EP0108515B1

EP0108515B1 - Dish aerial

Info

Publication number: EP0108515B1
Application number: EP83306128A
Authority: EP
Inventors: Russel John Eberhardt; John Ernest Reginald Houchin
Original assignee: Cambridge Electronic Industries PLC
Current assignee: Cambridge Electronic Industries PLC
Priority date: 1982-10-11
Filing date: 1983-10-10
Publication date: 1989-05-31
Also published as: EP0108515A1; DE3380008D1

Description

This invention relates to dish aerials, for example, for the reception of satellite broadcast signals, or othr electro-magnetic radiation, although it may also be useful for transmitting signals.
One object of the present invention is to provide a design of a dish aerial including primary and secondary reflecting components enabling it - or a substantial part of it - to be moulded from a structural plastics material, and without there being the need for fine adjustment of the reflecting components of the aerial in relation to each other. Another object of the invention is to provide an aerial design enabling the signal receiving electronic components to be positioned in a region which can be protected from the weather.
According to the present invention, a dish aerial includes a dish having a primary reflecting surface, a component having a secondary reflecting surface held located to receive signals reflected from the primary reflecting surface by a ring of circumferentially spaced struts, and a housing disposed around the principal axis of the dish for accommodating electronic equipment to receive signals reflected from the secondary reflecting surface. The dish, struts, and housing are integrally moulded from plastics material.
The secondary component may also be moulded from plastics material, but there are applications in which it is desirable to have alternative secondary components with different radii of curvature and then it may be easiest to form them from sheet metal.
The housing disposed around the principal axis of the disc enables the first stage of the receiving chain to be at the or near the focus for received radiation, while yet being protected in the housing from the weather.
The housing is conveniently defined by a moulded cylindrical wall, integral with the moulded dish and the space within it can be closed off at one end by a mounting plate for the electronic equipment, and at the other end by a thin sheet of signal-transparent insulating material.
The housing wall or tube is preferably positioned at least partly behind the dish.
Grunzweig's German patent specification DE-A-2240893 and British specification GB-A-1384677 teaches the idea of moulding a primary dish integrally with a housing for electronic equipment, but a secondary reflecting surface is held on a long mechanical member extending along the axis of the dish in the manner of a cantilever, and serving as a conductor for signals from the secondary reflecting surface to equipment in the housing. The arrangement is subject to vibration and is very unsatisfactory for locating the secondary surface accurately in relation to the dish.
Grunzweig also refers to prior art consisting of a main reflector, electronic equipment mounted at the back of the main reflector, and an auxiliary reflector supported by struts from the edge of the main reflector. However, he does not suggest that those struts should be in an integral moulding with the main reflector and a housing for the electronic equipment.
Kathrein's German specification DE-A-1918084 also discloses a receiver having primary and secondary reflecting surfaces, but say anything about how they are formed, or how one is mounted in relation to the other.
The invention may be carried into practice in various ways, and one embodiment will now be described by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a sectional elevation of a dish aerial taken on the Line A-A in Figure 2;
Figure 2 is a partial rear view of the aerial of Figure 1; and
Figure 3 is a section to an increased scale on the line B-B in Figure 1.

