GB2124431A - Improvements in or relating to reflectors - Google Patents

Abstract

A dish reflector is provided for use in a radio antenna which is built up of segments 9-28 each of which has a reflective surface consisting of a laminate of two perforated sheets 2, 3, of reflective material (e.g. stainless steel) each of which is formed into a desired shape, by virtue inter alia of its perforations without the use of a stretched forming technique. The two perforated sheets are formed into a desired shape by means of a former and united with the perforations 4 in one staggered relative to the perforations 5 in the other. The laminate sheet of each segment is backed by means of a box section, the interior of which, closed by its laminate sheet being filled with setable urethane resin. <IMAGE>

Description

SPECIFICATION Improvements in or relating to reflectors This invention relates to reflectors and in particular to dish reflectors as used in certain types of radio antenna.

A typical known method of constructing a dish reflector for use in a radio antenna consists of stretch forming an aluminium sheet to provide a required double curvature which is then rivetted on to an accurately constructed sub-frame consisting of a network of metal tubes. This subframe is then fixed to a main frame again formed as a tubular structure but, of course, without necessarily being made to the same degree of accuracy. The whole assembly then has to be set up by adjusting the curvature of the stretch formed aluminium surface to provide the required beam shape.

The above construction is subject to four main sources of error which may be summarised as (a) errors in the original stretch forming (b) errors associated with the sub-frame (c) the accuracy with which the stretch formed aluminium sheet is rivetted to the sub-frame (d) the accuracy with which the final setting up is carried out.

The whole construction process is a relatively complicated and time consuming one particularly if the accuracy of the final shape of the reflector is to be of a high order.

The present invention seeks to provide an improved reflector, and in particular an improved dish reflector for use in a radio antenna, in which one or more of the above mentioned difficulties is mitigated.

According to this invention in its broadest aspect, a reflector is provided having a reflective surface consisting of two perforated sheets of reflective material formed into a desired shape and arranged with the perforations in one staggered relative to the perforations in the other, said two sheets being fixed one to the other and to a supporting structure by means of which said reflector may be mounted.

According to a feature of this invention a reflector is provided having a reflective surface consisting of two perforated sheets of reflective material each of which sheets may, by virtue inter alia of its perforations, be formed into a desired shape without the use of a stretch forming technique, the two perforated sheets being formed into a desired shape and arranged with the perforations in one staggered relative to the perforations in the other, said two sheets being fixed one to the other and to a supporting structure by means of which said reflector may be mounted.

Preferably said two perforated sheets are fixed one to the other by means independent of the fixing of the combination of the two sheets to said supporting structure.

Particularly where said reflector is to form part of a radio antenna, each of said perforated sheets is of stainless steel in which case said means for fixing one to the other preferably comprises spot welding.

Preferably said supporting structure comprises an open metal box section which is closed by the combination of said two perforated sheets.

Preferably the interior of the closed box section formed by said open box section and the combination of said two perforated sheets is filled with a setable urethane resin.

Preferably said box section includes internal strengthening ribs which are perforated whereby to permit said urethane resin to interlock either side of said ribs.

Where said reflector is of relatively small size the entire reflector may be formed of the combination of one united pair of perforated sheets and one supporting box section.

Where the desired size of said reflector renders the use of the combination of a single united pair of perforated sheets inconvenient, preferably the reflector is made up of segments each of which consists of the combination of a united pair of perforated sheets supported by a box section.

In the last mentioned case, preferably said individual segments are located on and carried by a main supporting member with the box section of each segment being accurately located with reference to said main supporting member.

Preferably said main supporting member is itself a box section.

In the case of a circular dish reflector, said main supporting member preferably comprises a continuous hollow toroid of rectangular cross section, there being mounted on the outer and inner sides thereof said segments which together form said dish.

The invention is illustrated in and further described with reference to the accompanying drawings, in which Figure 1 illustrates the arrangement of two perforated sheets as used in one example of reflector in accordance with the present invention, Figure 2 is a view of the two sheets of Figure 1 taken in the direction of the arrow 1 in Figure 1, Figures 3, 4 and 5 illustrate the construction of a segment of reflector which may be united with other segments to form a complete reflector, Figure 6 is a view looking into a reflector formed of different segments and in accordance with the present invention, and Figure 7 shows a section along the line A. . A of Figure 6.

Referring to Figures 1 and 2 the reflective surface of the reflector consists of two perforated stainless steel sheets referenced 2 and 3.

Alternatively the sheets may be aluminium. The perforations in each case are circular ones, representative ones in sheet 2 being referenced 4 and those in sheet 3 being referenced 5. Each perforated sheet is thin (typically of the order of ten thousandths of an inch) and this, with the perforations therein, enables each sheet to be formed into a desired shape corresponding to the shape desired of the reflective surface to be provided, by pressing onto a former. Essentially stretching of the metal is not required in the sense that stretching is used in a stretch forming technique as hitherto common when a continuous sheet of aluminium was used.

Each sheet is formed into the desired shape having regard to the fact that when the sheets are united, the perforations in one are to be staggered relative to the perforations in the other. After forming, both sheets are united by spot welding around their peripheries. The shape of the reflective surface now provided is relatively stable.

Referring now particularly to Figures 3 to 5, it is assumed that the total reflector is to be a dish reflector made up of a plurality of segments as will later be described with reference to Figures 6 and 7.

