Annular gradient index lens for omni and sector antennas

Abstract

An antenna having a ring-shaped gradient-index lens is disclosed, in which a radiator can be disposed within the inner bore of the ring-shaped body. The antenna can include a mechanism to translate the radiator along the z-axis, in which "up" translation of the radiator along the z-axis tilts the antenna's elevation beam pattern downward. The radiator disposed within the bore of the ring-shaped lens can be a dipole or a multi-sector radiator such as a three-sector radiator. Two variations of the ring-shaped lens are disclosed: a ring shape and a cylindrical ring shape.

Description

Background of the Invention Technical Field

[0002] This invention relates to wireless communication, and more particularly to omnidirectional and sector RF antennas. Background Technology

[0004] Gradient-index lenses (of which Luneburg lenses are an example) are useful devices for focusing and planarizing the RF wavefront received / transmitted by an antenna. Conventional Luneburg lenses have a spherical shape. A current drawback of using Luneburg lenses is that, in order to produce an antenna with omnidirectional coverage, a set of radiators must be placed around the outside of the spherical lens. This can increase the complexity and cost of the antenna. This may be particularly important for small antennas intended for omnidirectional use in indoor spaces.

[0005] Conventional omnidirectional and quasi-omnidirectional antennas have multiple array surfaces, each with multiple radiators arranged in at least a vertical array. This allows the elevation angle of the antenna gain pattern to be controlled by differentially controlling the amplitude and phase of the different radiators along the vertical axis (often referred to as remote electrically tunable tilt (RET)). Each of these array surfaces requires complex circuitry and numerous solder joints, which increase manufacturing complexity and introduce the possibility of passive intermodulation distortion (PIM).

[0006] Therefore, there is a need for a simplified omnidirectional or sector antenna that utilizes the focusing / planarization characteristics of a gradient refractive index lens and has a simplified mechanism for controlling the tilt of the gain pattern. Summary of the Invention

[0007] Therefore, the present invention relates to a ring gradient refractive index lens for omnidirectional and sector antennas, which eliminates one or more problems caused by the limitations and disadvantages of related technologies.

[0008] One aspect of the present invention relates to an antenna comprising: an annular gradient refractive index lens; and a radiator disposed at the center of the annular gradient refractive index lens, the radiator being coincident with the annular z-axis.

[0009] It should be understood that the foregoing general description and the following detailed description are merely exemplary and illustrative, and do not limit the claimed invention. Attached Figure Description

[0010] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate a ring-shaped gradient refractive index lens for omnidirectional and sector antennas. Together with the description, the drawings further serve to explain the principles of the ring-shaped gradient refractive index lens for omnidirectional and sector antennas described herein, and thereby enable those skilled in the art to manufacture and use the ring-shaped gradient refractive index lens for omnidirectional and sector antennas.

[0011] Figure 1A illustrates an exemplary ring lens antenna according to this disclosure.

[0012] Figure 1B shows an exemplary ring lens antenna of Figure 1A as viewed from the z-axis along the center of the ring.

[0013] Figure 2 shows an exemplary annular lens of Figure 1A / Figure 1B, in which the dipole is translated vertically upward to tilt the antenna gain pattern downward.

[0014] Figure 3 illustrates an exemplary cylindrical annular lens antenna with a "canned fisheye" annular lens configuration according to this disclosure.

[0015] Figure 4A shows an exemplary elevation beam pattern of a dipole without a lens.

[0016] Figure 4B shows an exemplary elevation beam pattern of a dipole deployed within the "canned fisheye" annular lens configuration of Figure 3.

[0017] Figure 4C shows an exemplary elevation beam pattern of a dipole deployed within the annular lens of Figure 1A / Figure 1B.

[0018] Figure 5A shows an exemplary elevation beam pattern of a dipole with an annular lens of Figure 1A / Figure 1B deployed, wherein the dipole is translated along the z-axis as shown in Figure 2, thereby tilting the beam downward by approximately 6 degrees.

[0019] Figure 5B shows an exemplary elevation beam pattern of a dipole with the annular lens of Figure 1A / Figure 1B deployed, wherein the dipole is translated along the z-axis as shown in Figure 2, thereby tilting the beam downward by approximately 9 degrees.

[0020] Figure 6A illustrates an exemplary three-sector core radiator configuration from a top-down perspective.

[0021] Figure 6B shows an exemplary three-sector core radiator configuration from a side view.

[0022] Figure 7A illustrates an exemplary three-sector ring lens antenna with a first ring element thickness radius according to the present invention.

[0023] Figure 7B shows the exemplary three-sector ring lens antenna of Figure 7A from a side view perspective.

