Dual coaxial feed for tracking antenna

• US 6,222,492 B1
• Filed: 05/11/1995
• Issued: 04/24/2001
• Est. Priority Date: 05/09/1994
• Status: Expired due to Fees

• Current Assignee: Optim Microwave Inc.
• Original Assignee: Optim Microwave Inc.
• Inventors: Mahon, John
• Primary Examiner(s): Wimer, Michael C.
• Application Number:
  US08/471,309
• Time in Patent Office: 2,175 Days
• Field of Search: H01/Q 1.302, H01/Q 1.324, 343/776, 343/786
• US Class Current: 343/786
• CPC Class Codes: H01Q 13/0266 provided with a flange or a choke
• CPC Class Codes: H01Q 25/02 providing sum and difference patterns H01Q25/04 takes precedence
• CPC Class Codes: H01Q 25/04 Multimode antennas corrugated horns H01Q13/0208
• CPC Class Codes: H01Q 5/47 with a coaxial arrangement of the feeds

Abstract

A wide-band feed for a reflector antenna that provides a sum and a difference radiation pattern for tracking and for the transmission or reception of data. The feed utilizes two coaxially located, coaxial waveguides. The inner coaxial waveguide supports propagation of the TE11 mode and produces a sum radiation pattern. The outer coaxial waveguide supports propagation of the TE21 mode and produces a difference radiation pattern. The dimensions of the inner and outer waveguides are selected such that the dispersions of the TE11 mode in the inner coaxial waveguide and the TE21 mode in the outer coaxial waveguide are the same. Coaxial chokes located near the open ends of the wave guide modify the impedance match to free space of the fields within the waveguides and modify the radiation patterns generated by the waveguides. Probes within the waveguides generate the respective modes. Fins located in proximity to the probes operate as cutoff waveguides which terminate the probe end of the waveguides and which modify the impedance of the probes.

Claims

1. In a tracking antenna of the type having a feed for receiving electromagnetic energy from free space, the feed having a sum port and a difference port, the feed comprising,

a first coaxial waveguide having an input end and an output end, said waveguide being bounded longitudinally by an inner conducting surface and by an outer conducting surface, and

a second coaxial waveguide having an input end and an output end, said second waveguide being bounded longitudinally by an inner conducting surface and by an outer conducting surface,

the first coaxial waveguide being located inside of and coaxially with the second coaxial waveguide,

the first coaxial waveguide having an opening at its input end, the opening allowing electromagnetic energy to pass from free space into and propagate within the first coaxial waveguide, said electromagnetic energy propagating within the first coaxial waveguide in the TE11 mode, the TE11 mode having a dispersion,

the second coaxial waveguide having an opening at its input end, the opening allowing electromagnetic energy to pass from free space into and propagate within the second coaxial waveguide, said electromagnetic energy propagating within the second coaxial waveguide in the TE21 mode;

the TE21 mode having a dispersion,

the dimensions of the first coaxial waveguide and the dimensions of the second coaxial waveguide being selected such that the dispersion of the TE11 mode in the first coaxial waveguide is approximately the same as the dispersion of the TE21 mode in the second coaxial waveguide,

the first coaxial waveguide having a first coupling device connected to its output end, the first coupling device coupling energy between the sum port and electromagnetic energy propagating within the first coaxial waveguide,

the second coaxial waveguide having a second coupling device connected to its output end, the second coupling device coupling energy between the difference port and electromagnetic energy propagating within the second coaxial waveguide,

whereby the first coaxial waveguide provides a sum electromagnetic radiation pattern with respect to the electromagnetic radiation received from free space and the second coaxial waveguide provides a difference electromagnetic radiation pattern with respect to the electromagnetic radiation received from free space.

2. The device of claim 1 wherein the first coupling device comprises at least four exciters located in a circularly symmetric pattern within the first coaxial waveguide near the output end of the first waveguide, the output end of the first waveguide further including a plurality of fins oriented within the first waveguide so as to form a plurality of cutoff waveguides that terminate the output end of the first waveguide and modify the characteristics of the exciters,

and wherein the second coupling device comprises at least eight exciters located in a circularly symmetric pattern within the second coaxial waveguide, the output end of the second waveguide further including a plurality of fins oriented within the waveguide so as to form a plurality of cutoff waveguides that terminate the output end of the second waveguide and modify the characteristics of the exciters.

3. The device of claim 1 and further comprising at least one coaxial choke ring located adjacent to the input end of the first or second coaxial waveguides, whereby the coaxial choke ring modifies the shape of the sum or difference pattern provided by the first or second coaxial waveguide.

4. The device of claim 2 and further comprising at least one coaxial choke ring located adjacent to the input end of the first or second coaxial waveguides, whereby the coaxial choke ring modifies the shape of the sum or difference pattern provided by the first or second coaxial waveguide.