PHASED ARRAY LINE FEED FOR A REFLECTOR ANTENNA

Abstract

A phased array line feed for a reflector antenna, including a plurality of substantially parallel metallic rods and a phase/power switching matrix electrically connected to the metallic rods. The phase/power switching matrix may steer a beam of the reflector antenna by adjusting the phase and/or power difference between the metallic rods. The phased array line feed may also include a plurality of substantially parallel metallic disks. The metallic rods may extend through the metallic disks substantially perpendicular to the metallic discs. The metallic discs may be equally spaced and the diameter of the metallic disks may decrease along the length of the metallic rods. Alternatively, the diameters of the metallic discs may be equal and the distances between the metallic discs may decrease along the length of the metallic rods.

Claims

1. A reflector antenna, comprising: a spherical reflective surface; and a phased array line feed comprising: a plurality of substantially parallel metallic rods configured to receive or emit electromagnetic waves reflected off the spherical reflective surface, and a phase/power switching matrix electrically connected to the substantially parallel metallic rods.

2. The reflector antenna of claim 1, wherein the phase/power switching matrix steers a beam of the reflector antenna by adjusting a phase difference between the substantially parallel metallic rods.

3. The reflector antenna of claim 1, wherein the phase/power switching matrix controls the shape of the reflector antenna beam by adjusting a power difference between the substantially parallel metallic rods.

4. The reflector antenna of claim 1, further comprising: a plurality of substantially parallel metallic disks, wherein each of the substantially parallel metallic rods extends from a base of the phased array line feed through the substantially parallel metallic disks substantially perpendicular to the substantially parallel metallic disks to a vertex of the phased array line feed.

5. The reflector antenna of claim 4, wherein the substantially parallel metallic disks are spaced apart by a distance of approximately ½ of a wavelength of interest of the reflector antenna.

6. The reflector antenna of claim 4, wherein distances between the substantially parallel metallic disks decrease from a maximum at the base of the phased array line feed to a minimum at the vertex of the phased array line feed.

7. The reflector antenna of claim 4, wherein diameters of the substantially parallel metallic disks decrease from a maximum at the base of the phased array line feed to a minimum at the vertex of the phased array line feed.

8. The reflector antenna of claim 1, wherein: the substantially parallel metallic rods are spaced apart at a base of the phased array line feed by a distance of approximately N/4 of a wavelength of interest of the reflector antenna; and N is an integer.

9. The reflector antenna of claim 1, wherein distances between the substantially parallel metallic rods decrease from a base of the phased array line feed base to a vertex of the phased array line feed.

10. The reflector antenna of claim 1, wherein the phased array line feed has a length of approximately 12 percent of the diameter of the reflector antenna.

11. A method of making a reflector antenna having a wavelength of interest, the method comprising: providing a spherical reflective surface; and providing a phased array line feed by: providing a plurality of substantially parallel metallic rods configured to receive or emit electromagnetic waves reflected off the spherical reflective surface, and electrically connecting a phase/power switching matrix to the substantially parallel metallic rods.

12. The method of claim 11, wherein the phase/power switching matrix steers a beam of the reflector antenna by adjusting a phase difference between the substantially parallel metallic rods.

13. The method of claim 11, wherein the phase/power switching matrix controls the shape of the reflector antenna beam by adjusting a power difference between the substantially parallel metallic rods.

14. The method of claim 11, further comprising: providing a plurality of substantially parallel metallic disks, wherein each of the substantially parallel metallic rods extends from a base of the phased array line feed through the substantially parallel metallic disks substantially perpendicular to the metallic disks to a vertex of the phased array line feed.

15. The method of claim 14, wherein the substantially parallel metallic disks are spaced apart by a distance of approximately ½ the wavelength of interest.

16. The method of claim 14, wherein distances between the substantially parallel metallic disks decrease from a maximum at the base of the phased array line feed to a minimum at the vertex of the phased array line feed.

17. The method of claim 14, wherein diameters of the substantially parallel metallic disks decrease from a maximum at the base of the phased array line feed to a minimum at the vertex of the phased array line feed.

18. The method of claim 11, wherein: the substantially parallel metallic rods are spaced apart by a distance of approximately N/4 the wavelength of interest at a base of the phased array line feed; and N is an integer.

