AU592183B2 - A transmission delay line and method of manufacture - Google Patents

Description

PCT

AU-AI-7300 2 /87 R a WORLD INTELLECTUAL PROPERTY O 1 International Bureau INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT) (51) International Patent Classification 4 (11) International Publication Number: WO 87/ 06065 H01P 9/00, 9/02 Al (43) International Publication Date: 8 October 1987 (08.10.87) (21) International Application Number: PCT/AU87/00104 (74) Agent: COLLISON CO.; 117 King William Street, Adelaide, S.A. 5000 (AU).

(22) International Filing Date: 2 April 1987 (02.04.87) (81) Designated States: AU, DE (European patent), GB (31) Priority Application Number: PH 5293 (European patent), IT (European patent), SE (European patent), US.

(32) Priority Date: 2 April 1986 (02.04.86) (33) Priority Country: AU Published With international search report.

With amended claims.

(71) Applicant (for all designated States except US): THE COMMONWEALTH OF AUSTRALIA, care of THE SECRETARY DEPARTMENT OF DEFENCE [AU/AU]; Anzac Park West Building, Constitution Avenue, Canberra, ACT 2600 2 NOV 1987 (72) Inventor; and Inventor/Applicant (for US only) DADSWELL, Peter, John [AU/AU], 10 Duffield Street, Gawler, S.A. 5118 U.

AUSTRALIAN

This document co tains the 20 OCT 1987 amendmcnts mad e under Section 49 and is correct for PATENT OFFICE printing (54) Title: A TRANSMISSIGN DELAY LINE AND METHOD OF MANUFACTURE a L (57) Abstract A transmission delay line comprising a helical channel formed in the surface of a cylinder with a conductive sleeve fitted to said cylinder to close the channel, a helical conductive member is positioned within said channel (2) and spaced from the walls thereof by a dielectric material WO 87/06065 PCT/A U87/00104 1.

TRANSMISSION DELAY LINE AND METHOD OF

MANUFACTURE

This invention relates to an improved transmission line device for delaying electromagnetic energy and a method of manufacturing such a device.

BACKGROUND OF THE INVENTION Hollow metallic tubes (waveguides) of various cross-section exhibit well known properties which fit them for use as a delay mechanism for electromagnetic waves. Such tubes, which propagate TE waves, are characterised by a wide bandwidth capability and a low insertion loss which is essentially constant over the operating range.

The family of transmission lines which include suspended stripline, image line, co-axial line and so on, propagate TEM or quasi TEM waves and are also suitable for use as delay lines, but such devices, in general, exhibit a higher insertion loss due, in part, to energy losses in the dielectric component, The cost of amplification at microwave frequencies is high. Consequently insertion loss will be an important consideration where a design calls for a substantial delay. The use of waveguide may be indicated by virtue of its characteristic low insertion loss, but where the design is also sensitive to cost, weight and volumetric efficiency the deployment of many metres of commercial waveguide section is likely to pose a problem.

WO 87/06065 PCT/AU87/00104 2.

According to our earlier invention, as published under PCT No. AU85/00171, an improved waveguide delay line is disclosed comprising a helical conducting channel formed in a cylinder, such as by machining, such channel being closed by a tightly fitting conducting sleeve.

The method there disclosed of fabricating a waveguide delay line for use at microwave frequencies teaches a way of retaining the low insertion loss characteristic of waveguide whilst affording improved volumetric efficiency low weight and low cost of manufacture. In addition, a delay line so constructed can be integrated into a parent structure as a load-bearing member.

It will be appreciated that in many weight sensitive applications this duality of electronic function and mechanical load-bearing capability enhances the cost effectiveness of the method of fabrication disclosed.

In summary, a waveguide delay line as de:scribed in the earlier Patent specification confers certain advantages: a structure that can be integrated into a system as a load bearing member occupying minimum volume; extremely low weight per unit delay; low cost of manufacture; low cost penalty for varying design parameters; 3.

the low insertion loss characteristic of normal commercial waveguide.

The object of the present invention is to provide an improved transmission line device for use as a delay mechanism by using the general method of construction of the invention referred to earlier herein, but with the addition of a conducting member supported within the said helical channel.

With such an addition well known forms of transmission line suitable for use as a delay line can be fabricated such as, for example, suspended strip line and co-axial Ifne, but which now, by virtue of the present invention, show an improved electrical performance whilst also possessing the advantages indicated in and above.

BRiEF STATEMENT OF THE INVENTION o 20 Accordingly, the present invention comprises a transmission delay line comprising a single centre conductor formed in a helix and supported coaxially within an elongated helical channel formed in the wall of a cylinder so as to provide the channel with electrically conductive surfaces, the said channel being closed by a conductive sleeve in the co-axial line so formed being characterised by the space between the single centre conductor and the enclosing channel walls being substantially free of any dielectric material other than air or an introduced inert gas such mechanical support as is necessary to 30 maintain the single centre conducting helix co-axial within the closed channel being provided by supports of low density dielectric material to support the single centre conductor co-axially within the channel, the co-axial line so formed being further characterised by affording an unbroken and unimpeded passage for air or an introduced inert gas along the elongated helical passage formed between the single centre conductor and the outer enclosing conductive wall.

