Sparse phase-mode planar feed for circular arrays
A method and apparatus for phase-mode feeding a circular antenna array for beamsteering is provided. A Butler Matrix having M antenna-side ports and M input/output ports is coupled to beamsteering circuitry. The coupled input/output ports may include a port corresponding to a phase-mode having an order magnitude greater than one. The coupled input/output ports may include ports of three different order magnitudes of phase-mode. The Butler Matrix is coupled to M inner ports of a radial waveguide, and the antenna elements are coupled to N outer ports of the waveguide, where N>M. Where M=4, the input/output ports correspond to a zeroth order phase-mode, plus and minus 1 st order phase-modes, and a second order phase-mode. The zeroth order phase-mode may be used for beamsteering closer to the radial axis of the antenna array while the second order phase-mode may be used for beamsteering further from the radial axis.
1. An apparatus for feeding an array of antenna elements, comprising:
a 2M-port Butler Matrix comprising a plurality of M antenna-side ports and a plurality of M input/output ports operatively coupled to the M antenna-side ports, the plurality of input/output ports including a first port corresponding to a phase-mode having an order magnitude greater than one, at least the first port and one additional one of the plurality of input/output ports configured for operative coupling to beamsteering circuitry; and
a feed for the array of antenna elements comprising:
a radial waveguide forming a cylindrical cavity bounded by conductive material;
a plurality of N antenna-element probes symmetrically arranged about an axial center of the radial waveguide, the plurality of antenna-element probes operatively coupled to the radial waveguide; and
a plurality of M phase-mode feed probes symmetrically arranged about the axial center of the radial waveguide and disposed radially inward from the plurality of antenna-element probes, the plurality of phase-mode feed probes operatively coupled to the radial waveguide, a quantity M of the phase-mode feed probes being less than a quantity N of the antenna-element probes,
the plurality of M phase-mode feed probes being operatively coupled to the M antenna-side ports of the Butler Matrix, each of the N antenna-element probes for operatively coupling to a respective antenna element of the array,
wherein the array of antenna elements are arranged about a main axis and are each configured to radiate with a radiation pattern having a main lobe directed primarily in an axial direction parallel to the main axis,
wherein the feed is provided as a laminated planar structure, the antenna elements of the array comprise a planar ring or several concentric rings of antenna elements disposed overtop of the feed, and the Butler Matrix is provided in a planar circuit underneath the feed.
2. The apparatus of claim 1 , wherein the feed for the array of antenna elements further comprises:
electrically conducting first and second surfaces;
an electrically conducting outer wall electrically coupling the first surface to the second surface; the first surface, the second surface, and the outer wall defining the cylindrical cavity;
wherein each of the plurality of antenna-element probes has a first antenna probe portion electrically coupled to the first surface and a second antenna probe portion that protrudes into the cylindrical cavity through a respective aperture in the first surface; and
wherein each of the plurality of phase-mode feed probes has a first feed probe portion electrically connected to the second surface and a second feed probe portion that protrudes into the cylindrical cavity through a respective aperture in the second surface.
3. The apparatus of claim 1 , wherein the quantity M of the phase-mode feed probes is equal to four and wherein the first port corresponds to a second order phase-mode and wherein a second port of the plurality of input/output ports is configured for operative coupling to the beamsteering circuitry, the second port corresponding to a zeroth-order phase-mode.
4. The apparatus of claim 3 , further comprising a switch operable to selectably couple one of the first port and the second port to the beamsteering circuitry.
5. The apparatus of claim 3 , further comprising a variable ratio combiner configured to couple the first port and the second port to a port of the beamsteering circuitry in a controllable signal ratio.
6. The apparatus of claim 3 , wherein a third port of the plurality of input/output ports is configured for operative coupling to the beamsteering circuitry, the third port corresponding to a 1st order or −1st order phase-mode.
7. The apparatus of claim 1 , wherein the quantity M of the phase-mode feed probes is equal to four and wherein the M input/output ports correspond to a zeroth order phase-mode, a 1 st order phase-mode, a −1 st order phase-mode, and a second order phase-mode.
8. The apparatus of claim 1 , further comprising coupling circuitry for controllably coupling three or more ports of the Butler Matrix to the beamsteering circuitry, said controllable coupling based on a desired beam angle of a radiation pattern of the array of antenna elements.
9. The apparatus of claim 8 , wherein the beam angle is an angle φ which is relative to the main axis.
10. The apparatus of claim 1 , further comprising coupling circuitry for controllably coupling the M ports of the Butler Matrix to the beamsteering circuitry, said controllable coupling based on a desired beam angle of a radiation pattern of the array of antenna elements.
11. The apparatus of claim 10 , wherein the beamsteering circuitry comprises the coupling circuitry.
12. The apparatus of claim 10 , wherein the coupling circuitry comprises switches for switchably coupling selected ones of the M ports to selected ports of the beamsteering circuitry.
13. The apparatus of claim 1 , further comprising coupling circuitry for controllably coupling two of the plurality of input/output ports of the Butler Matrix to the beamsteering circuitry at a time, said two of the plurality of input/output ports having order magnitudes which differ by one.
14. The apparatus of claim 1 , wherein the plurality of N antenna element probes are operatively coupled to N antenna elements of the array.
15. The apparatus of claim 14 , wherein the antenna elements are disposed at substantially regular intervals about a circle centered on a main axis, and are configured having a radiation pattern directed in an axial direction parallel to the main axis.
16. The apparatus of claim 1 , wherein some or all of the antenna-element probes and the phase-mode feed probes are magnetic loops.
