Experimental verification of radio frequency interference mitigation with a focal plane array feed

Abstract

[1] 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-s integrated noise floor (the minimum detectable signal level was interference-limited and no longer decreased 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. Citation: Nagel, J. R., K. F. Warnick, B. D. Jeffs, J. R. Fisher, and R. Bradley (2007), Experimental verification of radio frequency interference mitigation with a focal plane array feed, Radio Sci., 42, RS6013,

Beamforming and imaging with the BYU/NRAO L-band 19-element phased array feed

“…Of particular emphasis in these experiments was the development of measurement techniques for aperture ef•ciency and system noise and careful validation of numerical models for the array and receiver front ends. These results build on earlier work reported by the authors in [1]- [3].…”

“…Array feeds enable the use of spatial •ltering algorithms for adaptive RFI mitigation [1]. This capability comes at the cost of increased signal processing complexity and data rates, since integration dump times on the order of tens of milliseconds are required to track rapidly moving RFI sources.…”

Signal Processing for Phased Array Feeds in Radio Astronomical Telescopes

“…We first successfully demonstrated beamforming and RFI mitigation with a seven element hexagonal array on a three meter reflector in 2006 [10]. A 19 element, L-band dipole array was deployed on the NRAO Green Bank 20-Meter Telescope in 2007 for a series of experiments to measure aperture and spillover efficiency, demonstrate multiple beam formation, and test RFI mitigation algorithms with real and simulated interference sources (see Figure 1).…”

Phased Array Feed Calibration, Beamforming, and Imaging

“…Table 1 shows measured and modeled results for the 19 element prototype array for the sensitivity, aperture efficiency, and system temperature for the center 0]) and the fullarray formed beam with peak sensitivity. The 12% discrepancy between measured and modeled aperture efficiency is expected, given that blockage and feed support scattering are not modeled and that numerical radiation patterns for any type of feed typically overestimate efficiency by roughly 10% (Murphy 1989).…”