How do passive homing systems primarily function?

Passive homing systems primarily function by receiving emitted energy from the target. They rely on detecting the signals or emissions that the target naturally produces, such as heat or radar signals. This enables the system to lock onto and track the target without needing to emit its own energy.

By listening for target emissions rather than creating a energy signal, passive homing is advantageous because it can operate stealthily, making it less likely to be detected by the target. This method is commonly used in various types of missiles and guided munitions, where the sensor is specifically designed to recognize and hone in on the target's emissions.

Other options describe different types of guidance systems that do not function similarly to passive homing. For instance, systems that transmit energy to the target would rely more on active homing mechanisms, which emit signals to guide towards their targets. This contrasts with the essence of passive systems that harness the ambient energy from the target itself to navigate.