[0024] Figure 7C illustrates an exemplary three-sector ring lens antenna according to the present invention, having a second ring element thickness radius greater than that of the first ring element.

[0025] Figure 8A shows an exemplary elevation beam pattern of an exemplary three-sector core radiator (without a lens) corresponding to Figure 6A, illustrating the gain pattern of one of the three sectors.

[0026] Figure 8B shows an exemplary elevation beam pattern of an exemplary three-sector ring lens antenna with a first ring element thickness radius corresponding to Figure 7A, illustrating one of the three sectors.

[0027] Figure 8C shows an exemplary elevation beam pattern of an exemplary three-sector ring lens antenna with a second ring element thickness radius corresponding to Figure 7C, illustrating one of the three sectors.

[0028] Figure 8D shows an exemplary elevation beam pattern of an exemplary three-sector ring lens antenna with a second ring element thickness radius corresponding to Figure 7C, wherein the three-sector core radiator is translated along the z-axis, thereby applying a downward tilt to the elevation gain pattern, showing one of the three sectors. Detailed Implementation

[0029] The implementation scheme of a ring gradient refractive index antenna for omnidirectional and sector antennas, based on the principles described herein with reference to the accompanying drawings, will now be discussed in detail. The same reference numerals in different figures may identify the same or similar elements.

[0030] Figure 1A illustrates an exemplary annular lens antenna 100 according to this disclosure. The annular lens antenna 100 includes a gradient refractive index annular lens 105 and a dipole 110 disposed along the annular center or "z" axis. The gradient refractive index annular lens 105 includes an annular central ring 115 and an outer surface 120. The annular central ring 115 may simply be an axis defined by the geometry of the annular body, rather than a physical feature within the gradient refractive index annular lens 105.

[0031] The gradient-index annular lens 105 has a varying refractive index such that the refractive index is at its maximum at the central annular ring 115 and decreases radially from the axis defined by the central annular ring, such that the refractive index is at its minimum at the outer surface 120. The maximum refractive index can be consistent along the central annular ring 110, and the minimum refractive index can be consistent across the entire outer surface 120. Typically, the refractive index gradient can be based on a conventional Luneburg distribution.

[0032]

[0033] Where n is the refractive index at a given point within the gradient refractive index annular lens 105; r is the radial distance from the annular central ring 115; and R is the distance from the annular central ring 115 to the outer surface 120.

[0034] The dielectric constant at the central ring 115 can be 2, resulting in a refractive index of the square root of 2 (sqrt(2)); and the dielectric constant at the outer surface 120 can be 1, resulting in a refractive index of 1. It will be understood that variations in the specific minimum and maximum refractive indices are possible and within the scope of this invention.

[0035] Figure 1B shows the annular lens antenna 100 viewed along the z-axis. Shown is a dipole 110 concentric with the z-axis; and a gradient-index annular lens 105 comprising a central annular ring 115, an inner diameter 125, and an outer diameter 130. Typically, the inner diameter 125 can be close enough to substantially contact the dipole 110. As used herein, substantial contact means that a gap may exist between the inner diameter and the dipole 110 to allow translation of the dipole 110 along the z-axis.

[0036] Figure 2 illustrates a ring lens antenna 100 with a dipole 110 vertically translated along the z-axis, causing the antenna gain pattern to tilt in the opposite direction. In other words, the upward translation of the dipole 110 tilts the gain pattern downward. The relevant dimensions of the gradient refractive index ring lens 105 include the thickness radius R of the ring element. t 150 and inner hole radius R h 155. Further relevant dimensions for achieving the tilt include the antenna translation height h. t and downward tilt angle a t 160. This will be discussed in further detail below.

[0037] Figure 3 illustrates an exemplary cylindrical annular lens antenna 300 with a "canned fisheye" annular lens configuration according to this disclosure. The cylindrical annular lens antenna 300 has a dipole 110 disposed within a cylindrical annular lens 305, which has a cylindrical outer surface 330 and an inner surface 320, wherein the inner surface 320 may be identical to the outer surface 130 of a gradient refractive index annular lens 105, except that the inner surface 320 terminates where it connects with the cylindrical outer surface 330. The cylindrical annular lens 305 may be substantially similar to the gradient refractive index annular lens 105, but with the portion of the annular body extending beyond the annular central ring 115 removed, thereby forming a cylindrical shape whose circumference coincides with the annular central ring 115. Therefore, the cylindrical annular lens 305 may be identical to the internal portion of the gradient refractive index annular lens 105 within the annular central ring 115. For the cylindrical annular lens 305, the peripheral axial ring 315 defines the position where the refractive index is at its maximum, similar to how the annular central ring 115 defines the position where the refractive index of the gradient refractive index annular lens 105 is at its maximum. The refractive index at any given point within the cylindrical annular lens 305 can be defined according to the Maxwell fisheye lens distribution as follows:

[0038]

[0039] Where n is the refractive index at a given point within the cylindrical annular lens 305; r is the radial distance from the circumferential axial ring 315 to the given point within the cylindrical annular lens 305; and R t It is the thickness radius of the annular element 350, or the distance from the axial ring 315 at the perimeter to the inner surface 320.