19. The method of claim 11, wherein distances between the substantially parallel metallic rods decrease from a base of the phased array line feed base to a vertex of the phased array line feed.

20. The method of claim 11, wherein the phased array line feed has a length of approximately 12 percent of the diameter of the reflector antenna.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Aspects of exemplary embodiments may be better understood with reference to the accompanying drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of exemplary embodiments, wherein:

[0014] FIG. 1 is a diagram illustrating a satellite with a spherical balloon reflector antenna according to U.S. patent application Ser. No. 15/154,760;

[0015] FIG. 2 is a diagram illustrating a prior art line feed;

[0016] FIG. 3 is a diagram illustrating a phased array line feed for a reflector antenna according to an exemplary embodiment of the present invention; and

[0017] FIG. 4 is a diagram illustrating a phased array line feed for a reflector antenna according to another exemplary embodiment of the present invention.

DETAILED DESCRIPTION

[0018] Preferred embodiments of the present invention will be set forth in detail with reference to the drawings, in which like reference numerals refer to like elements or steps throughout.

[0019] FIG. 3 is a diagram illustrating a phased array line feed 300 for a reflector antenna that operates at a wavelength of interest λ (e.g., the spherical reflective surface 144 illustrated in FIG. 1) according to an exemplary embodiment of the present invention.

[0020] As shown in FIG. 3, the phased array line feed 300 includes a plurality of (e.g., 3 or more) metallic rods 320a-320c and a phase/power switching matrix 340. The phase/power switching matrix 340 is electrically connected to each of the metallic rods 320a-320c, for example via coaxial connectors 342. The phased array line feed 300 may also include a plurality of metallic disks 310a-310n. The metallic rods 320a-320c may pass through the metallic discs 310a-310n, for example via coaxial feedthroughs 322.

[0021] The metallic disks 310a-310n are substantially parallel. The metallic rods 320a-320c may be arranged in a circular pattern (embodiments with three metallic rods 320a-320c, for example, may form a triangular pattern). At the base of the phased array line feed 300, the metallic rods 320a-320c may be separated by a distance of approximately λ/3.5 center-to-center. The metallic rods 320a-320c may be substantially parallel and pass through each of the metallic disks 310a-310n substantially perpendicular to the metallic disks 310a-310n. For example, the rods may be angled inward at an angle of approximately 1 degree (e.g., 1 degree±0.1 degree).

[0022] In embodiments that include metallic discs 310a-310n, the metallic discs 310a-310n divide the phased array line feed 300 into a series of independent subarrays of λ/2 vertical antennas. In essence, each of the metallic discs 310a-310n acts as a ground plane for each of the subarrays. The emergent beam angle θ from each subarray is a function of the phasing within each subarray and the diameter of the metallic discs 310a-310n separating the subarrays. As illustrated in FIG. 1, illumination of a spherical reflector requires the emergent beam angle θ to vary along the length of the phased array line feed 300 with the largest emergent beam angle θ occurring at the end of the feed closest to the reflective surface 144. In the embodiment shown in FIG. 3, the emergent beam angle θ varies along the length of the line feed, for example from 19 degrees to 64 degrees.

[0023] Compared to a conventional, stationary line feed (e.g., the line feed 200 illustrated in FIG. 2), the length of the phased array line feed 300 may be extended to intercept off-axis reflected rays that would otherwise be missed by the conventional line feed. To achieve scan angles of ±30 degrees, the length of the line feed may be approximately 12 percent (e.g., 12±1 percent) of the diameter of the spherical reflector being illuminated (e.g., the reflective surface 144).

[0024] In the embodiment illustrated in FIG. 3, the metallic disks 310a-310n may be equally spaced along the length of the metallic rods and the diameter of the metallic disks may decrease from the base to the vertex of the line feed. For example, the metallic disks 310a-310n may be separated by a distance of approximately λ/2 (e.g., λ/2±0.13) and the metallic discs may have a diameter of approximately λ/1.1 at the base of the line feed to approximately λ/1.8 at the vertex.

[0025] FIG. 4 is a diagram illustrating a phased array line feed 400 for a reflector antenna that operates at a wavelength of interest λ (e.g., the spherical reflective surface 144 illustrated in FIG. 1) according to another exemplary embodiment of the present invention.

