US2557781A

US2557781A - Radio-frequency transmission line

Info

Publication number: US2557781A
Application number: US737619A
Authority: US
Inventors: Christiansen Wilbur Norman
Original assignee: Amalgamated Wireless Australasia Ltd
Current assignee: Amalgamated Wireless Australasia Ltd
Priority date: 1946-06-19
Filing date: 1947-03-27
Publication date: 1951-06-19
Anticipated expiration: 1968-06-19
Also published as: GB631742A

Description

June 19, 1951 w. N. CHRISTIANSVEN RADIp-F'REQUENCY TRANSMISSION LINE Filed March 27, 1947 INCREASE 6 BY uw m ATTORN EY Patented June 19, 1951 UNITED STATES toria,

Australia, assignor to Amalgamated Wireless (Australia) Limited, Sydney, New South Wales, Australia, a company of New South Wales Application March 27, 1947, Serial No. 737,619 In Australia June 19, 1946 6 Claims.

The present invention relates to radio frequency transmission lines and more particularly to means for matching the characteristic impedance of a pair of multiple-Wire lines to the characteristic impedance of a single multiple-wire line over a wide range of impedance values.

When open wire lines are employed for the transfer of high frequency energy from a transmitter to a remotely locamd antenna or from a receiving antenna to a remotely located receiver, it is desirable respectively to prevent radiation from and pick-up by the transmission line system.

In order to fulfill these requirements it has been the practice in the past to employ multiplewire transmission lines. This type of line comprises a plurality of conductors connected electrically in parallel for conveyingcurrent in one direction, and another pluralit of conductors for returning the current connected electrically in parallel, and so located that the loci of the electrical centres of both sets of conductors coincide. Since alternating currents are being dealt with, the directions referred to are instantaneous only. With such an arrangement there is no physical displacement between the opposite electrical charges and there is therefore neither radiation or collection of energy.

In transmission lines of this type, there are usually employed four parallel conductors arranged as at the corners of an imaginary square, and at each end of the line diagonally opposite conductors are connected together.

In certain applications involvin the use of multiple lines of the 4-wire type it is necessary to effect a satisfactory impedance matching connection between a single -wire line and a pair of similar lines connected in parallel. In the past when this requirement has arisen, and matching at a plurality of frequencies is involved, the desired connection has been achieved by the use of a broad band impedance matching transformer.

This prior art method of coupling a single 4- wire line to a pair of 4-wire lines, has not been entirely satisfactory because of resistance losses introduced into the system by this form of coupling and its liability to damage by lightning.

The principal object of the present invention is to overcome the above-mentioned disadvantages and provide a transmission line arrangement for matchin the characteristic impedance of a pair of four-wire lines without employing the conventional transformer.

A further object of the invention is to provide a transmission line arrangement whereby a pair of 4-w1're lines may be conductively connected to a single -wire line in impedance matching relationship.

The above objects are achieved in accordance with the present invention preferably by the use of a multiple-wire transmission line section interposed between the ends of the pair of multiplewire lines and the ends of the single multiple- Wire line, said transmission line section comprising a plurality of conductors equal in number to the total number of conductors in said pair of multiple-wire lines and arranged about a common axis at equal radial distances therefrom. The foregoing arrangement is such that the conductors of said line section are disposed about the circumference of an imaginary circle having a diameter at one end of said transmission line section equal to the diagonal dimensions of each of said pair of multiple-wire lines, the individual conductors of which latter are alternately and sequentially connected to separate and alternate conductors of said transmission line section at said one end. The diameter of said imaginary circle at the other end of said transmission line section is equal to the diagonal dimensions of said single multiple-wire line whose individual conductors are separately and sequentially connected to pairs of adjacent conductors of said transmission line section, the alternate conductors of said line section being simultaneously and progressively varied in the same direction of angular movement about the common axis of the said transmission line section to cause a variation in the spacing between adjacent conductors at opposite ends thereof.

For a more complete understanding of the invention and the manner in which it is to be carried out attention is now directed to the following description in connection with the accompanying drawing in which:

Fig. 1 is a diagram illustrating the placement of the conductors of a transmission line according to the invention; and

Fig. 2 is an illustration of a practical construction of a transmission line according to the invention.

