Automotive traffic at level crossings can be hazardous because of the openness of the intersection and multiple vehicles often attempting to make the crossing at the same time. However, teaming millimeter-wave (mmWave) radar signals at 77 GHz with the right types of industrial-grade antennas can greatly increase the safety of pedestrians and cyclists at these level crossings. Such is the finding of researchers from Siena and Florence, Italy, as they attempt to apply mmWave radar-monitoring systems at 77 GHz to help enhance the safety of wide-open level-crossing traffic intersections.
Because of the sophisticated, commercial railway systems used for travel and transport throughout Italy, rail crossings are critical parts of the Italian (and throughout Europe) roadway systems. A rapidly growing population has underlined the needs for some form of automatic traffic-monitoring technology, such as mmWave, frequency-modulated-continuous-wave (FMCW) radar at 77 GHz, to maintain safe traffic/pedestrian flow at level crossings.
The high frequency of these radar systems has spurred the development of suitable antennas that meet the specific requirements of the systems under all operating conditions. These antennas also are capable of performance levels at 77 GHz based on a certain mounting distance above the ground and from the railway tracks.
Furthermore, the antennas are designed to monitor roadway crossings of a certain maximum road width (12 m), assuming a certain maximum detection distance to the target. Additional requirements consider maximum antenna size and target costs. Initial requirements included containing the monitoring antennas within a box measuring 16 cm on a side. Those initial requirements were quickly redefined as a result of experience from operating in the field.
The first antennas were designed for a bandwidth of 1 GHz centered at 76.5 GHz, providing more than 25 dBi gain and more than 70% efficiency. Early antenna designs were based on horn antennas, with further developments leading to lens horn antennas to decrease the beamwidth.
The researchers pursued many different mmWave antenna designs and their simulations, comparing the performance levels of the different configurations at 76.5 GHz, including reflectors, horns, and horn arrays. Tradeoffs in size, complexity, and manufacturing costs were evaluated to guide the choice of 77-GHz antennas for the safest railway level crossings possible.
See “Industrial Antenna Development for 77-GHz Level-Crossing Monitoring Radar,” IEEE Antennas & Propagation Magazine, Vol. 60, No. 5, October 2018, pp. 95-106.