US3506935A - Nonreflecting coaxial line section - Google Patents

Description

April 14, 1970 s. MxNlcH NONREFLECTING COAXIAL .LINE SECTION Filed oct. 11, 1965 INVENTOR BYM/ I MM ,dfn- ATTQENE 5 s /M @13H INW m United States Patent O 3,506,935 NONREFLECTING COAXIAL LINE SECTION Sam Minich, Euclid, Ohio, assignor to Bird Electronic Corporation, Solon, Ohio, a corporation of Ohio Filed Oct. 11, 1965, Ser. No. 494,687 Int. Cl. H03h 7/38 U.S. Cl. 333-34 4 Claims ABSTRACT OF THE DISCLOSURE A nonreflecting coaxial line section for coupling coaxial lines to devices such as line terminations. The subject invention is capable of coupling a coaxial line to another device such as a resistive line termination within the shortest possible axial length while maintaining a voltage standing wave ratio of less than 1.20 for frequencies from direct current to 3,000 mc. This is achieved by employing tapered inner and outer conductors in which the taper is in the range of 20 to 40` degrees. In one embodiment, the taper is achieved by series of steps of relatively short axial length on both the inner and outer conductors. In another embodiment, the coupling device is comprised of conical surfaces having angles in the range of 20 to 40 degrees.

One of the problems encountered in coupling devices for coaxial lines is that of compensating for the irregularities or discontinuities between coaxial sections of different diameters and diameter ratios and for compensating for discontinuities between a coaxial line and a coaxial line device such as a line termination having a hornshaped outer conductor and a cylindrical resistive inner conductor.

It is known in the art to employ inhomogeneous sections as coupling devices between homogeneous sections of different diameter. Attempts have been made to ernploy a plurality of quarter-wavelength steps on the inner and outer conductor sections as transformer sections between coaxial lines of different diameters. One example of such use is shown in Figures 6-5, page 311 of a text entitled, Microwave Transmission Circuits by Ragan, copyright 1948. Examples of coaxial sections employing tapered inner and outer conductors are disclosed in Rose U.S. Patent 2,627,550 and an article entitled, Reflection Co-efiicient Curves of Compensated .Discontinuities on 'Coaxial Lines and the Determination of the Optimum Dimensions by A. Krous in the Journal of the British Institute of Radio Engineers, volume 20, No. 2, February 1960, page 145. None of these disclosures, however, reveal a coaxial line discontinuity which is relatively short in axial dimension and which may be particularly adapted to connect a coaxial line to a coaxial line termination Kwithout appreciably increasing the physical dimensions 4of housing for the line termination.

Accordingly, it is an object of this invention to provide an improved coaxial line discontinuity for connecting a rst coaxial line section to a second coaxial line section or to a coaxial line device.

It is another object of this invention to produce a coaxial line discontinuity with a minimum amount of reflection and which is relatively short in axial dimension.

Still another object of this invention is to provide a coupling device for a coaxial line termination which coupling device is relatively short in axial dimension and which produces a minimum of reflection.

Yet a further object of this invention is to provide an improved coaxial line coupling device which is simple and economical in construction, easy to assemble and contains relatively few parts.

Briefly in accordance with aspects of this invention,

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a relatively short coaxial line coupling section includes an annular outer conductor assembly having an interior surface with a mean slope in the range of 20 to 40 and an inner conductor assembly having a Meinke step. This particular embodiment is provided with a plurality of steps on the outer conductor and a like plurality of steps on the inner conductor each of which steps have their apices positioned along substantially straight lines and with one series of steps slightly axially displaced relative to the other series. Preferably the projection of the mean slope of the outer conductor intersects the axis of the inner conductor of the coaxial line or the extension of the axis of the line termination at an angle of at least 20 and in the preferred embodiment this angle is in the range of 25 to 40. Further, the steps on the outer conductor assembly constitute equal increments in diameter, i.e., equal steps from one end to the other. Also, the steps on the other conductor assembly are preferably of equal increments. In the preferred embodiment, the equal steps on one conductor correspond to the steps on the other in number and are slightly axially displaced relative to each other.

