US1998960A

US1998960A - High frequency transmission system

Info

Publication number: US1998960A
Application number: US503866A
Authority: US
Inventors: Ira J Kaar
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1930-12-22
Filing date: 1930-12-22
Publication date: 1935-04-23
Anticipated expiration: 1952-04-23

Description

A ril 23, 1935'. 1. J; KAAR HIGH FREQUENCY TRANSMISSION SYSTEM.

Filed Dec. 22,1950 I Inventor v Ira J. Kaar,

QWQAZQ His Attci neg.

Patented Apr. 23, 1935 1,998,960 HIGH FREQUENCY TRANSMISSION SYSTEM Ira J. Kaar, Schenectady, eral Electric Company,

York

N. Y., assignor to Gena corporation of New I Application December 22, 1930, Serial No; 503,866

, V 11 Claims. My inventionrelates to high frequency transmission systems and more particularly to transmission lines for use in transmitting energy between a high frequency source and a radiating system, or other load circuit.

Where transmission lines of considerable length are employed to supply energy from a source to a radiating system it frequently occurs that considerable radiation of energy takes place from the transmission line itself. This radiation' has been found to be due largely to currents upon the line conductors of thefltransmission line having frequencies corresponding to certain harmonics of the fundamental frequency which it is desired to transmit through the line. Currents of the fundamental frequency, of course, flow in opposite directions in the two line conductors and therefore produce little or no radiation, but it has been found that currents: having one or more frequencies corresponding to certain harmonics of the fundamentals, and which are excited in the line due to inherent characteristics of thecoupling arrangements employed, flow in the same direction in the two line conductors; i. e. the two con-.

ductors oscillate in phase with respect to ground thereby causing undesired radiation'into' space.

One of the objects of my invention is toreduce undesired harmonic radiation into space from the conductors-of the transmission line.

A further object of the inventior'iis to' provide a path for the currents which produce uncle sired radiation whereby said currents'flow in I opposite directions in adjacent conductors: thereby to cause neutralization of radiation from the conductors.

.A further object of the invention is to provide means whereby the effective height of the transmission line conductors considered'as a radiator above ground is substantially reduced.

Still a further object of the invention is to: reduce reflected or standing waves of the un-' desired harmonic frequency onthe line.

The novel features which Ibelieve to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which Figs. 1, 2 3 and 4 represent different embodiments of my invention.

Referring to Fig. I of the drawing, I'have represented by means of a rectangule i any suitable equipment whereby high frequency oscillations of suitable power are generated and supplied through a transformer '2, transmission line 3 and transformer 4' to a suitable load circuit which may comprise a radiating system 5, th radiating system being arranged at some distance from the generating equipment I. The transmission line 3 is so designed that it efficiently transmits energy of the fundamental frequency which is to be radiated from the source to the antenna. To this end condensers 6 are connected in series across the line in parallel with the primary winding of the transformer 4, these condensers together with the inductance of the transformer 4, and antenna resistance and'capacitance being of such value thatthe line is terminated in an impedance which is equal to the surge impedance of the line. Because of the impedance of the antenna which is reflected back intothe circuit of the primary winding of the transformer 4', the condensers 6 must be of such value that the circuit com-, prising the condensers and the primary winding of the transformer are slightly off resonance but such that the power factor of currents flowing from the line into the circuit comprising condensers 6 and the primary winding of the transformer 4 is unity Atthe opposite end of the line condensers l are connected in series with the secondary winding of the transformer 2, these condensers being of such value as to exactly neutralize the inductance of the secondary ,windingof .the transformer 2 whereby the entire in duced. electromotive force in the secondary winding of thetransformer 2: transmission line.

It will be apparent from an inspection of the arrangement as thus described that currents which are supplied to the transmission line through the inductive action'of the transformer 2 flow in opposite directions in the two line conductors of the; transmission line, the energy of these'currents being transmitted to the load circuit through the inductive. action of the transformer 4'. w i

It frequently occurs, however, that due to the inherent nature of the source and the coupling arrangements: employed whereby energy issupplied to. the transmission line that oscillations having frequencies correspondingto certain of the harmonics of the fundamental wave which it is desired to transmit throughv the line flow in the same direction in the two line conductors. Thus, for examplaoassume that the sourceof oscillations t includes an electron discharge amplifier of the push: pull type of which the discharge devices are indicated at 8, the priis impressed upon the mary' winding of the transformer 2 being connected betweenthe two. anodes of the push pull circuit and the midpoint thereof being connected through the common portion. of the output circuit tothe' cathodes of the discharge device. In this type of circuit current impulsesv flow alternately to the two anodes of the discharge devices. Since that portion of the circuit, however, which is between the cathodes and the intermediate point on the primary winding of the transformer is common to the anode circuits of the two discharge devices, it is apparent that a certain voltage will be built up across this common portion of the circuit having a frequency corresponding to the second and other even harmonics of the fundamental wave. Since the cathodes are grounded the entire primary winding oscillates with respect to ground at these even harmonics. Due to the capacity effect between the primary and secondary windings these even harmonics are supplied to the transmission line conductors in phase causing these conductors to oscillate in phase with respect to ground. While I mention a source of oscillations including a push pull amplifier in the output stage in the way of illustrating one manner in which the harmonic oscillations are supplied to the two conductors of the transmission line in phase, it will be understood that I do not wish to be limited thereto since my invention also has application in connection with sources of other types.