[0026] Similar to the phased array line feed 300 illustrated in FIG. 3, the phased array line feed 400 includes a plurality of (e.g., 3 or more) substantially parallel metallic rods 320a-320c and a phase/power switching matrix 340 electrically connected to each of the metallic rods 320a-320c (e.g., via coaxial connectors 342). The phased array line feed 400 may also include a plurality of substantially parallel metallic disks 310a-310n. The metallic rods 320a-320c may pass through the metallic disks 310a-310n (e.g., via coaxial feedthroughs 322) perpendicular to the metallic disks 310a-310n. Again, the length of the phased array line feed 400 may be extended to approximately 12 percent (e.g., 12±1 percent) of the diameter of the spherical reflector being illuminated (e.g., the reflective surface 144) to intercept off-axis reflected rays that would otherwise be missed by a conventional, stationary line feed (e.g., the line feed 200 illustrated in FIG. 2).

[0027] In the embodiment illustrated in FIG. 3, diameters d of the metallic disks 310a-310n may be substantially equal. Similar to the phased array line feed 300 illustrated in FIG. 3, the metallic discs 310a-310n divide the phased array line feed 400 into a series of independent subarrays of λ/2 vertical antennas. In order for the emergent beam angles θ from each subarray to vary along the length of the phased array line feed 400 (e.g., from 19 degrees to 64 degrees), the distances between the metallic disks 310a-310n decrease from the base of the phased array line feed 400 to the vertex of the phased array line feed 400.

[0028] Each of the phased array line feeds 300 and 400 create an electrically steerable beam that illuminates the surface of the reflector antenna (e.g., the reflective surface 144) without rotating the phased array line feed 300 or 400. The phase/power switching matrix 340 steers the beam by adjusting the phase and/or power difference between the metallic rods 320a-320c.

[0029] A mathematical description of the resulting beam pattern from the phased array line feed 300 or 400 can be derived using the principle of pattern multiplication. Assuming the geometry of each radiating element in the array (here, a metallic rod 320 with metallic disks 310) is the same, then the combined radiation pattern may be prescribed, for example, by Equation 1:

[00001]$\begin{array}{cc}{f}_a\left(\theta ,\phi \right)=f_0\left(\theta ,\phi \right).Math.\underset{n=1}{\overset{N}{.Math.}}.Math.V_n.Math.e^{{\mathrm{jkd}}_n.Math.\sin .Math..Math.\theta .Math..Math.\cos .Math..Math.\phi }& \mathrm{Eq}..Math.1\end{array}$

where [0030] f.sub.a(θ,ϕ)=resulting radiation pattern [0031] f.sub.0(θ,ϕ)=common radiation pattern of each array element [0032] V.sub.n=A.sub.ne.sup.jα.sup.n=complex excitation to each element [0033] A.sub.n=signal amplitude at each element [0034] α.sub.n=phase at each element [0035] d.sub.n=element spacing relative to center of array [0036] k=2π/λ=propagation constant [0037] θ=polar angle [0038] ϕ=azimuthal angle [0039] λ=wavelength of operation [0040] n=element number (e.g., 1, 2, 3, etc.)

[0041] The above expression for f.sub.a(θ,ϕ) may also be presented in vector form as shown, for example, in Equation 2. The normalized power pattern, P.sub.n(θ,ϕ), of the array is then:

[00002]$\begin{array}{cc}{P}_n\left(\theta ,\phi \right)=\frac{{.Math.f_a\left(\theta ,\phi \right).Math.}^2}{{.Math.f_{\max }.Math.}^2}& \mathrm{Eq}..Math.2\end{array}$

where [0042] f.sub.max=maximum value of f.sub.a(θ,ϕ).

[0043] The foregoing description and drawings should be considered as illustrative only of the principles of the inventive concept. Exemplary embodiments may be realized in a variety of sizes and are not intended to be limited by the preferred embodiments described above. Numerous applications of exemplary embodiments will readily occur to those skilled in the art. Therefore, it is not desired to limit the inventive concept to the specific examples disclosed or the exact construction and operation shown and described. Rather, all suitable modifications and equivalents may be resorted to, falling within the scope of this application.