The RP-21 radar (designated CD-30 by the manufacturer), was installed in MiG-21 versions PFM to MF. It was designed to detect aircraft by day and night, inside and outside of clouds at altitudes from 1,000 meters up to the ceiling of the MiG-21. It is also designed to track aircraft for attacks with beam-guided and homing missiles as well as any other weapons normally carried. The radar operates in either seach mode or track mode to accomplish these tasks.
The RP-21 is a pulse radar. The transmitter produces high frequency radio pulses which the antenna forms into a directional beam. These radio pulses are reflected by aircraft, received by the antenna, and processed by the radar. The distance "D" is proportional to the time it takes for the signal to travel to the target and back.
The RP-21 was also produced in the following variants:
- RP-21M (CD-30TK or 830M)
- RP-21MA (CD-30M or 830MA)
In contrast to the RP-21M (MiG-21 PFM/SPS), the RP-21MA (MiG-21M/MF) works with the optical sight ASP-PF-21 or ASP-PFD-21 and is equipped with a more accurate rangefinder.
Most of the components, including the antenna, are fastened to a frame attached to the extendable nose cone. The controls, indicators, and display screen are in the cockpit.