US2490622A - High-frequency transmission line or cable and connector therefor - Google Patents

Description

Dec. 6, 1949 Eh C. CORK 2,490,622

HIGH-FREQUENCY TRANSMISSION LINE OR CABLE AND CONNECTOR THEREFOR Filed May l5, 1945 Patented Dec. 6, 1949 HIGH-FREQUENCY TRANSMISSION LINE OR CABLE AND CONNECTOR THEREFOR Edward Cecil Cork, Ealing, London, England, as-

signor to Electric & Musical Industries Limited, Hayes, Middlesex, England, a company of Great Britain Application May 15, 1943, Serial No. 487,166 En Great Britain `anuary 15, 1941 Section 1, Public Law .690, August 8, 1946 Patent expires January 15, 1961 8 Claims.

rihis invention relates to high frequency transmission lines or apparatus and connectors therefor.

High frequency transmission lines are usually in the form of cables comprising an outer tubular conductor and an inner conductor disposed centrally within the outer conductor, such form of cable being usually referred to as of the concentric type. It is customary to connect two lengths of such cable together or to connect a portion of a cable to high frequency apparatus or to connect two pieces of high frequency apparatus together by means of various types of connectors. The term connector herein employed is intended to cover a device comprising essentially two separable parts, each part comprising an inner conductor and an outer conductor insulated therefrom, whereby each part can be connected to a transmission line of the concentric type so as to form a continuation both of the inner and outer conductors of said line, the two parts being arranged to be separated as by the provision of plug and socket portions, bayonet connecting portions, screw-threaded portions or the like which permit disconnection without the necessity of disconnecting the line from either part of the connector, the two parts of the connector when in engagement with one another serving to connect electrically the inner and outer conductors of one line to the inner and outer conductors respectively of the other line. The term connector also includes constructions in which the outer conductor of one or both parts of the connector is flanged for connection to the screening box of high frequency apparatus.

When the transmission lines or cables or the apparatus are designed for operating on wavelengths of a few centimetres it is found that the connectors introduce irregularities due to the inductance and/or capacity of the connectors which become of increasing effect as the wavelength of the energy it is desired to transmit becomes smaller. At such centimetre wavelengths the connector must be considered as forming a Y 'the result that reflection occurs of the high frequency energy passing through the connectors.

One of the objects of the present invention is to overcome or reduce these diiiculties.

According to one feature of the invention, a high frequency transmission line or apparatus is coupled to another line or apparatus having a similar characteristic impedance by means of a connector which is of such a length and has such a characteristic impedance that the connector substantialiy matches the impedances of the coupled elements, whereby high frequency energy can be transmitted through said connector substantially without reflection.

When reference is made herein to a high freq ency transmission line or apparatus this means a transmission line or apparatus arranged to transmit energy of a wavelength up to 50 centimetres. The term high frequency energy means energy of a like wavelength.

According to another feature of the invention, a high frequency transmission line or apparatus is coupled to another line or apparatus having a similar characteristic impedance by means of a connector which preferably has a similar characteristic impedance and the length of which is equal or approximately equal to a half wavelength or to an integral multiple of half-wavelengths of the high frequency energy transmitted between said coupled elements, whereby said energy can be transmitted through said connector substantially without reflection.

In some cases it is desired to connect a high frequency transmission line or apparatus to another transmission line or apparatus having characteristic impedances which are not matched. In order to prevent reflection occurring due to mismatch it is the practice to insert between the elements to be coupled an impedance transforming device which at high frequencies is usually Ain the form of a transmission line.

According to another feature of the present invention, a high frequency transmission line or apparatus is coupled to another line or apparatus having a dissimilar characteristic impedance by means of a connector which has such a length and such a characteristic impedance that the connector acts as an impedance transformer whereby high frequency energy can be transmitted between said coupled elements substantially without reflection.

If desired, the connector may be provided with an adjustable element or elements arranged to afford a shunt or series loading impedance. This has the advantage that the electrical length of the connector need not be accurately determined since by adjusting the adjustable element the de- 3 sired electrical length or impedance can be imparted to the connector.

In the specification of United States Patent No. 2,270,416 issued January 20, 1942, to Edward Cecil Cork, there are disclosed various forms of filters in which the resistance, inductance and capacity of the filter can be introduced in the form of sections of transmission lines.

According to another feature of the invention one or both parts of said connector is or are provided with an additional portion or portions of transmission line which is or are so associated with said part or parts that the connector acts as a lter for some lcomponents of the high frequency energy transmitted between the coupled elements.

