US2454865A - Time-delay network - Google Patents

Description

1948- M. J. D] TORO 2,454,865

TIME-DELAY NETWORK Filed June is, 1945 lnducionce FIVG.3

Width v INVENTOR. MICHAEL J. Di TORO Patented Nov. 30, 1948 TIME DELAY NETWORK Michael J. Di Toro, Brooklyn, N. Y., assignor, by mesne assignments, to Hazeltine Research, Inc., Chicago, 111., a corporation of Illinois Application June 18, 1945, Serial No. 599;!)87

4 Claims.

This invention relates, in general, to time-del-ay networks for translating signal components included within a predetermined range of frequencies. It is especially directed to time-delay networks which include a distributed or elongated winding arranged in association with an elongated conductive member to simulate a transmission line having distributed inductance and capacitance.

Network-s of the type under consideration are well known in the art and may be either balanced or unbalanced arrangements. In the former, a second distributed winding serves as the conductive member having a distributed capacitance with the first-mentioned winding. In the latter, a conductive core member is generally utilized, the distributed winding being wound over the core and insulated from but electrically coupled thereto along its length. While such delay networks of the prior art have proved to be satisfactory for many installations, there are other installations where such arrangements have limited application in view of a particular type of distortion inherent in such networks. This distortion is frequently termed end effects and maybe attributed to the decrease or falling off of the inductance per unit length of the distributed winding in the Vicinity of its end portions. It results from the inter-turn inductive coupling of the winding which is a maximum in the central region and a minimum at the ends.

roposals have been made for overcoming or compensating such end effects. For example, it has been suggested that the inductance per unit length of the distributed winding be made uniform by providing an increase in inductance at the end portions of the winding. This maybe accomplished by increasing the number of turns per unit length or, in the case of an unbalanced network, by increasing the permeability of the core structure in these regions. This suggestion has limited application because of the difficulties encountered in constructing a variable pitch Winding or a core of variable permeability, especially where the resultant network is to exhibit predetermined values of total inductance and total capacitance.

In another arrangement of the .prior art, the area of the elongated conductive member is reduced under the end portions of the windings to decrease the distributed capacitance of the network in a manner so related to the decrease of inductance that the ratio of inductance to capacitance is substantially uniform along the winding.

This'method of correction is obviously unsuited'to balanced time-delay networks. Additionally, it has little practical value in unbalancednetworks including core structures of conductive and ma netic materials since a reduction of the core area in such a case further decreases the inductance.

It is an object of the present invention, therefore, to provide an improved time-delay network for translating signal omponents included within a predetermined range of frequencies and which avoids one or more of the above-mentioned limitations of prior art arrangements.

It is another object of the invention to provide an improved time-delay network for translatin signal components included within a predetermined range of frequencies and having a simplifled and inexpensiveconstruction to facilitate controlling its operating characteristics.

It is a specific object or the invention .to provide an improved time-delay network for translating signal components included within a predetermined range of frequencies and having a substantially constant impedance along the length of the network.

In accordance with the invention, a time-delay network for translating signal components included within a predetermined range of fre-- quencies comprises an elongated conductive member and an elongated winding mounted in concentric relationship with respect to the conductive member. A sheet of dielectric material is coiled in the space between the conductive member and the winding for insulating but electrically coupling the winding along its length to the conductive member to provide a distributed capacitance along the winding. The sheet of dielectric material has a length approximately equal to that of the winding, has a minimum width at least equal to the circumference of the conductive member and has a variation in width such that the thickness of the coil thereof varies in a predetermined manner along the length of the winding to efiect a desired variation of the distributed capacitance along the winding.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended .claims.

In the drawing, 'Fig. l is a schematic representation of a three-termina1 time-delay network in accordance with the present invention; Fig. 2 is a graph illustrating the inductance variation along thelength of the Fig. '1 network; Fig. 3 represents ash'eet .of dielectric material utilized in iabricat 3 ing the arrangement of Fig. 1; while Fig. 4 is a schematic representation of a four-terminal timedelay network embodying the teachings of the invention.

