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Search Publications by: Michael H. Francis (Assoc)

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Displaying 51 - 75 of 96

Estimating Multiple-Reflection Uncertainties in Spherical Near-Field Measurements

October 17, 2004
Author(s)
Michael H. Francis, Jeffrey R. Guerrieri, Katherine MacReynolds, Ronald C. Wittmann
We propose a method to estimate multiple-reflection effects on test-antenna pattern and gain uncertainties in the far field derived from spherical near-field measurements. To estimate these uncertainties we make a near-field measurements on two spheres

Practical Implementation of Probe-Position Correction in Near-field Planar Scanning Measurements

October 17, 2004
Author(s)
Jeffrey R. Guerrieri, Katherine MacReynolds, Michael H. Francis, Ronald C. Wittmann, Douglas T. Tamura
Planar near-field measurements require taking amplitude and phase data on an accurate and equal space grid on the plane in front of the antenna under test. The position accuracy on this grid has been determined to be '/50. As frequencies become higher

Standard Radiometers and Targets for Microwave Remote Sensing

September 24, 2004
Author(s)
James P. Randa, Amanda Cox, Dave K. Walker, Michael H. Francis, Katherine MacReynolds, Jeffrey R. Guerrieri
We describe the NIST effort to develop brightness-temperature standards for microwave and millimeter-wave frequencies. Results of preliminary measurements at 26 GHz are presented.

Linking Microwave Remote Sensing Measurements to Fundamental Noise Standards

July 2, 2004
Author(s)
James P. Randa, Dave K. Walker, Michael H. Francis
We outline the formalism for linking microwave remote-sensing measurements to fundamental noise standards and estimate the achievable uncertainty. Plans for the development and use of standard radiometers for this purpose are presented.

Uncertainty Analysis for Spherical Near-Field Measurement

October 19, 2003
Author(s)
Michael H. Francis, Ronald C. Wittmann
A general approach is introduced for estimating uncertainties in far-field paramenters from spherical near-field measurements. Although the analysis is incomplete at present, we expect that as the measurement radius increases, our results will transform

Spherical Near-Field Antenna Measurements Using Nonideal Measurement Locations

November 8, 2002
Author(s)
Ronald C. Wittmann, Bradley Alpert, Michael H. Francis
We introduce a near-field spherical scanning algorithm that relaxes the usual condition requiring data points to be on a regular spherical grid. Computational complexity is of the same order as for the standard (ideal-positioning) spherical-scanning

Spherical Scanning Measurements Using Truncated Data Sets

November 8, 2002
Author(s)
Ronald C. Wittmann, Carl F. Stubenrauch, Michael H. Francis
We discuss the mitigation of truncation errors in spherical scanning measurement. The main emphasis is the spherical harmonic representation of probe transmitting and receiving functions; however, our method is applicable to near-field measurement of

Remote, Near-Field Measurement of Large Antennas

August 17, 2002
Author(s)
Ronald C. Wittmann, Michael H. Francis
It is difficult to characterize many antenna systems in a laboratory environment. Size is the major consideration, but an increasing number of sophisticated antennas are being placed at remote sites where they are simply inaccessible. Of particular concern

Test-Chamber Imaging Using Spherical Near-Field Scanning

October 1, 2001
Author(s)
Ronald C. Wittmann, Michael H. Francis
Although the theory is straightforward, practical implementation of spherical near-field scanning for evaluating test chambers presents some significant challenges. Among these are the requirement for accurate probe positioning and the difficulty in

Antenna Range Imaging

October 1, 2000
Author(s)
Ronald C. Wittmann, Michael H. Francis
We present a preliminary evaluation of a microwave measurement system that has been designed to determine electromagnetic fields in the quiet-zone of an antenna measurement range and to produce an image of the sources, intended and unintended, of the