A liquid crystal switched passive Van Atta array for automobile radar target enhancement in heavy rainfall

Severe weather poses a major challenge to safe driving. Sudden precipitation or heavy fog can reduce visibility and extend braking distances, increasing the risk of an accident. To combat this, modern cars are adopting a wide variety of driver aids such as braking-assist, lane detection and blind spot alerts (P. Green et al, US D.O.T., Int. Vehicle-Based Safety Sys., 2008). These require vehicle sensors, the most popular being radar and VANETs (Vehicular Ad-hoc NETworks), which allow inter-car data sharing. Both use radio frequencies, which are more resistant to weather and obstacles than older optical systems. However, radar range is still degraded by heavy rainfall (M. I. Skolnik, Introduction to Radar Systems, 442–449, 2001). Also, global regulatory bodies have moved from 24 GHz radars to 76–82 GHz radars, which are even more susceptible. Regulatory power limitations imposed upon radar have also limited the success of increasing range with more powerful transmitters.