In the exemplary arrangement covered by the following description, the invention provides a matching system for connecting a pair of l-wire balanced transmission lines to one 4-wire balanced transmission line. In its simplest form the invention involves running the two sets of 4-wire feeders along a common axis thus forming an 8- wire line. The impedance of this 8-Wire line may be readily varied by rotating one set of 4-wires with respect to the other set.

At the point in the system where the conductors of the two 4-Wire lines coalesce the

conductors

2, 4, 6, 8 of one line and the conductors 3, 5, I, 9 of the other line, are alternately arranged and symmetrically disposed in any convenient manner about at common axis to form an 8-wire line of octagonal cross section as shown in Fig. 1 of the drawing. Although in order to clarify the explanation of the invention, the conductors comprising the separate 4'-'wire lines" have been shown in the drawing of different cross section, it is to be understood that all :of the conductors are preferably of the sameproportion and that the physical dimensions of' both of: the 4-wire lines are the same. In these circumstances when the conductors of the two lines are brought together to form the 8-wire lineof1octagon'al cross section as described above they are located at each of the vertices of the octagonand are thus symmetrically disposed about the circumference. of .a..circle having diameter-equal xtO; the diagonal dimensions of each of the i-wireilines andwhoseaxis coincides with the..a-x-is.-.of the compositeline.

Two conductors in each -wire line are shaded in the. drawing for the purposes or identification.

.By rotating one set-of conductors 2-, 4;: 6;: 8. with respect of .the other set 3; 5, l, Sso that the angle formed by the. intersection or two .lines joining the-diametrically-: opposite conductors ofeach .4ewire line is caused to vary,.theWaveimpedance along the composite line can he caused-to change inany desiredmanner, erg. exponentially-over a range-ofiimpedances greater than'two to one.

-It-has been found that there resultsa very" simple expression for the characteristic impedance of such a line, this bein where 'D is the 'cliameterof' the circle containing all the wires,

d is'the diameter of the wire, is the angle of rotation shown in-the drawing.

Alf. at the .end of the 8-wire line to which the pair of 4awire-lines are connected the conductors are disposedin the-physical arrangement shown .in.the.accompanying drawingthe angle 0 will be. .45. degrees and .the characteristicimpedance Z0 atthis end of the- 8ewire line will be equal to.half ..the value .ofthe .characteristic impedance of -each of the 4-wire lines. This facilitates an'impedancematching coupling between the pair of 4- wirelines and the composite '8-wire line bydirect connections.

.The characteristic impedance at theother end of the 8-wire line will depend'u-pon thephysical relationshiprofthe conductors and the value of the angle 0 at that end.

By simply rotating one: setof 4-wires--.with respectto theother set the angle Biscaused to vary and it'ispossible'toadjust the characteristic impedance of the line at that enduto any. 'Dredetermined value over range.

a wide impedance tors' 2, 4, 6, 8 in a clockwise directionabout h axis of the line so as to decrease the value of the angle 0 the characteristic impedance of the 8- wire line may be increased to a value such as will permit direct connection to a single l-wire .line in impedance matching relationship. It is possible; also, .to vary the angle 9 and the ratio currentrequirdto pass along the line and -(iii)-:the maximum deviation from the correct transform'ationratio that can be tolerated. The

higherithetransformation ratio or the lower the maximum frequency or the smaller the allowable ideviation, the longer must be the exponential line.

'The number of supports required for such an exponential line will be determined often by the requirement of mechanical stability. fApartfrom this, @however, there is; a minimum'mnnber of 'supports'that can be used if the exponentialform of the line is to be preserved. It is found possible at'the ends and one other pout.

