Dual reflector folding antenna

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 on a platform (11) to which it is pivotted about a first axis (14). A sub-reflector (26) is pivotted to the main reflector about a second 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.

BACKGROUND OF THE INVENTION 
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. 
SUMMARY OF THE INVENTION 
The invention provides a folding antenna comprising a supporting base and a 
reflector characterised in that the reflector is adapted to be held in a 
deployed position and in a stowed position where it lies relatively close 
to the base and in that the base forms part of a container which encloses 
the reflector when in the stowed position. 
The invention also provides a folding antenna comprising a base, a main 
reflector and a subreflector, characterised in that the reflectors are 
adapted to hinge relative to each other and relative to the base, from a 
stowed position where they lie relatively close to the base, to a deployed 
condition where they are relatively spaced from the base.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
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 the 
open position in both FIGS. 1 and 2 of the 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.degree. about a vertical axis 
passing through the boss 10. A clamp (not shown) is included to hold the 
frame 11 at the desired position along the rail 6. 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 (FIG. 2) which 
supports a main reflector 16, and an arm 17. 
Each arm 17 is pivotted to a collapsible stay 20 shown in more detal in 
FIG. 3. This stay 20 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 20D. A 
lever 20E is attached to the bolt to tighten the connection between the 
arms 20A and 20B 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. 
A boom or framework consisting of frame members 22, 23 and 24, is pivotally 
mounted on the arms 17 of member 13 for movement about an axis 21. This 
framework can be held in the position illustrated in FIG. 1 by removable 
pins 19 which pass through the members 22. When the pins 19 are removed, 
the framework can be pivotted about the axis 21 to the position 
illustrated in FIG. 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 FIG. 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 smaller dimension 
of the rectangular base, i.e., the length of the short sides containing 
the handles 9. For this reason the platform 11 and everything supported on 
it is rotated through 90.degree. by sliding over the rail 6 until the main 
reflector 16 faces in the direction of the short sides of the base 1. The 
reflector 16 is then adjusted in azimuth and held, in any position of the 
plus or minus 45.degree. excursion available relative to the center 
position, 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, with 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 FIG. 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 FIG. 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 26 to be locked in 
deployed or stowed positions. 
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 FIG. 2. During pivotting of the main reflector 
16 and associated parts about the axis 14 the arm 17 shown furthermost in 
FIG. 1 passes through a slot provided 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.