For example, each step may differ from the adjacent step by a change in diameter of 0.2 inch. In the instance of the outer conductor assembly, the cylindrical steps may have diameters of 3.4, 3.2, 3.0 and 2.8 inches, progressing toward the smaller coaxial line. Similarly, the inner conductor may have diameters of 0.9, 0.7, 0.5 and 0.3 inch, the steps of one series being substantially equal in axial length to the corresponding steps in the other series. Advantageously, an insulating sleeve encircles the smallest cylindrical section and projects beyond the endwall a limited distance into the housing to define with the adjacent larger cylindrical section of inner conductor a Meinke step.

In accordance with other aspects of the invention, a connector section or coaxial line discontinuity is provided in which the outer connector assembly is proivded with a frusto-conical inner surface which has a mean slope in the range of 20-40 toward a first apex and the inner connector assembly has a frustro-conical outer surface which tapers inwardly toward a second apex. In this particular embodiment, both frusto-conical surfaces taper along substantially parallel lines. This parallel relationship, however, is not critical. In the preferred embodiment for connecting a coaxial line to a line termination, the frusto-conical inner conductor portion tapers to a iirst cylindrical section having a diameter intermediate the diameter of the resistive inner conductor and the inner conductor of the coaxial line. This first cylindrical section is connected to a second cylindrical section the diameter of which is intermediate the diameter of the first cylindrical section and the pin which connects and is substantially equal in diameter to the inner conductor of the coaxial line. The insulating sleeve encircles this second cylindrical section and projects inwardly into the housing a relatively short distance to the first cylindrical section to define with the second cylindrical section a Meinke step.

These and various other objects and features of the invention will be more clearly understood from a reading of the detailed description of the invention in conjunction with the drawing in which:

FIGURE 1 is a fragmentary view in elevation, partly in section, of one illustrative embodiment of this invention; and

FIGURE 2 is a fragmentary elevational view, partly in section, of another illustrative embodiment of this invention.

Referring now to the 4drawing one illustrative embodiment of this invention is shown in FIGURE 1 in which a line termination 10 includes a lgenerally cylindrical housing 11 having oppositely disposed endwalls 12, 13, :ach secured to the housing 11 in fluid sealing relation- ;hip as will be subsequently described in detail. The housng 11 supports la plurality of radiating fins 14, only a few of which are shown for the sake of simplicity. A pair 3f Z-shaped feet 15 are secured to the lower portion of :he housing 11 as by Welding to support the housing 11.

The end wall 12 is secured to the housing 11 by a clampng ring 16 which is generally V-shaped in cross-section 1nd is securely held in position by a screw, not shown, which engages depending ears of the rin-g, also not shown. l`he clamping ring 16 engages a depending flange 17 of ;he housing 11 and also the edge of the endwall 12. The :ndwall 12 is provided with a recessed Ovring 18 which Jrevents the escape of the cooling dielectric fluid, not ihown, which substantially fills the housing 11.

A. coaxial connector 19 is mouned on endwall 12 for he purpose of connecting a coaxial line heat dissipating ermination 20 within the housing 11 to a coaxial line 51, shown in dotted outline. The coaxial connector 19 nay be of the type shown in Bird et al. Patent 2,966,- 545, issued Dec. 27, 1960 or it may be any other suittble type well known in the art. In this particular eximple, however, the connector substantially corresponds o the connector shown in FIGURE 3 of the above menioned Bird et al. Patent.

The heat dissipating line termination 20 includes an uter conductor 22 which is horn-shaped and which tap- :rs inwardly and is connected to a cylindrical resistive nner conductor 23 by means of a clamp 24 and a clampng screw 25. The line termination 20 is generally of the ype shown in Bird et al. Patent 3,158,823, issued Nov. 24, .964.

The line termination 20 is mounted on and connected o the endwall 12 by means of a novel nonreecting conlector section according to one illustrative e-mbodinent of this invention. The line connector section 30 ncludes an outer connector assembly 31 which is se- :ured to a cylindrical projection 32 of the endwall 12 y means of suitable screws such as screw 33. The outer `onnector assembly 31 includes a sleeve portion 34 which xtends over the screw 33 and extends within the cylinlrical portion of the outer conductor 22.

