What’s a passive radar?

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Passive radar systems receive but do not transmit signals, using reflections from other objects to identify targets. They are stealthy, less expensive and less complex than active radar, and can use a variety of objects as reflectors.

A passive radar is a radar system that receives only, instead of alternating transmit and receive. These systems are used in a variety of settings and have a number of advantages that make them targets of interest for many military technology developers. Essentially, a passive radar is a pair of very finely tuned ears sensitive to high frequency radio waves rather than sounds that can be heard by the human ear.

Many people are familiar with how radar works: a signal is transmitted and a receiver waits for the signal to return, making inferences from the returned signal about what kind of objects the signal interacted with and how far away they are. For example, a vessel could use radar to search for potential enemy vessels in the area. Unlike sonar, which uses sound, radar uses high-frequency radio waves.

Passive radar has the same ability to pick up microwave energy, but not transmit it. Instead, it uses reflections from other objects and the original source to gather information about targets, working passively rather than actively to identify objects in its vicinity. Using this information, your device can provide range, speed, and location information that can be used to make decisions. Passive radar on an aircraft, for example, could be used to identify other aircraft in the area for the purpose of avoiding them.

From a military point of view, the clear advantage of passive radar is that it is stealthy. Because it doesn’t transmit, it can be difficult for an enemy to locate, because there is no signal to track. Instead, passive radar simply sits and waits for signs of interest. Even if a passive radar array is identified, it can be difficult to jam it, because there is no way to know what frequencies it is using, although tactics can be used to spoof it to confuse it. Using passive covert radar can improve mission safety and allow people to have continuous access to radar data.

Passive radar detection of targets of interest is also less expensive and less complex than operating with an active radar system. This makes it less expensive to implement and can make it attractive in environments where radar needs to be operational quickly. Many different things can be used as a passive radar reflector, allowing the technology to use a variety of objects in its vicinity to gather information.

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