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United States Patent 3,601,716
BOLT ,   et al. August 24, 1971

STRIPLINE DIRECTIONAL COUPLING DEVICE

Abstract

A segment of a main transmission line is located equidistant between and parallel to a first and second coupling segment. The first coupling segment has an input terminal at one end thereof for connection to a stub line. The second coupling element has a terminating impedance located at the end thereof opposite said input terminal end of said first coupling segment. A conductor connects the other opposite ends of said first and second coupling segments so that a pulse travelling thru said main line segment or said first coupling segment in a direction away from said input terminal end of said first coupling segment will couple to the other travelling in the reverse direction.


Inventors: BOLT; Murray H. (N/A, NC), Nick; Howard H. (N/A, MD), UBERBACHER; Edward C. (N/A, NY)
Assignee: Corporation; International Business Machines (NY)
Appl. No.: 04/887,964
Filed: December 24, 1969


Current U.S. Class: 333/116
Current International Class: H01P 5/16 (20060101); H01P 5/18 (20060101); H01P 003/08 (); H01P 005/14 ()
Field of Search: 333/10,6,84,84M,11 340/170,172.5

References Cited

U.S. Patent Documents
3278864 October 1966 Butler
3516024 June 1970 Lange
Primary Examiner: Saalbach; Herman Karl
Assistant Examiner: Nussbaum; Marvin

Claims



What is claimed is:

1. A directional coupling device for coupling electrical pulses to and from a main line conductor comprising:

a main line conductor segment having a predetermined length adapted for connection at first and second ends thereof to a main line conductor;

a first conductor coupling segment having a predetermined length adapted for connection at a first end thereof to a branch conductor, said first coupling segment extending parallel to and closely spaced from said main line segment;

a second conductor coupling segment having a predetermined length extending parallel to and closely spaced from said main line segment;

terminating means connected at a second end of said second coupling segment for terminating electrical pulses arriving thereat; and

a connecting conductor connecting the second end of said first coupling segment to the first end of said second coupling segment, so that an electrical pulse travelling from the first end to said second end of said main line segment will couple to the first and second coupling segment travelling in the opposite direction and a pulse travelling from said first end to said second end of said first and second coupling segments will couple to said main line segment travelling in the opposite direction.

2. A directional coupling device according to claim 1, wherein said main line conductor segment and said first and second conductor coupling segments are sandwiched between first and second ground conductor planes.

3. A directional coupling device according to claim 2 wherein said main line conductor segment and said first and second conductor coupling segments are printed line conductors lying in the same plane.

4. A directional coupling device according to claim 3, wherein said first and second conductor coupling segments are equally spaced within coupling distance from opposite side edges of said main line conductor segment.

5. A directional coupling device according to claim 4, wherein said main line conductor segment and said first and second conductor coupling segments are of the same length, width, and thickness.

6. A directional coupling device according to claim 1, wherein said first and second conductor coupling segments are spaced within electrical coupling distance and equidistant from the main line conductor segment.

7. A directional coupling device according to claim 1, wherein an impedance matching means is connected to said second end of said main line conductor segment for matching the impedance of the coupling device to the main transmission line to which the coupling device is to be connected.

8. A directional coupling device according to claim 1, wherein said terminating means connected to a second end of said second coupling segment is a resistor having a valve equal to the characteristic impedance of the branch line to which said coupling device is to be connected.

9. A directional coupler according to claim 1, wherein a second directional coupler is provided, said main line conductor connecting the first end of said main line conductor segment to the first end of said main line conductor segment of said second directional coupler so that an electric signal applied at the first ends of said first coupling segments of said first and second directional couplers produces coupled electrical signals on said main conductor line travelling in opposite directions.

10. A directional coupler according to claim 1, wherein an electrical signal receiver is connected to the first end of each of said main line segments and an electrical signal driver is connected to the first end of each of said first coupling segments, a main transmission line having the first end of each of said main line segments connected thereto in parallel so that an electric signal applied by said driver to the first end of each of said first coupling segments couples to said main line segment travelling away from said second end of said main line segment towards said connection with said main transmission line where said signal divides going in opposite directions along said main transmission line thereby being received by all other of said receivers.

11. A directional coupler according to claim 1, wherein a plurality of said coupling devices are connected at first and second ends of the main line segments to a common main conductor line, the coupling devices at one end section of said conducting line being mirror images of the coupling devices at the other end section, receiver means located at each end of said main conductor line, the coupling devices of both end sections having a pulse applied at the first end of said first coupling segment so that the pulse couples to said main line segment travelling from the second end to the first end along said main line conductor receives at the other end of said main line conductor, a further receiver means connected to said main line conductor between said first and second end sections, said further receiver receiving pulses from the coupling devices of both end sections.
Description



This invention relates to directional couplers and more particularly, to an improved stripline directional coupling device.