According to another feature of the invention there is provided a connector for coupling together high frequency transmission lines or apparatus having similar characteristic impedances, said connector having a substantially uniform impedance throughout its length thus avoiding` lumped impedances along its length and the connector is such that if high frequency energy is transmitted therethrough of a wavelength such that the connector is a half wavelength long or a multiple of nali wavelengths long, said energy will be transmitted substantially without redection.

According to another feature of the invention there is provided a connector for coupling together high frequency transmission lines or apparatus having dissimilar characteristic impedances, said connector having a substantially uniform impedance along its length and has such a characteristic impedance that if high frequency energy is transmitted therethrough which is of a wavelength such that the connector is a quarter wavelength long or an odd integral multiple of quarter wavelengths and if said energy is transmitted via said connector from transmission lines or apparatus having such dissimilar characteristic impedance that the characteristic impedance of said connector is the geometric means of the impedance of said lines or apparatus, said energy will be transmitted substantially without reflection. Preferably the space between the inner and outer conductors of the elements of the conhector is filled with insulating material, the insulating material employed, of course, being taken into consideration in determining the electrical length of the connector as distinct from its physical length.

In this specification where reference is made to the length of the connector this means the electrical length as distinct from its physical length, unless the context implies otherwise.

In order that the features of the invention may be clearly understood andv readily carried into effect, they will now be described with reference to the accompanying drawings, in which:

Figure l illustrates a longitudinal section of one form of connector Vdesigned for use with transmission lines or apparatus having either similar impedance or dissimilar characteristic impedances, and

Figure 2 illustrates a longitudinal section of a connector designed to operate as a lter.

Referring now to Figure 1 of the drawing, the connector shown is of the plug and socket type comprising two parts 3 and 4 which are shown separated, each part comprising an outer tubular conductor 5 and 6 and an inner conductor 1 and S, the outer conductor 5 having a reduced portion 9 arranged as a sliding fit within the internally reduced portion i0 of the outer conductor 6, the inner conductor l being provided with a bore il whilst the inner conductor t is provided with a plug portion i2. The two parts of the connector are arranged to be plugged together in the well known manner so that the outer conductors 5 and 6 and the inner conductors l and 8 are electrically connected together respectively. The space between the outer conductor 5 and the inner conductor 'i is filled with insulating material i3, whilst the space between the outer conductor f5 and the inner conductor is also partially lled with insulating material i4, the arrangement being such that when the two portions are plugged together the whole space between the inner and outer conductors is filled with insulating material. In order to connect the outer conductor of a concentric line to the outer conductors 5 Vand and the inner conductor of the line to the inner conductors 'l and 8, any suitable clamping means may be provided for this purpose. In most cases the inner conductor of the line will be soldered to the inner conductors of the connector whilst the outer conductor of the line may be clamped to the outer conductors of the connector by a screw-threaded clamping device. The insulating material i3 and le may be of any suitable form such as that shown by the trade name Polythene, this material being a polymer of ethylene.

Where the device shown in Figure l is intended to couple together two elements such as a cable or high frequency apparatus having similar characteristic impedances, the lengthof the conductor should be approximately equal to a half wavelength of the high frequency energy transmitted along the cable or by the apparatus or an integral multiple of half wavelength. It is preferred that the characteristic impedance oi the connector should also be equal to the characteristic impedance of the elements to be coupled, it being readily possible to impart the desired impedance to the connector, taking into consideration its physical dimensions and the di-l electric constant of the insulating material employed in its construction.

It is preferred that the impedance of the conhector should be uniform throughout its length so as to avoid as far as possible .the introduction of lumped impedances at points along the length of the connector. This can be achieved with the construction shown in Figure l by lling the space between the inner and outer connectors with the insulating material and by avoiding the introduction of metal parts which have dimensions greatly diifering from one another in the two parts of the connector. Thus by employing a connector in this manner high frequency energy can be transmitted between the elements coupled by said connector without substantial reection.

Where the connector shown in Figure 1 is intended to be employed as an impedance matching transformer, its length should be equa-l or approximately equal to a quarter wavelength or to an odd integral multiple of quarter wavelengths of the high frequency energy transmitted. The characteristic impedance of the connector in this case should be chosen to be equal to the geometric mean of the impedances to be matched as to produce the required transformation ratio, thus again permitting the transmission of high frequency energy substantially without reflection.