17. A method for sparse phase-mode feeding of an array of antenna elements, the method comprising:
providing a Butler Matrix comprising a plurality of M antenna-side ports and a plurality of M input/output ports operatively coupled to the M antenna-side ports, the plurality of input/output ports including a first port corresponding to a phase-mode having an order magnitude greater than one, at least the first port and one additional one of the plurality of input/output ports configured for operative coupling to beamsteering circuitry;
providing a feed for the array of antenna elements comprising:
a radial waveguide forming a cylindrical cavity bounded by conductive material;
a plurality of N antenna-element probes symmetrically arranged about an axial center of the radial waveguide, the plurality of antenna-element probes operatively coupled to the radial waveguide; and
a plurality of M phase-mode feed probes symmetrically arranged about the axial center of the radial waveguide and disposed radially inward from the plurality of antenna-element probes, the plurality of phase-mode feed probes operatively coupled to the radial waveguide, a quantity M of the phase-mode feed probes being less than a quantity N of the antenna-element probes,
operatively coupling at least the first port to beamsteering circuitry;
operatively coupling the M antenna-side ports of the Butler Matrix to the plurality of M phase-mode feed probes; and
operatively coupling the N antenna-element probes to respective antenna elements of the array,
wherein the array of antenna elements are arranged about a main axis and are each configured to radiate with a radiation pattern having a main lobe directed primarily in an axial direction parallel to the main axis,
wherein the feed is provided as a laminated planar structure, the antenna elements of the array comprise a planar ring or several concentric rings of antenna elements disposed overtop of the feed, and the Butler Matrix is provided in a planar circuit underneath the feed.
18. The method of claim 17 , wherein some or all of the antenna-element probes and the phase-mode feed probes are magnetic loops.
19. The method of claim 17 , wherein the feed for the array of antenna elements further comprises:
electrically conducting first and second surfaces;
an electrically conducting outer wall electrically coupling the first surface to the second surface; the first surface, the second surface, and the outer wall defining the cylindrical cavity;
wherein each of the plurality of antenna-element probes has a first antenna probe portion electrically coupled to the first surface and a second antenna probe portion that protrudes into the cylindrical cavity through a respective aperture in the first surface; and
wherein each of the plurality of phase-mode feed probes has a first feed probe portion electrically connected to the second surface and a second feed probe portion that protrudes into the cylindrical cavity through a respective aperture in the second surface.
20. The method of claim 17 , wherein the quantity M of the phase-mode feed probes is equal to four and wherein the first port corresponds to a second order phase-mode and wherein a second port of the plurality of input/output ports is configured for operative coupling to beamsteering circuitry, the second port corresponding to a zeroth-order phase-mode.
21. The method of claim 20 , further comprising selectably coupling one of the first port and the second port to the beamsteering circuitry via a switch.
22. The method of claim 20 , further comprising coupling the first port and the second port to a port of the beamsteering circuitry in a controllable signal ratio using a variable ratio combiner.
23. The method of claim 20 , wherein a third port of the plurality of input/output ports is configured for operative coupling to the beamsteering circuitry, the third port corresponding to a 1st order or −1st order phase-mode.
24. The method of claim 17 , wherein the quantity M of the phase-mode feed probes is equal to four and wherein the M input/output ports correspond to a zeroth order phase-mode, a 1 st order phase-mode, a −1 st order phase-mode, and a second order phase-mode.
25. The method of claim 17 , further comprising coupling circuitry for controllably coupling three or more ports of the Butler Matrix to the beamsteering circuitry, said controllable coupling based on a desired beam angle of a radiation pattern of the array of antenna elements.
26. The method of claim 25 , wherein the beam angle is an angle φ which is relative to the main axis.
27. The method of claim 17 , further comprising controllably coupling the M ports of the Butler Matrix to the beamsteering circuitry, said controllable coupling based on a desired beam angle of a radiation pattern of the array of antenna elements.
28. The method of claim 17 , wherein the antenna elements are disposed at substantially regular intervals about a circle centered on a main axis, and are configured having a radiation pattern directed in an axial direction parallel to the main axis.
29. The method of claim 17 , further comprising controllably coupling two of the plurality of input/output ports of the Butler Matrix to the beamsteering circuitry at a time, said two of the plurality of input/output ports having order magnitudes which differ by one.
30. A wireless device comprising:
an array of antenna elements;
a transmitter/receiver comprising:
a source or destination for wireless signals;
beamsteering circuitry operatively coupled to the source or destination for wireless signals;
a Butler Matrix comprising a plurality of M antenna-side ports and a plurality of M input/output ports operatively coupled to the M antenna-side ports, the plurality of input/output ports including a first port corresponding to a phase-mode having an order magnitude greater than one, at least the first port and one additional one of the plurality of input/output ports configured for operative coupling to the beamsteering circuitry; and
a feed for the array of antenna elements comprising:
a radial waveguide forming a cylindrical cavity bounded by conductive material;
a plurality of N antenna-element probes symmetrically arranged about an axial center of the radial waveguide, the plurality of antenna-element probes operatively coupled to the radial waveguide; and
a plurality of M phase-mode feed probes symmetrically arranged about the axial center of the radial waveguide and disposed radially inward from the plurality of antenna-element probes, the plurality of phase-mode feed probes operatively coupled to the radial waveguide, a quantity M of the phase-mode feed probes being less than a quantity N of the antenna-element probes,
the plurality of M phase-mode feed probes being operatively coupled to the M antenna-side ports of the Butler Matrix, each of the N antenna-element probes for operative coupling to a respective antenna element of the array,
wherein the array of antenna elements are arranged about a main axis and are each configured to radiate with a radiation pattern having a main lobe directed primarily in an axial direction parallel to the main axis,
wherein the feed is provided as a laminated planar structure, the antenna elements of the array comprise a planar ring or several concentric rings of antenna elements disposed overtop of the feed, and the Butler Matrix is provided in a planar circuit underneath the feed.