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Search Publications by: Ronald Wittmann (Assoc)

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Displaying 26 - 50 of 79

Sources of Uncertainty for Near-Field Measurements

November 11, 2007
Author(s)
Michael H. Francis, Ronald C. Wittmann
We discuss the sources of uncertainty in near-field measurements and their impact on far-field antenna parameters. The methods of estimating these uncertainties can be considered in three broad categories: theoretical estimation (analytical), computer

Planar Near-Field Measurements Results up to 94 GHz Using Probe Position Correction

October 30, 2005
Author(s)
Jeffrey R. Guerrieri, Katherine MacReynolds, Michael H. Francis, Ronald C. Wittmann, Douglas T. Tamura
This paper presents results of planar near-field measurements at 16, 35 and 94 GHz using probe position correction algorithms. The algorithms correct for position errors of the probe near the scan plane. The probe?s actual position is measured using a

Proximity effects in the calibration of microwave radiometers

October 1, 2005
Author(s)
Ronald C. Wittmann, Amanda Cox, Randy Direen
Microwave, total-power radiometers are calibrated by observing sources of known brightness temperature. Free-space calibrations are usually performed assuming far-field interactions, although the actual calibration source may be well into the near-field

Uncertainties in Spherical Near-Field Antenna Measurements

August 3, 2005
Author(s)
Michael H. Francis, Ronald C. Wittmann, Jin-Seob Kang
A general approach is presented for estimating uncertainties in far-field parameters obtained from spherical near-field antenna measurements. The error is approximately bounded in terms of the uncertainty of the probe's receiving pattern and the

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

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

Computation of Causal Characteristic Impedances

June 12, 2000
Author(s)
Dylan F. Williams, Ronald C. Wittmann
We develop a numerical method of determining the magnitude of characteristic impedance required by causal power-normalized circuit theories from its phase using a Hilbert-transform relationship. We also estimate the uncertainty in the method.

Are the Formulas for Mode-Field Diameter Correct?

September 1, 1998
Author(s)
Ronald C. Wittmann, M. Young
We have found conceptual problems with the far-field formula 1 for mode field diameter First, the formulation is incomplete in that it ignores the obliquity factor; second, it assumes that the field at the end of a truncated fiber is identical to the mode