High resolution scanning reflectarray antenna

• US 6,081,235 A
• Filed: 04/30/1998
• Issued: 06/27/2000
• Est. Priority Date: 04/30/1998
• Status: Expired due to Fees

• Current Assignee: Administrator of The National Aeronautics and Space Administration
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Romanofsky, Robert R, Miranda, Felix A.
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): VANNUCCI, JAMES
• Application Number:
  US09/071,450
• Time in Patent Office: 789 Days
• Field of Search: 343/700 MS, 343/775, 343/778, 343/779, 343/781 CA, 343/753
• US Class Current: 343/700.0MS
• CPC Class Codes: H01P 1/181 using ferroelectric devices
• CPC Class Codes: H01Q 1/288 Satellite antennas
• CPC Class Codes: H01Q 3/46 Active lenses or reflecting arrays

Abstract

The present invention provides a High Resolution Scanning Reflectarray Antenna (HRSRA) for the purpose of tracking ground terminals and space craft communication applications. The present invention provides an alternative to using gimbaled parabolic dish antennas and direct radiating, phased arrays. When compared to a gimbaled parabolic dish, the HRSRA offers the advantages of vibration free steering without incurring appreciable cost or prime power penalties. In addition, it offers full beam steering at a fraction of the cost of direct radiating arrays and is more efficient.

Claims

1. A High Resolution Scanning Reflectarray Antenna (HRSRA) comprising:

an antenna plane including a plurality of microstrip patch radiator elements arranged in an array, each element having an associated phase shifter comprising a thin ferroelectric film layer positioned above a dielectric substrate layer and below a resistive film, wherein the dielectric substrate layer rests upon a conductive ground reference layer that is divided into squares of alternating low and high conductivity;

each element in communication with a power source through a beam steering computer;

a corrugated feed horn that illuminates each element of the array by emitting a microwave radiation;

a means for continuously variable phase shifting to achieve an electronic scanning of an arbitrary resolution without any physical movement of said antenna.

2. The HRSRA according to claim 1, each of the plurality of patch elements having a pair of stubs, each stub of the pair orthogonal to the other, and each of the stubs having varying lengths corresponding to a compensation factor respective to the length of each stub to compensate for a spatial phase shift between the horn and the elements away from a normal between the horn and the antenna plane.

3. The HRSRA of claim 2, wherein each of the plurality of patch elements communicates with two pair of orthogonally separated microstrip coupled lines, that are situated upon the ferroelectric film layer, and covered by the resistive layer to form a coupled line phase shifting element, for integration of the patch elements and phase shifting elements on a same surface of said antenna.

4. The HRSRA according to claim 3, further comprising a plurality of bias points communicating with said coupled lines of the plurality of patch elements for introducing a DC bias control signal input to each element of the array.

5. The HRSRA according to claim 4, wherein the coupled lines are lithographically defined on the ferroelectric film layer and the DC bias applied across said coupled lines alters the dielectric constant of the ferroelectric layer, thereby controlling a propagation velocity of an electromagnetic wave.

6. The HRSRA according to claim 5, the means for continuously variable phase shifting comprising a variation in the DC bias across the coupled lines for a consequent instantaneous, continuously variable phase shift and a desired electronic beam steering, without vibration and more immediate, than by mechanical positioning.

7. The HRSRA of claim 6, wherein the microwave radiation emitted from the horn comprises an incident polarized signal to each element of the reflectarray, communicating through the stubs to each coupled line phase shifter element, for a re-radiated signal from each patch element, whereby a phase shift is achieved for an infinite incremental resolution and a full hemispheric coverage consequent to the continuously variable phase shift.

8. The HRSRA of claim 7, the means for compensating comprising the stubs and coupled lines forming a pair of stubs-coupled lines arrangement connected to each of said plurality of patch elements, each of the pair of stubs-coupled lines arrangement having varying lengths, radiating outwardly away from each of the plurality of patch elements.

9. The HRSRA according to claim 8, wherein the phase shift is equal to twice the electrical length of the stubs-coupled lines arrangement.