Referring now more particularly to Fig. 1, the time-delay network there represented is of the unbalanced or three-terminal type for translating signal components included within a predetermined range of frequencies. The network is in the form of a simulated transmission line and comprises an elongated conductive member, specifically, a conductive core i0. Preferably, the material of core structure It] is such as to provide a high permeability for a purpose to be made clear hereinafter. This core ma include comrninuted graphite and iron particle molded into a conductive rod of any desired cross-section and longitudinal length. In order that signals translated through the network may undergo a minimum attenuation, it is desirable that core member ill have a construction as particularly dis closed in copending application Serial No. 582,283, filed March 12, 1945, in the name of Michael J. Di Toro, now Patent 2,413,607 issued December 31,- 1946, and assigned to the same assignee as the present invention.

The network also includes a uniformly distributed or elongated winding l I mounted in concentric relationship with respect to the conductive core member iii. A sheet 52 of dielectric material or paper is coiled about core member I ll in-the space between the core and winding II for insulating but electrically coupling the winding along its length to the conductive core to provide a distributed capacitance along the winding. This distributed capacitance is the capacitance between the winding and the core structure and, in conjunction with the inductance of winding H, determines the total time delay of the network. It is well understood that the total time delay of any such network is proportional to the geometric mean of its total effective series inductance and total effective shunt capacitance. The diameter, the length and permeability of core structure ill, the size and type of conductor utilized in fabricating winding l i, as well as the number and pitch of the winding convolutions are selected to afford such desired values of inductance and capacitance that the network produces a desired total time delay. In this connection, it will be appreciated that an increase in the diameter or length of the core structure and winding results in higher values of inductance and capacitance, while increasing the number of turns per unit length of the winding increases primarily only the inductance. Likewise, the inductance alone may be increased to a desired value by proportioning the constituent elements of core member ID for higher permeability.

It may be demonstrated from transmission-line theory that the response or operating characteristics of the described network may be controlled by Varying the distributed capacitance along winding it in a preselected manner. In the arrangement under consideration, the distributed capacitance is controlled by shaping the dielectric sheet I2 so that the coil thereof, obtained by wrapping the sheet about core ID, has a thickness which varies in a predetermined manner along the length of winding i i. In the instant embodiment of the invention, the dielectric sheet I2 is so shaped that the coil thereof has a selected number of turns in the central region of winding H but an increased number of turns in the vicinity of the end portions of the winding. By thus 4 by the paper shape of Fig. 3.

shaping the dielectric sheet 12 a control is obtained of the ratio of inductance to capacitance along winding H and is taken advantage of in order to secure minimum distortion for signals translated through the network. In the drawing, the thickness variations of the dieletcric coil are represented although it is not feasible to show the actual number of turns constiuting this coil.

A distributed winding, such as that utilized in constructing the network of Fig. 1, has an inductance per unit length which varies in the manner indicated by the curve of Fig. 2. In this curve it is seen that the inductance has a maximum value Li at the central region of the winding, designated by the ordinate line 0. To either side of the central region the inductance per unit length decreases having a minimum value L2 at the end portions. This represents the end efiects mentioned above which, unless corrected or compensated, introduce distortion into a translated signal. Compensation is obtained in the instant embodiment by shaping the dielectric sheet l2 in the manner represented in Fig. 3. The sheet has a preselected width W1 at the center and increases on either side thereof to a maximum width W2 at each end. The variation in the Width of the paper is such that when wrapped about the core member ill, the paper encircles the core a given number of times in the center region and a greater number of times in the vicinity of the ends. In a particular case, the dielectric coil may include two turns in the central region of the winding and ten turns at the end portions thereof, the number of turns varying between these limits as indicated The increased thickness of dielectric coil l2 at the end portions of winding it reduces the capacitance of the network in such manner as to compensate the loss of inductance and establish a. substantially uniform ratio of inductance to capacitance along the winding.

Winding ii is provided with an input terminal 13 and an output terminal it. The conductive core iii is coupled to a common terminal 15 of the network which is usually a ground connection.

The described arrangement will be seen to constitute an unbalanced network having an input terminal it, an output terminal i l and a third or common terminal l5. Due to the described shape of the dielectric material forming the di-- electric coil H, the network has uniformly distributed inductance and capacitance or a characteristic impedance which is substantially uniform and constant along the length of the winding. Signals applied to input terminal l3 are obtained with a predetermined delay at output terminal M and undergo minimum distortion of the type caused by end. effects and minimum at-- tenuation in the network.

