Physics-based modeling of wave propagation for terrestrial and space communications

This dissertation investigates the solutions to two important and challenging problems of radio wave propagation in wireless communication. The first problem pertains to modeling of wave propagation in foliage. The second problem involves a comprehensive study in enhancing the radio uplink between a ground station and a spacecraft using an array of reflector antennas. Solutions are developed using physics-based modeling which allows for realistic simulations of physical environments and gives insight into wave propagation mechanisms.; For the foliage problem, various models are developed for different applications. The foundation of these advanced models is an existing fractal-based coherent scattering model (FCSM). To extend the region of validity of FCSM, an enhanced version is developed by accounting for mutual coupling among leaves within leaf clusters. An outdoor path-loss measurement is conducted at Ka-band; comparison between measured and simulation results demonstrates a great improvement with the enhanced model. The difficulty of direct application of FCSM to estimate foliage path-loss over long distances is also resolved by analyzing a single block of forest and applying the wave propagation behavior to all forest blocks. This statistical wave propagation model (SWAP) is successfully validated. In order to develop a simple-to-use macro-model for foliage path-loss, sensitivity analysis is performed using a large number of SWAP model simulations. Then a physics-based parametric model is selected and its parameters are related to the foliage/system parameters. Examples of this Michigan foliage attenuation model (MIFAM) are presented for both deciduous and coniferous forests.; For the ground array problem, an external uplink phase calibration is needed due to the insufficient accuracy of determining the phase centers of an array of antennas. Three schemes are proposed. The first one presents a radar calibration procedure based on phase conjugation, and uses low earth orbit (LEO) satellites as calibration targets. These targets fall within the array near-field region, and a far-field correction scheme is developed so that the array can focus in the far-field at any desired direction. The second scheme is designed for an all-transmitter array. The Moon, which lies in the array far-field, is selected as the calibration target. InSAR (Interferometric Synthetic Aperture Radar) imaging is employed to deal with such a distributed target. The last scheme investigates the possibility of using existing VLBI (Very Long Baseline Interferometry) infrastructures. System modifications may be required since VLBI is based on downlink operation. However, baseline, delay, and phase measurements from VLBI all provide potential information for calibration.