U.S. patent application number 10/259889 was filed with the patent office on 2004-04-01 for method for fabricating luneburg lenses.
Invention is credited to Strickland, Peter C..
Application Number | 20040061948 10/259889 |
Document ID | / |
Family ID | 32029578 |
Filed Date | 2004-04-01 |
United States Patent
Application |
20040061948 |
Kind Code |
A1 |
Strickland, Peter C. |
April 1, 2004 |
METHOD FOR FABRICATING LUNEBURG LENSES
Abstract
A dielectric lens including a plurality of wedges being formed
from a dielectric material, each of the plurality of wedges being
substantially identical and orange-slice shaped and including two
planar surfaces separated by an angular width, and each of the
plurality of wedges having a plurality of gaps for altering an
effective permittivity of the dielectric lens, wherein the
plurality of wedges form the dielectric lens by connecting the
plurality of wedges along the planar surfaces such that each of the
planar surfaces intersect along a common line.
Inventors: |
Strickland, Peter C.;
(Ottawa, CA) |
Correspondence
Address: |
SHAPIRO COHEN
P.O. BOX 3440
STATION D
OTTAWA
ON
K1P6P1
CA
|
Family ID: |
32029578 |
Appl. No.: |
10/259889 |
Filed: |
September 30, 2002 |
Current U.S.
Class: |
359/664 ;
359/642 |
Current CPC
Class: |
H01Q 15/08 20130101 |
Class at
Publication: |
359/664 ;
359/642 |
International
Class: |
G02B 003/00; G02B
007/00; G02B 009/00; G02B 011/00; G02B 013/00; G02B 015/00; G02B
017/00; G02B 025/00 |
Claims
What is claimed is:
1. A method of fabricating a dielectric lens including the steps
of: a) forming a plurality of wedges from a dielectric material,
each of said plurality of wedges being substantially identical and
orange-slice shaped, each of said plurality of wedges having two
planar surfaces separated by an angular width, and each of said
plurality of wedges having a plurality of gaps for altering an
effective permittivity of said dielectric lens; and b) assembling a
hemispherical lens by connecting said plurality of wedges along
said planar surfaces such that each of said planar surfaces
intersect along a common line.
2. A method of fabricating a dielectric lens as defined in claim 1,
further including the step of forming said plurality of gaps in
each of said plurality of wedges.
3. A method of fabricating a dielectric lens as defined in claim 2,
wherein each of said plurality of gaps are air voids.
4. A method of fabricating a dielectric lens as defined in claim 3,
wherein said air voids are filled with a material having a
permittivity different from that of a surrounding lens.
5. A method of fabricating a dielectric lens as defined in claim 3,
wherein said plurality of gaps form a pattern of gaps within said
dielectric lens.
6. A method of fabricating a dielectric lens as defined in claim 5,
wherein said gaps provide an optimal permittivity distribution
within said dielectric lens.
7. A method of fabricating a dielectric lens as defined in claim 3,
wherein said plurality of gaps are formed approximately
perpendicular to at least one of said planar surfaces in each of
said plurality of wedges.
8. A method of fabricating a dielectric lens as defined in claim 3,
wherein said plurality of gaps are formed approximately
perpendicular to a central radius within each of said plurality of
wedges.
9. A method of fabricating a dielectric lens as defined in claim 1,
wherein each of said plurality of wedges is formed of cross-linked
polysterene.
10. A dielectric lens including a plurality wedges each being
substantially identical and orange-slice shaped and including a
plurality of gaps for altering an effective permittivity of said
dielectric lens.
11. A dielectric lens including a plurality of wedges being formed
from a dielectric material, each of said plurality of wedges being
substantially identical and orange-slice shaped and including two
planar surfaces separated by an angular width, and each of said
plurality of wedges having a plurality of gaps for altering an
effective permittivity of said dielectric lens, wherein said
plurality of wedges form said dielectric lens by connecting said
plurality of wedges along said planar surfaces such that each of
said planar surfaces intersect along a common line.
12. A dielectric lens as defined in claim 11, wherein said
dielectric lens forms a hemispherical dielectric lens.
13. A dielectric lens as defined in claim 11, wherein said
dielectric lens forms a spherical dielectric lens.
Description
BACKGROUND TO THE INVENTION
[0001] 1. Field of Invention
[0002] The present invention relates to a dielectric lens, such as
a Luneburg lens. More particularly, this invention relates to
fabricating a dielectric lens having gaps in the dielectric
material to provide an optimal permittivity distribution within the
lens.
