Conically scanning antenna system for tracking radars

• US 4,305,075 A
• Filed: 12/15/1978
• Issued: 12/08/1981
• Est. Priority Date: 12/22/1977
• Status: Expired due to Term

• Current Assignee: Thomson-CSF (Thales SA)
• Original Assignee: Thomson-CSF (Thales SA)
• Inventors: Bouko, Jean, Salvat, Francois
• Primary Examiner(s): Hubler, Malcolm F.
• Application Number:
  US05/969,949
• Time in Patent Office: 1,089 Days
• Field of Search: 343/7.4, 343/761, 343/839, 343/781 CA
• US Class Current: 342/78
• CPC Class Codes: H01Q 19/195 wherein a reflecting surface acts also as a polarisation filter or a polarising device
• CPC Class Codes: H01Q 25/001 Crossed polarisation dual antennas orthomode horns H01Q13/0258; cross-polarised rear feeds H01Q19/136; orthomode transducers H01P1/161
• CPC Class Codes: H01Q 3/20 wherein the primary active element is fixed and the reflecting device is movable

Abstract

An antenna system of the Cassegrain type, used with a tracking radar and adapted to conically scan incoming waves reflected by outlying targets, comprises a paraboloidal main reflector and two hyperboloidal auxiliary reflectors confronting same. One of the auxiliary reflectors is semitransparent and coaxial as well as cofocal with the main reflector whereas the other is solid with an axis inclined to that of the main reflector about which it rotates while keeping its foci in the focal planes of the semitransparent reflector.

Claims

1. An antenna system comprising:

a main reflector with a paraboloidal concave surface centered on a principal axis;

feed means on said principal axis for emitting linearly polarized outgoing waves with an electric-field vector oriented in a predetermined first direction transverse to said principal axis and for receiving linearly polarized incoming waves with an electric-field vector oriented in a second direction orthogonal to said first direction;

a first auxiliary reflector confronting said paraboloidal surface and said feed means with a hyperboloidally curved first convex surface centered on said principal axis, said first auxiliary reflector being substantially transparent to said incoming waves but reflecting said outgoing waves from said feed means onto said paraboloidal surface for transmission in the direction of said principal axis;

a second auxiliarly reflector confronting said paraboloidal surface and said feed means with a hyperboloidally curved solid second convex surface centered on an axis inclined to said principal axis at an acute angle, said first auxiliary reflector lying between said main reflector and said second auxiliary reflector whereby incoming waves reflected from said paraboloidal surface toward said second auxiliary reflector and redirected by the latter toward said feed means pass twice through said first auxiliary reflector; and

drive means coupled with said second auxiliary reflector for rotating same about said principal axis, thereby subjecting said incoming waves to a conical scan.

2. An antenna system as defined in claim 1 wherein said second convex surface has a focal point in a plane transverse to said principal axis passing through a common focus of said first convex surface and said paraboloidal surface.

3. An antenna system as defined in claim 2 wherein said second convex surface has an apex on said principal axis and another focal point in another plane transverse to said principal axis passing through a second focus of said first convex surface.

4. An antenna system as defined in claim 3 wherein said feed means has a phase center coinciding with said second focus.

6. An antenna system as defined in claim 1, 2, 3, 4 or 5 wherein said first auxiliary reflector has a grid structure with wires generally parallel to said first direction.

5. In a tracking radar, in combination:

transmission means generating linearly polarized outgoing waves;

a horn centered on a principal axis, said horn having an input guide coupled to said transmission means for axially emitting said outgoing waves with an electric-field vector oriented in a predetermined first direction transverse to said principal axis and further having an output guide for conveying incoming waves echoed by outlying targets with an electric-field vector oriented in a second direction orthogonal to said first direction;

receiving means coupled with said output guide;

a main reflector with a paraboloidal concave surface centered on said principal axis;

a first auxiliary reflector confronting said paraboloidal surface and said horn with a hyperboloidally curved first convex surface centered on said principal axis, said first auxiliary reflector being substantially transparent to said incoming waves but reflecting said outgoing waves from said horn onto said paraboloidal surface for transmission in the direction of said principal axis;

a second auxiliary reflector confronting said paraboloidal surface and said horn with a hyperboloidally curved solid second convex surface centered on an axis inclined to said principal axis at a acute angle, said first auxiliary reflector lying between said main reflector and said second auxiliary reflector whereby incoming waves reflected from said paraboloidal surface toward said second auxiliary reflector and redirected by the latter toward said horn pass twice through said first auxiliary reflector, said reflectors forming an antenna system; and

drive means coupled with said second auxiliary reflector for rotating same about said principal axis, thereby subjecting said incoming waves to a conical scan.