Figure of merit for low frequency anechoic chambers based on absorber reflection coefficients

Return loss as a function of frequency and angle of incidence is studied to determine the effectiveness of the absorbing material used in an anechoic chamber. This alone is not enough to determine a figure of merit for an anechoic chamber or to compare the figure of merit for one anechoic chamber to that of another. While the information gained from return loss calculations and measurements as a function of angle of incidence is valuable, an overall measure of anechoic chamber effectiveness is necessary in order to compare different designs. In this paper, a new chamber figure of merit which is based on the decay time of the chamber is introduced. This decay time is, in turn, based on the average power absorbed by the chamber walls. The resulting model is simple and does not require intensive numerical computation. Calculations of the figure of merit for anechoic chambers which contain different types of absorbing materials are shown, and calculated and measured values of decay time for a primary standards calibrations facility are compared.

[1]  C. Holloway,et al.  A low-frequency model for wedge or pyramid absorber arrays-II: computed and measured results , 1994 .

[2]  Motohisa Kanda,et al.  Bistatic scattering of absorbing materials from 30 to 1000 MHz , 1992 .

[3]  J. M. Dunn,et al.  Local, high-frequency analysis of the fields in a mode-stirred chamber , 1990 .

[4]  David A. Hill,et al.  Aperture coupling to a coaxial air line: theory and experiment , 1993 .

[5]  D. A. Hill,et al.  A reflection coefficient derivation for the Q of a reverberation chamber , 1996 .

[6]  L. Carin,et al.  Wave-oriented data processing for frequency- and time-domain scattering by nonuniform truncated arrays , 1994, IEEE Antennas and Propagation Magazine.

[7]  Philip M. Morse,et al.  Sound Waves in Rooms , 1944 .

[8]  G. Millington,et al.  A MODIFIED FORMULA FOR REVERBERATION , 1932 .

[9]  Motohisa Kanda,et al.  Evaluation of off-axis measurements performed in an anechoic chamber , 1986 .

[10]  K. Kunz,et al.  Analysis of compact electromagnetic anechoic chamber performance using finite difference time domain methods , 1991, IEEE Proceedings of the SOUTHEASTCON '91.

[11]  Carl F. Eyring,et al.  Reverberation Time in “Dead” Rooms , 1930 .

[12]  C. Holloway,et al.  A low-frequency model for wedge or pyramid absorber arrays-I: theory , 1994 .

[13]  Ramakrishna Janaswamy,et al.  Oblique scattering from lossy periodic surfaces with applications to anechoic chamber absorbers , 1992 .

[14]  T. Ellam.  An update on the design and synthesis of compact absorber for EMC chamber applications , 1994, Proceedings of IEEE Symposium on Electromagnetic Compatibility.

[15]  S. Shtrikman,et al.  A Variational Approach to the Theory of the Effective Magnetic Permeability of Multiphase Materials , 1962 .

[16]  Motohisa Kanda,et al.  Time-domain measurements of the electromagnetic backscatter of pyramidal absorbers and metallic plates , 1993 .

[17]  Edward F. Kuester,et al.  Comparison of approximations for effective parameters of artificial dielectrics , 1990 .

[18]  M. T. Ma.  Understanding Reverberating Chambers as an Alternative Facility for EMC Testing , 1988 .

[19]  W. J. Sette.  A NEW REVERBERATION TIME FORMULA , 1933 .

[20]  Christopher L. Holloway,et al.  Modeling semi-anechoic electromagnetic measurement chambers , 1996 .

[21]  Motohisa Kanda,et al.  A time-domain method for characterizing the reflection coefficient of absorbing materials from 30 to 1000 MHz , 1991 .

[22]  J. M. Jarem,et al.  Electromagnetic field analysis of a four-wire anechoic chamber , 1990 .

[23]  V. Liepa,et al.  Full wave analysis of infinitely periodic lossy wedges , 1990, International Symposium on Antennas and Propagation Society, Merging Technologies for the 90's.

[24]  C. L. Holloway,et al.  Improved low-frequency performance of pyramid-cone absorbers for application in semi-anechoic chambers , 1989, National Symposium on Electromagnetic Compatibility.