[0003] 2. Discussion of the Prior Art
[0004] In the field of antenna engineering, lens antennas have many
applications in the higher Radio Frequency (RF) bands, particularly
in the microwave and higher portions of the electromagnetic
spectrum Both the lens antenna and the reflector antenna are
capable of producing a scanning beam without the motion of the lens
or the reflector, or a motion of the entire antenna assembly.
However, the lens antenna is more versatile than the reflector
antenna in terms of producing wide-angle scanning beams.
[0005] A dielectric lens antenna, such as a Luneburg lens, is
capable of producing a beam in any chosen direction by locating the
feed at the focal point on the opposite side of the lens from the
desired beam peak. In the case of the hemispherical Luneburg lens
over a conductive plane, a beam peak may be produced within the
hemisphere containing the lens. The hemispherical Luneburg lens is
of interest for aeronautical applications due to its low profile
and correspondingly low drag. The hemispherical Luneburg design may
reduce the height of the antenna by as much as 50% for a given
beamwidth.
[0006] For further background, the "Mathematical Theory of Optics",
written by R. K Luneburg, published by the University of California
Press, Berkeley, 1964, discusses the theory of the Luneburg lenses
applicable to this document.
[0007] Hemispherical lenses are generally discussed in "Fields and
Waves in Communication Electronics", written by Ramo, Whinnery, and
Van Duzen, published by John Wiley & Sons, Section 12.19 Lenses
for Direction of Radiation, pp.676-678.
[0008] The fabrication of Luneburg lenses is typically very costly.
The use of conventional techniques to produce Luneburg lenses
requires multiple shells--each different from the others and
manufactured to exacting tolerances. A technique has not yet been
devised for the manufacture of such lenses that work acceptably
well at frequencies at or above 44 GHz.
[0009] Most Luneburg lenses that exist today have been fabricated
using the shell technique. Essentially, the Luneburg lens is
fabricated from layers of concentric spherical surfaces. Each
surface has a finite thickness and a slightly different index of
refraction from the others such that the permittivity of the
overall structure approximates the desired continuously varying
index of the lens. This shell technique is commonly referred to as
the "onion" model method of fabrication. While the shell technique
is effective in most low frequency terrestrial applications, it is
unsuitable in high frequency aeronautical applications. In
particular, the shells must be very thin and large in number to
obtain good focusing at high frequencies. This makes the lenses
complex and costly to produce. The large number of junctions
between the surfaces results in discontinuities that reduce the
gain of the antenna system formed from the lens. The materials used
in these shell type lenses have problems with out-gassing at
altitude and this can detrimentally alter the lens characteristics
over time.
[0010] Fabrication of the lens from parallel slices has been
proposed as a manner of solving the out-gassing problem and
increasing the number of layers implemented. The principal problem
with the slice technique is its cost. The slice technique requires
that each slice be different from the other slices in the
hemispherical lens if the slices are horizontal. As a result, a
large number of different pieces are machined, assembled and
laminated together at great cost.
[0011] The tapered hole approach has been proposed as a means of
making low cost lenses. However, it has been found that the large
hole diameter in the outer surface results in gaps that introduce
excessive discontinuities particularly when the polarisation of the
electric field is aligned with the length of the hole.
[0012] U.S. Pat. No. 5,677,796, issued to Zimmerman, discloses a
method of constructing a spherical lens. Zimmerman teaches the use
of a spheroid of uniform isotropic material that has a uniform
dielectric constant throughout the fabrication process. Holes are
drilled along a longitudinal axis extending radially from the
centre of the lens in order to alter the lens dielectric constant.
In a particular embodiment, Zimmerman adjusts the cross-sectional
area of the holes to alter the dielectric constant of the lens. In
contrast to the present invention, Zimmerman discloses the
fabrication of the lens from a spheroid of uniform isotropic
material, and not a sphere formed from identical wedges having
identical permittivity distributions. Furthermore, the holes are
drilled in order to alter the effective permittivity of the entire
lens, as opposed to altering the permittivity of each individual
wedge.
[0013] U.S. Pat. No. 3,470,561, issued to Horst, discloses a
spherical dielectric lens constructed from a number of identical
orange-slice shaped wedges. The wedges are fabricated from a
dielectric material having a varying concentration of conductive
slivers embedded inside each wedge. The concentration of the
slivers in each wedge varies its dielectric constant in directions
normal to the thickened edge of each wedge. Horst does not teach
varying the dielectric constant of the individual wedges by
drilling holes in a pattern into each orange-sliced wedge.