The modification of Fig. 4 represents a balanced or four-terminal time delay network which is generally similar in construction to that of Fig. 1. In Fig. l, however, the distributed winding H is insulated from but electrically coupled along its length to an elongated conductive member provided by a second uniformly distributed winding 20. The dielectric sheet 12 serves to insulate but electrically couple windings H and 20 and is shaped as aforedescribed so that the thickness of the dielectric coil varies along the length of the windings to control the distributed capacitance therebetween. In the case under consideration, the shape of the dielectric sheet I Z is again selected so that the number of turns of the dielectric coil increases in the vicinity of the end portions of the windings to compensate or correct the above-mentioned end effects. A core member l of insulating material supports windings H and and may be of such nature as to provide a high permeability and a high value of inductance in the network. Input terminals I3 and I3 are coupled respectively with adjacent ends of windings I l and 20 while output terminals l4 and 14' are coupled to the opposite adjacent ends of these windings.

While a single dielectric sheet 12 has been described as coiled between the winding II and its associated elongated conductive member in the arrangements of Figs. 1 and 4, it will be understood that a plurality of superimposed dielectric sheets may be utilized if desired. Where a plurality of such sheets is used, at least one may be shaped to provide a thickness variation in the dielectric coil along the length of winding H as required to effect a desired variation of the distributed capacitance along the winding.

While there have been described what are at present considered to be the preferred embodiments of this 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 modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A time-delay network for translating signal components included within a predetermined range of frequencies comprising, an elongated conductive member, an elongated winding mounted in concentric relationship with respect to said conductive member, and a sheet of dielectric material coiled in the space between said conductive member and said winding for insulating but electrically coupling said winding along its length to said conductive member to provide a distributed capacitance along said winding, said sheet of dielectric material having a length approximately equal to that of said winding, having a minimum width at least equal to the circumference of said conductive member and having a variation in width such that the thickness of the coil thereof varies in a predetermined manner along the length of said winding to effect a desired variation of said distributed capacitance along said winding.

2. A time-delay network for translating signal components included within a predetermined range of frequencies comprising, an elongated conductive member, a uniformly distributed elongated winding mounted in concentric relationship with respect to said conductive member and having an inductance per unit length which decreases in the vicinity of the ends of said winding, and a sheet of dielectric material oiled in the space between said conductive member and said winding for insulating but electrically coupling said winding along its length to said conductive member to provide a distributed capacitance along said winding, said sheet of dielectric material having a length approximately equal to that of said winding, having a minimum width at the central portion at least equal to the circumference of said conductive member and having an increase in width at the end portions such that the thickness of the coil thereof increases in the vicinity of the ends of said winding to compensate said decrease of inductance and establish a substantially uniform ratio of inductance to capacitance along said winding.

3. A three-terminal time-delay network for translating signal components included within a predetermined range of frequencies comprising, an elongated conductive core member, an elongated winding mounted in concentric relationship with respect to said core member, and a sheet of dielectric material coiled around said core member in the space between said core and said winding for insulating but electrically coupling said winding along its length to said core member to provide a distributed capacitance along said winding, said sheet of dielectric material having a length approximately equal to that of said winding, having a minimum width at least equal to the circumference of said core member and having a variation in width such that the thickness of the coil thereof varies in a predetermined manner along the length of said Winding to effect a desired variation of said distributed capacitance along said winding.

4. A four-terminal time-delay network for translating signal components included within a predetermined range of frequencies comprising, a first elongated winding, a second elongated winding mounted in concentric relationship with respect to said first Winding, and a sheet of dielectric material coiled in the space between said first and second windings for insulating but electrically coupling said windings along their lengths to provide a distributed capacitance therealong, said sheet of dielectric material having a length approximately equal to that of said windings, having a minimum width at least equal to the circumferential path between said windings and having a variation in width such that the thickness of the coil thereof varies in a predetermined manner along the lengths of said first and second windings to effect a desired variation of said distributed capacitance along said windings.

MICHAEL J. DI TORO.

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

UNITED STATES PATENTS Number Name Date 2,213,093 Reese Aug. 2'7, 1940 2,297,514 Von Baeyer et a1. Sept. 29, 1942 2,387,783 Tawney Oct. 30, 1945

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