Normally the conductors of the transmission line are arranged at a considerable distance above the earth, thereby to avoid the effects of snow and ice upon the ground, and for other purposes. As such the line has considerable effective height above ground when considered as a radiator of these harmonic frequency oscillations.

To avoid the effects of this radiation, in accordance with my present invention, a third conductor 9 is arranged symmetrically between the two line conductors 3 and in proximity thereto. This conductor is connected to the transmission line at a point between the condensers 6 at the load end of the line and'is grounded at a number of different points along the line. In this way the conductors 3 are brought effectively closer to ground and the effective height thereof when considered as a radiator of the harmonic frequencies is materially reduced, thereby substantially reducing the radiation into space.

It will be seen further that currents of the harmonic frequency which flow in phase in the conductors 3 find a return path through the conductor 9 and flow in'this conductor in opposite direction to the current of the same frequency in the conductors 3. Near the load end of the line these currents in the conductor 9 are substantially equal to the sum of the currents of the same frequency in the conductors 3, and accordingly any radiation from the two conductors is substantially neutralized. Of course a cer tain' amount of the return current is led to ground through the successive ground connections Iii and accordingly the neutralization is gradually less effective at points along the line increasingly remote from the antenna 5 but at all points 'ofthe line the conductor 9 is equally effective in reducing the effective height of the transmission line. a

In Fig. 2 I have shown a further arrangement which may be employed. In this figure the point between the condenser E at the load end of the line is connected to ground through an impedance H equal to the surge impedance of the path through which the undesired harmonic frequencies flow namely, the two conductors 3 in parallel. This arrangement is disclosed and claimed in a copending application of John W. Labus. Serial No. 503,867 entitled High frequency circuits and filed simultaneously herewith and which is assigned to the same assignee as my present application, The purpose of this impedance is to prevent reflection of currents of the undesired harmonic frequencies from the end of the line remote from the transmitter thereby avoiding any standing waves upon the transmission line conductors. This arrangement may be made more effective by connecting a simi lar impedance I 2 between the opposite end of the line and ground, these two impedances thus serving each to prevent reflection from its respective end of the line of currents received from the opposite end of the line. Thus if reflection occurs at the load end of theline the reflected currents are prevented by the impedance l2 from being again reflected at the transmitting end of the line.

In Fig. 3 I have shown an arrangement in which the advantages of both Figs. 1 and 2 may be secured, the conductor 9 being connected between the impedances H and I2 and arranged symmetrically in proximity to the conductors 3, this conductor being grounded at the opposite ends thereof, and at additional points, if desired. As such the conductor serves both to reduce the effective height of the line conductor 3 and also to neutralize the radiation therefrom.

Fig. 4 shows a further arrangementin which the conductor 9 is connected to the transmission line at a point between the condensers 6 and is extended symmetrically throughout the length of the line in proximity to the conductors 3 and is there connected to ground through an impedance which is equal to the surge impedance of the line, the two conductors thereof being considered as connected in parallel-and the conduc tor 9 serving as a return path. In this arrangement it will be seen that the currents flowing in the same direction in the conductors 3 find a return path through the conductor 9 and substantially neutralize the field of conductors 3 throughout the entire length of the line and the impedance I I prevents standing waves upon the line.

While I have shown particular embodiments of my invention, it will of course be understood that I do not wish to be limited thereto since difierent modifications may be made, and that I contemplate by theappended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In combination, a source of high frequency oscillations of a certain fundamental frequency, a radiating antenna, a transmission line comprising line conductors connected between said source of high frequency oscillations and said radiating antenna to carry currents of said fundamental frequency in opposite directions, and means to reduce radiation of energy from said transmission line due to currents flowing in the same direction in the two conductors of said line, said means comprising a third conductor extending symmetrically between said conductors in proximity to said two line conductors and arranged to carry in the opposite direction currents which flow in' said two line conductors in the same direction whereby radiation from said two line conductors is neutralized by radiation from said third conductor.

