US2000032A

US2000032A - Transmission line

Info

Publication number: US2000032A
Application number: US463610A
Authority: US
Inventors: Nils E Lindenblad
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1930-06-25
Filing date: 1930-06-25
Publication date: 1935-05-07
Anticipated expiration: 1952-05-07
Also published as: GB379796A

Description

May 7, 1935. N. E LINDENBLAD 2,000,032

TRANSMISSION LINE Filed June 25, 1933 5 OUTPUT cmcu/r H/GH rfisauzwr I INPUTC/RCU/T t 2 I INVENTOR NILS E. LINDEN BLAD ATTORNEY Patented May 7, 1935 more TRANSMISSION LINE Nils E. Lindenblad, Port Jefierson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application June 25, 1930, Serial No. 463,610

13 Claims.

This invention relates to transmission lines and has as its prime object the provision of a new and useful'method and means for insulating-high h frequency transmission lines from their supports and for coupling together a plurality'oftransmission lines.

- Much diificulty has been encountered in supporting transmission lines used in transmitter -work, for example, wherein high frequency high voltage alternating currents are encountered. In order to prevent radiation from the transmission lines, it is desirable that they be kept together as close" as possible since, with lines of opposite instantaneous polarity, there is mutual radiation cancellation. T However, to keep the lines close together and yet at their supporting points to keep them properly insulated from the supports was heretofore impossible of accomplishment for the reason that, due to the high voltages involved, the insulators had to 'be of extremely large size. Hence, at the supporting points at least the transmission lines had to diverge.

' The foregoing difliculty is overcome by the "present invention which has, as a further object, the-utilizationin the support and connection of -transmission lines,'oftheprinciple that a U- shaped path one-half wave length long offers very high-impedance to electrical energy whose frequency corresponds to the frequency for which the pathisone-half wave-length long. This object is carried out by connecting or coupling across .the transmission lineat points where it is to be supported a path of low impedanceto-radio frequency currents, preferably a dead short circuit, and this "short circuiting connection-is directly connected by means of supporting cables or the liketo a support. Coupling to another transmission line is accomplished by tapping on to the transmission line theline .tobe coupled thereto at one-quarter wave length or less away from the short circuiting connection.

[As the short circuiting connection is at a voltage nodarpoint by virtue of the reflections set up thereby, it may be safely grounded or,in other '45 wordsnconnected to a support without danger and without loss of power. As the coupled lines are connected together at points one quarter wavelengthaway from the short circuiting connection, the portions of the short circuited line betweenthe short circuit and the tapping points is substantially one-half wave length long, substantially U -shaped, and hence, ofiers substan- ;t ially infinite impedance to energy transferred by either of the lines so connected together.

" In the event that a transmission line is to be of the present invention.

supported intermediate its. ends, it is a further object of this invention to provide a path paral-' leling the transmission line at the pointat which it is to be supported which path is substantially one-half wave length long and which may, there:-

5 fore, be safely connected to a"supportiby even conductive cables or the like at its voltagenodal point} Here also, the reason why this mayribe done is'the fact that the path offers substantially infiniteimpedance to energy transferred by :the line which it supports. a 3

The invention may further be understood by referring to the accompanying drawing wherein 3 Figure l is illustrative of the presentinvention, showing terminal and intermediate supports for a transmission line coupled to other transmission lines, I

Figure 2'discloses the present invention applied to a bent transmission line supported at the bendingpoint, I 20 Figure 3 is a detailed view in elevation of a short circuiting connection used, for example, in Figures 1 and 2, and

Figures 4 and 5 are given by way of explanation .25 Turning to Figure 1 a high frequency inputcircuit 2 supplies energyov'er' transmission lines 4, 6 and. 8 to an output circuit In; a i Ordinarily, as'transmission line 6 is mounted some distance above the ground and is fairly long it must be, as indicated, supported at its ends and intermediate its ends. To support linet at its ends A; B, by means of ordinary insulators would involve spreading of the lines, undue radiation, and large losses. To overcome these objections, paths of low impedance to the high frequency current transmitted by the line 6; namely, short-circuiting straps I2 are connected directly across the line 6 at its terminal supporting points A, B. The straps may be bolted together bysuitable bolts M of suitable number. At end A'the two wires forming the transmission line 6 may be brought together at point it, passed over a pulley l8 mounted onsupport 2G and pulled taut by weight 22. At point B the wires forming transmission line 6 may be fastened in any suitable fashion to a support 24. o

Transmission line 4 coupling-the input circuit 2 to transmission line 6 is connected or tapped adjustably at

points

26, 28 to transmission-line 6 symmetrically and one-quarter wave length away .po'itlng elements of -a weight 54. -means of an intermediate line 56 adjustably tap- By virtue of the foregoing connection, and be- .cause of the fact that strap I 2 is of negligible length relative to the portion of transmission line 6 included between

adjustable tapping points

26, 28 and strap l2, strap I2 is at a voltage nodal point and may be safely fastened without energy loss to a support. In other words, the supply to the transmission line 6 is through line 4 to

points

26, 28 which looking towards point A face into an effective infinite impedance by virtue of the fact that the U-shaped portion of the line formed by the strap l2 and the portion of the line 6 included between it and points 25, 28 acts as a tuned circuit. V Y

The tapping of

points

26, 28 to the line 6 is not critical but may be somewhat more or less than one-quarter wave length away from short clrcuiting strap l2. Even with the lessened or increased distance the portion of the line between the tapping points and the support oifers an exceptionally high impedance as indicated by the graph forming Figure. It is not until the tapping points are brought very close to the strap I! or a half way position that impedance, is reduced to' such an extent that it becomes dangerousto directly support-the line by metallic elements to a grounded support.

