REFLECTOR ARRANGEMENT

Abstract: A folding antenna for use in a satellite communication system comprises a box having a base 1 which forms the supporting structure for the antenna. A main reflector 16 is mounted a platform 11 to which it is pivotted about an axis 14. A sub-reflector 26 is pivotted to the main reflector about an axis 21. By pivotting the sub-reflector and the main reflector downwardly they can be stowed into a position close to the base 1 and the lids 8 of the box closed to protect the system during transportation.

Description: This invention relates to a folding antenna. The invention arose in the design of an antenna for use as part of a mobile earth station forming part of a satellite communication system for news gathering purposes. The size of antenna required for this purpose presents a problem with regard to transportability. It is believed that this problem can be greatly eased by employing the present invention. US 4086599 discloses an antenna structure comprising a main reflector mounted on a base by a mechanism which allows it to be pivoted relative thereto. A sub-reflector is supported on the main reflector by a tripod arrangement. While the position of the main reflector can be adjusted relative to the base, there is no means for varying the position of the sub-reflector relative to the main reflector, so limiting the transportability of the structure. In GLOBECOM '82, IEE GLOBAL TELECOMMUNICATIONS CONFERENCE, Miami, 29th November - 2nd Decmeber,1982, Volume 3, pages 1258-1262, an article by A.SAITTO et al discloses an antenna structure having a main reflector which is mounted on a base so as to hinge relative thereto. A sub-reflector is fixed to the base, the only way of varying the relative positions of the main and sub-reflectors being the hinging movement of the main reflector relative to the base restricts the range of useful movement of the main reflector relative to the base. The invention provides a folding antenna reflector arrangement comprising a base, a main reflector mounted on the base so as to hinge relative thereto between a stowed position and an erected deployed operating position and a sub-reflectior mounted on said main reflector; characterised in that the sub-reflector is mounted on the main reflector by means of a framework which is hinged relative to the main reflector and relative to the base, the sub-reflector being adapted to be moved between a stowed position where it lies relatively close to the base and a deployed position where it is relatively spaced from the base. One way in which the invention may be performed will now be described by way of example with reference to the accompanying drawings in which:- Figure 1 is a perspective view of an antenna constructed in accordance with the invention and shown in a position between its stowed and deployed conditions; Figure 2 illustrates a vertical cross-section through the same antenna in its stowed condition but with its protective lids shown hinged back ready for deployment of the antenna; and Figure 3 illustrates in detail stays 20 and screen clamps 20c of Figures 1 and 2. Referring to the drawings the illustrated antenna comprises a base 1 having a floor 2, sides 3 and adjustable feet 4. Bracing strips 5 support a rail 6. Lugs 7 attached to the base are hinged to lids 8 which are shown in position in both drawings. Handles 9 on each end of the base 1 (which is rectangular) allow the whole antenna to be lifted by two people, one at each end. The base 1 includes a central boss 10 which provides a pivot for a frame 11. This frame 11 sits on the rail 6 so that it can be rotated through more than 90 o about a vertical axis passing through the boss 10. A clamp (not shown) is included to hold the frame at the desired position along the rail. The frame 11 is pivotted to two L-shaped supporting members 13 about a first horizontal axis 14. Each L-shaped supporting member 13 has an arm 15 (Figure 2) which supports a main reflector 16; and an arm 17. Each arm 17 is pivotted to a collapsible stay 20 shown in more detail in Fig 3. This comprises two lower arms 20A and an upper arm 20B. The top ends of the arms 20A are pivotted by a bolt 20C to the lower end of the arm 20B with the interposition of high frictional washers 20P. A lever 20E is attached to the bolt to tighten the connection between the arms and to prevent pivotting when the antenna is deployed. The top of the arm 20B has a hole which receives a pivot (not shown) by which it is attached to the arm 17 so as to allow relative rotation. The bottom of each arm 20A also has a hole which receives a pivot pin passing through lugs attached to frame 11. The stay 20 thus allows the boresight of the reflector 16 to be adjusted in elevation. The members 13 are pivotted about an axis 14 to a framework consisting of frame members 22, 23 and 24. This framework can be held in the position illustrated in Figure 1 by the pins 19 which pass through the members 22. When the pins are removed the framework can be pivotted about the axis 21 to the position illustrated in Figure 2. The framework supports, by means of the cross-member 23, a feed horn 25 which receives microwave energy along a flexible waveguide (not shown) and directs it to a concave sub-reflector 26 held on the cross-member 24 of the frame. From there the energy is reflected to the main reflector 16 and thence to a receiving station (not shown) via a satellite (also not shown). Referring now in particular to Figure 1 the antenna is shown almost in its deployed condition. In fact it would operate in the position illustrated but would be relatively unstable in high wind conditions because the wind force on the main reflector 16 would be supported by the small dimension of the rectangular base. For this reason the platform 11 and everything supported on it is rotated through 90 o by sliding over the rail 6 until the main reflector faces in the direction of the short sides of the base 1. The reflector 16 is then held, in any position of the plus or minus 45 o excursion available, by the clamp referred to previously. The stay 20 is adjusted to align the boresight of the antenna with the satellite being used. Coarse azimuth adjustment is achieved by moving the whole structure using the handles 9: the adjustable feet being used to ensure that the base 1 is either horizontal or is inclined to the horizontal at a desired angle. In this connection it should be explained that the main reflector 16 is generally of elliptical shape having one axis (the horizontal axis as shown in Figure 1) longer than another axis normal thereto. In order to pack the antenna assembly away the platform 11 is rotated about an aximuth axis on the boss 10 back to the position illustrated in Figure 1. A location plate 26B and pins not shown which pass through the plate 26B and the framework 22, 23, 24 enable the sub-reflector to be locked in deployed or stowed position. Releasing the screw clamps 20C of stays 20 allows the reflector 16, and the framework 22, 23, 24 carrying the sub-reflector, to pivot downwards about axis 14; until the framework 22, 23, 24 rests on the long side 3A of the base 1. Removing the pins 19 allows the reflector 16 to continue to pivot downwards about axis 14. Simultaneously the framework 22, 23, 24 pivot with respect to the arms 17 about the axis 21. It is notable that during pivoting of the reflector 16 the axis 21, because of its spacing from the axis 14, is lowered towards the base 2, this resulting in a more compact arrangement when the antenna is in its stowed position as shown in Figure 2. During pivotting of the main reflector 16 and associated parts about the axis 14 the arm 17 shown furthermost in Figure 1 passes through a slot in the supporting rail 6 but not visible in the drawings. The final operation is to close the lids 8 which are held in their closed positions by a suitable catch mechanism (not shown). The need for the pivotting movement about the central boss 10 and for the rail 6 arises from the desirability of making the box formed by the base 1 and lids 8 longer than it is wide to conform with the shape of the main reflector 16 which is also longer than it is wide. An antenna of this shape is particularly desirable for satellite communication purposes but it is of course possible that reflectors of other shapes, for example circular or square, could be used; in which case the need would not arise for rotation about the central boss and for sliding on the rail 6. The ability of the antenna to be folded away or otherwise collapsed into a confined space can be of benefit in other transportable systems e.g., where the antenna is mounted on a vehicle or craft. In this connection the features of the present invention can be of value not only in communication systems but also in land and sea based radars.

