2368 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 59, NO. 6, JUNE 2011 Analysis and Modeling of Near-Ground Wave Propagation in the Presence of Building Walls Fikadu T Dagefu, Student Member, IEEE, and Kamal Sarabandi, Fellow, IEEE Abstract—An efficient semi-analytic model for near-ground wave propagation in indoor scenarios is presented. For trans- ceivers deployed in indoor environments on or near the ground, since RF wave propagation is dominated by Norton surface waves, these higher order waves and their interactions with building walls and other indoor obstacles have to be captured for accurate field calculations. Existing ray tracing routines which are commonly used for indoor field prediction, are inadequate for evaluating signal coverage of transceiver nodes very close to the ground (less than a wavelength above ground) since such routines neglect higher order surface waves. In addition, geometrical optics alone is inadequate to treat finite-size and possible irregular-shaped obstacles at low radio frequencies (VHF and lower UHF). Our approach for calculation of near-ground wave propagation and scattering is based on a hybrid physical optics and asymptotic expansion of dyadic Green’s function for a half-space dielectric medium. Equivalence principle in conjunction with physical optics approximation is utilized to handle scattered field from building walls which are the dominant scatterers in indoor settings. Simu- lation results for various indoor propagation scenarios based on the new approach is validated by using both measurement results and full-wave numerical solvers. Index Terms—Indoor field prediction models, near-ground wave propagation. I. INTRODUCTION E LECTROMAGNETIC field prediction models for in- door and urban environments have several applications including wireless channel characterization, radar through-wall imaging and distributed sensor networks for environmental and subsurface sensing [1], [2]. Through-wall imaging and detection techniques, which have applications in many areas including fire and earthquake rescue missions and security systems (detection of intruders), often require a fast and accu- rate forward model which takes into account scattering from indoor obstacles. Another application pertains to positioning and tracking of robotic platforms deployed in complex envi- ronments including urban and indoor scenarios for military Manuscript received June 04, 2010; revised October 14, 2010; accepted Jan- uary 15, 2011. Date of publication April 21, 2011; date of current version June 02, 2011. This work was supported by the U.S. Army Research Laboratory under contract W911NF and prepared through collaborative participation in the Microelectronics Center of Micro Autonomous Systems and Technology (MAST) Collaborative Technology Alliance (CTA). The authors are with the Radiation Laboratory, Department of Electrical En- gineering and Computer Science, The University of Michigan, Ann Arbor, MI 48109 USA (e-mail: fikadu@umich.edu; saraband@umich.edu). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TAP.2011.2144555 applications to enhance tactical situational awareness. A spe- cific example of this is assisting the aforementioned platform in high-resolution navigation. There are also other military ap- plications including sensor networks deployed in the battlefield for communications between soldiers on the ground. Examples of such systems that researchers have been working on include the self-healing minefield (SHM) system sponsored by DARPA [3] which is an anti-vehicle landmine system that utilizes a networked communication among the various mines and the networked embedded systems technology (NEST) which is also a DARPA program intended to be deployed in various environments [4]. The antennas used in such systems are often very close to the ground. For example, the antenna height of the SHM system is 7 cm [5]. One of the main goals of this paper is to present an indoor wave propagation model that accurately captures the Norton surface waves that are dominant at low transceiver heights. In the literature, various indoor field prediction models have been presented. Ray tracing routines are used as the primary methods to predict field coverage in indoor and urban settings [6]–[16]. In [17], a hybrid technique that combines a full-wave approach with ray tracing is developed. In [18], a path loss prediction model that utilizes a parabolic approximation of the Helmholtz equation is proposed. There are also various high-frequency techniques including the Geometrical theory of diffraction (GTD) and Uniform theory of diffraction (UTD) that are devised to include diffraction effects from edges and corners [19]–[21]. Geometrical optics alone does not take into account finiteness and possible irregularities of building walls and other indoor scatterers. This is because of the inherent assumption used when the Fresnel reflection and transmission coefficients are derived in which the building wall is treated as an infinite homogeneous dielectric slab. Several researchers have focused on developing indoor field prediction models that are based on measurement results es- pecially for lower frequency applications [22]–[28]. Although models based on measurement could give a more accurate es- timate of the received field compared to ray tracing routines, the drawback of such models is the fact that they are site-spe- cific and hence are not versatile. Also, developing a measure- ment-based model is expensive and does not provide insight into the various scattering mechanisms. Pure numerical solvers that are based on methods such as MoM, FEM, FDTD, etc. are usu- ally not preferred due to the high computational cost resulting from the large size of realistic indoor propagation scenarios in terms of wavelength. These methods are limited to low frequen- cies and small building scenarios and require high-performance computers. 0018-926X/$26.00 © 2011 IEEE