Karl F. Warnick

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8m3 Spatial filtering and subspace projection methods have been pro-imaging arrays [1][2]. Given the fact that RA signal levels are often difficult to form the accurate interference signal parameter an imaging may, it is possible to overcome this problem. Using rejection by tens of decibels. New extensions to subspace projec-posed for removing interference(More)
— The calculus of differential forms has significant advantages over traditional methods as a tool for teaching electromagnetic (EM) field theory: First, forms clarify the relationship between field intensity and flux density, by providing distinct mathematical and graphical representations for the two types of fields. Second, Ampere's and Faraday's laws(More)
—Interferometric image synthesis in radio astronomy is plagued by signal corruption from man-made sources. The very weak signals of interest can be overwhelmed by such interference. Recent work has proposed using array signal processing techniques of adaptive beamforming, adaptive filtering, and subspace projection to remove interference prior to image(More)
This thesis has been read by each member of the following graduate committee and by majority vote has been found to be satisfactory. As chair of the candidate's graduate committee, I have read the thesis of Michael I. Duersch in its final form and have found that (1) its format, citations, and bibliographical style are consistent and acceptable and fulfill(More)
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(More)
— 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(More)
We present a numerical comparison of the so-called 'linear sampling' inverse scattering methods developed by Colton and Kirsch, published in this journal, and linearized tomographic inverse scattering algorithms based on either holographic filtered backpropagation principles or a plain matrix inversion scheme. Although we restrict ourselves to(More)
Adaptive interference canceling beamformers are known to suffer from beampattern distortion, particularly when inter-ferers approach the nominal mainlobe. In some applications such as radio astronomy, even small pattern variations can be problematic. We address the issue of computing power spectral density (PSD) estimates at the output of a beamform-ing(More)