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JPH1093335

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DESCRIPTION JPH1093335
[0001]
FIELD OF THE INVENTION The present invention relates to planar arrays having broad
frequency range applications for signal source location, signal source imaging, or target
illumination with a projection beam. Previous attempts at working with planar array designs have
focused on single frequency applications and do not address circular symmetry problems due to
the limited number of array elements, and / or long distance applications And therefore does not
address comprehensively, near-field, circularly symmetric, and broadband applications for source
mapping or target illumination with a projection beam.
[0002]
Regular arrays are known in the prior art in which the array elements are positioned in a periodic
arrangement, such as a square, triangular or hexagonal grid. In these arrangements, adjacent
elements are spaced within half a wavelength of each other to avoid that the pattern of the array
has multiple main lobes other than the pointing direction, that is, the phenomenon commonly
referred to as spatial aliasing or grating lobes. Need to be placed. This half wavelength
requirement can be prohibitive in terms of the number of array elements required in a wide
frequency range of applications. Because the lowest frequency for the intended application acts
to make the aperture size of the array larger (to achieve proper array resolution), the highest
frequency is the spacing of the elements (to avoid spatial aliasing) Because it works to make
[0003]
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Random arrays are known in the prior art as providing a way to address the problem of grating
lobes inherent in regular arrays. The irregular array eliminates periodicity in element positioning.
In the prior art, random arrays are known as a form of irregular array. Random arrays are limited
in their ability to predictably control the worst case sidelobes. If the positioning of the elements
of the array can be controlled, use an algorithm that guarantees irregular spacing and allows
more predictable control of the worst case sidelobes in determining the positioning of the
elements. be able to. The prior art includes many instances of randomly spaced linear arrays,
many of which are non-redundant. That is, the spacing between any given set of elements is not
repeated. This non-redundancy provides some degree of optimization for the design of the array
in that it controls grating lobes.
[0004]
The prior art for designing irregular planar arrays is primarily ad hoc. As in the prior art, there
are only a few examples of simple non-redundant planar arrays, such as a relatively small
number of elements or a simple arrangement of elements such as around a circle. It seems to be.
In the prior art, for positioning to place any number of elements throughout the aperture of the
array (rather than just putting it on the circumference) in a controlled manner to ensure nonredundant and circular symmetry. The technology of non-redundant planar array design seems
to be lacking.
[0005]
One of the objects of the present invention is that the number of available elements is between
the elements that meet the half-wavelength criteria typically required to avoid grating lobe
contamination in the source mapping or projection beam. Gratings over a wide frequency range,
even if substantially less than the number required to construct a regular (ie, equally spaced
elements) array with a spacing of It is to provide a planar array design without the presence of
lobes.
[0006]
Another object of the invention is to provide a planar array design with circular symmetry so that
the resolution of the source mapping or the projected beam width is substantially independent of
the dimensions of the array (ie the azimuth angle) .
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[0007]
A further object of the present invention is to provide a planar array design that optimally utilizes
a limited number of array elements in the sense that the array is non-redundant.
[0008]
A still further object of the invention is to provide the flexibility to reduce the spatial density in
the design of the array, thus enabling a tradeoff between beam width and side lobe level of the
array in the array design.
[0009]
A still further object of the invention is to provide a general method for distributing any number
of elements to circular planar apertures of any diameter in such a manner as to guarantee
circular symmetry and non-redundancy in spatial sampling intervals. It is.
[0010]
SUMMARY OF THE INVENTION The sensing or transmitting elements (eg, microphones or
antennas) are spaced along the same set of logarithmic spirals at various arc lengths and radii,
with the elements of the spiral set being Are evenly angularly spaced about the origin and have
lower worst case side lobes over a wider frequency range than arrays or random arrays where
the elements are uniformly distributed (eg square or rectangular grids) , A planar array with
better grating lobe reduction.
The array is circularly symmetric and the array is non-redundant if the number of spirals is odd.
An example of a preferred spiraling specification is to position the elements of the array
concentrically to form the radial geometric center of the annular area of equal area, and the
performance of the array at the highest frequency used. To improve, it is combined with
positioning on the innermost concentric circle whose radius is selected independently.