Advantageously the cylindrical outer connector section 1 has an inner surface which contains a first series of :ylindrical steps 38, 39, and 41 which are of pro- ;ressively decreasing diameter, in the direction of the oaxial line 21. Preferably, the apices of each of these `ylindrical steps is positioned on a sraight line 42 which epresents the mean slope of the inner surface and makes ,n angle of 'at least 20 with the axis of the coaxial lfne nd the coincident axis of inner conductor 23. In the preerred embodiment, the angle which line 42 makes with he axis 43 is at least 26, is in the range of 26-40 .nd in one particular instance was 261/2 The novel con- .ector section 30 also includes an inner connector secion 45 which contains a slotted sleeve portion 46 for nugly engaging the periphery of the terminal of the reistive inner conductor 23 in good electrical conducting elationship in a manner well known in the art. The inner onnector section 45 also includes a series of cylindrical teps 47, 48, 49 and 50 which are of progressively dereasing diameter in the direction of the coaxial line 21. `he smallest cylindrical section 50 has a bore 52 on the nterior thereof to receive a connector pin 53 of the co- `xial connector 19 in a manner well known in the art. ldvantageously, the apices of the cylindrical steps 47, 8 and 49 lie on a substantially straight line 54 which lakes an agle with the coaxial line axis 43, which angle i substantially equal to the angle formed by the line 42 :rough the apices of the steps on the outer connector ection 31. In other words, the line 54 is substantially arallel to the line 42.

In accordance with an important feature of the invenon, an insulating sleeve 55 encircles the cylindrical section 50. Sleeve 55 includes a reduced cylindrical portion 56 lying entirely within endwall 12 and a larger diameter cylindrical portion 57 which projects slightly into the interior of the housing 11. The projecting segment of sleeve portion 57 and the cylindrical section 50 comprise a Meinke Step which is a well known form 0f coaxial line discontinuity. For best results the projecting segment should not project beyond the endwall 12 more than .250. Also, the portion 57 of sleeve 55 should have a diameter greater than the dia-meter of section 49. In this particular embodiment, the diameter of section 57 is approximately equal to the diameter of inner connector section 47. The diameter of section 56 is substantially equal to that of connector section 48. The cylindrical steps of progressively decreasing diameter on the inner conductor 45 and on the outer connector section 31 are easy to machine and are therefore preferred fro-m the economy standpoint. Further, because of their relatively short axial dimension the inner and outer connector sections 45 and 31, respectively, provide for coupling between the coaxial line 21 and the line termination 20 within a relatively short axial dimension regardless of the large differences in diameters. Because of their peculiar electrical characteristics, the connector section 30 provides relatively low reflection while coupling coaxial sections which vary widely in diameter ratios. In one particular illustrative embodiment the diameter ratios are of the order of 10-1 and provide for good electrical transfer of energy in a range measured up to 3 kmc. with a voltage standing wave ratio which was less than 1.38.

Another illustrative embodiment of connector section is shown in FIGURE 2 for connecting the line termination 20 to the coaxial connector 19. In this particular embodiment, a connector section 60 is employed, which connector section includes an outer connector assembly 61 having a frusto-conical inner surface 62, a sleeve member 63 which encircles the member y61 and receives the cylindrical portion of the horn-shaped outer conductor 22, and an inner connector element `64 having a frusto-conical outer surface 65 which connects a slotted sleeve section 66 to a first reduced cylindrical section 67, intermediate in diameter to the diameter to the cylindrical sleeve section 66 and a second cylindrical section 68. The reduced cylindrical section 68 has a bore on the interior to receive the connector pin of the coaxial connector 19 in a manner similar to that of section 50 of FIGURE 1. Also, the insulating sleeve 55 of FIGURE 1 is employed in the embodiment of FIGURE 2 with section 57 projecting a relatively short distance into the interior housing 11, not shown in FIGURE 2. The section 57 preferably projects less than .250 beyond the endwall 12 and cooperates with cylindrical inner conductor section 68 to define a Meinke step. The outside diameter of section 57 is less 'than the outer diameter of resistor 23 and greater than the diameter of section 72. The diameter of section 56 of sleeve 55 is greater than the diameter of inner conductor section 72 and less than the diameter of section 57.

Advantageously the frusto-conical surface 62 tapers along a line 70 at an angle of the order of 26 and in the particular example illustrated is 26%". The frusto-conical surface 65 on the inner connector assembly 64 preferably tapers along a line 72 substantially parallel to the line 70 In this particular example the line 72 forms an angle of approxiamtely 25 with the axis of the coaxial line termination 20. The assembly of FIGURE 2 constitutes an irnproved embodiment relative to the first embodiment shown in FIGURE 1 from the electrical standpoint. However, the embodiment of FIGURE 2 is more difficult to machine and therefore more expensive. The embodiment in FIGURE 2 constitutes an arrangement for producing a compensated discontinuity or coupling section which is relatively short and offers a minimum of reflection between coaxial line sections of a coaxial line section and a coaxial device where the diameter ratios are relatively large.