[0014] In view of the above shortcomings in the prior art, the
present invention seeks to provide a dielectric lens that is
fabricated from a number of identical wedges having specific
patterns of gaps in the dielectric material--i.e, patterns of
holes. The number of wedges may be selected to achieve any desired
approximation to the ideal Luneburg lens permittivity distribution.
Finer discretization of the permittivity allows the lens to be used
at higher operating frequencies.
SUMMARY OF THE INVENTION
[0015] The present invention provides a low cost method for
fabricating a hemispherical or spherical Luneburg lens. The lens is
manufactured from a number of identical elements, hereinafter
termed wedges, where each wedge is defined by two planes having a
common line which passes through the center of the lens. A
plurality of holes, hereinafter termed gaps in the dielectric, are
cut in each wedge at a position approximately normal to the radial
direction of the lens. The position of the gaps in the dielectric
alters the effective permittivity distribution within each
individual wedge. Theses gaps are drilled, molded or produced by
other means in a pattern on each wedge such that their permittivity
varies radially so as to approximate the ideal permittivity
distribution of a Luneburg lens. The gaps may have any shape,
circular, square, or other. The permittivity can also be altered
either by producing the gaps partially through the lens or all the
way through the lens The gaps in the dielectric are essentially air
voids, or voids filled with an alternative dielectric, that alters
the effective permittivity of the lens. This has the particular
advantage of ease of manufacture. In one embodiment, the gaps are
produced offset to each other along different wedges in order to
minimize discontinuities and resonances in the lens once the wedges
are laminated together into a hemispherical or spherical
structure.
[0016] In an alternate embodiment, the gaps in the dielectric may
be constructed by cutting holes in the wedges and then filling
these holes with material that has an alternative permittivity. The
alternative permittivity may be lower or higher than that of the
surrounding lens. The distribution of gaps is quite different in
the two cases however. Filling of the gaps with material could
minimize problems associated with ingress of moisture.
[0017] One advantage of the present invention is that the lens is
fabricated from a number of identical pieces, thereby reducing the
cost of manufacturing. Furthermore, the method of producing gaps in
the dielectric into the individual wedges optimizes the
permittivity of the entire lens. The end result is a hemispherical
or spherical lens that operates at higher frequencies, and which
has lower manufacturing costs than the methods of the prior art.
Smaller hole sizes at closer spacing allow operation at higher
frequencies. Furthermore, the present invention enables the lens to
be fabricated with materials that do not have out-gassing
problems.
[0018] In a first embodiment, the present invention provides a
method of fabricating a dielectric lens including the steps of:
[0019] a) forming a plurality of wedges from a dielectric material,
each of said plurality of wedges being substantially identical and
orange-slice shaped, each of said plurality of wedges having two
planar surfaces separated by an angular width, and each of said
plurality of wedges having a plurality of gaps for altering an
effective permittivity of said dielectric lens; and
[0020] b) assembling a hemispherical lens by connecting said
plurality of wedges along said planar surfaces such that each of
said planar surfaces intersect along a common line.
[0021] In a second embodiment, the present invention provides a
dielectric lens including a plurality of wedges being formed from a
dielectric material, each of said plurality of wedges being
substantially identical and orange-slice shaped and including two
planar surfaces separated by an angular width, and each of said
plurality of wedges having a plurality of gaps for altering an
effective permittivity of said dielectric lens, wherein said
plurality of wedges form said dielectric lens by connecting said
plurality of wedges along said planar surfaces such that each of
said planar surfaces intersect along a common line.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a side sectional view of a hemispherical
dielectric lens formed of identical shaped wedges according to the
present invention.
[0023] FIG. 2 is an isometric view of a wedge of FIG. 1 in further
detail, illustrating a particular gap pattern in the wedge
according to the present invention.
[0024] FIG. 3 is a sectional view of the wedge of FIG. 2
illustrating the location of particular gaps relative to the
central radius of the wedge.
DETAILED DESCRIPTION
[0025] The invention will be described for the purposes of
illustration only in connection with certain embodiments; however,
it is to be understood that other objects and advantages of the
present invention will be made apparent by the following
description of the drawings according to the present invention.
While the preferred embodiment is disclosed, this is not intended
to be limiting. Rather, the general principles set forth herein are
considered to be merely illustrative of the scope of the present
invention and it is further understood that numerous changes may be
made without straying from the scope of the present invention.
[0026] The present invention will now be described with reference
to the drawings. Referring now to FIG. 1, a dielectric lens 10 of
the present invention is illustrated. The dielectric lens has an
outer surface 15 that has a substantially hemispherical or
spherical shape. The hemispherical shape is formed by a finite
number of orange-slice shaped wedges 20A, . . . , 20H. Each of the
wedges 20A, . . . , 20H are identical in shape and size.
