Michael G. Cotton; Edward F. Kuester; Christopher L. Holloway

Abstract: In this study we investigated the geometric optics (GO) approximation to the fields of an infinitesimal electric dipole above a half plane for geometries typical of wireless indoor communications. This inspection was motivated by efforts to establish a ray trace model to characterize indoor radio propagation channels. Eight canonical geometries were examined to isolate near-surface and near-field effects that are not accounted for in the GO approximation. Common building materials and physical dimensions (i.e., antenna separation and height) as small as 1 cm were investigated for frequencies up to 8 GHz. Theoretical fields were calculated via numerical evaluation of Sommerfeld integrals and compared to corresponding GO approximations. As expected, near-field and nearsurface (e.g., surface wave) mechanisms which invalidate GO were observed. Close to the surface, an interesting interference pattern in the frequency domain was identified. Mathematical manipulation showed that this so-called ‘‘pseudolateral wave’’ phenomenon was caused by adjacent fields in the two media propagating at different speeds. Next, we transformed the results to the time domain and used delay spread as a metric to quantify GO error. We also show that the pseudolateral wave manifests itself in the time domain as an additional pulse that arrives at a delay associated with the speed of a wave traveling in the lossy media.

Keywords: antenna; geometric optics; indoor propagation channel; ray-trace model; electromagnetic theory

To request a reprint of this report, contact:

Lilli Segre, Publications Officer
Institute for Telecommunication Sciences
(303) 497-3572
LSegre@ntia.gov

For technical information concerning this report, contact:

Michael G. Cotton
Institute for Telecommunication Sciences
(303) 497-7346
mcotton@ntia.doc.gov

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