Passive radar, a technology that uses both ambient radio and microwave signals to track targets in the air and at sea, is called passive radar. Although passive radar is not intended to replace stealth, it can be used as a complement tool to activate higher-fidelity active sensors.
A passive radar system consists of two main components: an observation channel, and a refer channel. The observation channel detects echoes from a target and receives an illuminating message from the transmitter. The algorithm can calculate the direction of arrival using the signals' returns.
The precision of the passive radar signal can be less than that of an RF signal. The illuminating beam can be broadcast radio, TV, or FM radio. Passive radar cannot be used in remote, high-density areas. It must be mounted on both ships and stationary ground vehicles.
Passive radar is also limited due to the radiation from ambient RF. The range of detection depends on the radiation and reflection energy of the receiver, the deployment geometry, and other noise.
While passive radar does have many advantages, it's not perfect. Passive radar was limited in its capabilities to detect frequencies within a small area. It also required more data and processing time than other systems. But, thanks to digital receivers, computing power has soared. The passive's effectiveness may be enhanced by the use radar absorbing coateds with higher performance. But passive radar technology continues to evolve and has great potential.
One of the most interesting developments in passive radar is the application of signal processing to the detection and tracking of moving objects. Several research systems have been developed that incorporate phase-difference of arrival to determine the direction of arrival. Cross-correlation, on the other hand, can be used to calculate bistatic Doppler Shift.
A radar-absorbing coating is another exciting advancement in passive radar. It reduces the impact of reflected and radiative energy. While these systems are currently in prototype stages, they are expected to become available within the next several years.
Advanced infrared search-and-track (IRST), combined with passive radar, are the most practical passive radar systems. These systems have the potential of tracking and possibly locking onto aircraft. They may eventually be able to lock onto stealthy aircraft.
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 is complex and not yet tested so it is not suitable in all cases.
As of now, the most advanced passive radars are stationary ground-based systems. These include the Czech TAMARA and VERA systems, and the Ukrainian Kolchuga system. Software Defined Radio is (SDR) technology enables processing of radiowaves in the microwave spectrum. These systems do not have the same power or range as passive airborne radar applications.