10. The HRSRA according to claim 9, wherein the plurality of patch elements of the array is arranged in columns and rows, each of said plurality of bias points communicating with a respective column and row of the array through said couple lines for a bias control signal input to each row and each column and simplification in biasing of the array.

11. The HRSRA according to claim 10, wherein a single voltage is applied to each row of the microstrip array.

12. The HRSRA according to claim 11, wherein a single voltage is applied to each column of the microstrip array.

13. The HRSRA according to claim 12, the array comprising a total of N² microstrip patch radiator elements and having only 2N control signals as opposed to N² control signals for biasing the array.

14. The HRSRA according to claim 13, the computer communicating with the array through a plurality of ribbon cables for control of a varied bias to the array and an enhanced beam steering control.

15. The HRSRA described in claim 14, wherein the horn is positioned at a predetermined distance from the antenna.

16. The HRSRA according to claim 15, wherein the antenna plane has an essentially flat profile, an essentially round perimeter and a diameter;

and,

wherein the feed horn is in a far field of the antenna, said predetermined distance optimally comprising 2D² /λ

₀ from the antenna plane, where D is the diameter of the antenna plane, whereby the array is uniformly illuminated in amplitude and phase, at the expense of a spillover efficiency.

17. The HRSRA of claim 16, further comprising nonmetallic struts that attach the horn to the antenna, for an HRSRA that is conformal except for the feed horn.

18. The HRSRA according to claim 17, wherein the horn produces a circularly polarized microwave radiation and each of the plurality of patch elements is circularly polarized, whereby the radiation emitted from the horn provides a circular polarization to each of the plurality of microstrip elements of the array.

19. The HRSRA according to claim 17, wherein said horn emits a linearly polarized microwave radiation;

and,

wherein each of the patch elements of the array is adjusted in phase to form a main beam in an arbitrary direction for an optimal response to the linear polarized microwave radiation.

20. The HRSRA described in claim 18, wherein each of said plurality of patch elements has an arbitrary identical shape and an optimal area.

21. The HRSRA described in claim 20, wherein each of said plurality of patch elements has an identical essentially square shape with the optimal area.

22. A High Resolution Scanning Reflectarray Antenna (HRSRA) comprising:

a reflectarray antenna having an essentially flat antenna plane with a plurality of microstrip patch radiator elements each having an independent voltage input through two pair of coupled lines defined on a thin ferroelectric film layer with a bias across each pair of coupled lines comprising a pair of phase shifters each having a continuously variable phase shift beyond 360°

without any quantization error;

a feed horn connected to the antenna for emitting a microwave signal that is re-radiated by each element;

a means for compensating for a spatial phase shift between the horn and the antenna plane; and

,

a means for controlling the continuously variable phase shift versus a discrete phase shift, for a full hemispherical coverage of the antenna.

23. The HRSRA according to claim 22, wherein the thin ferroelectric film is positioned above, and separated from, a conductive ground layer by an electrically thin dielectric substrate layer and covered by a resistive layer;

and,

wherein the thin ferroelectric film layer includes dielectric properties for alteration by a minimal DC voltage input.

24. The HRSRA according to claim 23, the plurality of microstrip patch radiator elements comprising a total of N² elements arranged in an array of columns and rows, each column and row having an associated bias point for input of an independent voltage to each column and row comprising 2N control signals to bias the array.

25. The HRSRA according to claim 24, wherein the ferroelectric film layer has a thickness and a phase shift directly proportional to the thickness of the ferroelectric film layer.

26. The HRSRA according to claim 25, the thickness of the ferroelectric film layer comprising essentially one-thousandth of a guided wavelength, for maximum tunability within achievable ferroelectric film process constraints.

27. The HRSRA according to claim 26, the ferroelectric film layer including an electromagnetic wave having a phase velocity with even and odd mode fields;

and,

wherein the phase velocity is dominated by the odd mode fields for a maximum effectiveness of said ferroelectric film.

28. The HRSRA according to claim 27, wherein each of the plurality of patch elements has a side length, wherein the side length of each patch element is approximately λ

g/2, whereby the patch element side length is inversely proportional to a frequency.

