US1977751A

US1977751A - Wave transmission network

Info

Publication number: US1977751A
Application number: US661593A
Authority: US
Inventors: Zobel Otto Julius
Original assignee: American Telephone and Telegraph Co Inc
Current assignee: AT&T Corp
Priority date: 1933-03-18
Filing date: 1933-03-18
Publication date: 1934-10-23
Anticipated expiration: 1951-10-23

Description

Oct. 23, 1934. o. J. ZOBEL 1,277,751

WAVE TRANSMISSION NETWORK Filed March 18, 1933 INVENTO? 0. J. ZOBEL Patented Oct. 23, 1934 1,977,751 WAVE TRANSMISSION NETWORK Otto Julius Zobel, New York, N. Y., assignor to American Telephone and Telegraph Company, a corporation of New York Application March 18, 1933, Serial No. 661,593

12 Claims. (01. 118-44) This invention relates to wave transmission networks and more particularly to reactance networks, such as broad band wave filters, of the unbalanced type in which one side of the circuit may be grounded.

An object of the invention is to provide a new and improved type of wave transmission network which is equivalent in its transmission characteristics to known types of networks, but the component reactances of which fall within a different range of values. Anotherobject is to permit the construction of transmission networks of the bridged-T type which otherwise would require the use of reactance elements which are too large or too small to be builtcommercially.

A further object of the invention is to reduce the cost of manufacturing wave filters, especially those of the unbalanced type.

The, bridged-T type of network is commonly employed in unbalanced circuits since, for such circuits, it provides a network having the same degree of generality in transmission characteristics as is given by the lattice network for balanced systems. In'one form, the bridged-T network comprises a bridging branch and a central branch, connected by means of a unity ratio transformer the'two windings of which are connected series aiding and have substantially perfect coupling. In certain instances, however, the component reactance elements required to build the bridging branch used in this type of network may involve inductance coils which are too large for economical manufacture, or condensers which are too small to permit the required precision of adjustment. In accordance with the present invention these di iiiculties are obviated by resort- 1 branch fall within an entirely different range of values than they otherwise would. The inductance coils'may then be manufactured more economically and the condensers may be adjusted with the required precision. This desirable result is accomplished by shunting all or a part of the bridging impedance across one only of the windings of the coupling transformer.- The transmission and impedance characteristics of the network are left undisturbed b l his modifica ion; 7 I

The nature of the invention will be more fully understood from the following detailed description and by reference to the accompanying drawing, of which Figures 1 and 2 show schematically a transmission network of the bridged-T type, to which the inventionis applicableyand I Figs. 3, 4, 5 and 6 illustrate various embodiments of the invention.

' The transmission network shown schematically in Fig. 1 is of the well known bridged-T type.

It comprises a transformer having two equal windings L, L connected series aiding with mutual inductance M equalsubstantially to L, a bridging impedance Z1 connected between the

outer terminals

10, 12 of the transformer, and a shunt impedance Z2 connectedfrom the common terminal 11 of the two inductances-L, L to the other side of the line, which may be grounded or otherwise fixed in potential. The impedances Z1 and Z2 may comprise reactances only, or both resistance and reactance elements, and generally they will have dilferent impedance characteristics. The network has the same degree of generality in respect to its transmission and impedance characteristics as can be obtained with any fourterminal transmission network made up wholly of passive impedance, and it may be made either 5 balanced or unbalanced in form. For a more detailed description, explaining how the network may be designedto'have any desired transmission characteristics, reference is made to the patent to H. W. Bode,,No. 1,828,454, issued October '90 20, 1931. Y a

In certain instances it has been found that the network shown in Fig. 1 may be built more economically if the impedance required for the branch Z1 is reduced in magnitude. For example; the inductances may be so large that they cannot be conveniently wound on a single core, or the capacitances may beso small that it is .impossible to obtain the necessary precision of adjustment. Inaccordance with the invention theserestric- 10o tions areremoved by resorting to a new type of network section in which apart or all of the impedance 'Z1.is shunted across oneonlyof the transformer windings L. Inone embodiment of the invention, shown schematicallyin Fig. 3;the bridging impedance Z1 isreplaced by two impedanceseach equal to A2 Z1, one being shunted across each of the windings L. The inductances form- .ing the impedance /2 Z1 will, of course, be only one-half the magnitude of those required for the 1110 by a factor of four, as compared with the corre sponding elements required in the impedance Z1.

In this way the elements required for the bridging branch are made to fall within an entirely different range of values, permitting the convenient building of the inductance coils and allowing the requisite close adjustment of the condensers.

In a modification of the invention only a part of the bridging impedance is relocated. In Fig. 2 the impedance Z1 has been replaced by thethree branches Za, Zb and Zc, the parallel impedance of which is equal to Z1. 1 In equation form,

1 l 1 1 zfz. Z1, 2.

