In recent years, considerable effort has been devoted to systems which provide a low peak power, but which employ a very wide transmitter pulse; during the pulse, the transmitter frequency changes. In some applications, in the receiver, a frequency-sensitive delay system offers more delay to higher frequencies, causing the pulse to pile upon itself, to be compressed into a narrow pulse, with a higher peak power. In other applications, there may be several receivers. Wide, frequency-modulated, pulses, which overlap in space, may still be separated, because of the compression and different frequency content in the overlapped portions; thus, the receiver compression, and narrow-pulse range resolution, yield the accepted name of the expansion-compression technology, compressed, high-resolution, pulse (CHIRP). Whether by clever intent or accident, the comparison to the changing frequency in the transmitter pulse, and the chirping of a bird, is both amusing and fitting.

CHIRP systems have been employed in many variations. In some cases, the frequency must be stepped, from one precise value to another; such a technique may be necessary for phased-array antennas; it also provides for the portions of the pulse to be amplified by multiple receivers. In other cases, the transmitter is linearly frequency-modulated during the burst. An important use of CHIRP in recent years has been in the use of low-power, solid-state, transmitting systems. By combining the output of a multitude of low-power transmitters, over a very wide pulse, the need for dangerous and high-failure-potential units is significantly decreased.