GB2142782A

GB2142782A - Method of producing a circular polariser radome

Info

Publication number: GB2142782A
Application number: GB08317641A
Authority: GB
Inventors: William John Cole
Original assignee: Decca Ltd
Current assignee: Decca Ltd
Priority date: 1983-06-29
Filing date: 1983-06-29
Publication date: 1985-01-23
Also published as: GB8317641D0

Abstract

The application discloses a method of producing a circular polarising radome having coaxial inner and outer cylinder shells 5 and 7 respectively. The method includes the steps of forming the inner and outer radome shells by extrusion of a plastics material, printing a circular polarising grid network 11 on to the outer surface of the cylinders, mounting the inner cylinder coaxially with the outer cylinder. At least one of the extruded cylinder shells includes radial flanges 2 adapted to maintain the cylinders coaxial. The inner cylinder also includes axially facing retainers 12 adapted to locate with and maintain in position a microwave antenna 3, 4. A ring 9 encircling the outer shell can screw on to a reciprocal thread on an open end of a microwave waveguide 10 in order to attach the radome to the microwave waveguide. <IMAGE>

Description

SPECIFICATION Method of producing a circular polariser radome This invention relates to circular polariser radomes and methods of manufacture thereof.

It is known to produce a circular polariser radome by forming inner and outer cylinder shells from fibre glass, attaching a circular polarising grid network to one or both of the cylinder shells and maintaining the inner and outer shells in coaxial alignment by filling the space therebetween with a suitable free foaming material. A linear microwave antenna located within the inner cylinder radiates linear microwaves which are circularly polarised by the radome.

There is provided according to the invention a method of producing a circular polarising radome having coaxial inner and outer cylinder shells including the steps of a. forming the inner and outer radome cylinder shells by extrusion of a plastics material b. printing a circular polarising grid network onto the surface of said cylinders, and c. mounting the inner cylinder coaxially in the outer cylinder.

By forming the radome using this method the inner and outer shells can be produced cheaply and quickly and the circular polarising grid does not need mounting with regard to the cylinder shells. Conveniently alternative forms of polarising grid can be printed on the surfaces of the cylinders. Preferably at least one of the cylinder shells includes radial flanges adapted to maintain the cylinders coaxial. These flanges can be produced during the process of extrusion of the inner and outer shells thereby removing any necessity to fill the space between the inner and outer cylinder shells with a free foaming material. Furthermore the inner extruded cylinder can conveniently include axially facing retainers which can be adapted to locate with and maintain in position a microwave antenna.The upper end of the coaxial cylinders can be sealed and the radome outer surface then coated with a suitable microwave transparent protective skin.

The lower end of the outer cylinder can be extruded to include a flange which it is adapted to locate with a threaded ring for attachment to a flange of an open end of a microwave wave guide.

Examples of the present invention will now be described with reference to the accompanying drawings, in which Figure 1 illustrates a partially cut-away perspective view of a circular polarising radome embodying the invention.

Figure 2 illustrates a horizontal section through the radome shown in Fig. 1, along line ll-ll.

Referring to the drawings, a circular polarising radome comprises an inner cylinder 5 and an outer cylinder 7 produced by extruding a plastics material. A circular polarising grid network 11 is printed onto the outer surface of the cylinders, although clearly the network could be printed on both inner and outer surfaces of the cylinders. The network can be printed by means of for example, silk screen printing or photolithographic printing. The inner cylinder 5 is mounted coaxially in the outer cylinder 7 and maintained in coaxial alignment by means of radial flanges 2 which can be formed during the extrusion of one or both of the cylinders.

Retainers 1 2 can also be formed during extrusion of the inner cylinder 7. These retainers are adapted to maintain in position a board 3 carrying a microstrip array antenna 4 printed thereon. It will be apparent that other forms of microwave antenna could be held by the retainers. The micro-strip array antenna 4 radiates iinearly polarised microwaves taken from a wave guide 10. The microwaves pass through the circular polarising grid network 11 which, as is known, converts the radiation to circular polarised microwaves.

The lower end of the outer cylinder 7 can be formed during extrusion to have a lower flange (not shown) which locates with a threaded ring 9 which is adapted to screw onto a flange 10 provided at an open end of the microwave wave guide. Dowels 8 in the flange 10 can.be employed to aid alignment of the radome with the flange. The radome upper end can be sealed and a protective skin 6 can be applied to the radome outer surface, clearly the protective skin will be suitably microwave transparent.

Therefore a simple and cheap method of production of a circular polarising radome is disclosed which is also simple and quick to assemble.

1. A method of producing a circular polarising radome having coaxial inner and outer cylinder shells including the steps of a. Forming the inner and outer radome cylinder shells by extrusion of a plastics material b. printing a circular polarising grid network onto the surface of said cylinders, and c. mounting the inner cylinder coaxially in the outer cylinder.