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WO 87/06065 PCT/AU87/00104 DESCRIPTION OF THE DRAWINGS To enable the invention to be fully appreciated, embodiments thereof will now be described with reference to the accompanying drawings, but the invention need not necessarily be limited to the form shown.

In the drawings, FIG. 1 and 2 10.

FIG. 3 FIG. 4 are longitudinal sectional views and a transverse section on line 2.2 of FIG, 1 respectively of a preferred form, shows the components before assembly, shows a method of assembly, show examples of dielectric support geometry suitable for circular section conductors and shows a support geometry suitable for a strip conductor, and are longitudinal sectional views and a transverse section on line 7.7 of FIG. 6 of a second preferred form.

FIG. 5 (a) and (b) (c) FIGS. 6 and 7 WO 87/06065 PCT/AU87/00104 DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 to 5 the cylinder 1 has in it a helical channel 2 formed between peripheral walls 3, the channel having positioned in it the helical conducting member 4 supported by spaced dielectric spacers The helical conducting member 4 may be pre-formed as a spring and during assembly may be counter wound as shown in FIG. 4 on to a tubular support 6 which is placed over cylinder 1 in which the helical channel 2 is formed, and when the tubular support 6 is axially withdrawn the convolutions of the helical conductor 4 contract into position in the helical channel 2.

After positioning the helical conductor 4 in the channel the helical conductor can have its ends coupled to the centre conductor of short lengths of semirigid cable mounted in segmental blocks 8 engaged in and secured to the helical channel 2.

The structure is completed by the sleeve 7 which is assembled over the cylinder I to close the helical channel.

Thus the helical conducting member 4 is separated from the walls of the chahnel 2, the dielectric spacers being such that air is the predbminant dielectric material.

WO 87/06065 PCT/A U87/00104 6.

FIG. 5 shows three alternate forms of dielectric section, embodiments A and B being suitable for a circular sectioned conductor, with embodiment A having a groove or recess in one surface of a block, while embodiment B has spaced legs to bear on the bottom of the channel. Embodiment C shows a further alternative suitable for a strip conductor, the spacer having a pair of notched arms into which the strip conductor may be fitted.

In a further preferred form of the invention as shown in FIGS. 6 and 7, the dielectric support is a dielectric bed 10 in the form of a continuous strip laid in the channel 2. This eliminates the need to assemble separate supports in staggered pattern and thus eliminates cyclic build up of losses which would occur with regular spacing. Preferably the dielectric material is a low density foam material.

The improved electrical performance of the delay line here disclosed flows from the geometry which permits the line to be virtually air-cored whilst retaining those mechanical properties appropriate to the maintenance of electrical performance even when exposed to high forces. With air as the substantial dielectric the surface area of the conducting elements can be increased for any given Z 0 with a subsequent reduction in 12 losses there being an optimum Z 0 at which such losses can be minimised whilst retaining the same mode-free bandwidth. Further, the insertion loss due to a solid load bearing dielectric such as that normally associated with coaxial cable, for example, is virtually eliminated.

_r WO 87/06065 PCT/A U87/00 104 7.

Dimensioned to be mode-free in the K band, for example, an insertion loss of 15 dB/100 ft at 18 GHz is readily achieved by the co-axial form of the present invention, with a significant weight advantage per unit delay over typical low-loss co-axial cable.

A further cost/weight advantage flows from the mechanical load bearing capability of the line here disclosed.

In additic- to low weight, high strength and low insertion loss, further advantages which stem from a virtually air-cored line constructed according to the present invention are: enhanced phase stability; relative freedom from phase change with temperature; relative freedom from increased attenuation due to ageing or the permanent increase in attenuation often induced by exposure to high temperature.

The method of construction consists of machining or otherwise forming a conducting channel, preferably of square or rectangular section, in the wall of a first member, preferably tubular, and assembling a conductive l:*'ement within the channel so formed, the location of the conductive element being determined I by the geometry of the supporting dielectric placed in the channel.

WO 87/06065 PCT/AU87/00104 8.

The geometry of the delay line is such that the dielectric need occupy only half of the channel section to support the centre conducting helix. Further, the dielectric is not required to resist the mechanical stresses normally associated with a flexible co-axial cable; the dielectric of the helical line need resist only the distributed forces generated by the light-weight centre helix under operational conditions.

Thus, the material chosen for the dielectric can have a dielectric constant approaching that of air whilst still possessing sufficient mechanical strength to support the helix.

The outer conductive thin wall sleeve can be assembled over the first tubular member by a simple differential heat process to close the open helical channel.

In the co-axial form, with air as the substantial dielectric, the centre conductor which may be of aluminium alloy will normally be of a diameter such that it can be pre-wound as a self-supporting helix on a mandrel, the mandrel being so dimensioned that upon release the helix will spring to a greater diameter than the orginal winding but still such as to exert a 'grip' upon the supporting dielectric support when assembled. The centre conductor can be silver plated and protected by a suitable conformal coating. Feed connections to the inner conductor can be by standard commercial connectors.

