A proper model of RF absorber must be developed based on information such as absorber reflectivity, in magnitude and phase, for various angles of incidence, and for parallel and perpendicular polarizations. Unfortunately, these data are not available due to the practical limitations of the test fixtures to measure the RF absorber performance. Manufacturer data sheets normally specify only the magnitude of the absorber reflectivity for normal incidence. A model has been developed in this paper for pyramidal RF absorber with pyramid length shorter than a quarter wavelength and poor reflectivity performance. Since the reflection from the metal backing would be much higher than the reflection and scattering from the pyramid tips, the metal boundary may be modeled as a lossy dielectric with certain effective dielectric constant, εeff , and effective conductivity, Ïƒeff , and the thickness extends to infinity. The appropriate values of εeff and Ïƒeff can be derived based on the reflectivity information given by the manufacturer's data sheet. The reflectivity at oblique incidence is calculated and compared with the results of method of homogenization and moment method. A reasonable match between the different models is obtained. The plane-boundary dielectric model can be used to evaluate the degradation of reflectivity level with respect to angle of incidence. It can be used in a simulation tool for design of anechoic chamber.
2. Holloway, C. L., R. R. DeLyser, R. F. German, P. McKenna, and M. Kanda, "Comparison of electromagnetic absorber used in anechoic and semi-anechoic chambers for emission and immunity testing of digital devices," IEEE Transactions on EMC, Vol. 39, No. 1, 33-47, 1997.
3. Pues, H., Electromagnetic absorber measurement in a large waveguide, 8th International Symposium on EMC, 253-258, 1989.
4. Pues, H., Electromagnetic absorber measurement in a large coax, 9th International Symposium on EMC, 541-546, 1991.
5. Kuester, E. F. and C. L. Holloway, Improved low-frequency performance of pyramidal-cone absorbers for application in semianechoic chambers, 1989 IEEE International Symposium on EMC, 394-398, 1989.
6. Janaswamy, R., "Oblique scattering from lossy periodic surfaces with application to anechoic chamber absorbers," IEEE Transactions on Antennas & Propagation, Vol. 40, 162-169, 1992.
7., "Methods of measurement of radio-noise emissions from lowvoltage electrical and electronic equipment in the range of 9 kHz to 40 GHz," American National Standard Institute, Vol. C63.4, 1992.