Loading...
Sparse phased array antennas on planar and conformal platforms based on low-discrepancy sequences
Torres, Travis
Torres, Travis
Citations
Altmetric:
Advisor
Editor
Date
Date Issued
2022
Date Submitted
Keywords
Collections
Research Projects
Organizational Units
Journal Issue
Embargo Expires
Abstract
Numerous applications in sensing, radar, and long-distance communication require antenna arrays with very directive beams. In order to achieve the high directivity, the array
aperture size has to be very large, which significantly drives the cost due to the large number
of elements needed on the aperture with traditional Nyquist sampling. The cost-effective
solution to this problem is by using sparse arrays, i.e. a reduced number of elements that
undersample the aperture. These sparse arrays have an average element spacing larger than
1 wavelength, and significantly reduce the cost of the antenna array. The biggest issue with
sparse arrays however is that due to undersampling, grating lobes appear in the visible region
which degrade the array performance. To mitigate this issue, synthesis approaches for sparse
arrays work to spread the energy of the grating lobes in space in order to reduce the sidelobe
levels of the antenna. In addition to the grating lobe issue, many applications in defense and
first responder operations also require real-time techniques for sparse array synthesis.
Despite decades of work on sparse antenna arrays, a cost-effective and time-efficient solution for synthesis of large sparse arrays was not available. Random element spacing removes
the grating lobes but produces large variations in element density across the aperture. In
fact, some areas are so dense that the elements will overlap. This work presents the first
solution to this problem by using low discrepancy sequence (LDS) sampling. Analytical
methods, numerical methods, statistical and probabilistic approaches, have been studied
over the years, and it is shown that none of these methods can yield a solution even close
to the true optimum. The difficulty is due to the fact that side lobe level depends on the
element spacing in a highly nonlinear manner, and in general there is no analytical method to
determine the highest side lobe level or the angular direction where the highest side lobe may
occur, unless an entire three dimensional pattern is computed. As such, the only adopted
solution thus far is based on optimization approaches which are: 1) computationally slow, 2) not hierarchical, and 3) typically require amplitude and phase control over the elements
which significantly increase the cost. A cost effective sparse array uses elements with unity
amplitude and zero phase. This significantly simplifies the feed network and amplification
circuits, which reduce the cost. The only existing work that is comparable are thinned arrays. However, we show that thinned arrays cannot achieve a low side lobe performance
once average element spacing exceeds one wavelength. Moreover, our proposed approach is
directly applicable to non-planar surfaces without the need for any modifications. In this
dissertation, a complete analysis of LDS methods for synthesis of large planar and cylindrical sparse arrays is presented. In summary the primary intellectual merits of this work
are: 1) The first cost-effective and time-efficient solution to synthesis of large sparse arrays,
with the elements having a unity amplitude and zero phase, 2) The synthesis algorithm
is based on mathematical sequences that are hierarchical, enabling real-time synthesis of
sparse arrays over planar and non-planar apertures, 3) The approach is transformative as it
promises revolutionary improvements over existing sparse analog techniques, and it applies
to a broad range of applications in electromagnetics including measurements, sensing, and
communications.
Associated Publications
Rights
Copyright of the original work is retained by the author.