2. A method as claimed in claim 1, wherein the grid network is printed only on the outer surface of the cylinder shells.

3. A method as claimed in claim 1 or 2 wherein at least one of the extruded cylinder shells includes radial flanges adapted to maintain the cylinders coaxial.

4. A method as claimed in any preceding claim wherein the extruded inner cylinder includes axially facing retainers adapted to locate with and maintain in position a microwave antenna.

5. A method as claimed in any preceding

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Method of producing a circular polariser radome This invention relates to circular polariser radomes and methods of manufacture thereof. It is known to produce a circular polariser radome by forming inner and outer cylinder shells from fibre glass, attaching a circular polarising grid network to one or both of the cylinder shells and maintaining the inner and outer shells in coaxial alignment by filling the space therebetween with a suitable free foaming material. A linear microwave antenna located within the inner cylinder radiates linear microwaves which are circularly polarised by the radome. There is provided according to the invention a method of producing a circular polarising radome having coaxial inner and outer cylinder shells including the steps of a. forming the inner and outer radome cylinder shells by extrusion of a plastics material b. printing a circular polarising grid network onto the surface of said cylinders, and c. mounting the inner cylinder coaxially in the outer cylinder. By forming the radome using this method the inner and outer shells can be produced cheaply and quickly and the circular polarising grid does not need mounting with regard to the cylinder shells. Conveniently alternative forms of polarising grid can be printed on the surfaces of the cylinders. Preferably at least one of the cylinder shells includes radial flanges adapted to maintain the cylinders coaxial. These flanges can be produced during the process of extrusion of the inner and outer shells thereby removing any necessity to fill the space between the inner and outer cylinder shells with a free foaming material. Furthermore the inner extruded cylinder can conveniently include axially facing retainers which can be adapted to locate with and maintain in position a microwave antenna.The upper end of the coaxial cylinders can be sealed and the radome outer surface then coated with a suitable microwave transparent protective skin. The lower end of the outer cylinder can be extruded to include a flange which it is adapted to locate with a threaded ring for attachment to a flange of an open end of a microwave wave guide. Examples of the present invention will now be described with reference to the accompanying drawings, in which Figure 1 illustrates a partially cut-away perspective view of a circular polarising radome embodying the invention. Figure 2 illustrates a horizontal section through the radome shown in Fig. 1, along line ll-ll. Referring to the drawings, a circular polarising radome comprises an inner cylinder 5 and an outer cylinder 7 produced by extruding a plastics material. A circular polarising grid network 11 is printed onto the outer surface of the cylinders, although clearly the network could be printed on both inner and outer surfaces of the cylinders. The network can be printed by means of for example, silk screen printing or photolithographic printing. The inner cylinder 5 is mounted coaxially in the outer cylinder 7 and maintained in coaxial alignment by means of radial flanges 2 which can be formed during the extrusion of one or both of the cylinders. Retainers 1 2 can also be formed during extrusion of the inner cylinder 7. These retainers are adapted to maintain in position a board 3 carrying a microstrip array antenna 4 printed thereon. It will be apparent that other forms of microwave antenna could be held by the retainers. The micro-strip array antenna 4 radiates iinearly polarised microwaves taken from a wave guide 10. The microwaves pass through the circular polarising grid network 11 which, as is known, converts the radiation to circular polarised microwaves. The lower end of the outer cylinder 7 can be formed during extrusion to have a lower flange (not shown) which locates with a threaded ring 9 which is adapted to screw onto a flange 10 provided at an open end of the microwave wave guide. Dowels 8 in the flange 10 can.be employed to aid alignment of the radome with the flange. The radome upper end can be sealed and a protective skin 6 can be applied to the radome outer surface, clearly the protective skin will be suitably microwave transparent. Therefore a simple and cheap method of production of a circular polarising radome is disclosed which is also simple and quick to assemble. CLAIMS

5. A method as claimed in any preceding claim wherein the step of printing comprises photographic printing.

6. A method as claimed in any preceding claim including the step of forming the lower end of the outer shell to have a flange capable of attachment to an open end of a microwave wave guide by a retaining means.

7. A method as claimed in claim 6 wherein the retaining means comprises a circular threaded ring having a ring flange on an upper side thereof encircling the outer shell so that when the ring is screwed into a reciprocal thread provided on the waveguide the ring flange bears against the shell flange to attach the radome to the microwave waveguide.

8. A method as claimed in any preceding claim including the step of sealing the upper end of the coaxial cylinder and coating the radome outer surface with a protective skin substantially transparent to radiation to be radiated therefrom.

9. A circular polarising radome having coaxial inner and outer cylinder shells with a circular polarising grid network printed onto the surfaces of said shells as produced by a method according to any preceding claim.

10. A circular polarising radome having coaxial inner and outer cylinder shells with a circular polarising grid network printed onto the surface of said cylinder, substantially as herein described with reference to the accompanying drawings.

11. A method of producing a circular polarising radome having coaxial inner and outer cylinder shells, substantially as herein described with reference to the accompanying drawings.