[0040] The dielectric constant at the circumferential axial ring 315 can be 4, resulting in a refractive index of 2; and the dielectric constant at the inner surface 320 can be 2, resulting in a refractive index of the square root of 2. It will be understood that variations in specific minimum and maximum refractive indices are possible and within the scope of this invention.

[0041] Although Figures 1A, 1B, 2, and 3 (as shown) illustrate the distance between the inner aperture radius 155 / 355 and the dipole 110, this is for illustrative purposes. It will be understood that the inner aperture radius 155 / 355 allows the dipole 110 to be close enough to essentially contact the inner diameter, and this distance can be greater for longer wavelengths without significantly degrading performance. As used herein, essentially contact means that a gap may exist between the inner diameter and the dipole 110 to allow the dipole 110 to translate along the z-axis, and the permissible length of this gap depends on the frequency at which the annular lens antenna 100 operates.

[0042] The dimensions of the gradient refractive index annular lens 105 or the cylindrical annular lens 305 (annular element thickness radius 150 / 350) can be selected based on the desired elevation beamwidth of the antenna 100 / 300. Generally, if the inner aperture radius 155 / 355 remains constant, the larger the annular element thickness radius 150 / 350, the narrower the elevation beamwidth.

[0043] Figure 4A shows the elevation beam pattern of the dipole 110 without a lens; Figure 4B shows the elevation beam pattern of the antenna 300 including the dipole 110 with a cylindrical annular lens 305; and Figure 4C shows the elevation beam pattern of the antenna 100 including the dipole 110 with a gradient refractive index annular lens 105.

[0044] Figure 5A shows an exemplary elevation beam pattern for antenna 100, where dipole 110 is translated "up" by 0.736" along the z-axis, thereby applying a downward tilt of approximately 6 degrees. In this example, the aperture radius 155 is 1" and the annular element thickness radius 150 is 6". The pattern shown was excited at 3 GHz.

[0045] Figure 5B shows an exemplary elevation beam pattern for antenna 100, where dipole 110 is translated "up" along the z-axis by a distance of 1.109”, thereby applying a downward tilt of approximately 9 degrees. In this example, the aperture radius 155 is 1” and the annular element thickness radius 150 is 6”, the same as in Figure 5A. The pattern shown was excited at 3 GHz.

[0046] Figure 6A shows an exemplary three-sector core radiator 600 from a top-down perspective. In the configuration described herein, the three-sector core radiator 600 can be used in place of the dipole 110. The three-sector core radiator 600 includes three panels 605 arranged in a triangular configuration, with a radiator 610 disposed on each of the three panels 605. The combination of the three panels 605 and the radiator 610 can be identical. They can be fed separately to form three different sectors, or they can be fed with a single RF source to form a quasi-omnidirectional antenna. It will be understood that such variations are possible and within the scope of the invention. Figure 6B is a side view of one of the pairs of panels 605 and radiator 610.

[0047] Figure 7A illustrates an exemplary three-sector annular lens antenna 700A according to the principles described herein. Antenna 700A has a gradient refractive index annular lens 705A having a first annular element thickness radius of 3” and an inner aperture radius of 2” 155. A three-sector core antenna 600 is shown disposed within the inner aperture of the gradient refractive index annular lens 705A. Figure 7B is a side view of antenna 700A.

[0048] Figure 7C illustrates an exemplary three-sector annular lens antenna 700B according to the principles described herein. Antenna 700B has a gradient refractive index annular lens 705B having a first annular element thickness radius of 6” and an inner aperture radius of 2” 155. A three-sector core antenna 600 is shown disposed within the inner aperture of the gradient refractive index annular lens 705B.

[0049] Figure 8A shows exemplary elevation beam patterns at multiple frequencies of one sector of a three-sector core antenna 600 radiating at 5.15 GHz, 5.25 GHz, 5.35 GHz, 5.55 GHz, 5.75 GHz, and 5.925 GHz without a lens. Figure 8B shows an exemplary elevation beam pattern of antenna 700A at the same frequencies, which includes a three-sector core antenna 600 (only one sector is active) and a gradient refractive index annular lens 705A with a first annular element thickness radius of 3”; and Figure 8C shows an exemplary elevation beam pattern of antenna 700B at the same frequencies, which includes a three-sector core antenna 600 (only one sector is active) and a gradient refractive index annular lens 705B with a second annular element thickness radius of 6”. It will be apparent that there is a considerable improvement in directional gain along the zero azimuth and elevation angles of the gain pattern, which is caused by the presence of a gradient refractive index annular lens with an increased annular element thickness radius.