With the increase in operating speed of devices, such as computers, into the nanosecond range, it has been found that directional couplers can be utilized to couple these high-speed pulses to and from transmission lines with respect to stub lines leading to and from various peripheral devices. In copending U.S. application, Ser. No. 609,083, filed Jan. 13, 1967, and now U.S. Pat. No. 3,516,065, issued June 2, 1970, a system for transmitting digital data between a plurality of data-processing devices using stripline directional couplers is disclosed. The use of the directional coupler in this system eliminates the stub length limitations and allows any stub or stub lines connecting individual devices to the transmission line to be limited in length only by the degradation of a signal passed along the line.

As is known, a stripline directional coupler is a device wherein two parallel adjacent printed circuit striplines sandwiched between two ground planes are inductively and capacitively coupled so that the edges of a first pulse, of fast rise and fall time characteristics, propagating along one line, produces a positive pulse and a negative pulse in the other line. The lines are back coupled or directional in that the thus produced pulses propagate along the second line in a direction opposite to the direction in which the first pulse propagates along the first line. The energy transferred between the coupling segments of the two-element directional coupler is affected by the various physical characteristics of the directional coupler such as the length, width and distance between the coupling segments. Accordingly, the long coupling element lengths needed to obtain a good energy transfer between the segments of the coupler introduces obvious disadvantages in packaging the two-element directional coupler, especially where a large number of such devices are to be combined in the same package.

It is an object of the present invention to provide a directional coupler which provides a higher energy transfer than the prior art directional couplers.

It is another object of the present invention to provide a stripline directional coupler which provides a higher voltage magnitude coupling with shorter coupling segments.

It is a further object of the present invention to provide a stripline directional coupler in which a pulse passing through the main segment is subject to a shorter or smaller through put delay.

It is another object of the present invention to provide a stripline directional coupler which can be packaged in a much smaller space.

Briefly, a directional coupler is provided for coupling to and from a main line conductor. The coupler comprises a segment of a main transmission line conductor which is located equidistant between and parallel to a first and second coupling segment. The first coupling segment is part of a stub line conductor connecting the main transmission line to peripheral devices. The second coupling element has a terminating resistance located at the end thereof opposite said end of said first coupling segment connected to said stub line. A connecting conductor is connected between the other opposite ends of the first and second coupling segments so that a pulse travelling in a given direction along said main transmission line or said stub line will couple in the opposite travelling direction to said stub line or main transmission line, respectively.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings.

FIG. 1 is a schematic diagram of the prior art two-element directional coupler showing the input and output waveforms thereof.

FIG. 2 is a schematic diagram of the three-element directional coupler showing the input and output waveforms thereof.

FIG. 3 is a schematic diagram showing the three-element directional coupler connected in a full duplex scheme.

FIG. 4 is a schematic diagram of the three-element directional coupler connected in a full multiplex system.

FIG. 5 is a schematic diagram of the three-element directional coupler connected in a directional multiplex system.

Referring to FIG. 1, there is shown a schematic diagram of the prior art two-element directional coupler which consists of two conductive segments 10 and 12 extending parallel to one another from an end A to an end B. Usually, the conductors are mounted on a substrate 14 made of a nonconductive material such as epoxy glass and are arranged between two ground planes 16 and 18 which usually consist of sheets of copper arranged over and under the conductors. Each conductive element 10 and 12 has a terminal 20, 22 at the end B of the coupler serving as an input or output terminal. Each conductor 10, 12 has a terminating resistance 24, 26 connected at the A end of the coupler which matches the coupler to the characteristic impedance of the lines to which it is connected. The coupling takes place along the length of the segments 10, 12. The coupler operation depends upon the steepness of the incident pulse rise and falltime. The width or duration of the pulse produced by the coupling is determined by the lengths L of the two segments 10, 12 in parallel. The performance of the coupler is related to the impedances offered to signals on the transmission lines and the coupling ratio, which are determined by the widths of the lines in the coupled region, the thickness of the lines, the distance between ground planes, and the relative dielectric constant of the material. It has been determined that coupling segments of electrical length L will produce a pulse having a time duration equal to 2 L. For example, a 1-volt amplitude input signal applied to the input terminal 20 of segment 10 when the coupler has a coupling ratio of 1 to 4 and an electrical length L of 2nsec, will produce an output pulse having a time duration of 4nsec and a pulse amplitude of 1/4 volt. The input pulse can be generated by a driver connected to the coupler by a stub transmission line. As shown in FIG. 1 by arrows, the coupled pulse travels in an opposite direction in the main line segment 12 to the direction of travel in the coupling segment 10. It will be appreciated, that a pulse travelling from B to A along the main transmission line 12 will likewise be coupled to the coupling segment 10 in the opposite direction. A stripline coupler is operated by the edge of the wave passing along one of the lines and this wave edge should have a rise or falltime that is twice as fast as the time duration of the pulse induced in the coupling in order that the relationship of the height of the induced pulse be related to the height of the driving pulse in the manner defined by the coupling ratio.

