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Gain and aperture efficiency for a reflector antenna with an array feed
- IEEE Antennas and Wireless Propagation Letters
, 2006
"... Abstract—A figure of merit for array antennas can be defined using the signal processing concept of signal-to-noise ratio (SNR) gain. The resulting array efficiency metric reduces to aperture efficiency for an isolated array and to a combination of aperture and spillover efficiency for an array feed ..."
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Abstract—A figure of merit for array antennas can be defined using the signal processing concept of signal-to-noise ratio (SNR) gain. The resulting array efficiency metric reduces to aperture efficiency for an isolated array and to a combination of aperture and spillover efficiency for an array feed. These results provide a practical way to measure aperture efficiency for active arrays and array feeds. Index Terms—active arrays, antenna array feeds, aperture efficiency, array gain, gain. I.
Signal processing for phased array feeds in radio astronomical telescopes
- IEEE JOURNAL OF SELECTED TOPICS IN SIGNAL PROCESSING
, 2008
"... Relative to traditional waveguide feeds, phased array feeds (PAFs) for radio telescopes can increase the instrument field of view and sky survey speed. Unique challenges associated with PAF observations, including extremely low signal levels, long-term system gain stability requirements, spatially ..."
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Cited by 9 (3 self)
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Relative to traditional waveguide feeds, phased array feeds (PAFs) for radio telescopes can increase the instrument field of view and sky survey speed. Unique challenges associated with PAF observations, including extremely low signal levels, long-term system gain stability requirements, spatially correlated noise due to mutual coupling, and tight beamshape tolerances, require the development of new array signal processing techniques for this application. We propose a calibration and beamforming strategy for PAFs including interference mitigation with power spectral density (PSD) estimation bias correction. Key efficiency metrics for single-feed instruments are extended to the array case and used to verify performance of the algorithms. These techniques are validated using numerical simulations and experimental data from a 19 element PAF on the Green Bank 20-Meter Telescope.
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 time-varying spatial response of an adaptive beamformer (“pattern rumble”) causes estimation bias in the PSD of bo ..."
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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 time-varying 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 pattern-distortion-induced PSD bias and spatial response errors over the long-term 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 multi-antenna sensors and adaptive interference cancellation for radio astronomy, remote sensing, and other sensitive radiometry applications where cancellation has not been feasible.
Characterization of a phased array feed model
, 2008
"... This Thesis is brought to you for free and open access by BYU ScholarsArchive. It has been accepted for inclusion in All Theses and Dissertations by an ..."
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This Thesis is brought to you for free and open access by BYU ScholarsArchive. It has been accepted for inclusion in All Theses and Dissertations by an
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.
Radio Science, Volume???, Number, Pages 1–8, Experimental Verification of RFI Mitigation with a Focal Plane Array Feed
"... We demonstrate the use of spatial filtering algorithms for radio frequency interference (RFI) mitigation in conjunction with a focal plane array of electrically small elements. The array consists of a seven-element hexagonal arrangement of thickened dipole antennas with 1600 MHz designed center freq ..."
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We demonstrate the use of spatial filtering algorithms for radio frequency interference (RFI) mitigation in conjunction with a focal plane array of electrically small elements. The array consists of a seven-element hexagonal arrangement of thickened dipole antennas with 1600 MHz designed center frequency backed by a circular ground plane at the focal plane of a 3 m parabolic reflector. Rooftop-mounted signal sources were used to simulate a weak signal of interest at boresight and a strong, broadband interferer in the reflector sidelobes. Using an adaptive beamformer, the amplitude of the interfering signal was reduced sufficiently to recover the signal of interest. For an interference to noise ratio of 15 dB as measured at the center array element, the interferer was suppressed to the level of the fluctuations of the 10-second integrated noise floor (the minimum detectable signal level was interference-limited and no longer decreases after 10 s integration). Similar cancellation performance was demonstrated for a nonstationary interferer moving at an angular velocity of 0.1 ◦ per second. Pattern rumble due to beamformer adaptation was observed and quantified. For a moving RFI source, the degree of pattern rumble was found to be unacceptably large in terms of its effects on the maximum stable integration time and receiver sensitivity. An array feed with more elements together with specialized signal processing algorithms designed to suppress pattern rumble will likely be required in order to use adaptive spatial filtering for astronomical observations. 1.
Summary
, 2007
"... Brigham Young University and NRAO have had on ongoing research collaboration to develop RFI mitigation techniques. The principle investigators in this effort are Brian Jeffs and Karl Warnick (BYU) and Rick Fisher and Rich Bradley (NRAO). Our current effort focuses on development of array feeds for l ..."
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Brigham Young University and NRAO have had on ongoing research collaboration to develop RFI mitigation techniques. The principle investigators in this effort are Brian Jeffs and Karl Warnick (BYU) and Rick Fisher and Rich Bradley (NRAO). Our current effort focuses on development of array feeds for large reflectors coupled with adaptive signal processing for removal of RFI. Prototypes deployed on small reflectors demonstrate that this approach is feasible. Several development issues remain that require a larger aperture and a more stable platform to resolve, including determination of achievable aperture efficiency, spillover efficiency, and sensitivity and demonstrating the performance of new signal processing algorithms designed for high gain stability while adaptively canceling nonstationary RFI. We propose to employ the 20 meter reflector at the Green Bank site as an array feed testbed to resolve these issues and move towards a scientifically useful array feed.
RESEARCH IN RADIO FREQUENCY INTERFERENCE MITIGATION
, 2005
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