This course aims at teaching the basic principles of high-frequency technologies, focusing on the fundamental problem any telecommunication engineer phases: information (energy) transmission with the smallest possible distortion and attenuation. The course begins with an overview of the electromagnetic wave propagation phenomena in infinite space, emphasising at attenuation and dispersion (distortion). The analysis then continues with propagation phenomena in transmission lines. The role of wave impedance in transmission lines is investigated in detail, in order to determine the optimal energy transfer from the source towards the load. Various impedance matching techniques are presented (matching circuits). Propagation in metallic waveguides with rectangular and circular cross-sections is analysed next. The properties of coaxial and microstrip transmission lines are also examined thoroughly. The method waveguides are studied provides the foundations for engineers to be able to investigate other waveguide types, variations of the existing ones and even new models. The third course unit involves microwave network theory, which is based on the integratino of circuit theory into wave propagation and microwave device properties via the concept of scattering matrices. Apart from theoretical exercises, the course comprises laboratory exercises, which involve the use of CAD/CAE for the above-mentioned subjects.