Fig. 6. Residual as a function of iteration number, I r = I = I = 3. up to 3 may be regarded as extreme. Fig. 2 shows the far-field pattern obtained if the data are processed without position correction; that is, assuming that the measurement points lie on the ideal grid. This pattern bears no resemblance to the true pattern. Figs. 3 -5 show the difference between the computed pattern and the original after 1, 15, and 56 iterations. (Execution time was about 3 min per iteration on a 2 GHz personal computer.) At 15 iterations (Fig. 4), errors are about 1 dB at a sidelobe level 40 dB below peak, which is usually adequate in practice.(10) is less than 10 05 . Fig. 6 shows the residual as a function of iteration number.With less severe probe-position errors, fewer iterations are required.For example, when I r = I = I = 0:25 (still extreme relative to desired tolerances), only 13 iterations are required to reach " = 10 05 . IV. SUMMARYWe have developed a spherical near-field scanning algorithm that does not require data to be measured on a regular grid. Computational complexity for probe-position correction is of the same order as for the standard (ideal-positioning) spherical-scanning algorithm. The new algorithm is robust: we have successfully tested it for transverse probeposition deviations of up to 3 maximum sample intervals (1), and for radial deviations of up to three wavelengths (). The software is available from the authors. REFERENCES[1] R. C. Wittmann, B. K. Alpert, and M. H. Francis, "Near-field antenna measurements using nonideal measurement locations,"Abstract-The transient response of a coated cylinder to a plane-wave excitation is examined. It is shown that the early-time response has a component very close to the resonance representation for a planar structure, which may be isolated by subtracting the response of an uncoated cylinder. This component can be used with the E-Pulse technique to diagnose changes in coating parameters.

The activation energy of phosphorus substituted into Sil-,Ge, alloys (0 5 x 0.27) is investigated by IR absorption. A weak shift of the activation energy with germanium content is found: E(A,) = (45.5 -262) meV. This can be explained by multivalley effective mass theory with a phenomenological central cell potential which does not depend on alloy composition within the investigated range. The experiments show that P atoms are distributed a t random in the alloy and that their positions are uncorrelated to those of the Ge atoms.Die Aktivierungsenergie des Phosphorgrundzustandes in Sil-,Ge,-Mischkristallen im Bereich 0 x 5 0,27 wird mit IR-Absorptionsmessungen untersucht. Mit zunehmendem Germaniumgehalt verringert sich diese Energie urn 262 meV. Dies kann mit der Effektiv-Massen-Naherung erklart werden, wenn ein im untersuchten Bereich von der Zusammensetzung des Kristalls unabhangiges ,,Zentral-Zellen-Potential" angenommen wird. P-und Ge-Atome sind statistisch im Mischkristall eingebaut.

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