RADAR MONOPULSE ANTENNAS WITH CONVERTING POLARIZATION

• US 3,701,160 A
• Filed: 06/23/1971
• Issued: 10/24/1972
• Est. Priority Date: 06/25/1970
• Status: Expired due to Term

• Current Assignee: Daniel Edmond Beguin
• Original Assignee: Daniel Edmond Beguin
• Inventors: Beguin, Daniel Edmond
• Primary Examiner(s): Lieberman, Eli
• Application Number:
  US05/155,940
• Time in Patent Office: 489 Days
• Field of Search: 343/754,755,756,786,840,909
• US Class Current: 343/755
• CPC Class Codes: G01S 13/4409 HF sub-systems particularly adapted therefor, e.g. circuits for signal combination multi-lobing aerials or aerial systems H01Q25/00
• CPC Class Codes: H01Q 21/245 provided with means for varying the polarisation polarising devices H01Q15/24; tracking by comparing linear polarisation compounds G01S3/146; reducing depolarisation effects H04B7/00; polarisation diversity H04B7/10
• CPC Class Codes: H01Q 25/02 providing sum and difference patterns H01Q25/04 takes precedence

Abstract

A monopulse antenna comprising an assymetrical parabolic reflector illuminated by a monopulse horn. A circular polarizing array cover adapted for selective emplacement over the horn aperture is provided. Changing from linear to circular polarization by placing the polarizer, by itself, over the horn produces an angular shift in antenna boresite (axis). A dielectric lens is provided for insertion over the polarizer to introduce a linear corrective phase shift, thereby eliminating the said axis shift.

Claims

1. In a radar antenna system which includes a generally parabolic reflector illuminated by an offset primary source to provide a plane wave, the combination comprising:

a polarizing device located between said primary source and said reflector;

phase correction means inserted between said polarizer and said reflector for introducing a phase shift so as to produce a beam axis for said antenna system which is coincident with said beam axis in the absence of said polarizer.

2. A monopulse radar antenna system which includes an asymmetrically-shaped parabolic reflector and an offset monopulse feed horn for radiating and receiving a monopulse beam pattern, comprising the combination of:

means comprising a polarizer over the aperture of said horn for circularly polarizing energy radiated from said horn and for responding to correspondingly polarized received energy;

phase correction means comprising a dielectric lens employed over said polarizer in the field between said polarizer and said reflector, for introducing a phase shift to cause the axis of said monopulse beam pattern in circular polarization operation to coincide with the axis of the monopulse beam pattern produced in the absence of both said phase correction means and said polarizer.

3. Apparatus according to claim 2 in which said reflector extends in a first dimension symmetrically and in a second dimension unilaterally with respect to the axis of said horn, and said horn is oriented to illuminate substantially the entire surface of said reflector.

4. Apparatus according to claim 3 in which said horn is of rectangular cross-section with a median partition, thereby to provide two feed channels for monopulse implementation, and in which said lens comprises a tapered dielectric prism, said taper extending across the dimension of said horn normal to said median partition.

5. Apparatus according to claim 4 in which said taper produces a substantially linear prism thickness in the path of energy passing through said horn, said thickness varying from substantially zero adjacent one short side wall of said rectangular horn to a maximum adjacent the opposite short side wall of said horn.

6. Apparatus according to claim 5 in which said prism is constructed of dielectric material of approximately unity dielectric constant.

7. Apparatus according to claim 5 in which said prism is constructed of polyurethane foam having a dielectric constant approximately 1.10.

8. Apparatus according to claim 5 in which said prism thickness maximum is substantially equal to 2La/ Square Root B - 1, where L is the deviation on said reflector between the maxima of the two primary lobes of the difference channel of said monopulse radar antenna, a is the angular deviation between the aNtenna axis in linear and circular polarization.