A three-element directional coupler, forming the present invention, is shown schematically in FIG. 2. The middle segment 28 corresponds to the main line segment 12 of the prior art directional coupler of FIG. 1. The coupling segment 30, having a terminal 32 at the right hand or B end, corresponds to the coupling segment 10 as shown in FIG. 1. In addition to the arrangement as shown in FIG. 1, a further coupling segment 34 extends parallel to and spaced from the other side of the main line segment 28. The spacing of the further coupling segment 34 from the main line segment 28 is the same as the spacing S between the input coupling line segment 30 and the main line segment 28. This further coupling segment 34 is of the same width as the input coupling segment 30. The input coupling segment 30 and the further coupling segment 34 each have an opposite end thereof connected together by a stub connector 36. Thus, the input coupling segment 30 has the left end A connected to the right end B of the further coupling segment 34. The left end A of the further coupling segment 34 is terminated in a terminating resistance 38 of a value equivalent to the characteristic impedance of the line in which the segment is connected. s shown, one end of terminating resistor 38 is connected to ground by a ground connection 40. The A end of the main transmission line 28 is likewise terminated in an impedance 42 having the same characteristic impedance as the line.

As was previously mentioned in connection with FIG. 1, the directional coupler segments are stripline-type conductors which are well known in the art. These conductors are usually closely packed and can best be manufactured by utilizing one of the well known masking and etching techniques used extensively in the manufacture of printed circuits. It is necessary to have the appropriate ground planes for operation of the directional coupler. These can consist of thin sheets of copper 46 arranged both below and above the conductors. The segments 28, 30, 34 are located on the polyglass base 44 which serves as a dielectric to electrically isolate the segments from the below located ground plane 46. Of course, a dielectric sheet can be included between the upper ground plane and the segments for electrical isolation. If the schematic arrangement shown in FIG. 2 has 8 mil wide segments separated from one another by 6 mil spacings S, and the segment length L is approximately 2 nanoseconds in electrical length or approximately 11 inches in polyglass, and the epoxy glass stripline package is approximately 1/8 inches thick, a 1 to 4 coupling ratio results. The two-element prior art directional coupler shown in FIG. 1 also has a 1 to 4 coupling ratio and a segment electrical length of 2 nanoseconds. With a 1 to 4 coupling ratio, an input pulse of 1-volt amplitude applied at the input terminal 32 of the input coupling segment 30 provides an output pulse on the main line conductor 28 as indicated in FIG. 2. It should be observed that the 1-volt amplitude pulse applied to the input terminal 32 of the coupling segment 30 is the same as the pulse applied to the coupling segment 10 of the prior art in FIG. 1. It should also be noted that the resulting output pulses are quite different. In FIG. 2, it can be seen that the output pulse has a 6 nanosecond duration and is half a volt high in the center 2-nanosecond portion thereof. Thus, a three-element directional coupler having the same coupling ratio and segment electrical length as a two-element prior art directional coupler is capable of producing a coupled output pulse having a greater duration and a greater voltage amplitude.

A comparison of the energy content between the two output pulses shows that the energy content of the two-element coupler output pulse of FIG. 1 equals 0.278 ergs while the energy content of the tri-coupler output pulse of FIG. 2 equals 0.834 ergs. The percentage increase in energy content between the two-element and the tri-coupler directional coupler equals 200 percent. The two-element directional coupler has an average voltage height of 0.167 volts over a 6 nanosecond time period while the average voltage height of the tri-coupler output pulse is 0.333 volts over a 6 nanosecond time period. The percentage increase in average voltage height for an equivalent time period between the two-element and the tri-coupler directional coupler is 100 percent. The three-segment coupler or tri-coupler may be packaged in 40 percent less space than the equivalent two-element coupler. Because of the greater energy and voltage amplitudes obtained through the use of the tri-coupler arrangement, greater loads may be driven over longer lengths of cable than is possible in the equivalent two-element coupler. It will be appreciated that an equivalent energy pulse output from the tri-coupler requires less coupling length of segments than is required in the prior art two-element coupler. Thus, the tri-coupler can be packaged in a much smaller unit. Also, because of less line length required in the coupling region to produce an "equivalent" output pulse as compared to the two-element coupler, less time is required for a pulse to pass through the main segment of the tri-coupler. This can be an important feature when a number of tri-couplers are connected to the main line.