This result is applicable over a wide wavelength band, for example a ratio of 10 to 1, and is
useful in a phased acoustic microphone or speaker array or a phased electromagnetic antenna
array.
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When the number of array elements is small, it is superior to the random array.
Another spiral specification embodiment is an alternative to the reduction in array spacing
density that allows flexibility in array design and tradeoff of array performance between array
beam width and sidelobe levels I will provide a.
[0011]
The above and other objects and features of the present invention will be apparent from the
following description together with the preferred embodiments with reference to the attached
drawings. Like parts in the figures are indicated by like reference numerals.
[0012]
DETAILED DESCRIPTION This planar array design 15 shown in FIG. 1 shows elements 12 of the
array represented by circles. The subset of elements 14 is marked to emphasize that it is located
along the logarithmic spiral 16. The elements 14 to be emphasized may be positioned along the
spiral in any of several ways. One preferred embodiment, as shown in FIG. 1, is sampling of isoannular area, where the outermost M-1 elements of the spiral including M elements are
concentric equal-area annular It is positioned to coincide with the geometric radial center of the
region. The Mth element is independently located at a radius smaller than the innermost radius
of the M-1 elements to improve the performance of the array at the highest frequency in the
intended application. Circular symmetry is achieved by accurately creating a circular array of N
elements of elements 17 positioned at equal intervals from each of the spiral elements 14 as
shown in FIG. If the number of elements in the circular array is odd, the resulting array has zero
redundancy in spatial sampling intervals. This is illustrated by the co-array shown in FIG. FIG. 2
shows the set of all vector spacings between elements 12 in the array aperture of FIG. Each point
18 in the co-array indicates the vector difference between the positions of the two elements in
the array. In this planar array design 15, none of these vector differences are repeated.
[0013]
An alternative method of spacing the spiral elements is shown in FIGS. In FIG. 3, the spiral
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elements 14 are spaced along the spiral 16 at equal radial increments between the inner to outer
radial specifications. In FIG. 4 the spiral elements 14 are positioned at intervals along the spiral
16 with logarithmically increasing radial increments between the outer to inner radial
specifications (i.e., The radial increment between the spiraling elements increases as the spiraling
is traced from the outermost to the innermost element). This is called the inward log radius
interval. Another method, referred to as outward log-radial spacing, positions the spiral-like
elements in logarithmically increasing radial increments along the spiral between inner to outer
radial specifications . These and other spiral spacing techniques exhibit a tradeoff between the
width of the main lobe of the array (ie, the resolution of the array) and the level of the side lobes.
Arrays with elements concentrated near the circumference, such as array 18 of FIG. 3, have
narrower main lobes and correspondingly higher average side lobe levels. Arrays with elements
concentrated near the center, such as the array 19 of FIG. 4, have wider main lobes and
correspondingly lower average side lobe levels. The embodiments comprising FIGS. 1, 3 and 4
and the outwardly facing logarithmic radius intervals are merely representative of the radial
spacing arrangement according to the invention.
[0014]
The parameters of the general design of this array are as follows. (1) angle of logarithmic spiral,
(2) inner radius, (3) outer radius, (4) number of elements for spiral, (5) number of elements per
circle (ie, number of spirals), And (6) a method of spacing the elements in a spiral shape.
Circularly symmetric, non-redundant planar arrays (with an odd number of elements per circle),
with particularly low worst case sidelobe characteristics over a wide frequency range, compared
to what can be achieved with regular or random arrays, with these parameters A wide variety of
forms).
[0015]
The array pattern for the embodiment of FIG. 1 is shown in FIG. 5 for the 1 kilohertz case, in FIG.
6 for the 5 kilohertz case, and in FIG. 7 for the 10 kilohertz case, the array is 54 inches off
broadside Focus on showing the absence of grating lobes over a wide frequency range and wide
scan area, and showing the circularly symmetric nature of the array. These typical array patterns
have been determined for frequencies corresponding to the atmospheric propagation of sound
waves using a propagation velocity of 1125 feet per second. The worst case sidelobe
characteristics for the embodiment of FIG. 1 are shown in FIG. 8 for 1 kilohertz, in FIG. 9 for 5
kilohertz, and in FIG. 10 for 10 kilohertz, and the array is 54 inches off broadside. The strong
grating lobe suppression over a wide frequency range for -90- to + 90- elevation angles with
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focus is shown. Figures 8, 9, and 10 show the envelope of the array pattern formed by taking the
maximum from 45 azimuths that cuts the array pattern at each elevation of 91.
