The daily life on Earth more and more relies on satellites and space missions. These missions are increasingly at risk by the growing amount of space debris. As even small particles can destroy active satellites, it is necessary to build up an up-to-date catalog of all objects in space. While there are good results using optical systems for high altitude objects e.g. at geostationary orbits, for low earth orbit objects the use of highly sensitive radar sensors is necessary. For the proper design of these radar systems the signal-to-noise-ratio (SNR) is a key factor. While the SNR’s signal part is mainly dependent on system parameters like transmit power or antenna gain, the system’s noise figure is influenced by a multitude of parameters. For short range radar systems the receiver noise temperature dominates the calculation, whereas for space surveillance radar systems the calculation is more complex.
While the individual factors of a system’s noise figure have been discussed in various publications, the combination of all these factors and their relative importance is considered only rarely. This paper provides an overview over all effects concerning the noise figure calculation for space surveillance radar. After a short introduction to the basic concepts of noise figure calculations, each effect influencing the noise figure is discussed in detail for two example radar systems, one for detection and another one for imaging. These calculations include external parameters like the noise effects of the sun or atmospheric losses as well as the system specific factors like feed line losses, noise figure of low noise amplifiers (LNA) and sidelobe effects.
The proper calculation of a system’s noise figure plays an important role for the design of a space surveillance radar system. The next step to get a full model of space surveillance radar systems is to consider ionospheric and space weather related effects.