Several studies have characterized the path loss properties in industrial environments. However most of them have focused on one frequency, and some two or maximum three frequencies, usually cellular telephone frequencies or the unlicensed ISM bands that are commonly used in various industries. Few, if any, have characterized a larger part of the useable frequency range.This thesis is taking that challenge and investigates the path loss characteristics over a large frequency range, 300 MHz – 3 GHz, in industrial environments.

First a measurement system suitable for the harsh environments found in industries is designed and verified. The measurement system is designed as two asynchronous stand-alone units that can be positioned at an arbitrary position to measure the path loss characteristics in any environment without interfering with the normal activities at the location.

After that a measurement campaign involving three different types of environments is carried out. The environment types are: first, one highly absorbing – a paper warehouse at a paper mill; second, one highly reflective – a furnace building filled with metal objects and constructions and third, a mine tunnel – located 1 km below the surface of earth which is neither highly reflective nor absorbing but exhibits somewhat wave-guide like characteristics.

The environments are shown to have very different behavior when it comes to propagation characteristics. Observations in the first environment reveal an environment that almost cancels out certain frequency bands and only line-of-sight communication is possible, hence no improvement will be achieved if installing systems that take multipath propagation into account, like MIMO. In the second environment reflections are legion; there are so many reflecting surfaces at different angles so any polarization of the signal is almost completely eliminated. Large fading variations were observed.The third environment is the underground mine where signals propagate inside the tunnels like in waveguides. It is shown that there are regions in the spectrum where the path loss dips and that these dips at least partly can be modeled with a simple two-beam propagation model normally used for outdoor propagation over infinite fields.

The overall conclusion is that industrial environments are more heterogeneous regarding propagation characteristics than commonly assumed when selecting communication solutions. And that the only way to really know if a radio system will work at a certain location is to measure and characterize the environment.