A schematic arrangement of a full duplex system using tri-coupler directional couplers is shown in FIG. 3. The arrangement consists of two tri-couplers, one on each of the cards 50 and 52. A driver circuit 54 is shown connected to one end of the coupled segment 30 and a terminating resistance 38 is placed at the opposite end of the other coupled segment. The other ends of the two coupling segments are then joined together by a conductor. This arrangement is now further modified by placing a receiver circuit 56 at the left end of the main line segment with a terminating resistor 42 as shown on card 50. The arrangement as shown on card 52 of FIG. 3 is a mirror image of the arrangement shown on card 50. If the open end of each main line segment 28 is joined as is shown between cards 50 and 52, a full duplex system is provided. In such a system, both drivers may simultaneously produce a voltage ramp which, upon traversing the coupled region, will produce a pulse coupled to the now joined main segment 28. These two pulses will travel simultaneously towards the opposite tri-coupler receivers 56. Thus, the pulse coupled to the main line segment 28 on card 50 derived from its own driver 54 will travel toward the receiver 56 on card 52. Likewise, the pulse coupled to the main line segment 28 derived from driver 54 of card 52 will travel towards the receiver 56 of card 50.

FIG. 4 shows a schematic diagram of a plurality of tri-couplers connected so as to provide a full multiplex system. Referring to card 60, a driver 62 is connected to one end of one of the coupled elements 30, and a terminating resistor 38 is placed at the opposite end of the other coupled segment 34; the remaining ends of the two segments are then joined together by connecting stub 36. This arrangement is now further modified by placing a receiver 64 on one end of the main segment 28. The other end of the main segment 28 is joined directly to a main transmission line 66. Card 70 contains a further tri-coupler arrangement which is the same as that shown on card 60. Further, tri-couplers may be similarly connected along the transmission line 66. The main line 66 has a terminating resistor 72, 74 placed at the left side and right side of the tri-couplers, respectively. A third tri-coupler, on card 80, is connected to the main transmission line 66 with the main line segment 28 forming part of the main transmission line. This tri-coupler card is located at the left of the terminating resistor 72 and has a receiver 82 connected to the left end of the main transmission line 66. A pulse provided at any one of the drivers 62 will latch up each of the other receivers 64. For example, a pulse generated by the driver 64 on card 60 will produce a pulse on the main segment 28 travelling toward the junction of the main segment 28 and the main transmission line 66. Upon reaching the main transmission line 66, the pulse forms two pulses each of which then travels in opposite directions along the main transmission line 66 toward the ends thereof. The pulse which is travelling toward the tri-coupling coupler as shown on card 70 is sensed by that receiver 64 and is latched up. The pulse travelling in the opposite direction is sensed by the receiver 82 at the left end of the transmission line 66. Thus, it will be appreciated that each driver pulse applied at any one of the tri-coupler card drivers 62 will affect each of the other receivers 64, 82.

Referring to FIG. 5, a directional multiplex system is shown wherein a number of tri-coupling devices are connected so that a particular receiver or receivers will receive information only from a particular driver or drivers. The main transmission line 84 is shown having receivers 86 and 88 at either end and receivers 89, 90, 91 located at discrete positions along the length thereof. A number of tri-coupling devices 92, 93 and 94 are shown each having a driver 95, 96, 97, respectively, at one of the ends of the coupling segment 30 and terminating resistor 38 at the opposite end of the further coupling segment 34. Connection is made between the opposite ends of both segments 30, 34 in each device 92, 93, 94 by a respective connecting stub 36. Noting the orientation of the tri-coupling devices, for example, tri-coupling devices 93 and 94 are oppositely oriented, it will be appreciated that the single receiver 86 at the left end of the main transmission line 84 will receive information from driver 97 of coupling device 94 only. Receiver 89 will receive information from driver 97 also. The three receivers 88, 90, 91 at the right end of the transmission line 84 and the receiver 89 will receive information from drivers 95 and 96 of coupler devices 92 and 93 only. The unique feature here is the fact that by virtue of its placement along the main line 84, the receiver can receive information from all drivers on the line or like receivers 86 and 88 can be made dependent upon selected drivers for their information.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.

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