Passive radar uses microwave signals from distant transmitters and ambient radio to track and detect targets in the air or sea. This technology cannot replace stealth. However, it can be used to complement higher-fidelity active sensor cues.
A passive radar system is composed of two components. The reference channel and the observation channel. The observation channel receives an illuminating signal from the transmitter and detects echoes of the reflected signal bounced off a target. The algorithm determines the direction of arrival by using the return signals.
The passive radar signal itself isn't as precise as a direct RF signal. An illuminating signal could be radio, television, FM radio broadcast, or a TV. Passive radar is not suitable for remote or high-density locations. It must only be used on ships or stationary ground vehicles.
Passive radar suffers from the effects of ambient RF radiation. The range of detection depends on the radiation and reflection energy of the receiver, the deployment geometry, and other noise.
Although passive radar can have many benefits it isn’t perfect. In the past, the technology was limited to a small range of frequencies, and it required more data and processing than other systems. With the advent of digital receivers the computing power has increased dramatically. The passive's effectiveness can also be greatly improved by the use of advanced radar absorbing materials. The long-term evolution in passive radar technology is still very promising.
Signal processing is a method of detecting and tracking moving objects. This is one of the latest developments in passive radar. Several research systems have been developed that incorporate phase-difference of arrival to determine the direction of arrival. Likewise, the use of cross-correlation can provide estimates of bistatic Doppler shift.
Passive radar has also seen a lot of exciting developments, including radar-absorbing coatings that reduce the effects of reflected or radiated energy. While these systems are currently in prototype stages, they are expected to become available within the next several years.
Passive radar systems that combine an advanced infrared track and search (IRST) system with a passive radar are the most useful. These systems can track and lock onto aircraft. They could eventually lock onto stealthy planes.
Passive radar has been used in many different ways, including surveillance and reconnaissance. There are many uses for passive radar in cell phone base stations. Passive radar can be complicated and not always reliable.
At the moment, passive radars that are most advanced are still ground-based systems. These systems include the VERA and Czech TAMARA systems and the Ukrainian Kolchuga system. Software Defined Radio is (SDR) technology enables processing of radiowaves in the microwave spectrum. Nevertheless, these systems have only minimal power and range, making them incompatible with the broader spectrum of passive airborne radar applications.