Claims (5)

1. 4-+ AMENDED CLAIMS [received by the International Bureau on 12 August 1987 (12.08.87) original claims 1-9 replaced by amended claims 1-8 (3 pages)] 1. A co-axial transmission delay line comprising: a single centre conductor formed in a helix and supported co-axially within an elongated helical channel formed in the wall of a cylinder (1) so as to provide the channel with electrically conductive surfaces, the said channel being closed by a conductive sleeve in the co-axial line so formed being characterised by the space between the single centre conductor and the enclosing channel walls being substantially free of any dielectric material other than air or an introduced inert gas such mechanical support as is necessary to maintain the single centre conducting helix co-axial within the closed channel being provided by supports of low density dielectric material to support the single centre conductor co-axially within the channel, the co-axial line so formed being further character- ised by affording an unbroken and unimpeded passage for air or an introduced inert gas along the elongated helical passage formed beteen the single centre conductor and the outer enclosing conductive wall. 2. A co-axial transmission delay line as defined in claim 1 characterised in that the helical channel is formed on the outer surface of a metallic conducting cylinder and a metallic conductive sleeve(7) is shrunk over said cylinder by a different- ial heat process to provide a mechanical load bearing structure. -oU C) i: WO 87/06065 PCT/AU87/00104 \0 3. A co-axial transmission delay line as defined in claim 1 characterised in that said dielectric support material comprises small shaped spacers spacing said single centre conductor from the bottom of said channel with air or an introduced inert gas thus forming the predominant dielectric material. 4. A co-axial transmission delay line as defined in claim 1 characterised in that said dielectric support material comprises a profiled bed support- ing said single centre conductor from the bottom of said channel w5'.h air or an introduced inert gas thus forming the predominant dielectric material A co-axial transmission delay line as defined in claim 1 or in claim 3 characterised in that said single centre conducting helix is a pre-formed helical spring so that the convolutions thereof contract onto the dielectric support
2. 6. A co-axial transmission delay line as defined in claim 4 characterised in that the single centre conductor is wound directly onto the continuous dielectric bed set within the channel
3. 7. A co-axial transmission delay line as defined in claim 1 is characterised in that said single centre conducting helix is connected at each of its ends to c semi-rigid cable mounted in segmental blocks secured in said helical channel
4. 11. 8. A method for manufacturing a coaxial transmission delay line, comprising providing a cylindrical tube of electrically-conductive material having a radially outwardly-extending helical wall cycling helically thereabout between axially opposite ends of said cylindrical tube on a radially outer peripheral surface of said cylindrical tube, said helical wall having a radially outer edge which is disposed a constant radial distance from said radially outer peripheral surface of said cylindrical tube, successive turns of said heJical wall being axially spaced so as to define a helical slot of space; providing support means made of low density dielectric material, said support means being received in said helical slot so as to be present at at least a plurality of sites per helical turn of said helical slot, said support means being supported from said radially outer peripheral surface of said cylindrical tube and having a thickness, extending S: radially outwardly of said radially outer peripheral surface of said cylindrical tube, which is less than said constant radial distance, whereby a helical gap remains between a radially outer surface of said S* support means and said radially outer edge of said helical wall, said support means having a radially outwardly-facing seat means provided thereon, said seat means being located laterally intermediate respective adjacent turns of said helical wall, said seat means extending helically with said helical slot so as to be located generally centrally of said helical slot at said sites; providing a single center conductor as a spring-like member formed in a helix having a given internal diameter when in a radially unexpanded state; 30 providing a tubular support member having an end and having an outer peripheral surface which has a larger diameter than said given internal diameter, said tubular support having an inner peripheral "surface which is at least as large as the radially outer diameter of said helical wall; radially resiliently expanding said single center conductor into a radially resiliently expanded state and sleeving said single center conductor in said radially resiliently expanded state onto said outer 7T peripheral surface of said tubular support member;. i
5. 12. sleeving said tubular support member bearing said single center conductor in said radially resiliently expanded state onto said cylindrical tube, radially outwardly of said helical wall; while progressively axially de-sleeving said tubular support in relation to said cylindrical tube, progressively slipping said single center conductor off said end of said tubular support so that said single center conductor at least partially recovers towards said radially unexpanded state thereof and progressively becomes supported in said seat means of said support means; providing a sleeve of electrically-conductive material having a radially inner peripheral surface; and sleeving said sleeve of electrically conductive material onto said cylindrical tube so that said sleeve of electrically-conductive material radially surrounds said helical wall between said axially opposite ends So. of said cylindrical tube and said radially inner peripheral surface *c engages said radially outer edge of said helical wall, thereby defining a 20 radially outer limit to said helical slot of space so that said helical slot of *004 space forms a helical channel having a given transverse cross- sectional shape, viewed on a longitudinal section of said coaxial transmission delay line. S.. DATED this 13th day of February, 1989. THE COMMONWEALTH OF AUSTRALIA, By their Patent Attorneys, COLLISON CO. i 0 0