Wide scanning spherical antenna

• US 5,459,475 A
• Filed: 12/22/1993
• Issued: 10/17/1995
• Est. Priority Date: 12/22/1993
• Status: Expired due to Fees

• Current Assignee: Virginia Tech Intellectual Properties, Inc.
• Original Assignee: The Center For Innovative Technology, Virginia Polytechnic Institute and State University, Virginia Tech Intellectual Properties, Inc.
• Inventors: Shen, Bing, Stutzman, Warren L.
• Primary Examiner(s): Hajec, Donald
• Assistant Examiner(s): PHAN, THO GIA
• Application Number:
  US08/172,127
• Time in Patent Office: 664 Days
• Field of Search: 343/781 R, 343/781 P, 343/754, 343/837, 343/761, 343/839, 343/781 CA
• US Class Current: 343/781.00P
• CPC Class Codes: H01Q 19/191 wherein the primary active element uses one or more deflecting surfaces, e.g. beam waveguide feeds
• CPC Class Codes: H01Q 3/20 wherein the primary active element is fixed and the reflecting device is movable

Abstract

A novel method for calculating the surface shapes for subreflectors in a suboptic assembly of a tri-reflector spherical antenna system is introduced, modeled from a generalization of Galindo-Israel'"'"'s method of solving partial differential equations to correct for spherical aberration and provide uniform feed to aperture mapping. In a first embodiment, the suboptic assembly moves as a single unit to achieve scan while the main reflector remains stationary. A feed horn is tilted during scan to maintain the illuminated area on the main spherical reflector fixed throughout the scan thereby eliminating the need to oversize the main spherical reflector. In an alternate embodiment, both the main spherical reflector and the suboptic assembly are fixed. A flat mirror is used to create a virtual image of the suboptic assembly. Scan is achieved by rotating the mirror about the spherical center of the main reflector. The feed horn is tilted during scan to maintain the illuminated area on the main spherical reflector fixed throughout the scan.

Claims

1. A method for scanning a spherical antenna having a stationary main spherical reflector in the θ

direction, comprising the steps of;

defining a z-axis passing through an illuminated aperture portion on a main spherical reflector surface said z-axis having its origin at the spherical center of said main spherical reflector;

rotating a suboptic assembly including an electromagnetic feed, about the spherical center in the θ

direction to define a z'"'"'-axis, where θ

is the angle between said z-axis and said z'"'"'-axis;

tilting said electromagnetic feed relative to said z'"'"'-axis during said rotating step such that said illuminated aperture portion on said main spherical reflector surface remains fixed

defining a feed to aperture normalization factor as ##EQU12## where U_f is feed radiation intensity, S_ap is aperture power intensity distribution, and R is the radius of the main spherical reflector, and determining a feed tilting angle, θ

_f according to the formula ##EQU13##

2. A scanning tri-reflector spherical antenna system, comprising:

a fixed main spherical reflector;

a fixed suboptic assembly;

a flat mirror for forming a virtual image of said suboptic assembly, said flat mirror moving relative to said fixed suboptic assembly to perform a scan function; and

a tilting feed horn for directing electromagnetic waves to said suboptic assembly, said tilting feed horn tilting when said flat mirror is performing said scan function thereby causing the electromagnetic waves to illuminate a fixed aperture area on said main spherical reflector,

wherein said suboptic assembly comprises a tertiary reflector, and a sub-reflector, the surface shapes of which are modeled by solving partial differential equations derived by requiring equal-optical lengths from said tilting feed horn to said fixed aperture area, and requiring an isotropic-feed-to-uniform-aperture radiation intensity transformation to correct for spherical aberration and provide uniform, feed-to-aperture mapping.

3. A scanning tri-reflector spherical antenna system as recited in claim 2 wherein said tertiary reflector reflects electromagnetic waves from said tilting feed horn to said sub-reflector, said sub-reflector reflects electromagnetic waves to said flat mirror, and said flat mirror reflects electromagnetic waves to said main spherical reflector.