Karl F. Warnick

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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(More)
—For phased array receivers, the accuracy with which the polarization state of a received signal can be measured depends on the antenna configuration, array calibration process, and beamforming algorithms. A signal and noise model for a dual-polarized array is developed and related to standard polarimetric antenna figures of merit, and the ideal(More)
A low phase error X-band eight-channel SiGe PIN diode phased array receiver for 9.5-11.5 GHz application has been proposed and fabricated in a commercial 0.18-μm SiGe BiCMOS process. High performance PIN diode switches used in phase shifters ensure low phase error for all phase states. The 9.5-11.5 GHz receiver, which consists of LNAs, VGAs, PIN(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)
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)
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)
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)
—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(More)