[0050] Figure 8D shows an exemplary elevation beam pattern corresponding to the exemplary three-sector ring lens antenna 700B (Figure 7C), which has a second ring element thickness radius of 6”, wherein the three-sector core radiator 600 is translated 1.109” along the z-axis, thereby applying a downward tilt of approximately 9 degrees in the elevation gain pattern. The gain pattern of one of the sectors is shown.

[0051] While various embodiments of the invention have been described above, it should be understood that these embodiments are presented by way of example only and not by way of limitation. It will be apparent to those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope of the invention. Therefore, the breadth and scope of the invention should not be limited to any of the exemplary embodiments described above, but should be defined solely by the appended claims and their equivalents.

Claims

1. An antenna comprising: Annular gradient refractive index lens; as well as A radiator is disposed at the center of the annular gradient refractive index lens, the radiator is coincident with the annular z-axis, and the radiator is configured to translate along the annular z-axis.

2. The antenna according to claim 1, wherein the radiator comprises a dipole.

3. The antenna according to claim 1, wherein the radiator comprises a multi-sector radiator.

4. The antenna according to claim 3, wherein the multi-sector radiator comprises a three-sector radiator.

5. The antenna of claim 1, wherein the inner diameter of the annular gradient refractive index lens is such that the annular gradient refractive index lens contacts the dipole.

6. The antenna of claim 1, wherein the annular gradient refractive index lens comprises: The annular central ring region corresponding to the maximum refractive index; as well as The outer surface corresponding to the minimum refractive index.

7. The antenna of claim 1, wherein the annular gradient refractive index lens comprises a cylindrical outer surface.

8. The antenna of claim 7, wherein the annular gradient refractive index lens comprises: The axial ring region corresponding to the maximum refractive index; as well as The inner surface corresponding to the minimum refractive index.

9. The antenna according to claim 1, wherein the radiator is in contact with the inner diameter of the annular gradient refractive index lens.

10. The antenna according to claim 5 or 9, wherein the dipole is translatable along the z-axis.

11. The antenna of claim 6, wherein the maximum refractive index is 2 and the minimum refractive index is 1.

12. The antenna of claim 8, wherein the maximum refractive index is 4 and the minimum refractive index is 2.

13. The antenna according to any one of claims 1-5, wherein the cross-section of the annular gradient refractive index lens is circular.

14. The antenna according to any one of claims 7-8, wherein the cross-section of the annular gradient refractive index lens is semi-circular.

15. The antenna of claim 1, wherein the radiator comprises a multi-sector radiator, the multi-sector radiator comprising a plurality of panels arranged in a polygonal configuration and a radiator component on each of the plurality of panels, the polygonal configuration having a polygonal cross-section, the number of sides of the polygonal cross-section corresponding to the number of the panels.

16. The antenna of claim 15, wherein the three-sector radiator comprises three panels arranged in a triangular configuration and three radiator components.

17. The antenna of claim 1, wherein the annular gradient refractive index lens has a first annular element thickness of 3 inches and an inner aperture radius of 2 inches.

18. The antenna of claim 1, wherein the annular gradient refractive index lens has a first annular element thickness of 6 inches and an inner aperture radius of 2 inches.

19. The antenna according to claim 17 or 18, further comprising a three-sector core antenna disposed within the inner hole f of the annular gradient refractive index lens.

20. The antenna according to any one of claims 1-9, comprising a gap between the inner diameter of the annular gradient refractive index lens and the radiator, wherein the length of the gap depends on the frequency at which the antenna operates.

21. The antenna according to any one of claims 1-9, wherein the size of the annular gradient refractive index lens is selected based on the desired elevation angle beam.

22. The antenna of claim 21, wherein if the inner aperture radius is constant, the greater the radius thickness of the annular element, the narrower the elevation beamwidth.

23. A method for tilting the gain pattern of an antenna according to any one of the preceding claims, the method comprising: The radiator is translated along the z-axis of the annular gradient refractive index lens within the inner diameter of the annular gradient refractive index lens.

24. The method of claim 23, wherein the upward translation of the antenna causes the gain pattern to tilt downward.

25. The method of claim 23 or 24, wherein the tilt of the gain pattern imparted to the antenna is related to the thickness radius of the annular element, the inner hole radius, the antenna translation height, and the downtilt angle.

Images