US2288030A - Transmission line structure - Google Patents

Description

June 30, 1942. H. SALINGER- TRANSMISSION LINE STRUCTURE Filed Jan. 10, 1941 I Sheets-Sheet 1 INPUT OUTPUT mvtmon 'SALINGER TRANSMISSION LINE STRUCTURE Filed Jan. 10, 1941 2 Sheets-Sheet 2 FlG.3 I

INPUT OUTPUT 'NPUT OUTPUT I Th4 INVENTOR SALINGER surface.

Patented June 30, 1942 I 2,288,030 TRANSMISSION LINE STRUCTURE.

Hans Salinger, Fort Wayne, Ind., assignor to Farnsworth Television and Radio Corporation, a corporation of Delaware Application January 10, 1941, Serial No. 373,869

3 Claims.

This invention relates to transmission-line structures including a plurality of transmissionline elements and particularly relates to a shielding means for such transmission-line structures.

In certain transmission-line structures including a plurality of transmission-line elements having inner conductors and shield conductors which represent reactance networks, it often becomes necessary so to connect two conductors that current fiows along the inner surface of one of the conductors and also incidentally along its outer The current flowing along the outer surface of such a conductor can readily fiow through distributed capacitance to adjacent filter elements or to ground, thereby constituting a radiation loss as well as changing the transmission characteristics of the filter. Such a condition, however, is most unsatisfactory.

Certain shield structures have been proposed for the prevention of radiation losses. Such structures, however, are designed for one predetermined frequency only, are ineffective at other frequencies, and are therefore not desirable for transmission of wide frequency bands.

The object of the present invention, therefore, is to provide a new and improved transmissionline structure in which the current incidentally fiowing along the outer surface of a conductor is returned to the transmission-line structure and radiation loss and other detrimental effects avoided independently of frequency;

In accordance with the present invention there is provided a transmission-line structure including a plurality of transmission-line elements having inner conductors and shield conductors connected so as efiectively to constitute a reactance network. The transmission-line structure includes a connection between two of its conductors whereby current fiows along the inner surface of one of the conductors and also incidentally along its outer surface. There is also provided a shield conductor disposed adjacent the last-mentioned conductor and connected thereto at one of its ends, while its other end is connected to another conductor of the transmission-line structure, thereby providing a return flow of the incidental current to the transmission-line structure.

For a better understanding of the invention, together with other and further objects thereof,

reference is had to the following descriptiontaken in connection with the acccompanying drawings and its scope will be pointed out in the appended claims.

In the accompanying drawings:

Fig. 1 shows a circuit diagram of a lattice-type filter, while Fig. 2 schematically shows a transmission-line structure constituting such a filter. Fig. 3 schematically shows another transmissionline structure embodying the present invention and representinga bridged-T filter-section, while Fig. 4 shows a diagram of its equivalent circuit. Referring now more particularly to Fig. 1 of the drawings there is shown a schematic diagram of a lattice-type filter having a pair of inputterminals I, 2 and a pair of output terminals I4; I5. The input terminals I, 2 are connected to points I3 and II, respectively, of the filter between which the series combinations of reactances Z1 and Z2, and Z3 and Z4, respectively, are connected, as shown. The junction point I6 between reactances Z and Z4 and the junction point il between reactances Z1 and Z: are connected to the input terminals I4 and I5, respectively, as is conventional.

Fig. 2 shows a transmission-line structure constructed of coaxial transmission-line elements and constituting a lattice-type filter as shown in Fig. 1. Corresponding elements and points are indicated by the same reference numerals in the two figures. Corresponding to the input terminals I, 2 of Fig. 1 there is provided an input terminal line having an inner conductor I and a shield conductor 2 which form the "input line feeding the transmission-line structure. For the purpose of providing the reactances Z1 and Z2 between points I3 and II there is provided a transmission-line means 3 having an inner conductor 4, a first shield conductor 5 of predetermined diameter, and a second shield conductor 6 of greater predetermined diameter, all arranged concentrically with respect to each other. For the purpose of providing reactancesZa and Z4 between points I3 and I I there is provided a second transmission-line means 1 comprising an inner conductor 8, a first shield conductor 9 of predetermined diameter, and a second shield conductor III of greater predetermined diameter, also concentrically arranged with respect to each other. The shield conductor 2, as well as second shield conductors 6 and I0, are all joined together to form a unitarystructure and their junction is generally indicated at I I which represents a substantially equipotential area since this area is small as compared with the actual length of the transmission-line elements. The inner conductors I, 4 and 8 are connected together at a point I3.

