Analysis of Electromagnetic Interference in S-Band Doppler Radar Systems Being Used by IMD

This study investigates the issue of electromagnetic interference (EMI) in Doppler weather radar (DWR) systems employed by the India Meteorological Department (IMD). IMD utilizes a range of radar systems operating in S-band, C-band, and X-band frequencies to monitor precipitation, intensity, movement, and type (rain, hail, snow, etc.). These radar systems rely on the extrapolation of radar backscattered echoes and numerical model predictions, integrated with radar data, to forecast weather phenomena and location. Notably, transmitted signals are quite powerful (800 kW) and the received echo signal by the radar antenna is relatively weak (~3-16 W). Raindrops are typically 0.5–5 mm in diameter with a distance between two raindrops ~5 cm, due to which, a small fraction of transmitted energy hits the raindrops and is scattered back. Consequently, a weather radar system performs its functions with high sensitivity while navigating for the target in the dynamically changing electromagnetic environment. However, as electricity within a circuit is never absolutely enclosed, electronic devices inevitably emit some amount of electromagnetic radiation, which can interfere with weather radar signals when emitted at the same or near close frequency. This interference can disrupt measurements and distort output images, potentially displaying spokes, spots, or stripes that limit the value of radar pictures. Moreover, electromagnetic emissions within the transmitter chain can impact the transmitter's performance by introducing spurious and harmonics in the pulse shape. This paper examines the nature of the problem faced by S-band Doppler radar systems used by IMD across India and discusses potential techniques for mitigating the issue.