As shown in Fig. 5, the portion of the bridging impedance represented by the impedance Zb may be replaced by an impedance in magnitude equal to A1 Zb shunted across only one of the windings L, between the terminals 11, 12. Likewise, the part of Z1 represented by Zc may be replaced by the impedance Zc shunting one of the transformer windings L, between terminals 10, 11. The two impedances Zb and V Zc may, if desired, be connected across the same winding L, for example, between the terminals 10, 11. In this way the portion of the bridging impedance Z1 having elements which are satisfactory in size is left undisturbed, whereas the other parts of Z1 are altered in magnitude by a factor of four and connected in parallel with only one of the transformer windings L. As shown in Fig. 6 the impedance A1 Zb of Fig. 5 may be replaced by two impedances each equal to /2 Zb, one being-shunted across each of the windings L. Other combinations and permutations involving the impedances Za, Zb and Z0, which may be advantageously employed under certain circumstances, will readily suggest themselves. However, the networks illustrated by Figs. 5 and 6 are representative.

In the arrangements shown in Figs. 3, 5 and 6 if the impedances connected in parallel with the transformer windings comprise a shuntingv capacitance its value may be decreased to compensate individually for the inevitable interwinding capacitances of the two windings, L, Lof the-transformer, effective, respectively, between the terminals 10, 11 and between the terminals 11, 12. When this is done an improvement is effected in the transmission and impedance characteristics of the networks. I

As mentioned above, the networks of the invention may be employed where any other four-terminal transducer, comprising only passive impedances, may be used. The invention is applicable, for example, to'wave filters, phase correctors, delay networks and other transmission networks.

What is claimed is:

. 1. A wave transmission network comprising a pair of equal inductances, inductively coupled, in series with one side of the line, said inductances being connected in series aiding relation, two impedances, one shunted across each of said inductances, and a third impedance connected from the junction of said inductances to the other side of the line.

2. A wave transmission network comprising in one side of the line a pair of equal inductances connected series aiding with unity coupling factor, a pair of equal impedances, one of said impedances being connected in parallel with each of said inductances, and a third impedance connected between the common terminal of said pair of inductances and the other side of the line. Y 3. A wave transmission network having a pair of input terminals and a pair of output terminals, said network comprising an electrical path between each input terminal and a corresponding output terminal, in one of said paths a transformer having, two equal windings connected series aiding with unity coupling factor, two general impedances, one of said impedances shunting each of said transformer windings, and a third general impedance connected between the junction point of said transformer windings and a point in the other of said paths.

4. A wave transmission network having a pair of input terminals and a pair of output terminals, said network comprising an electrical path between each input terminal and a corresponding output terminal, a pair of equal inductances connected series aiding with unity coupling factor in one of said paths, a pair of equal impedances, one of said impedances shunting each of said inductances, and a third impedance included in a shunt path between the junction point of said inductances and a point in the other of said paths.

5. A wave transmission network comprising a pair of input terminals and a pair of output terminals, said network comprising an electrical path between each input terminal and a corresponding output terminal, a pair of equal inductances connected series aiding with unity coupling factor in one of said paths, a pair of equal reactances, one of said reactances shunting each of said inductances, and a third reactance connected between the junction point of said inductances and a point in the other of said paths.

' 6. A wave transmission network comprising a pair of input terminals and a pair of output terminals, said network comprising an electrical path between each input terminal and a corresponding output terminal, a pair of equal inductances connected series aiding with unity cou pling factor in one of said paths, a general impedance connected in parallel with one of said inductances, and a second general impedance connected between the junction point of said inductances and a point in the other of said paths.

7,. A wave transmission network comprising a pair of input terminals and a pair of output terminals, said network comprising an electrical path between each input terminal and a corresponding output terminal, a pair of equal inductances connected series aiding with unity coupling factor in one of said paths, a general impedance connected in parallel with said inductances between the outer terminals thereof, a pair of equal inpedances, one of said pair of impedances being connected in parallel with each of said inductanceS and a fourth general impedance connect- .ed between the junction point of said inductances and a point in the other of said paths.

' 8. A wave transmission network comprising a pair of input terminals and a pair of output terminals, said network comprising an electrical path between; each input terminal and a corresponding output terminal, a pair of equal inductances I pedance shunting one of said inductances, a third general impedance shunting the other of said inductances, and a fourth general impedance connected between the junction point of said inductances and a point in the other of said paths.

9. A wave transmission network in the form of a T-network, the series arms of the T-network comprising a pair of equal inductances connected in series aiding relation with mutual inductance therebetween, a general impedance shunting one of said inductances, and a second general impedance shunting the other of said inductances, and the shunt arm of the T-network comprising a third general impedance.

10. A wave transmission network in the form of a T-network, the series arms of the T-network comprising a pair of equal inductances connected in series aiding relation with mutual inductance therebetween substantially equal in magnitude to the self-inductance of one of said equal inductances, and a general impedance shunted across one of said inductances, and the shunt arm of the T-network comprising a second general impedance having a characteristic differing from that of said first-mentioned general impedance.

11. A wave transmission network of the ladder type comprising a pair of equal impedances connected in series in one side of the line and a third impedance in shunt with the line, connected between the common terminal of said pair of equal series impedances and the other side of the line, said equal series impedances comprising two equal inductances connected in series aiding relation with unity coupling factor, and a pair of equal impedances, one shunting each of said inductances.

12. An electric wave filter comprising a pair of equal inductances connected series aiding with unity coupling factor, a reactive impedance shunting one of said inductances, a second reactive impedance shunting the other of said inductances, and a third reactive impedance having one of its terminals connected to the junction point of said pair of equal inductances.

O'I'IO J. ZOBEL.