2. In combination, a source of high frequency oscillations of a certain fundamental frequency,- a radiating antenna, a transmission line com= prising line conductors connected between said source of high frequency oscillation and said radiating antenna to carry currents of said fundamental frequency in opposite directions, and means to reduce radiation of energy from said transmission line due to currents flowing in the same direction in the two conductors of said line said means comprising a third conductor extending along said line in proximity to said two line conductors and arranged to carry in the opposite direction currents which flow in said two line conductors in the same direction, whereby radiation from said two line conductors is neutralized by radiation from said third conductor and an impedance connected in said third conductor having a value equal to the surge impedance of the path through which said currents flow.

3. In combination, a source of high frequency oscillations of a certain fundamental frequency, a radiating antenna, a transmission line comprising line conductors connected between said source of high frequency oscillations and said radiating antenna to carry currents of said fundamental frequency in opposite directions, and means to reduce radiation of energy from said transmission line due to currents flowing in the same direction in the two conductors of said line having a frequency which is a harmonic of said fundamental frequency, said means comprising an impedance connected between each end of said line and ground, each of said impedances having a value to prevent reflection at the respective end of the line of currents of said harmonic frequency received from the opposite end of the line and flowing in the same direction in said two line conductors.

4. In combination, a source of high frequency oscillations of a certain fundamental frequency, a radiating antenna, a transmission line comprising line conductors connected between said source of high frequency oscillations and said radiating antenna to carry currents of said fundamental frequency in opposite directions, and means to reduce radiation of energy from said transmission line due to currents flowing in the same direc- 7 tion in the two conductors of said line, said means comprising an impedance connected between each end of said line and ground, each of said impedances having a value to prevent reflection at the respective end of the line of currents received from the opposite end of the line and flowing in the same direction in said two line conductors and a third conductor connected between said two impedances and arranged in proximity to said two line conductors.

5. In combination, a source of high frequency oscillations of a certain fundamental frequency, a radiating antenna, a transmission line comprising line conductors connected between said source of high frequency oscillations and said radiating antenna to carry currents of said fundamental frequency in opposite directions, and means to reduce radiation of energy from said transmission line due to currents flowing in the same direction in the two conductors of said line said means comprising a third conductor eX- tending along said line in proximity to said two line conductors and arranged to carry in the opposite direction currents which flow in said twoline conductors in the same direction whereby radiation from said two line conductors is neutralized by radiation from said third conductor and a plurality of connections from said third conductor to ground said connections being disposed at different points along the line.

6. In combination, a source of high frequency oscillations of a certain fundamental frequency, a load circuit, a transmission line arranged to transmit oscillations of said fundamental frequency from said source to said load circuit, said transmission line comprising a pair of line conductors, and a coupling between said source and said transmission line whereby current of said fundamental frequency is caused to flow in'opposite directions in said line and currents having the frequency of certain harmonics of said fundamental frequency are caused to flow in the same direction in said line, said line conductors being arranged above the ground at a distance to produce undesired radiation into space, and a third conductor arranged in proximity to said line conductors and connected in circuit relation with said line conductors with respect to said certain harmonics of said fundamental, and means for maintaining said third conductor substantially at ground potential thereby to reduce the effective height of said line conductors.

7. A method of reducing radiation of undesired harmonic energy from an unshielded transmission line elevated above the earth and isolated from grounded conducting objects, the two sides of'said transmission line conducting desired currents in opposite phase and an undesired harmonic thereof in like phase, which includes the step of reducing the effective height of the transmission line above the earth for said undesired harmonic currents flowing in phase in the opposite sides of said transmission line, while maintaining the actual height of said transmission line.

8. The method of reducing undesired harmonic radiation of energy from an unshielded transmission line elevated above the earth and isolated from grounded conducting objects which includes producing a field of ground potential at the undesired harmonic frequency in proximity to a substantial portion of the transmission line.

9. In a system for transmitting high frequency energy from a source to a load comprising a transmission line connected between said source and load, the method of reducing radiation from said line produced by currents flowing in the same direction in opposite sides of said line having a frequency which is a harmonic of the frequency to be transmitted over said line, which includes neutralizing the field in space produced by said harmonic currents.

V 10. In a system for transmitting high frequency energy from a source to a load comprising a transmission line, connected between said source and load, the method of reducing radiation from said line produced by currents flowing in the same direction in opposite sides of said line, which includes transmitting said currents in the opposite direction along said line thereby toproduce a field in space opposing the field produced by currents in said opposite sides of said line.

11. In a system for transmitting high frequency energy from a source to a load comprising a transmission line connected between said source and load, the method of reducing radiation from said line produced by currents flowing in the same direction in opposite sides of said line in which desired currents flow in opposite directions, which includes neutralizing the field in space produced by said currents and reducing the effective height of the transmission line above the earth while maintaining its actual height.

IRA J. KAAR.