Planeamento
Aulas Teóricas
Course overview
Overview of subjects, assessment method, study elements.
Introduction
Introduction to radiowave propagation. Recap of the analytical representation of a wave. Plane wave and spherical wave. Free space wave propagation: Friis formula and radar equation.
Wave reflection in planar dielectric interfaces
Characterization of wave reflection from planar smooth interfaces. Fresnel coefficients. Dependence with polarization and incidence angle. Example for sea water and for dry soil.
Ground reflection considering a flat Earth model. Interpretation of the interference pattern.
Ground reflection (cont)
Extension of ground reflection formulation for spherical Earth. Equivalent flat ground model. Divergence factor.
Scattering from rough ground
Coherent and difuse components from rough ground reflection. Rayleigh roughness criterion.
Introduction to the scattering model. Scattered power. Introduction to the scattering cross section model
Scattering from rough ground
Introdution to the scattering model. Definition of the scattering cross section function. Validity and interpretation. Simplifications. Determination of the Effective Scattering Area size.
Scattering from rough ground (cont)
Main dimensions of the active scattering area in a microwave link near rough ground cont). Calculation of the scattered power. Interpretation.
Scattering from rough ground (cont)
Scattered power from rough ground. "Reflective" and "difuse" cases. Influence on communications and on radar target detection.
Introduction to diffraction attenuation by isolated obstacles.
Attenuation by knife-edge obstacle
Application of the Green Theorem for the calculation of the attenuation caused by a knife-edge type of obstacle, for plane wave incidence. Interpretation of the result.
Knife-edge obstacle with spherical wave incidence.
Experimental demonstration of difraction of ligth by a small hole.
Experimental lab set-up
Experimental demonstration of basic microwave antenna and propagation concepts at the Microwave and RF Lab from Instituto de Telecomunicações (IT in LIsbon).
Attenuation by knife-edge obstacle (cont)
Definition of the Fresnel ellipsoid. Physical interpretation based on Green Theorem. Microwave link clearance criterion.
Review and merging of all previous models for propagation near the Earth, within the radio-horizon.
Introduction to the diffraction by the Earth.
Diffraction by spherical Earth
Definition of the reference transmitter. Attenuation curves for different ground electric parameters, antenna height and frequency. Interpretation.
Extension of the interference zone and relation to the Fresnel Ellipsoid.
Introduction to refraction at the lower atmosphere.
Radio propagation in the lower atmosphere
Dependence of air refraction index with atmospheric parameters and height. Ray trajectory in planar and spherical stratified layers with decreasing refractive index.
Ray propagation models
Equivalent Earth radius model. Modified refractive index model.
Duct propagation (cont.)
Advantage of the modified refractive index models for radio link design. Trajectory equation.
Introduction to duct propagation. Physical mechanism. Ray propagation in ducts.
Duct propagation (cont.)
Case of linear dependence of the refraction index with height. Criteria for energy trapping.
Duct propagation (cont.)
Case of parabolic dependence of the refraction index with height. Criteria for energy trapping.
Attenuation by atmospheric gases
Introduction to wave attenuation in the lower atmoshpere. Attenuation rate formulation for inhomogenous media. Attenuation by water vapor and oxygen. Concept of effective length.
Attenuation by rain
Basic mechanisms. Attenuation rate formulation starting from the scattering cross-section of rain drops and rain drop radius distribution. Ryde formula and effective lenght.
Fading
Transmission matrix calculation taking into account drops canting angle. Cross polarization discrimination and isolation coefficients.
Introduction to signal fading and related physical mechanisms. Common distribution functions in radio propagation problems. Rayleigh distribution, properties and propagation scenarios.
Wave propagation for mobile communications
Introduction to mobile communications. Scenarios and implications on radio propagation issues. Different approaches for propagation modelling in mobile communications: determinsitic, statistical and hybrid propagation modelling.
Wave propagation in mobile communications (cont.)
Ray propagation models. Propagation in rural micro-cells. Break-up distance. Interpretation. Calculated and experimental examples.
Propagtion in mobile communications (cont)
Ray-based propagation model for urban micro-cells. Street crossings.
Micro-cells at millimeter waves. Specific issues.
Propagation models for mobile communications
Multiple obstacle modelling in macro-cells. Distribution functions to model fading in mobile radio scenarios.