29. The HRSRA according to claim 28, the means for compensating comprising a pair of stubs connected to each of said plurality of elements, the stubs having varying lengths, radiating outwardly away from each of the plurality of elements;

and,

wherein each stub of the pair of stubs is orthogonal to the other.

30. The HRSRA of claim 29, wherein each of the stubs of a stub pair has an associated compensating factor determined by a stub length, such that the compensating factor of each stub is essentially equal to twice an electrical length of that stub.

31. The HRSRA described in claim 30, further comprising a computer communicating with the array through a pair of ribbon cables, each cable having a plurality of wires for biasing each column and row of the patch elements;

and,

wherein said means for controlling a variable phase shifting comprises a variation in a bias across the coupled lines of each element, said variation controlled by the computer, with a commensurate infinitely variable phase shift of the array for electronic scanning and a consequent beam steering without any physical movement or vibration of the antenna.

32. The HRSRA according to claim 31, further comprising a stepper motor associated with the computer, the motor having a shaft that articulates with that antenna plane, a rotary coupler communicating with the array through said cables for application of a bias to the array using said coupler;

and,

the motor in articulation with said plane through the shaft for rotation of the plane as a turnstile, with rotation of the antenna in combination with electronic scanning to provide scanning in the azimuth (φ

) direction by a rotation between 0 and 180 degrees in an azimuthal tracking, concomitant with an elevation Θ

tracking achieved by an electronic phase shifting and beam steering, for hybrid electronic and mechanized scanning over all visible space while maintaining a simple biasing scheme.

33. A High Resolution Scanning Reflectarray Antenna (HRSRA) comprising:

an antenna reflector including a plurality of metallic microstrip patch radiator elements positioned in an array on a reflectarray plane, wherein each of the plurality of microstrip elements communicates with a power source through a phase shifter, comprising a thin ferroelectric film layer having a dielectric constant and two pair of orthogonally separated microstrip coupled lines;

a corrugated feed horn situated in a far field from the reflectarray plane for emitting a microwave radiation to illuminate the reflectarray plane;

a means for a continuously variable phase shifting of the antenna by altering the dielectric constant of the ferroelectric layer; and

,

the power source comprising an independent voltage source in communication with each said element of the plurality through interconnecting bias points and the couple lines of the reflectarray.

34. The HRSRA according to claim 33, each of the plurality of patch elements and coupled microstrip lines comprising High Temperature Superconducting (HTS) patch antenna elements, each element having a predetermined area, and each of the elements arranged in columns and rows in the array of the reflectarray plane.

35. The HRSRA according to claim 34, wherein each of said plurality of HTS elements has an essentially square shape with an area identical to the predetermined area.

36. The HRSRA according to claim 34, wherein each of the plurality of HTS elements has an essentially circular shape with an area equal to the predetermined area.

37. The HRSRA according to claim 34, wherein each of said plurality of HTS elements has any arbitrary shape with an area equal to said predetermined area.

38. A Scanning Antenna comprising:

an antenna plane including a plurality of microstrip patch radiator elements comprising coupled line phase shifters, formed of a thin ferroelectric film, positioned above a dielectric substrate that is situated on a conductive ground layer, the elements arranged in an array columns and rows on the plane;

a corrugated feed horn that illuminates the array by emitting a microwave radiation;

further comprising a mechanical turnstile positioned beneath the reflectarray; and

,

wherein scanning is achieved electronically by applying a minimal DC bias, for phase shifting the thin ferroelectric film as opposed to a high bias required to tune a bulk ferroelectric material, to bias points associated with each column and row of the array for beam steering in the azimuth direction, with a hybridized mechanical steering by use of the mechanical turnstile over all visible space.

39. The Scanning Antenna according to claim 38, wherein each of the plurality of microstrip patch elements having no resistive layer, and a consequent essentially zero resistance, with an equal voltage applied to each element in a given row or column, with a consequent scanning as a function of an angle of elevation theta (Θ

), with an azimuth angle phi (φ

), fixed at zero or ninety degrees.