Radio and radar receivers must be capable of processing very small signals, necessitating the use of very sensitive circuit blocks that can contain fragile semiconductors. Many of these systems must also be capable of surviving very large incident signals, without damage to the sensitive components they contain. The receiver protection limiter, most often referred to simply as a limiter, can protect the receiver from large input signals and also allow the receiver to function normally when these large signals are not present.
Limiters are most often employed in radar transceivers, whose transmitters and receivers are tuned to the same frequency. The transmitter produces a signal, the peak level of which is in most systems in the kilowatts or megawatts order of magnitude, which is applied to an antenna that is typically also utilized by the receiver. The receiver must be capable of reliably detecting and processing very weak reflected signals, so it has a sensitive, low noise amplifier (LNA) at its input, although some receivers apply the received signal directly to the input of a downconverter mixer.
Both of these circuit blocks employ sensitive semiconductor components that will very likely be damaged by even a small portion of the transmitter signal that might be coupled to the receiver input, either by reflection from the antenna or by other means. A limiter can protect these components.