If desired the lengths of the connectors need not be accurately made equal to a half or quarter Wavelength Qr their equivalents, as the case may be, but may be made approximately equal thereto and the desired electrical length and impedance can be imparted toI the connector by providing an adjustable element or elements so as to afford either a series or a shunt loading impedance, as suggested in the specication of British Patent No. 489,704. ThusV the length of the connector may besuch as to afford a partial impedance match and a loading impedance is provided to eiect an accurate match. The loading impedance may take the term of an adjusting screw I 5, which is threaded. intoa part of theA connector at right angles thereto so as effectivelyto provide a shunt loading impedance or a screw threaded sleeve I6 may be provided, surrounding the outer conductor 6 and arranged so that it can be caused to engage, forexample, an abutment in the part 3 so that instead of the two parts when plugged together being` disposed with the insulating material I3 and I4 abutting, a space is left so. as to constitute a series loading impedance.

Figure 2 of the drawings illustrates a connector which is providedy with additional portions or" transmission line so that the connector can runen tion as a lter. A wide variety of iilters can be constructed in accordance with this feature of the invention, and in the example shown each part 3 and 4 of the connector is provided with a lateral extension in the form-f a portion o a transmission line, which in some cases may be a quarter of a wavelength long, the two portions being indicated by the reference numerals I and I8. The outer conductors ofthe portions Ii' and I8 are directly connected to the outer conductors 5 and 8 respectively of the parts 3A and 4, whilst the inner conductors I 8 and 2B of the portions I! and I8 may be coupled to the inner conductors T andy 8. Capacity coupling is shown in the ngure, but other coupling'means may be used ifY desired. This capacity coupling is aiTOrded in the example shown by disposing the ends of the inner conductors I9 and 2li in proximity to the inner conductors 'I and 8, and in some cases this capacity coupling can be increased by enlarging the diamn eter of the inner conductors I and 8 as. indicated at 2l and 22 and byy providing the ends of the conductors Irland' 29 with plates 23 and 2t. The spaces between the outer and inner conductors of the portions I'!V and I8 are also preferably filled with insulating material. The length of transmission line between the portions I'l and I3 will dependA on the type and design of the nlter. The length of the conductor can, however, be such as to constitute a matchingimpedance or a transformer, as described above.

What I claim is:

1. A connector for connecting together high frequency transmission lines including a pair of separable parts, each part including at least a pair of electrically conductive members maintained in position relative to one another by solid insulating means, each ofl the electrically conductive members ofV one part having a correspond-- ing member in theA other part, and arranged for telescopic engagement with the corresponding member in said other part, saidsolid insulating means being so arranged` that when said parts are in engagement the space between said conductive members is substantially entirely filled by solid insulating means, said connector having an electrical length, when said parts are in engagement, substantially equal to an integral mul tiple of one-quarter wavelength, the spacing between said conductive members and their dimensions being so related to the length of said connector that energyy Qn one of said transmission lines is transferredv tothe other ofvsaid transmis sion lines without reflection, the conductive members of said parts beingv so arranged that the spacing and dimensionsl or said members. isy uni form over their entire length when said parts are in engagement.

2. A connector for connecting together high frequency transmission lines of similar characteristic impedance, including; a pair of separable parts, each part includingA at least, a pair of electrically conductive members,l maintained in position relative to one another'by solid insulating means, each of the electrically conductive members of one part having al corresponding member in the other part and arranged for telescopic engagement with the corresponding member in said other part, said solid insulating meansbeing so arranged that when said parts are in engagement the space between said conductive members is substantially entirely lled by solid insulating means, said connector having an electrical length, when said parts are in engagement, sub.- stantially equal to the integral multiple ofi one-r half wavelength, the spacing between said conductive members and their dimensions being so related as to not greatly differ in the twoy parts of said connector.

3. A connector for connecting together high frequency transmission lines including a pair of separable parts, each partv including at least a pair of electrically conductive members'maintained in position relative to` one another by solid insulating means, each of the electrically'conductive members of one part having a corresponding member in the other part, and arranged for telescopic engagement with the corresponding memloer in said other part, said solid insulating means being so arranged that when said parts are in engagement the space between said conductive members is substantially entirely iilled. by solid insulating means, said connector having an electrical length, when said parts are in engagement, substantially equal to an integralmultiple of one-half wavelength, the spacing between said conductive members and theirv dimensions being so related that the characteristic impedance of said connector is equal to that of: saidj lines whereby energy on one of said.. transmission. lines is transferred to the other ofV said. transmission lines without reiiection, the conductive members of said parts being so arranged. that the spacing and dimensions of said members is uniform over their entire length when saidv parts are: in engagement.