In anotheraspect, it may be said that by tapping the

lines

4 and 8 to the transmission line 0 .inthe manner described, a U-shaped circuit is effectively connected thereacross as shown in Figure 5.- Point 30 when the. U-shaped element 32 is properly slid along the

tapping points

26,28

, would be at zero potential and could be supported by any metallic supporting element 34. Point 30 would correspond to the strap l2 of Figure l and element 34 to the supporting cables and sup- Figure l for thetransmission line 6.

To support the line 6 of Figure 1 intermediate it's ends, it is only necessary, in the light of the invention so far described, to provide a half-wave length path paralleling the transmission line intermediate its ends and'fastened at its voltage nodal point to a support. In Figure 1 elements 36, 38 are each approximately one-quarter wave length long and extend from line 6 to short circuiting strap 40 and form with this strap a path U=shaped and one-half wave length or less long paralleling transmission line 6 and, as at points A and B, this pathor looped, U-shaped connec- "tion may be-fasten'ed to any suitable support 42.

If desired, an additional U-shaped support extending from the line 6 may be placed on the other side of the line 6 asat 44.

The application of the present'invention to a bent transmission line is shown in Figure 2.

Energy may be considered as traveling from point C to point D. The line C is short circuited by means ofstrap 46 and the line D by a strap 48. The wires forming the lines may be brought .together at 50, wound about a pulley fastened to asupport at 52 and counterweighted by means of The lines arejoined together by pedto the lines C and D at

points

58, 60, 62 and 64 at points not over one-quarter wave length away from the

short circuiting straps

46, 48.

Having thus described my invention, what I claim is:

1. In combination, in high frequency apparatus, an input circuit, an output circuit, a transmission line for transferring energy from the input circuit to the output circuit, means at the terminal ends of the line having low impedance to high frequency energy, and connections between the input and output circuits and the line, these connections being coupled to points on the line each approximately one-quarter wave length away from said last mentioned means.

2. The combination, in high frequency apparatus, of an input circuit, an output circuit, a transmission line for transferring energy from the input circuit to the output circuit, short circuiting connections terminating the line, and connections between the input and output circuits and the line, these connections being coupled to the line approximately one-quarter wave length away from the short circuiting connections.

3, The combination as claimed in claim 1 having in additionmeans having an overall length of approximately one-half wave length or less paralleling the line intermediate its ends and fastened at its voltage nodal point to a support.

4. The combination as claimed in claim 2 having in addition a looped conductor having an overall length of approximately an odd multiple of one-half wave length paralleling the transmission line and connected thereto intermediate its ends, said looped conductor being fastened to .a support substantially at its voltage nodal point.

5. In a transmission system wherein high 'frequency high voltage alternating currents are utilized, a two wire transmission line terminating in a loop, said loop being approximately one-half wave length long at the fundamental frequency and offering very high impedance to electricalenergy in said transmission line of the fundamental frequency, and high frequency apparatus connected across said transmission line at the terminals of said loop.

6. A high frequency system utilizing high voltage alternating currents having, in combination, a two wire transmission line, a metallic strap comprising a path of .low impedance to radio frequency currents across said line, an input circuit, and means from said input circuit topoints on said two wire line which are substantially symmetrically placed with respect to. said pathand separated from each other approximately an said line and path.

7. In combination, a short circuited two wire transmission line, a second short circuited two wire transmission line, and connections between said two lines extending from points on one of said lines, each pointbeing approximately onequarter wavelength away from the short circuit thereof to points on the other line also each approximately one-quarter wave length away from the other short circuit. I

8. A high frequency system utilizing high voltage alternating currents having, in combination, a two wire transmission line, a metallic strap comprising a path of low, impedance to radio frequency currents across said line, an input circuit, and connections from said input circuit to points on said two wire line which are each substantially symmetrically placed with respect to said path and separated from each other approximatelyan odd multiple of a half wave length along said line and path. g

9. In combination, a two wire transmission line supported at least at one end thereof, a short circuit connection across said transmission line at said one end, and high frequency apparatus connected across said transmission line at points approximately one quarter wave length from said short circuit connection, said short circuit connection being substantially a voltage nodal point at which said line is supported.

10. In combination, a two wire transmission line supported at least at one end thereof, a path of low impedance to high frequency energy connected across said transmission line at said one end, and high frequency apparatus connected across said transmission line at points approximately an odd multiple of a quarter wave length from said path of low impedance, said path of low impedance being substantially a voltage nodal point at which said line is supported.

11. A system in accordance with claim 10 characterized in this, that said transmission line is adjustable with respect to said high frequency apparatus at said points of connection thereto.

12. In a high frequency high voltage communication system, in combination, two high frequency conducting elements, each element comprising a pair of collaterally spaced linear wires, connections joining together the ends of the wires of each element, each connection comprising a U shaped loop substantially one half wave length long having its legs connected to the wires through substantially non-radiating paths, said elements being connected together at the terminals of one of said U shaped loops.

13. In combination, high frequency apparatus, a two conductor transmission line having bridged thereacross a path of low impedance to direct current, and a two wire connection extending from said high frequency apparatus to said line, each wire of said connection being coupled to a point on one of said conductors of said transmission line, the overall distance between said coupling points as measuredon said two conductor transmission linethrough said path of low impedance being approximately an odd multiple of a one-half wave length.

NILS E. LINDENBLAD.