[0016]
FIG. 11 shows a block diagram for an apparatus, signal conditioning, data acquisition, signal
processing and display for the acoustic application of the array of FIG. The N channel array
design 1 is implemented by positioning the N microphones at appropriate spatial positions so
that the positions of the centers of the microphone diaphragms with respect to each other match
the array design specifications (ie spatial coordinates) Ru. The N microphone devices include a
microphone button (element of the array) 12, a preamplifier 3 and a transmission line 4 and are
connected to the N corresponding input modules 5. Each input channel includes programmable
gain 6, an analog anti-aliasing filter 7, and a sample-hold analog-to-digital converter 8. The input
channels share a common trigger bus 9 so that sample and hold are simultaneous. The common
system bus 10 hosts the input module and provides simultaneously acquired time series data to
the beamformer 11. The beamformer may be one or more of several conventional time and / or
frequency domain beamforming processes, which provide data to readout means including the
graphic display 13.
[0017]
As an example, frequency domain beamformer 11 provides signal processing from the planar
array of N microphone elements 12 and 14 of FIGS. 1 and 11 and performs the following steps.
[0018]
1.
Fourier transform is performed on each channel to generate a narrow band signal. 2. Pairwise
products of narrowband signals are integrated over time to give an NxN correlation matrix.
[0019]
3. Find an N-dimensional complex steering vector for each of the potential directions of arrival
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(for plane wave beamforming) or directions of source location (for spherical beamforming).
[0020]
4. The correlation matrix is multiplied by the steering vector to produce an estimated source
power for each direction of arrival or source location.
[0021]
The graphics device 13 then shows a contour plot of the estimated source distribution.
[0022]
While certain devices have been described, it is understood that this description is given by way
of example only and is not intended to limit the scope of the present invention as set forth in the
purpose and appended claims. It must be done.
[0023]
Brief description of the drawings
[0024]
FIG. 1 is a diagram of a circular planar array consisting of an array of multiple logarithmic spirals
of elements spaced in iso-annular area according to an embodiment of the invention, wherein one
array of spirals is highlighted FIG.
[0025]
2 is a co-array showing the set of all vector spacings between elements in the apertures of the
array according to an embodiment of the present invention.
[0026]
FIG. 3 is a diagram of a circular planar array consisting of an array of multiple logarithmic spiralshaped arrays spaced in equal radial increments according to an embodiment of the invention,
with the elements in one of the spirals highlighted FIG.
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[0027]
FIG. 4 is a view of a circular planar array consisting of an array of multiple logarithmic spiralshaped arrays spaced inwards by logarithmic radial increments of elements according to an
embodiment of the invention, in one of the spirals FIG. 5 is a diagram in which the element is
emphasized.
[0028]
5 is a diagram of a typical array pattern for single frequency operation using the array of FIG. 1
focused on a 54 inch off broadside point.
[0029]
6 is a diagram of a typical array pattern in single frequency operation when using the array of
FIG. 1 with a focus at 54 inches off broadside at 5 kilohertz.
[0030]
7 is a diagram of a typical array pattern in single frequency operation when using the array of
FIG. 1 with a focus at 54 inches off broadside at 10 kHz.
[0031]
FIG. 8 is a plot of the worst case sidelobe characteristics in single frequency operation when
using the array of FIG. 1 with a focus at 54 inches off broadside at 1 kilohertz.
[0032]
9 is a plot showing the worst case sidelobe characteristics in single frequency operation when
using the array of FIG. 1 with a focus at 54 inches off broadside at 5 kilohertz.
[0033]
10 is a plot showing the worst case sidelobe characteristics in single frequency operation when
using the array of FIG. 1 with a focus at 54 inches off broadside at 10 kHz.
[0034]
FIG. 11 is a block diagram illustrating microphone input, signal conditioning, signal processing,
and display from the planar array of FIG. 1 for noise source location mapping.
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[0035]
Explanation of sign
[0036]
12 array elements 15 planar array design 16 logarithmic spirals
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