The aerial includes a primary dish element 10 moulded from a thermoplastics structural foam comprising a low density cellular core enclosed within a solid integral skin. Thermoplastics structural foams are described in two papers in Materials in Engineering, Volume 3, at page 354, and 443 by P. R. Hornsby and many of the materials described in those papers can be used in dependence upon the application. In a preferred embodiment the plastics material is polypropylene with glass fibre reinforcing filler.
The dish element 10 has a parabolic cross section with a central opening leading to a space for electronic equipment to be described later. A secondary reflecting surface is defined by another element 30 pressed from sheet metal with a hyperbolic reflecting surface and that is held located in relation to the primary dish element by a circumferential ring of struts 11 disposed around the periphery of the secondary element 30 and the opening in the primary element 10.
The struts 11 are moulded integrally with the primary dish element 10 and engage in and are fixed in slots 13 in the edge of the secondary element 30.
After assembly, the primary and secondary reflecting elements are held in fixed relative positional relationship by the struts so that parallel radiation indicated generally at 14 in Figure 1, is reflected first to the secondary element 30, and then to a secondary focus 15 on the axis 12 within a space 16 defined at the rear of the primary dish element 10 by an integrally moulded rearwardly extending cylindrical housing 17.
The reflecting surfaces of the primary and secondary elements 10 and 30, if the latter is moulded integrally, are metallised or bear metal foil, and this may be on the front surface or the rear surface of the wall defining the element. The advantage of having the metallised layer on the first surface- encountered by the radiation is that the radiation is not refracted and does not have any loss due to having to traverse the thickness of the element twice at each reflecting surface. The advantage of having the metallised surface at the rear is that the metallised surface is not exposed to the atmosphere but is protected by the material of the element. The particular application will probably determine which system is used. Of course, if the secondary element is a metal pressing the convex face can be polished to define the reflecting surface.
It will be appreciated that some of the incoming signal will be lost from the secondary element 30 because of the presence of the struts 11, but this loss is likely to be quite small and not enough to outweigh the great advantage of being able to mount the two elements in a symmetrical arrangement about the principal axis 12 without having a separate supporting mechanism which has to be subsequently assembled with the dish.
The space 16 houses a wave guide horn 18 and an amplifier and down converter 19, mounted on a plate 21 held in position by bolts (not shown) in rod-like protuberances 22 surrounding the sleeve 17. An external coaxial cable 23 takes the signal from the converter 19 to remote signal processing equipment, and may be used to bring power to the amplifier and down converter. The wave guide horn 18 is mounted at the focus 15 of radiation from the secondary element 30.
Once the converter 19 and wave guide horn 18 have been positioned in the space 16, the rear of the space is closed off by the plate 21, and the front can also be closed off by a plate at 24, or even a sheet of plastics material so that the space 16 is protected from dirt and moisture from the atmosphere.
At the rear of the primary dish element 10 is provided with reinforcing ribs indicated generally at 25, and also three mounting lugs 26. Only two lugs are shown in Figure 2, which is an incomplete view although it is symmetrical about an axis parallel with and slightly to the left of the line AA.
It will be appreciated that different types of electronic equipment may be mounted in the housing at the start of the receiver chain. The position in the housing of the wave guide horn for receiving the reflected signal and feeding the chain will depend on the type of the equipment used and may require an appropriate secondary reflecting element to produce a focus at the wave guide horn, and to produce a cone of energy conforming to the waveguide horn acceptance angle.
In one preferred embodiment, the diameter of the primary dish 10 is about one metre, and the average wall thickness of the moulded components is about 6mm.

Claims

1. A dish aerial including a dish (10) having a primary reflecting surface, a component (30) having a secondary reflecting surface held located to receive signals reflected from the primary reflecting surface by a ring of circumferentially spaced struts (11), and a housing (17) disposed around the principal axis (12) of the dish for accommodating electronic signal-receiving equipment (19); characterised in that the dish (10), struts (11) and housing (17) are moulded of plastics material in a single integral moulding.

2. An aerial as claimed in Claim 1 in which closing means (21, 24) protects the interior of the housing from the environment.

3. An aerial as claimed in either of the preceding claims including a mounting means (26) for the dish integrally moulded at the rear of the dish.

4. An aerial as claimed in any of the preceding claims in which the secondary reflecting surface is on a component (30) which is removably attached to the holding means (11).

5. An aerial as claimed in any of Claims 1 to 3, in which the secondary reflecting surface is on a component (30) which is integrally moulded with the holding means, dish, and housing.

6. An aerial as claimed in any of the preceding claims in which the plastics material is in the form of a thermo-plastics structural foam comprising a low density cellular core enclosed within a solid integral skin, and possibly containing a reinforcing filler.

7. An aerial as claimed in any of the preceding claims in which either or each reflecting surface is defined by a metallic layer on a moulded plastics surface.