Furthermore, each wedge is defined by a planar, surface on either
side of the wedge that passes through the central point 30 of the
lens. The planar surface is illustrated by the planes 40A, . . . ,
40H shown in FIG. 1. Essentially all planes 40A, . . . , 40H cross
along a common line, at the central point 30. In the case of the
hemispherical lens, the common line may be horizontal and passing
through the centre of the lens--the centre being defined as the
centre of the flat circular surface (not shown) of the
hemispherical lens.
[0027] The angular spacing between each pair of adjacent planes
40A, . . . , 40H is equal and in turn the angular width of the
wedges 20A, . . . , 20H is also the same. The angular width of a
single wedge will define the number of wedges required to fabricate
a complete lens. For a high frequency operation and for large-sized
dielectric lenses, the angular width is small to provide a higher
accuracy approximation for optimal permittivity distribution.
[0028] It should be noted that dissimilar wedge angular widths may
be utilized but this will typically increase manufacturing costs.
The use of dissimilar widths could, however, produce desirable
performance characteristics, such as more uniform gain over a band
of frequencies, in some implementations of the present
invention.
[0029] In FIG. 2, a single wedge 20A having a plurality of gaps in
the dielectric 50 is illustrated according to the present
invention. The angular width 60 of the wedge 20A is also clearly
shown in FIG. 2. Each of the wedges 20A, . . . , 20H have gaps
which are cut, molded, drilled, or produced by other means,
approximately perpendicular (normal) to the radial direction of the
lens. According to one embodiment of the present invention, the
gaps are produced perpendicular to the radial direction in the lens
approximately perpendicular to the planes defined by the wedge. The
radial direction is along any line extending from the center of the
lens to the outside surface of the lens. The gaps 50 provide a
means of controlling the effective permittivity within the lens 10.
In the wedge 20A of FIG. 2, the gaps 50 form a pattern such that
the effective permittivity of the wedge varies radially in order to
focus the incident radiation. As previously mentioned, the gaps are
essentially air voids, however it is within the intended scope of
the present invention that other material be utilized within the
gaps to vary the permittivity of a particular wedge and effectively
lens. The material within the gaps may be of a higher or lower
permittivity than that of the surrounding lens. Different material
may be used in different regions to produce a desired material or
electromagnetic characteristic.
[0030] The gaps may be linearly formed either through the wedge, or
partway through the wedge, from either side. Consequently, the gaps
50 need not be precisely perpendicular to the radial direction over
the entire angular width 60 of the wedge 20A. As the number of
wedges in the lens fabrication increases, the angular width of the
wedges decreases. Accordingly, the accuracy in the circumferential
direction of the gaps and the approximation to an optimal
permittivity distribution improve. Thus, increasing the number of
wedges utilized in the lens enables the continuous pattern of gaps
to approximate more closely an arc-shaped curve of gaps.
[0031] Referring now to FIG. 3, the single wedge 20A of FIG. 2 is
illustrated in a sectional view. A gap 50A, belonging to the gap
pattern 50 of FIG. 2, is linearly formed perpendicular to a central
radius 70 of the wedge 20A. Although the gap 50A is not in turn
perpendicular to the planes 40A, 40B, the hole may alternatively be
drilled partway or right through and directed perpendicular to
either planes 40A or 40B. In contrast to the gap 50A, a gap 50B is
an example of one such gap directed perpendicular to the plane 40A.
The gap 50B is only drilled partway through the wedge 20A. A
pattern of gaps which are drilled either partway or entirely
through the wedge may be advantageous for fabrication purposes.
Gaps 50C and 50D are examples of gaps formed perpendicular to
planes 40A and 40B, respectively.
[0032] While the cross-section of the gaps is shown in FIG. 2, it
is within the intended scope of the present invention that other
cross-sectional gap shapes such as square, rectangular, or oval may
be suitable in the fabrication of the lens. For manufacturing
purposes, in a molded structure this is a minor change in the
tooling.
[0033] According to the present invention, the dielectric lens may
also be spherical in shape and comprised of an additional number of
wedges, twice that of an equivalent hemispherical lens. In the case
of spherical lens, the common line, where the respective planes of
the wedges converge, may be any line that passes through the centre
of the spherical lens.
[0034] It should be understood that the preferred embodiments
mentioned here are merely illustrative of the present invention.
Numerous variations in design and use of the present invention may
be contemplated in view of the following claims without straying
from the intended scope and field of invention herein
disclosed.
* * * * *