Radar, within the context of a collision avoidance system, is a specialized technology that uses radio waves to determine the range, angle, or velocity of objects in order to detect potential hazards or obstacles that may cause a collision. It operates by emitting electromagnetic signals and subsequently receiving any return signals that are reflected back from objects. This information is then processed to calculate the distance, orientation, speed, and other critical details of the detected object. This real-time situational awareness enables an effective collision avoidance system, making it possible to prevent or minimize the impacts of impending collisions, enhancing safety in navigation for vehicles, aircraft, and marine vessels.

1. Marine Radar System: Used in ships and boats, this radar system helps in collision avoidance by detecting obstacles such as other ships, icebergs, etc. in the marine environment. It can detect objects and their movement, regardless of weather conditions, providing time to maneuver and avoid a collision. 2. Airborne Collision Avoidance System (ACAS): This radar system is used in aircraft to reduce the risk of mid-air collisions. It senses other aircraft in its proximity, calculates the risk of a collision, and establishes maneuvers to avoid potential collisions. 3. Automotive Radar System: These systems are emerging in road vehicles for functions such as adaptive cruise control and collision warning systems. They help to increase the vehicle's safety and convenience by informing the driver about other vehicles' distance and speed, helping avoid accidents. 4. Ground Proximity Warning System (GPWS): This radar technology is used in aircraft and warns the pilot if they are in immediate danger of flying into the ground or colliding with an obstacle. 5. Weather Radar System: Even though primarily used for weather prediction, such systems help aviators to avoid dangerous weather conditions that might lead to a collision, such as severe thunderstorms or hurricanes.

Radar, a technology predominantly known for military and aviation purposes, plays a vital role in modern collision avoidance systems. It acts as the 'eyes' of the system, emitting radio waves that bounce back after hitting an object. This allows the system to determine an object's distance, size, and relative speed, helping to prevent potential collisions. One exciting aspect is that this system not only works in perfect visibility conditions but also at night or in harsh weather when human visibility is compromised, making it a key component in the development of autonomous vehicles.