Conventional radar systems are designed with both a transmitter and receiver located together, often sharing the same antenna. They function by sending out pulsed signals and then measuring the time it takes for these pulses to travel to an object and return. This measurement helps in determining the distance of the object from the radar.

Passive radar systems, on the other hand, operate differently as they do not have their own dedicated transmitters. Instead, they make use of existing external transmitters within the environment. The receiver in a passive radar system captures the signal coming directly from these external transmitters and also the signal that bounces back from an object. By analyzing the time difference between the arrival of the direct signal and the reflected signal, the system can calculate the bistatic range, which is the combined distance the signal travels from the transmitter to the object and then to the receiver.

Moreover, a passive radar system not only determines the bistatic range but also measures the bistatic Doppler shift and the direction from which the echo arrives. These measurements are crucial in accurately calculating the position, direction, and speed of the object. In more advanced setups, multiple transmitters and/or receivers may be utilized.