Engineering topics

Ellingson, Steven W.

Publications and source records attributed to Ellingson, Steven W..

4 records

NASA NTRS2005

Digital Receiver for Microwave Radiometry

A receiver proposed for use in L-band microwave radiometry (for measuring soil moisture and sea salinity) would utilize digital signal processing to suppress interfering signals. Heretofore, radio frequency interference has made it necessary to limit such radiometry to a frequency band about 20 MHz wide, centered at .1,413 MHz. The suppression of interference in the proposed receiver would make it possible to expand the frequency band to a width of 100 MHz, thereby making it possible to obtain greater sensitivity and accuracy in measuring moisture and salinity

Ellingson, Steven W.↗

NASA NTRS2003

Characterization of L-Band RFI and Implications for Mitigation Techniques

We describe measurements of radio frequency interference (RFI) in the 1200-1800 MHz band as observed from NASA s P-3 research aircraft during a flight along the Mid-Atlantic coast of the U.S. at altitudes of 2,000 and 20,000 ft. Both power spectra and coherently-sampled waveform data were obtained. Our results indicate that the spectrum below 1400 MHz is typically dominated by pulses from ground based radars, which, while very strong, individually have transmit duty cycles of on the order of 0.1%. We detect but are unable to identify some relatively weak intermittent RFI inside the 20 MHz protected band centered at 1413 MHz. We detect no significant RFI above 1420 MHz, but the limited sensitivity of this particular experiment makes it impossible to rule out the presence of RFI at levels damaging to total power radiometry. Implications for radiometer design, including possible active countermeasures for RFI mitigation, are discussed.

Ellingson, Steven W.↗

NASA NTRS2003

Design of an L-Band Microwave Radiometer with Active Mitigation of Interference

For increased sensitivity in L-band radiometry, bandwidths on the order of 100 MHz are desirable. This will likely require active countermeasures to mitigate RFI. In this paper, we describe a new radiometer which coherently samples 100 MHz of spectrum and applies real-time RFI mitigation techniques using FPGAs. A field test of an interim version of this design in a radio astronomy observation corrupted by radar pulses is described.

Ellingson, Steven W.↗

NASA NTRS1990

Analysis of blended rolled edge reflectors using numerical UTD

The uniform geometrical theory of diffraction (UTD) concept is used to predict the scattered fields in the target zones of compact-range blended rolled-edge reflectors. Since the necessary diffraction coefficients are not known in a closed form, a numerical method to calculate the diffraction coefficients is described. In the numerical method, the problem is reduced to two dimensions, and physical optics line integration is used to compute the diffraction coefficients. Thus, the method is computationally efficient. The method is used to analyze two compact-range reflectors. The results obtained using the numerical UTD show good agreement with the scattered fields obtained using a corrected physical optics surface integration.

Ellingson, Steven W.↗