Planeamento
Aulas Teóricas
Course overview
Solution of the homogeneous wave equation
The continuity equation.
Development of the homogeneous wave equation for an unbounded media.
Homogeneous solution of the wave equation for unbound media. Interpretation of the solution. Definition of plane wave.
Poynting Theorem and Boundary condition
Poynting Vector and power balance.
Conditions that electromagnetic fields satisfy at the flat interface between two semi-unlimited material media. Particularization for the case of the interface between two perfect dielectric media, and for the case of the interface between a perfect dielectric and a good conducting medium.
Introduction to the problem of the incidence of a plane wave at the plane interface between two semi-unlimited dielectric media.
Wave propagation near the interface of two unbounded dielectrics
Analytical formulation. Identification of the direction of propagation of the reflected and transmitted waves, by imposing boundary conditions.
Definition of parallel and perpendicular polarizations. Derivation of reflection and transmission coefficients' equation factor for parallel polarization.
Dependence of the reflection coefficients with the angle of incidence and medium characteristics. Visualization of fields near the dielectric boundary using animated graphics.
Infinite transmission lines
General formulation for infinite transmission lines (physical structures supporting TEM fields). Equivalent electrostatic problem. Derivation of general equations for voltage, current and characteristic impedance.
The coaxial cable as an example of transmission line. Brief overview of the microstrip line; concept of effective dielectric.
Microstrip lines. Concept of effective permittivity. Characteristic impedance.
General formulation of the terminated transmission line problem. Reflection and transmission factor. Relation between impedance and reflection factor.
Graphical animation of the standing wave ratio.
Smith chart
Experimental demonstration of the standing wave ratio.
Concept of Voltage Standing Wave Ratio. Relation to the reflection factor at the load. Reflection factor and input impedance as a function of the transmission line length. Locus of the reflection factor in the complex plane.
Smith chart
Application of thee Smith Chart for the design of lambda/4 impedance transformers. Stub matching design.
Antenna fundamental concepts
Introduction to antennas. Radiation mechanism.
Analysis of the radiation of an elementary current filament - the Hertz Dipole. General expression of the fields. Particularization for the far-field. Power density and radiation intensity. Radiation patterns: representation formats. Beam width. Anechoic chamber configuration.
Characterization of radiation patterns. Concept of Directivity and Gain. Estimation of Directivity.
Antenna fundamental concepts (cont)
Input impedance of an antenna. Application to the Hertz dipole.
Recap of polarization concept. Polarization mismatch coefficient. Antenna bandwidth. Concept of effective aperture and relation to directivity and gain. Transmission between antennas.
Antenna arrays
Introduction to array antennas. Formulation for liner uniform arrays.
Array elements
Overview of different array elements: half-wavelength dipole, slot antenna, helical antenna, patch antenna.
Overview of the equivalence principle. Radiation from waveguide open-end, horn and reflector antennas.
Practical aspects of antennas.
Introduction to propagation in the presence of terrain. Effect of ground reflections. Efeito da interferência entre raios directo e reflectido.
Ground reflection
Effect of distance, antenna height and frequency.
Diffraction atenuation
Introduction to rough surface scattering. Roughness criterion.
Diffraction by spherical Earth.
Diffraction by Knife edge obstacle. Fresnel ellipsoid and clearance criteria.
Effect of the atmosphere
Effect of atmospheric refraction. Concept of equivalent Earth radius.