Noise in hyper frequencies - Origin and modeling

Interest in microwave noise (UHF or decimetre band or RF, SHF or centimetre band, EHF or millimetre band) arose when these bands were used for standard equipment for wireless applications. There were also many special technical aspects – to the components used, the architectures implemented, and the applications – had to be worked on to meet the requirements, and created a highly innovative field.

Generally speaking, noise is defined as "any phenomenon that is superimposed on a signal and limits the transmission of information" (Le Robert). By extension, we have come to call noise the stochastic physical phenomena that cause these limitations – for example, the thermal noise of electric current, and the various sources of physical noise that accompany its propagation in a component. The definition of noise does not include the distortions created by the signal itself, which are the non-linearities of the circuit. Nor does it include phenomena that are slower than useful signals (temperature drift, ageing, etc.) – We will, however, mention them when describing certain problems encountered in hardware.

This document includes a description of natural external electromagnetic noise sources and those linked to human activities, as well as the physical sources of noise specific to equipment and linked to its operation. Noise is then analyzed for the various components and functions used in the equipment, revealing very different situations and explaining the complexity of the architectures used. The impact of noise on system performance is discussed using representative examples (readers are referred to the bibliographic references for more detailed information on the microwave systems concerned). The final paragraph shows that noise can also be used as an advantage in the design of specific devices.