arrangements. Then for a determined ratio of load conductance Y1 to line admittance Yu from curve 63 the susceptance which must be added by the second section may be determined and from curve 64 impedance which must be added by the series section may be determined. Then from known relationships of the reactive properties oi short-circuited line sections, the required length' of each line section may be determined.

While I have illustrated a particular embodiment of the present invention, it should be clearly understood that it is not limited thereto since many modications may be made in the several elements employed and in their arrangement and it is, therefore, contemplated by the appended claims to cover any such modications as fall within the spirit and scope of the invention.

I claim:

1. An impedance matching circuit adapted to be inserted in a coaxial transmission line having an inner conductor and an outer sheath conductor and including adjustable series and shunt reactance elements, said series element being connected in said inner conductor of said line, each of said elements including short-circuited coaxial transmission line sections of adjustable length coaxially arranged, said series element being within said shunt element.

2. An impedance matching circuit adapted to be inserted in a coaxial transmission line and including adjustable series and shunt reactance elements, each of said elements including short-circuited coaxial sections of adjustable length, each of said sections including an inner conductor and an outer shell, said sections being coaxially arranged with the outer shell of said series element forming the inner conductor of said shunt element.

3. An impedance matching element including an outer casing, a tubular conductor member and an inner conductor all coaxially arranged with respect to one another, means for connecting said outer casing and said tubular conductor member together at a selected position intermediate their ends, means for connecting said tubular conductor member and said inner conductor together at a selected position intermediate their ends, a pair of input connections and a pair of output connections, one of each of said pairs of connections being connected to said outer casing, one end. of said tubular conductor member being connected to one of the remaining ones of said connections and one end of said inner conductor said outer casing and said tubular conductor'4 member and movable along the length thereof,

a second conductive ring between said tubular conductor member and said inner conductor and' movable along the length thereof, a pair each of input and output connections, one connection of each pair being connected to said outer casing, one end of said tubular conductor member being connected to one of the remaining of said connections and one end of said inner conductor being connected to the other of the remaining of said connections.

5. `An impedance matching element including an outer casing, a tubular conductor member and an inner conductor all coaxially arranged with respect to one another, a conductive ring between said outer casing and said tubular conductor member and movable along the length thereof, a second conductive ring between said tubular conductive member and said inner conductor and movable along the length thereof, a pair each of input and output connections, one connection of each pair being connected to said outer casing, one end of said tubular conductor member being connected to one of the remaining of said connections and one end of said inner conductor being connected to the other of the remaining of said connections.

6. An impedance matching element including an outer casing, a tubular conductor coaxially arranged within said casing and a pair of inner rods arranged in coaxial end to end relationship within said tubular conductor, said tubular conductor having a pair of apertures therein at its midpoint, means for connecting each inner rod to said tubular conductor at selected positions along the length thereof, means for connecting said tubular conductor to said outer casing at a pair of selected positions at each side of the midpoint of said tubular conductor, a pair each of input and output connections, one of each of said pair of connections being connected to said outer casing and the remaining connections being connected to each of said inner rods at theiradjacent ends and passing through the apertures in said tubular member.

7. An impedance matching element including an outer casing, a tubular conductor coaxially arranged within said casing and a pair of inner rods arranged in coaxial end to end relationship within said tubular conductor, said tubular conductor having a pair of apertures therein at its midpoint, a. conductive ring between each of said inner rods and said tubular conductor and movable along the length of said inner rods, a pair of other conductive rings between said tubular conductor and said outer casing, one of said other rings being movable along the length of said tubular conductor at each side of the midpoint thereof, a pair each of input and output connections, one of each of said pairs of connections being connected to said outer casing, the remaining connections being connected to each 7 otsaidinner rods atvtheir adjacent ends. and passing ythrough the apertures in said tubular conductor.'

8. An impedance matching element including an outer casing closed at eachend by conductivev end plates, a tubular conductor coaxially arranged, within said casing and a pair of inner rods arranged in coaxial end to end relationship Within said tubular conductor, said tubular conductor having a pair of apertures'therein at its mida point, a conductivefring between each of saidY inner rods and said tubular conductor and movable along the length of said inner rods, a pair of other conductive rings between said tubular conductor and said outer casing, onerof said other rings being movable along the length of said tubular: conductor at each side lof the midpoint thereof', a pair each rof input' and output'xconn'ections, one of each of said-pairs' of corinectionsbeing' connected to said outer' casing, rthe remaining connections being connected to each ofi-said innert rods at their adjacent ends and passingzthrough.

the apertures in said tubular' conductor..

PHILIPS. CARTER.

REFERENCES CITED,

The fol-lowing references are ofv recordIi-nfthe o file of Vthis patent:

UNITED STATES RATENTS Trevor V A Nov. 121, 1940

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