Topic outline

  • Topic 5 (last), radiowave propagation

    The last topic of this course is a teaser of very interesting subject: propagation of radiowaves. The extent of the topic is only half of other topics - i.e., about one week. The simplest way to explain the propagation of a wave is the ray theory (or geometrical optics) which says that a wave propagates along a thin line connecting transmitting (TX) and receiving (RX) points. If a ray hits a solid obstacle on the line, its propagation is fully blocked and there is a geometrical shadow behind the obstacle. Everyday experience says that the nature of light is like this. However, it does not hold for radiowaves because a point-to-point link implemented with radio waves typically requires a much bigger “tube” than a thin ray in order to propagate without disturbance. In addition, the ray theory does not work very good for radio waves as it completely ignores the wave effects used in the physical optics, such as interference that occurs when two or more waves at the same frequency combine. This "tube" in which a free-space radiowave propagates is called the Fresnel zone, and the size of it dictates the space that should be left free of solid obstacles in order to ensure that an original radio wave can propagate unhindered. The size of the Fresnel zone depends upon the frequency and the length of the link. Other concepts that are crucial when considering the propagation of radiowaves are the free-space loss due to the spherical nature of the radio waves (Friis transmission equation), the effect of the atmospheric conditions (air, moisture, rain, fog), scattering from small objects, reflections from the ground and other objects, the curvature of the Earth, and the bending (refraction) of radio waves in atmosphere.

    (Propagation of radiowaves can be studied more in the course ELEC-E4750 Radiowave propagation and scattering which is taught for the next time in the autumn of 2022. The main teacher of the course is Katsu. Welcome!)

    This part of the course addresses the following learning outcomes:

    • The student is able to explain the basic principles of radio wave propagation.
    • He/she can calculate the basic characteristics (such the size of the Fresnell ellipsoide) of radio links based on basic propagation models. 

    In this topic one should command the following subjects:

    • Chapter 14.5 Microwave propagation (Pozar book, edition 4)
    • Chapter 10 Propagation of radio waves (Räisänen/Lehto book)

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Topic 4, radio systems