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Interference Mitigation Using a Focal Plane Array
"... We consider the use of spatial filtering algorithms for radio frequency interference (RFI) mitigation in conjunction with a focal plane feed array of electrically small elements. Numerical simulations are used to study the performance of 7 and 19 element hexagonal dipole arrays with a 25 meter refle ..."
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Cited by 9 (7 self)
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We consider the use of spatial filtering algorithms for radio frequency interference (RFI) mitigation in conjunction with a focal plane feed array of electrically small elements. Numerical simulations are used to study the performance of 7 and 19 element hexagonal dipole arrays with a 25 meter reflector at an operating frequency of 1612 MHz. Using the maximumSNR algorithm to generate array weights, an interfering signal was attenuated by 40 dB or more. The effective sensitivity of the system, including interferer power in the system noise temperature, was comparable to the sensitivity attained in the absence of RFI. Moving the interferer through the reflector pattern sidelobes caused fluctuations in the gain and system sensitivity. This effect was exacerbated by a reflector model with random surface distortions. These results indicate that array feeds are a promising approach for RFI migitation, but achieving stable radiation patterns in the presence of an interferer may require a tradeoff between pattern control and maximum attainable sensitivity.
Bias corrected psd estimation for an adaptive array with moving interference
, 2008
"... We address the issue of computing power spectral density (PSD) estimates at the output of a beamforming sensor array in the presence of strong moving interference. It is shown that the timevarying spatial response of an adaptive beamformer (“pattern rumble”) causes estimation bias in the PSD of bo ..."
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Cited by 6 (3 self)
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We address the issue of computing power spectral density (PSD) estimates at the output of a beamforming sensor array in the presence of strong moving interference. It is shown that the timevarying spatial response of an adaptive beamformer (“pattern rumble”) causes estimation bias in the PSD of both the signal of interest (SOI) and noise. In applications such as radio astronomy with stringent sensitivity requirements, even small pattern variations can be problematic because the resulting higher variance noise spectrum estimates make it impossible to detect signals of interest which are many decibels below the noise floor. Distortion in beam mainlobe shape also introduces errors in SOI direction estimates. To overcome this problem, an extension of the method described in Leshem et al., 2000, is developed which eliminates patterndistortioninduced PSD bias and spatial response errors over the longterm PSD averaging window. Both simulated and real data experiments demonstrate algorithm effectiveness in realizing an undistorted effective (average) beam spatial response while maintaining a low noise floor level. This algorithm will enable PSD estimation using multiantenna sensors and adaptive interference cancellation for radio astronomy, remote sensing, and other sensitive radiometry applications where cancellation has not been feasible.
Multidimensional (MD) Circuits and Systems for Emerging Applications Including Cognitive Radio, Radio Astronomy, Robot Vision and Imaging
"... Advances in the performance of VLSI circuits are leading to a number of emerging applications of multidimensional (MD) filters. Early progress was focused on the numerical design of two dimensional (2D) transfer functions and the challenging stability issues associated with lowcomplexity infinite ..."
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Cited by 2 (1 self)
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Advances in the performance of VLSI circuits are leading to a number of emerging applications of multidimensional (MD) filters. Early progress was focused on the numerical design of two dimensional (2D) transfer functions and the challenging stability issues associated with lowcomplexity infinite impulse response (IIR) implementations. However, over the last decade or so, important practical advances have occurred in the design of 3D and 4D IIR filters, leading to some important emerging applications. In this tutorial article, some of these applications are described, with emphasis on 2D spatiotemporal beamforming and 4D light field processing. In particular, advances in spatiotemporal beamforming for cognitive radio systems and for synthetic aperture radio telescopes are considered. In the 4D case, we describe a class of 4D light field filters for image processing, 4D hyperfan filters for lowlight imaging, depth filtering, denoising and the attenuation of distracting objects, with applications in computational photography and habitat monitoring. Both analog and digital systolic VLSI circuit implementations are described with emphasis on recent progress using field programmable gate array (FPGA)based and digital VLSI circuits that can potentially operate at radio frequencies in the multiGHz range. These new innovations open up exciting possibilities for realtime MD filters having frames rates in the multiGHz for emerging radio frequency (RF) antenna signal processing and imaging systems.
Spectral Bias in Adaptive Beamforming . . .
, 2008
"... It is shown that adaptive canceling arrays which track interference by regular updates of the beamformer weights can introduce a spectral null at the excised interference frequency. This PSD estimation bias effect we call “spectral scooping” is most prominent for narrowband interference (i.e. occu ..."
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It is shown that adaptive canceling arrays which track interference by regular updates of the beamformer weights can introduce a spectral null at the excised interference frequency. This PSD estimation bias effect we call “spectral scooping” is most prominent for narrowband interference (i.e. occupying only a few spectral bins at the desired PSD estimation resolution). Scooping is problematic in radio astronomy where bias in either the weak signal or noise floor spectra can corrupt the observation. The mathematical basis for scooping is derived, and an algorithm to eliminate it is proposed. Both simulated and real data experiments demonstrate the effectiveness of the proposed algorithm.
Aperture Arrays for the SKA: Dense or Sparse?
"... We briefly consider some design aspects of aperture arrays for use in radio astronomy, particularly contrasting the performance of dense and sparse aperture arrays. Recent insights have emerged in the final design phase of LOFAR which suggest that sparse aperture arrays have the best prospects for c ..."
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We briefly consider some design aspects of aperture arrays for use in radio astronomy, particularly contrasting the performance of dense and sparse aperture arrays. Recent insights have emerged in the final design phase of LOFAR which suggest that sparse aperture arrays have the best prospects for costeffective performance at radio frequencies below about 500 MHz; exceeding those of both dense aperture arrays and parabolic reflectors by an order of magnitude. Very attractive performance, of 10,000 – 20,000 m 2 /K, can be achieved with a sparse design that covers the 70 – 700 MHz range with two antenna systems that share receiver resources. Costeffective systems of this type represent only a modest increment in system complexity over that being deployed in LOFAR and are achievable with today’s technology. 1.