Planeamento
Aulas Teóricas
Course overview
Overview of subjects, assessment method, study elements.
Introduction
Introduction to radiowave propagation. Recalling the analytical representation of a wave. Plane wave and spherical wave. Free space wave propagation: Friis formula.
Wave reflection in planar dielectric interfaces
Exercise T1.1. Radar equation. Charcaterization of wave reflection from planar interfaces.
Wave reflection in planar dielectric interfaces
Charcaterization of wave reflection from planar, smooth metal and dielectic interfaces (continuation). Dependence with polarization and incidence angle. Example for sea water and for dry soil.
Introduction to the interference caused by ground reflection.
Ground reflection
Ground reflection of radio waves: interferenece between direct and reflected waves considering flat Earth model. Interference pattern. Implications on radio services. Introduction to the spherical Earth case. Radio horizon.
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 criterium.
Introdution to the scattering model. Scattered power.
Scattering from rough ground
Introdution to the scattering model. Definition of the scattering cross section function. Validity and interpretation. Simplifications.
Scattering from rough ground (cont)
Main dimensions of the active scattering area in a microwave link near rough ground.
Scattering from rough ground (cont)
Scattered power from rough ground. "Reflective" and "difuse" cases. Influence on communications and on radar target detection.
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
Introduction to diffraction and attenuation by isolated obstacles. 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.
Attenuation by knife-edge obstacle (cont)
Knife-edge obstacle with spherical wave incidence.
Experimental demonstration of difraction of ligth by a small hole.
Definition of Fresnel ellipsoid. Physical interpretation based on Green Theorem. Microwave link clearance criterium.
Diffraction by spherical Earth
Review and merging off all previous models for propagation near the Earth, within the radio-horizon.
Introduction to diffraction by the 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.
Radio propagation in the lower atmosphere
Introduction to radiowave propagation in the lower atmosphere. Dependence of air refraction index with atmospheric parameters and height. Ray trajectory in planar stratified layers with decreasing refractive index.
Ray propagation models
Ray trajectory in spherical stratified layers with decreasing refractive index.
Equivalent Earth radius model. Modified refractive index model. Advantage of these models for radio link design. Trajectory equation.
Duct porpagation
Introduction to duct propagation. Physical mechanism. Ray propagation in ducts. Wave equation for non-uniform media, with height dependent index of refraction.
Duct propagation (cont.)
Solution of the wave equation for linear dependence of the modified refraction index with height. Case of unbounded media above the duct. Determination of the wavenumber and cutoff frequency for parallel polarization case. Interpretation and criteria for energy trapping.
Duct propagation (cont.)
Case of parabolic dependence of the refraction index with height. Criteria for energy trapping.
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. Transmission matrix calculation taking into account drops canting angle. Cross polarization discrimination and isolation coefficients.
Fading
Introduction to signal fading and related physical mechanisms. Common distribution functions in radio propagation problems: Rayleigh, Rice, Log-Normal. Propability density functions and cumulative distributin functions, Diversity techniques: motivation and strategies.
Wave propagation and mobile communications
Introduction to mobile communications. Scenarios and implications on radio propagation issues. Different approaches for propagation modelling in mobile communications: determinitic, statistical and hybrid propoagation 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.
Propagtion in mobile communications (cont)
Videos of MBS and SAMBA project demonstrations.
Introduction to macro-cell deterministic models. Attenuation by staggered obstacles: Walfish-Bertoni model for macro cell propagation. Analysis of simpilfying assumptions. Study of the multipath effect.
Advanced obstacle modelling
Finalisation of the Macro-cell propagation modelling
Statistical charaterization of signal variability in mobile communication scenarios
Improved models for common obstacles in mobile communication scenarios. Obtacles with finite depth: comparison of single knife-edge with double knife-edge and with topped double-knife-edge. Obstacles with finite width. Attenuation through the wall: generalized transmission coefficient. Modelling of walls with openings (windows or doors). Concept of "window gain".
Body area propagation models
Overview of propagation problems in body-area communication systems and biomedical applications.