Using Adaptive Estimation to Minimize the Number of Samples Needed to Develop a Pattern to a Specified Uncertainty
关键词:
Using Adaptive Estimation to Minimize the Number of Samples Needed to Develop a Pattern to a Specified Uncertainty摘要
Obtaining far-field patterns in electromagnetics or acoustics, although generally not as computationally expensive as solving for the sources induced on an object, can none-the-less at times be a substantial fraction of the overall computer time associated with some problems. This can be especially the case in determining the monostatic radar cross section of large objects, since the current distribution must be computed for each incidence angle or when using physical optics to determine the radiation patterns of large reflector antennas. In addition, when employing the point sampling and linear interpolation of the far field that is most often used to develop such patterns, it can be necessary to sample very finely in angle to avoid missing fine details such as nulls. A procedure based on model-based parameter estimation is described here that offers the opportunity of reducing the number of samples needed while developing an easily computed and continuous representation of the pattern. It employs windowed, low-order, overlapping fitting models whose parameters are estimated from the sparsely sampled far-field values. The fitting models themselves employ either discrete-source approximations to the radiating currents or Fourier models of the far field. For the cases investigated, as few as 1.5 to 2 samples per far-field lobe are found to be sufficient to develop a radiation-pattern estimate that is accurate to 0.1 dB, and 2.5 samples per lobe for a simple scatterer. In general, however, the sampling density is not determined by the lobe count alone, but by the effective rank of the field over the observation window, which in turn is a function of both the aperture size and the spatial variation of the source distribution within that aperture.
##plugins.generic.usageStats.downloads##
参考
E. K. Miller (1995), Model-Based Parameter Estimation in
Electromagnetics: I--Background and Theoretical Development,
Applied Computational Electromagnetics Society Newsletter,
(3), November, pp. 40-63; (1996), II--Applications to EM
Observables, 11 (1), pp. 35-56; (1995), III--Applications to
EM Integral Equations, Applied Comptational Electromagnet-
ics Society Journal, 10 (3), pp. 9-29.
E. K. Miller (1998), Computing Radiation and Scattering
Patterns Using Model-Based Parameter Estimation, IEEE AP-S
International Symposium, Renaissance Waverly Hotel, Atlanta,
GA, June 21-26, pp. 66-69.
E. K. Miller and T. K. Sarkar (1999), An Introduction to
the Use of Model-Based Parameter Estimation in Electromagnet-
ics, in Review of Radio Science, 1999 URSI General Assembly,
pp. 139-174.
R. J. Allard, D. H. Werner, J. S. Zmyslo, and P. L. Werner,
"Spectral Domain Interpolation of Antenna Radiation Patterns
Using Model-Based Parameter Estimation and Genetic Algo-
rithms", Proceedings of the 14th Annual Review of Progress in
Applied Computational Electromagnetics (ACES), Vol. 2, pp.
-971, 1998.
D. H. Werner and R. J. Allard, "The Simultaneous Interpola-
tion of Antenna Radiation Patterns in Both the Spatial and Fre-
quency Domains Using Model-Based Parameter Estimation",
IEEE Transactions on Antennas and Propagation, Vol. 48, No.
, pp. 383-392, 2000.
O. M. Bucci and G. Franceschetti, On the Degrees of Free-
dom of Scattered Fields, IEEE Antennas and Propagation So-
ciety Transactions, Vol. 37, No. 7, pp. 918-929, July 1989.
O. M. Bucci, C. Gennarelli and C. Savarese, Optimal Inter-
polation of Radiated Fields Over a Sphere, IEEE Antennas and
Propagation Society Transactions, Vol. 39, No. 11, pp. 1633-
, November 1991.
O. M. Bucci, C. Gennarelli and C. Savarese, Representation
of Electromagnetic fields Over Arbitrary Surfaces by a Finite and
Nonredundant Number of Samples, IEEE Antennas and Propa-
gation Society Transactions, Vol. 46, No. 3, pp. 315-359,
March 1998.
R. W. Hamming, Numerical Methods for Scientists and
Engineers, Dover Publications, Inc., New York, 1962.
C. A. Balanis, Antenna Theory: Analysis and Design,
Harper & Row, Publishers, New York, 1982.
E. G. Knott, J. F. Shaeffer and M. T. Tuley, Radar Cross
Section, 2nd Edition, Artech House, Boston, 1993.