While two illustrative embodiments have beed described in detail, it is understood that the concepts thereof could be employed in other embodiments without departing from the spirit and scope of this invention. For example, while the mean slope of line 42 relative to axis 43 of FIG- URE 1 and line 70 relative to 71 are substantially the same, i.e., 261/2 it is understood that suitable results are obtained if the mean slope exceeds 20 and is less than 40. The number of steps in the embodiment of FIGURE 1 on the inner connector element 4S should be substantially equal to and slightly displaced from the corresponding steps 38 through 41 on the outer connector assembly 31.

The term mean slope means the effective slope of a line through the projecting apices of a plurality of steps or the slope of a smooth wall, both relative to the axis of the inner conductor.

I claim:

1. A couplig device for connecting a coaxial line to a coaxial line termination having front and rear ends, and having a voltage standing wave ratio less than 1.38 for frequencies up to 3 kilomegacycles, an outer elongated circular sectioned sleeve conductor tapering inwardly from a relatively large diameter at its front end to a relatively small diameter at its rear end, a resistor coaxially mounted within and generally spaced from said sleeve, one end of said resistor being electrically connected to the rear end of said sleeve conductor and a fluid tight housing enclosing said line section, including an endwall cornprising:

outer connector means adapted to connect said outer f conductor of said coaxial line to said sleeve conductor; and

inner connector means for connecting the other end of said resistor to the inner conductor of said coaxial line, said outer connector means having a section which has a mean slope toward the axis of said coaxial line in the range of between 20 and 40 and wherein said inner connector means includes at least two cylindrical sections of dilferent diameters and an annular insulating member encircling the smaller of said two cylindrical sections and having its major portion positioned within said endwall and having a minor portion projecting beyond said endwall into said housing.

2. A coupling device for connecting a coaxial line to a coaxial line termination having front and rear ends, and having a voltage standing wave ratio less than 1.38 for frequencies up to 3 kilomegacycles, an outer elongated circular sectioned sleeve conductor tapering inwardly from a relatively large diameter at its rear end, a resistor coaxially mounted within and generally spaced from said sleeve, one end of said resistor being electrically connected to the rear end of said sleeve conductor and a lluid tight housing enclosing said line section, including an endwall comprising:

outer connector means adapted to connect said outer conductor of said coaxial line to said sleeve conductor; and

inner connector means for connecting the other end of said resistor to the inner conductor of said coaxial line, said outer connector means having a section which has a mean slope toward the axis of said coaxial line in the range of between 20 and 40 and wherein said inner connector means includes at least two cylindrical sections of different diameters and an annual insulating member encircling the smaller of said two cylindrical sections and having its major portion positioned within said endwall and having a minor portion projecting beyond said endwall into said housing; said section of said outer connector means including a plurality of stepped cylindrical portions; said inner connector means having the same number of stepped cylindrical sections as the number of stepped cylindrical portions on said outer connector means.

3. A coaxial line discontinuity connecting a first coaxial line section to a second coaxial line section of larger diameter than said first section while exhibiting a voltage standing wave ratio less than 1.38 for frequencies up to 3 kilomegacycles comprising:

outer conductor means connecting the outer conductors of said iirst and second line sections and having a series of right angle transitions on its inner surface wherein the apices of all of the right angles of the series lie on a straight line, said straight line having a mean slope in the range of between 20 and 40;

inner conductor means connecting the inner conductors of said rst and second line sections and having a second series of right angle transitions, and an insulating sleeve on one portion of said inner conductor means and dening therewith a Meinke step.

4. A discontinuity according to claim 3 wherein said mean slope is at least 26.

References Cited UNITED STATES PATENTS 3,095,545 6/1963 Bird et al. 333-22 2,793,352 5/1957 Bird 339-177 3,213,392 10/1965 Hedberg 333-122 3,350,666 10/1967 Zeigler 333-33 3,296,560 1/ 1967 Calderhead 333--22 3,311,856 3/1967 Conney 333--22 2,968,774 1/1961 Rodriguez 333-22 HERMAN KARL SAALBACH, Primary Examiner C. BARAFF, Assistant Examiner U.S. Cl. X.R.

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