4. A connector for connecting together high frequency transmission lines including a pair of separable parts, each part including atleast a pair of electrically conductivev members maintained in position relative to one another by solid insulating means, each of the electrically conductive members of one part having a corresponding member in the other part, and adapted to engage the corresponding member in said other part, said solid insulating means being so arranged that when said parts are-in engagement the space between said conductive members is substantially entirely lled by solid insulating means, and arranged for telescopic engagement with the corresponding member in said other part, said connector having an electrical length, when said parts are in engagement, substantially equal to an integral multiple of one-half wavelength, the spacing between said conductive members and their dimensions being so related that the characteristic impedance oi said connector is equal to that of said lines whereby energy on one of said transmission lines is transferred to the other of said transmission lines without reflection, one of said pair of electrically conductive members being in the form of a tubular sheath concentrically arranged about another of said members as an inner conductor, the conductive members of said parts being so arranged that the spacing and dimensions of said members is uniform over their entire length when said parts are in engagement.

5. A connector for connecting together high frequency transmission lines of dissimilar characteristic impedance, including a pair of separable parts, each part including at least a pair of electrically conductive members maintained in position relative to one another by a solid insulating means, each of the electrically conductive members of one part having a corresponding member in the other part and arranged for telescopic engagement with the corresponding member in said other part, said solid insulating means being so aranged that when said parts are in engagement the space between said conductive members is substantially entirely filled by solid insulating means, said connector having an electrical length when said parts are in engagement substantially equal to an odd multiple of one-quarter wavelength, the spacing between said conductive members and their dimensions being so related as to not greatly differ in the two parts of said connector, and further so related to the length of said connector that energy on one of said transmission lines is transferred to the other` of said transmission lines without reflection.

6. A connector for connecting together high frequency transmission lines of dissimilar characteristic impedance, including a pair of separable parts, each part including at least a pair of electrically conductive members maintained in position relative to one another by a solid insulating means, each of the electrically conductive members of one part having a corresponding member in the other part and arranged for telescopic engagement with the corresponding member in said other part, said solid insulating means being so arranged that when said parts are in engagement the space between said conductive members is substantially entirely filled by solid insulating means, said connector having an electrical length when said parts are in engagement substantially equal to an odd multiple of one-quarter wavelength, then spacing between said conductive members and their dimensions being so related as to not greatly diier in the two parts of said connector, and further so related to the length of said connector that energy on one of said transmission lines is transferred to the other of said transmission lines without reiiection, one of said pair of electrically conductive members being in the form of a tubular sheath concentrically arranged about another of said members as an inner conductor.

7. A connector for connecting together high frequency transmission lines of similar characteristic impedance, including a pair of separable parts, each part including at least a pair of electrically conductive members maintained in position relative to one another by solid insulating means, each of the electrically conductive members of one part having a corresponding member in said other part, and adapted for telescopic engagement with the corresponding member in said other part, said connector having an electrical length, when said parts are in engagement, substantially equal to an integral multiple oi onequarter of a Wavelength, said solid insulating means being so arranged that when said parts are in engagement the space between said conductive members is substantially entirely filled by solid insulating means, the spacing between said conductive members and their dimensions being so related as to not greatly diier in the two parts of said connector, and an adjustable shunt loading impedance connected between said conductive members near one end of at least one of said parts.

8. A connector for connecting together high frequency transmission lines of similar characteristic impedance, including a pair oi separable parts, each part including at least a pair of electrically conductive members maintained in position relative to one another by solid insulating means, each of the electrically conductive members of one part having a corresponding member in the other part and arranged for telescopic engagement with the corresponding member in said other part, said solid insulating means being so arranged that when said parts are in engagement the space between said conductive members is substantially entirely filled by solid insulating' means, said connector having an electrical length, when said parts are in engagement, substantially equal to an integral muitiple of one-half wavelength, the spacing between said conductive members and their dimensions being so related as to not greatly differ in the two parts of said connector, and an adjustable shunt loading impedance connected between said conductive members near one end of at least one ci said parts, said impedance including a screw threaded member in engagement with one of said conductive members and in adjustable capacitive coupling relation with another of said members.

EDWARD CECIL CORK.

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

UNITED STATES PATENTS Number Name Date 2,207,690 Cork et al July 9, 1940 2,233,166 Hahn Feb. 25, 1941 2,241,582v Buschbeck et al May 13, 1941 2,267,371 Buschbeck Dec. 23, 1941 2,332,952 Tischer et al Oct. 26, 1943 2,401,344 Espley June 4, 1946 2,402,540 Espley June 25, 1946 FOREIGN PATENTS Number Country Date 488,254 Great Britain June 23, 1938

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