Attenuation Statistics for X-band Radar Design

Abstract

It is well known that the reliability of radar measurements to characterize targets is dependent upon the signal-to-noise ratio of echoes. The power of received signal becomes weak as range increases as described by radar equation in free space. For weather radar, the echoes can suffer extra power loss due to propagation in rain media. A set of system parameters need to be determined in radar design to assure the received signal in sufficient quality at given range. However, rain attenuation is dependent on rain intensity and path length. Therefore attenuation statistics can predict the power loss due to precipitation. This is especially important for radar designers to leverage the transmit power and maximum range. The higher the frequency the greater the amount of power attenuation the signal will suffer as it travels along its path mainly through precipitation as well as other attenuating medium. Conventionally long range weather radar operates at S- band where the attenuation is almost negligible and the application of X-band radars to weather sensing has seen limited application. X-band radars typically operate at frequencies in the neighborhood of 8-12 GHz with respective wavelengths between 3.75 cm to 2.5 cm, and S-band radars operate in the range of 2-4 GHz with wavelengths between 15 cm and 7.5 cm respectively. However the use of X-band radars in comparison to S-band radars has some advantages particularly in the physical size of the radar where the width of the dish decreases as the frequency of the radar increases. Therefore, the costs of building and maintaining a smaller radar can outweigh the costs of larger radars. This can then lead to the usage of multiple radars in place of a single large radar. Further more, the size of an X-band radar can lends itself to portability. So with the size advantage the statistics can give insight into X-band radar design.