Starting with a suitably shaped double laminate sheet 2, 3, in plan as shown in Figure 4 and in cross-section as illustrated in Figure 1, the double laminate sheet 2, 3 is attached by rivetting to a supporting open box section as illustrated in Figure 5 and constructed of steel sheet or plate, galvanised. This forms a closed box section of which the double laminate sheet 1, 2 forms the face. Within the box section are supporting ribs 7 (each as shown in side elevation in Figure 3). The ribs 7 are themselves perforated with circular holes such as those referenced 8. Whilst not shown, the back of the box section is provided with an aperture through which is introduced, when the double laminate sheet 2, 3 is in position, setable urethane resin which passes through the holes in the rib 7 to form an interlocking bonding filling giving additional support to the laminate sheet 2, 3.It will be noted that the setable urethane resin bonds not only to the surface of the sheet 3 but also, via the holes 5 in sheet 3, to the surface of sheet 2.

In Figure 4, the positions of the ribs 7 when the laminate sheet 2, 3 is united with the box section shown in Figure 5 is represented in dotted outline at 7'.

Referring to Figures 6 and 7, the whole reflector illustrated therein is formed of a plurality of segments each of which is constructed essentially as already described with reference to Figure 1 to 5. The main supporting structure consists of a continuous hollow toroid 8 (shown in dotted outline in Figure 6) of rectangular cross-section.

Extending around and mounted upon the outside of the toroid 8 is a series of segments referenced 9 to 20. Similarly on the inside of the toroid 8 is mounted a series of segments referenced 21 to 28. As mentioned previously the segments 9 to 28 are each individually formed as already described with reference to Figures 1 to 5. Inner segments 21 to 28 are formed to provide a central aperture 29 through which, in this particular example, the feed for a horn (not shown) is intended to pass.

In order to locate the segments 9 to 28 accurately, each is provided with ledges such as those which in Figure 7 are referenced 30 and 31 in the case of segment 20; 32 and 33 in the case of segment 28; 34 and 35 in the case of segment 25 and 36 and 37 in the case of segment 15.

Adjacent ledges, such as 31 in the case of segment 20 and 30 in the case of segment 28, abut. Whilst not shown, alignment is maintained by bolts or screws passing through the ledges such as 30 to 37 into accurately positioned threaded holes in the walls of the toroid 8 - if necessary using weld nuts therewithin. Dowels may be used in combination with the ledges, or as an alternative to achieve location of the segments.

As will be appreciated the whole structure of the dish reflector provided by the present invention and as illustrated in Figures 6 and 7 is of very stable construction and may be found to be more weather resistant than a conventional structure since the reflecting surface is now of stainless steel and the metal piate or sheet forming the backing box sections of the segments can be galvanised before final assembly. It may also be found that the method of construction enables accuracy to be obtained and maintained relatively readily throughout construction so that final assembly, with alignment effected by means of the method of mounting the segments upon the toroid 8, provides a dish reflector which does not require final setting up as did a dish reflector provided by a conventional method of construction as outlined hereinbefore.

Claims (14)

1. A reflector having a reflective surface consisting of two perforated sheets of reflective material formed into a desired shape and arranged with the perforations in one staggered relative to the perforations in the other, said two sheets being fixed one to the other and to a supporting structure by means of which said reflector may be mounted.

2. A reflector having a reflective surface consisting of two perforated sheets of reflective material each of which sheets may, by virtue inter alia of its perforations, be formed into a desired shape without the use of a stretch forming technique, the two perforated sheets being formed into a desired shape and arranged with the perforations in one staggered relative to the perforations in the other, said two sheets being fixed one to the other and to a supporting structure by means of which said reflector may be mounted.

3. A reflector as claimed in claim 1 or 2 and wherein said two perforated sheets are fixed one to the other by means independent of the fixing of the combination of the two sheets to said supporting structure.

4. A reflector as claimed in any of the above claims and wherein each of said perforated sheets is of stainless steel in which case said means for fixing one to the other preferably comprises spot welding.

5. A reflector as claimed in any of the above claims and wherein said supporting structure comprises an open metal box section which is closed by the combination of said two perforated sheets.

6. A reflector as claimed in claim 5 and wherein the interior of the closed box section formed by said open box section and the combination of said two perforated sheets is filled with a setable urethane resin.

7. A reflector as claimed in claim 6 and wherein said box section includes internal strengthening ribs which are perforated whereby to permit said urethane resin to interlock either side of said ribs.

8. A reflector as claimed in any of claims 5 to 7 and wherein the entire reflector is formed of the combination of one united pair of perforated sheets and one supporting box section.

9. A reflector as claimed in any of claims 5 to 7 and made up of segments each of which consists of the combination of a united pair of perforated sheets supported by a box section.

10. A reflector as claimed in claim 9 and wherein said individual segments are located on and carried by a main supporting member with the box section of each segment being accurately located with reference to said main supporting member.

11. A reflector as claimed in claim 10 and wherein said main supporting member is itself a box section.

12. A circular dish reflector as claimed in claim 10 or 11 and wherein said main supporting member comprises a continuous hollow toroid of rectangular cross-section, there being mounted on the outer and inner sides thereof said segments which together form said dish.

1 3. A reflector as claimed in any of the above claims and forming part of or intended to form part of a radio antenna.

14. A dish reflector forming part of or intended to form part of a radio antenna substantially as herein described with reference to the accompanying drawings.