For the purpose of providing the structure with a signal output means there is provided an 2 equal to any predetermined values obtain the desired filter action.

It will be noted that in such a structure current flowing from the point Ii to the shield'conductor I will flow along the inner surface of conductor I5 as well as incidentally also along its outer surface. This, however, as was mentioned before, is an undesirable condition. For the purpose, therefore, of returning the current incidentally flowing from the point It along the Z4 and Z5 is effective between points II and I6,

the transmission-line structure must be so de- .signed that the resultant reactance is of suitable value to render the desired filter characteristic.

Fig. 3 shows a bridged T-fllter-s'ection comprising coaxial transmission-lineelements and of a general structure which is identical with that shown in Fig. 1 with the exception that certainelectricalconnections within the filter structure are different,,so as to obtain the effect of a bridged T-fllter-section. points are indicated by the same reference numerals as in Fig. 1. In contrast to the struc- 'tureof Fig. l the point I6'is connected to the 'inner conductor 4, while the inner conductor I4 is connected to the junction point. I3 and the point I1 is connected to the shield conductor I5.

Fig. 4 shows the diagram of thecircuit electrically equivalent to the structure of Fig. 3.

Again in Fig. 4 points corresponding to those of Fig. 3 are marked by the same numerals and the equivalents to the reactances represented by the transmission-line elements of Fig. 3 are indicated by the labelled blocks.-

F'lg. 4 shows that the equivalent reactance elements Z5, 6 and Zn, 19, the latter including the shield I8, are connected in parallel relation with each other. By properly designing the transmission-line elements and theshield I8 the resultant reactance of Z5, 0 and Z13, m can readily be made to have the proper value desired in the filter secon. I

While the structures of Figs. 1 and 3 have been marked with input and output ends, it will be understood that the input and output ends may also be interchanged as is well known to those skilled in the art.

In the above there have been shown and described transmission-line structures provided with a shield for prevention of radiation losses and other detrimental effects which is so connected in these transmission-line structures, that the reactance constituted by the shield and another part of the transmission-line structure be- I comes a useful reactance element of the'network represented by transmission-line structure.

While there has been described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention and it is, therefore, aimed in the appended claims to cover all such changes and Like parts and Y necessary to modifications as fall within the true spirit and scope of the invention. I

What is claimed is:

1. A transmission-line structure including a single input terminal line and a single output terminal line, each having an inner conductor and an outer conductor, a plurality of transmission-line elements having inner conductors and shield conductors connected so as effectively to constitute a reactance network between said input and said output lines, a connection between one of said transmission line element conductors and the outer conductor. of one of said terminal lines whereby current flows along the inner surface of said last-named outer conductor and also incidentally along its outer surface, and a shield conductor disposed adjacent said lastnamed outer conductor and connected thereto at one ofits ends and to another conductor of said structure at the other of its ends, thereby to provide a return flow of said incidental current to said structure, the reactance of the transmission line element formed by said last-named shield conductor and said last-named outer conductor being electrically connected in parallel relation to the reactance of one of said transmission line elements.

2. A transmission-line structure including a single input terminalline and a single output terminal line, each having an inner conductor and an outer conductor, a plurality of, transmission-line elements having inner conductors and shield conductors so as effectively to constitute a reactance network between said input and said output lines, a connection between one of said transmission line element conductors and the outer conductor of one of said terminal lines whereby current flows along the inner surface of said last-named outer conductor and also incidentally along its outer surface, and a cylindrical shield conductor concentrically disposed about said last-named outer conductor and connected thereto at one of its ends and to another conductor of said structure at the other of its ends, thereby to provide a return flow of said incidental current to said structure, the reactance of the transmission line element formed by said last-named shield conductor and said lastnamed outer conductor being electrically connected in parallel relation to the reactance of one of said transmission line elements.

3. A transmission-line structure comprising a single input line including an inner conductor and a shield conductor, transmission-line means providing a reactance networkand including an inner conductor, a first shield conductor of predetermined-diameter, and a second shield conductor of greater predetermined diameter, said input'line shield conductor and said second shield conductor being joined to form a unitary outer shield structure,; a single output line including an inner conductor and a shield conductor, means for connecting said first shield conductor of said transmission-line means to said last-mentioned shield conductor, and shielding means concentrically arranged about said output line shield conductor and joined at its opposite ends to said unitary structure and said last-mentioned shield conductor, the reactance of the transmission line element formed by said shielding means and said output line shield conductor being electrically connected in parallel relation to oneof the reactances of said reactance network.

HANS SALJNGER.

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