Space fed antenna system with squint error correction

• US 4,743,914 A
• Filed: 04/14/1986
• Issued: 05/10/1988
• Est. Priority Date: 04/14/1986
• Status: Expired due to Fees

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Schuss, Jack J., Hanfling, Jerome D.
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US06/852,041
• Time in Patent Office: 757 Days
• Field of Search: 343/753, 343/754, 343/781 P, 343/781 CA
• US Class Current: 343/754
• CPC Class Codes: H01Q 3/2658 Phased-array fed focussing structure
• CPC Class Codes: H01Q 3/267 Phased-array testing or checking devices
• CPC Class Codes: H01Q 3/46 Active lenses or reflecting arrays

Abstract

A space fed antenna system is adapted to correct for beam pointing (squint) errors and collimation errors caused by frequency variations of the R.F. energy radiated by the antenna system. A subarray of radiating elements is spatially positioned between an electronic lens and the focal point of said lens. The subarray radiates R.F. energy with a spherical wavefront for illuminating the electronic lens, such spherical wavefront having a focal point coincident with the focal point of the electronic lens. A programmer is provided which controls the electronic lens to collimate and direct the R.F. energy from the subarray. A corporate feed is provided which couples to a plurality of phase shifters which feeds corresponding time delay units, which in turn feeds corresponding radiating elements in the subarray. The phase shifters, responsive to the programmer, provide the spherical wavefront to the R.F. energy radiated by radiating elements in the subarray. The time delay units, also responsive to the programmer, vary the phase of the R.F. energy radiated by said elements to correct the squint and collimation errors.

Claims

1. A space fed antenna system comprising:

lens means for collimating and directing R.F. energy into a planar wave in a predetermined direction;

radiating means, disposed between the lens means and the focal point of the lens means, for illuminating the lens means with R.F. energy having a diverging wavefront, the diverging wavefront having a focal point; and

control means, coupled to the radiating means, for maintaining coincidence of the focal point of the diverging wavefront with the focal point of the lens means.

2. The space fed antenna system as recited in claim 1 further comprising:

programmer means for controlling the space fed antenna system; and

wherein the lens means and control means are responsive to the programmer means.

3. In a space fed antenna system having an electronic lens with a focal point a distance F from the electronic lens, for collimating and directing a planar wave of R.F. energy in a predetermined direction, a feed apparatus for illuminating the electronic lens comprising:

means having a plurality of output ports for dividing R.F. energy from a source to the plurality of output ports;

a plurality of phase shifting means, each coupled to a corresponding one of the plurality of output ports, for providing corresponding predetermined phase shifts of the R.F. energy;

a plurality of time delay means, each coupled to a corresponding one of the plurality of phase shifting means, for providing predetermined corresponding time delays of the R.F. energy; and

a plurality of radiating means, arranged in a plane about a centroid and coupled to corresponding ones of the plurality of time delay means, for illuminating the electronic lens with R.F. energy having a spherical wavefront, the spherical wavefront having a focal point;

wherein the predetermined time delays from the time delay means maintain the focal point of the spherical wavefront coincident with the focal point of the electronic lens.

4. The feed apparatus as recited in claim 3 further comprising a controller means for controlling the electronic lens to collimate and direct the planar wave of R.F. energy, wherein the plurality of time delay means and the plurality of phase shifting means are additionally responsive to the controller means.

5. The feed apparatus as recited in claim 4 wherein each one of the plurality of time delay means has a desired electrical length of

6. The feed apparatus as recited in claim 5 wherein each one of the plurality of time delay means is a tapped delay line having tap spacing of λ

_c, where λ

_c is the wavelength of the center frequency f_c of the operating bandwidth of the space fed antenna system, the tap being selected in response to the controller means to provide an electrical length, Nλ

_c, which length approximates the desired electrical length, for an integer value of N.

7. The feed apparatus as recited in claim 6 wherein each one of the plurality of phase shifting means provides a phase shift of ##EQU5## wherein c is the speed of light, and f0_i is the center frequency of a selected portion of the operating bandwidth.

8. A space fed antenna array comprising:

corporate feed means;

a plurality of radiating means, each coupled to a corresponding output terminal of the corporate feed means, and responsive to radio frequency energy thereat for radiating a divergent radio frequency beam having a spherical wavefront, the divergent beam diverging as from a point of illumination;

lens means for receiving and collimating the divergent beam into a directed planar radio frequency beam; and

a plurality of time delay means, each disposed between a corresponding one of the corporate feed means output terminals and a corresponding radiating means, for delaying radio frequency energy passing therebetween and for correcting squint errors of the directed planar beam which result from changes of the operating frequency of the radio frequency energy.

9. Apparatus as in claim 8 wherein at least one of the time delay means further comprises:

a tapped delay line having a plurality of settable taps with differential electrical lengths between taps of λ

_c, where λ

_c is equal to the wavelength of the center operating frequency of the antenna array; and

means responsive to the difference between the center operating frequency and the instantaneous frequency of the radio frequency energy for setting the appropriate tap.

10. A method for correcting squint errors caused as a space fed antenna array operates over a band of frequencies, the space fed antenna having a corporate feed that provides radio frequency energy at a plurality of output terminals, and further having an electronic lens for collimating and directing the energy, the method comprising the steps of:

phase shifting the energy at the plurality of output terminals to create a diverging radio frequency beam having a spherical wavefront, the spherical wavefront having a focal point; and

time delaying the energy at the plurality of output terminals, to cause the electronic lens focal point to maintain coincidence with the spherical wavefront focal point.

11. A space fed antenna system comprising:

lens means, responsive to a planar wave of R.F. energy received from a predetermined direction, for directing the R.F. energy into a beam converging toward a focal point;

array element means, disposed between the lens means and the focal point of the lens means, for receiving the converging beam of R.F. energy; and

control means, coupled to the array element means, for maintaining coincidence of the focal point of the converging beam with the focal point of the lens means.

12. The space fed antenna system as recited in claim 11 further comprising programmer means for controller the space fed antenna system, wherein the lens means and control means are responsive to the programmer means.