:tl'fllflSfOIll'lfltlOllfflOlTl 131: ohms to 262 ohms.

one-design for such a line, illustrated in Fig. 2

with'the 8'-wire line, described here, to achieve a line that'ina two-toone range of impedance departs by less than one-per cent from the true exponential form, when the line is supported only As an example of this consider a line designed for animpedance In "of the drawing; supports are provided atthe ends 1 pass through apertures and Over one half of the line the and 23 are provided with apertures 8| 32 and 33, respectively. 'Apertui'es 32 and 33 are of thesame diameter and smaller than aperture 3|. Crossshaped members 4|, 42 and 43 'having feed :through insulators'2? located near the ends are arranged on one side respectively of supports 2|,

'22 and23 and members 5|, 52 and 53 similarly fashioned are arranged on the other side respectively, the rotatable complementary members 1 being held in place after adjustment by clamp action brought about by bolts 54 of like fasteners. Insulators 21 are placedso that conductors The dimensions of the line at the three supporting points are respectively:

(1) 0=6'7.5,D/d=1 90 (2) 0=22, D/d= (3) 0=6.2, -D/d=660.

' What I claim is:

1. Improvements in radio frequency transmission lines of the multiple-wire type, residing in an arrangement for varying .the characteristic impedance of a parallel connected pair of such lines over a Wide range of impedance values, said arrangement consisting in disposing the individual conductors of said lines in parallel relationship with each other, and alternately and symmetrically about a common axis, at equal distances therefrom, the arrangement being such as to provide for simultaneous rotation of the conductors of either of said lines about said com- 'mon axis 'soas to vary the spacing between adjacent conductors.

2. Improvements in radio frequency transmission lines of the multiple-wire type, residing in an arrangement for Varying the characteristic impedance of a pair of parallel connected e-wire transmission lines over a wide range of impedance values, said arrangement consisting in disposing the individual conductors of said 4-wire lines in parallel relationship with each other, and alternately and symmetrically about a common axis, at equal distances therefrom, the arrangement being such as to provide for simultaneous rotation of the conductors of either of said lines about said common axis so as to vary the spacing between adjacent conductors.

3. Improvements in radio frequency transmission lines of the multiple-wire type, residing in an arrangement whereby a pair of parallel connected. i-wire lines may be directly connected to a single 4-wire transmission line in impedance matching relationship, said arrangement consisting in disposing the individual conductors of said i-wire lines in parallel relationship with each other, and alternately and symmetrically about a common axis, at equal distances therefrom, the arrangement being such as to provide for simultaneous rotation of the conductors of either of said lines about said common axis so as to vary the spacing between adjacent conductors.

4. Improvements in radio frequency transmission lines of the multiple wire type, characterized by a multi-Wire transmission line section interposed between the ends of a pair of multiplewire lines and the ends of a single multiple-wire line the impedance of which is to be matched with said pair, said transmission line section comprising a plurality of conductors equal in numher to the total number of conductors in said pair, and arranged alternately and symmetrically about a common longitudinal axis, the arrangement being adapted for simultaneously rotating said alternate conductors about said common axis to vary the spacing between adjacent conductors.

5. Improvements in radio frequency transmission lines of the multiple-Wire type, residing in an arrangement for varying the characteristic impedance of a pair of parallel connected fourwire transmission lines over a wide range of impedance values, said arrangement consisting in disposing the individual conductors of said four-Wire lines in parallel relationship with each other, and alternately and symmetrically about a common axis, at equal distances therefrom to constitute an eight-wire line, the arrangement being such as to provide for simultaneous rotation of the conductors of either of said lines about said common axis so as to vary the spacing between adjacent conductors permitting of impedance matching coupling between said eightwire line and said pair of four-Wire lines by direct connection.

6. Improvements in radio frequency transmission lines of the multiple-wire type, residing in an arrangement for varying the characteristic impedance of a pair of parallel connected fourwire transmission lines over a wide range of impedance values, said arrangement consisting in disposing the individual conductors of said four-wire lines in parallel relationship with each other, and alternately and symmetrically about a common axis, at equal distance therefrom, the arrangement being such as to provide for simultaneous rotation of the conductors of either of said lines about said common axis so as to vary the spacing between adjacent conductors, said arrangement of said lines being supported only at the ends thereof and at one other point.

WILBUR NORMAN CHRISTIANSEN.

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

UNITED STATES PATENTS Number Name Date 1,860,052 Peterson May 24, 1932 2,165,087 Alford July 4, 1939 2,404,797 Hansen July 30, 1946 FOREIGN PATENTS Number Country Date 515,121 Germany Jan. 3, 1931