Collision Avoidance Radar: Aircraft

Detection and collision avoidance of obstacles of small physical cross section has always been an important problem for low-flying aircrafts. High voltage power lines and power line towers are particularly hazardous in this respect. Many collision warning techniques have been suggested in the past.
Among the most promising techniques are laser radar and millimeter wave radar, particularly the latter when used in the synthetic aperture imaging mode. Available methods, however, suffer from a number of shortcomings. A major limitation of laser systems is atmospheric attenuation under fog and cloudy conditions, which would hamper target detection considerably. The problem with microwave and millimeter wave radars lies in the fact that current models used for characterizing the scatter by powerlines are inadequate.

The radar uses a linearly polarized wave and transmission lines are modeled as long perfectly conducting circular cylinders. The description imposes a significant restriction on the ability of radar to detect power lines. The choice of frequency and polarization have not been examined in previous measurements and models in order to optimize the detection of power lines by radars. The fact that a high voltage power line is made up of strands of wires in a helical arrangement can be exploited with regard to backscattering detection of the power lines. At high frequencies the helical geometry of powerlines becomes an important factor influencing the scattering behavior of electromagnetic waves which can be taken advantage of in detecting powerlines at off-specular directions. The surface of the cables is periodic along the axis of the cables and usually the period is only a fraction of the helical pitch. The effect of the helicity and the periodicity of the surface in backscatter at millimeter wave frequencies and incidence angles away from normal incidence will be investigated.

Collision Avoidance Radar: Low-Flying Aircraft