Feeder link antenna

• US 5,870,060 A
• Filed: 05/01/1996
• Issued: 02/09/1999
• Est. Priority Date: 05/01/1996
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: TRW Inc. (Northrop Grumman Corporation)
• Inventors: Kwon, Young Suck, Chen, Chun-Hong Harry
• Primary Examiner(s): Wimer, Michael C.
• Application Number:
  US08/641,602
• Time in Patent Office: 1,014 Days
• Field of Search: 343/781 R, 343/786, 343/756, 343/761, 343/839, 343/765, 343/DIG. 2
• US Class Current: 343/761
• CPC Class Codes: H01Q 13/0208 Corrugated horns waveguide mouth antenna with corrugated flange H01Q13/065; manufacturing details H01Q13/0283
• CPC Class Codes: H01Q 13/0241 radiating a circularly polarised wave H01Q13/0258 takes precedence; polarisation converters H01Q15/244, in a waveguide H01P1/17
• CPC Class Codes: H01Q 3/20 wherein the primary active element is fixed and the reflecting device is movable
• CPC Class Codes: H01Q 5/45 using two or more feeds in association with a common reflecting, diffracting or refracting device
• CPC Class Codes: Y10S 343/02 Satellite-mounted antenna

Abstract

A steerable feeder link antenna is formed of a steerable reflector and a stationary feed horn assembly. A novel feed horn assembly allows dual mode transmit and receive functions for circularly polarized microwaves. The feed horn assembly includes a four arm turnstile junction coupled to a feed horn through the feed horn'"'"'s side wall to couple transmit frequencies and an axially coupled transmission line for the receive frequencies. Each turnstile junction arm incorporates chokes for the receive frequencies. The transmission line'"'"'s cut off frequency is above the transmit frequency to prevent transmit signals from interfering with receive signal receivers.

Claims

1. A steerable microwave antenna assembly for a space satellite, comprising:

a microwave reflector having a concavely curved surface defining a focal point and a predetermined focal length;

a platform for mounting to said space satellite;

a container, said container being of a predetermined height, having top and bottom surfaces and being fixed to an upper surface of said platform with said bottom surface of said container abutting said platform, whereby said container'"'"'s top surface is elevated in position above said upper surface of said platform; and

a bracket, said bracket including a first portion positioned overlying said top surface of said container and a second portion extending at an incline from said top surface of said container to a laterally spaced position located on said platform and underlying said top surface of said container, wherein both said bracket and said container are supported upon said platform;

gimbal means coupled to said microwave reflector for positioning the attitude and elevation of said microwave reflector about a first location on said first portion of said bracket;

a feed horn;

said feed horn for receiving at least a portion of microwave energy of a first frequency incident upon and reflected from said concavely curved surface to a microwave receiver and, alternately, for propagating microwave energy of a second frequency from a microwave energy source to said concavely curved surface; and

said feed horn being mounted to a second location on said second portion of said bracket to maintain the position of said feed horn stationary in position relative to said first location;

wherein said microwave reflector is adjustable in directional orientation by said gimbal means independently of said feed horn;

said feed horn including a first end oriented facing said concavely shaped surface of said microwave reflector; and

said first end being located more proximate said concavely shaped surface than said focal point, irrespective of the directional orientation of said concavely shaped surface.

2. The invention as defined in claim 1, wherein said curved surface further defines a circular perimeter of a predetermined diameter and wherein a ratio of said focal length to said predetermined diameter is greater than 0.7.

3. A steerable microwave antenna assembly for mounting on a space satellite, said microwave antenna assembly for transmitting microwave energy of frequency f1 and receiving microwave energy of frequency f2, comprising:

a platform for mounting to said space satellite;

a container, said container being of a predetermined height, having top and bottom surfaces and being fixed to an upper surface of said platform, whereby said container'"'"'s top surface is elevated in position above said upper surface of said platform; and

a bracket, said bracket including a first portion positioned overlying said top surface of said container and a second portion extending from said top surface of said container at an incline to a position located on said platform adjacent to said container underlying said container'"'"'s top surface, wherein both said bracket and said container are supported upon said platform;

a microwave reflector having a curved surface and a circular periphery of diameter D, said curved surface defining a focal point and having a focal length L, and wherein the ratio of said L to said D is greater than 0.7;

a feed horn;

said feed horn being electromagnetically coupled to said microwave reflector for coupling of microwave energy therebetween;

gimbal means coupled to said microwave reflector for positioning the attitude and elevation of said microwave reflector at any position within a predefined hemisphere;

said gimbal means being mounted at a first location along said bracket overlying said top surface of said container, whereby said microwave reflector is positioned in attitude and elevation about said first location on said bracket; and

said feed horn being mounted upon said bracket at a second location thereon spaced from said container and underlying said top surface of said container, whereby said attitude and elevation of said microwave reflector is positionable without changing the position of said feed horn;

said feed horn comprising;

a hollow right cone having a conical wall, a first large diameter circular opening at one end and a second small diameter circular opening at an opposed end with said first and second openings being spaced from one another along a central axis and a short length circular waveguide integrally connected to said second circular opening coaxial with and of the same diameter as said second circular opening defining a feed horn throat;

said conical wall including an inner surface, said inner surface further comprising a corrugated surface containing surface corrugations oriented transverse to said central axis; and

said conical wall further including four passages radially extending therethrough, said passages being located at a predetermined axial position and being equally circumferentially spaced about said central axis to provide a microwave energy propagation path into the interior of said hollow right cone;

said predetermined axial position being spaced from both said feed horn'"'"'s first and second circular openings at a position that permits maximum coupling of microwave energy through said microwave energy propagation path into said feed horn;

first waveguide transmission line means for propagating microwave energy of frequency f2 from said feed horn to an external microwave receiver;

said first waveguide transmission line means including;

an input end connected to said feed horn throat;

circular waveguide means, said circular waveguide means containing a polarizer;

a circular to rectangular waveguide transition coupled to said circular waveguide means in spaced relation to said polarizer; and

a rectangular waveguide flange to provide an output end to said first waveguide transmission line means;

said second small diameter circular opening to said feed horn having a frequency cut off characteristic of a predetermined frequency f3, where said frequency f3 is higher than said frequency f1, whereby said microwaves of frequency f1 are inhibited from propagating into said first transmission line means;

a turnstile junction;

said turnstile junction including an input for receiving microwave energy of frequency f1 from a microwave transmitter and four outputs outputting said microwave energy of frequency f1 at four spaced positions and in relative electrical phase relationship at said frequency f1 of zero, ninety, one hundred and eighty and two hundred and seventy degrees, to thereby produce in combination of said four outputs circularly polarized microwave energy of frequency f1;

said four turnstile junction outputs being connected to respective ones of said four passages through said conical wall of said hollow right cone, whereby in response to microwave energy of frequency f1 from said microwave transmitter a circularly polarized microwave of frequency f1 is excited in said feed horn for radiation from said feed horn;

each of said turnstile junction outputs including;

RF choke means for passing microwave energy of frequency f1 and inhibiting propagation of microwave energy of frequency f2 from said feed horn into said respective turnstile junction output to prevent any microwave energy of frequency f2 received at said first large diameter circular opening of said feed horn propagating within said hollow right cone to said first transmission line means from being diverted to said turnstile junction.