Claims: A folding antenna reflector arrangement comprising a base (1), a main reflector (16) mounted on the base (1) so as to hinge relative thereto between a stowed position, and an erected deployed operating position and a sub-reflector (26) mounted on said main reflector (16); characterised in that the sub-reflector (26) is mounted on the main reflector (16) by means of a framework (22,23,24) which is hinged relative to the main reflector (16) and relative to the base (1), the sub-reflector (26) being adapted to be moved between a stowed position where it lies relatively close to the base (1) and a deployed position where it is relatively spaced from the base (1). A reflector arrangement according to claim 1 in which the main reflector (16) is hinged to the base (1) about a first axis (14) and in which the sub-reflector (26) is connected to the main reflector (16) by an arm (22) which is hinged to the main reflector (16) about a second axis (21) spaced from the first axis (14) so that hinging of the main reflector (16) about the first axis (14) from the deployed to the stowed position moves the second axis (21) towards the support. A reflector arrangement according to claim 2 in which the arm (22) is hinged to the sub-reflector (26) about a third axis (26A). A reflector arrangement according to claim 1, 2 or 3 including an elevation adjustment mechanism (20) for adjusting the elevation of a boresight of the antenna when in its deployed condition, the elevation adjustment mechanism (20) also being adapted to hinge relative to the base (1) between deployed and stowed positions. A reflector arrangement according to claim 1, 2, 3 or 4 in which the base (1) forms part of a container adapted to enclose the reflectors (16,26) when in a stowed condition.

Inventors: MATTHAMS, ERIC GEORGE, PAYNE, BERNARD FREDERICK, WILLIAMS, ANDREW
Applicants: THE GENERAL ELECTRIC COMPANY, P.L.C.
Application year: 1985
Main classification: H01Q1
IPC codes: H01Q1, H01Q19, H01Q15