For a ground based or an airborne radar, when a first pulse is transmitted, a subsequent second pulse is restrained from transmitting until the reflected signal of the first pulse is returned to the radar. On the other hand, in space missions, the delay of a receiving signal to a transmission signal generally spans a few thousands microseconds due to long range observation. An efficient sampling can be achieved by transmitting a second pulse successively without waiting for the first returned signal. Consequently, the reflected signal of the first pulse is designed to be received between the n-th and (n+1)-th transmissions, and the second one is received between the (n+1)-th and (n+2)-th transmissions and so forth, where the integer n is typically set at 5 to 15 depending on operation.

In the GPM, a satellite is planned to carry a dual frequency radar system with frequencies of 13.6 GHz (Ku-band) and 35.5 GHz (Ka-band) to increase information on precipitation. Both the Ku- and Ka- band channels scan the beams in the cross-track direction to broaden observation areas. In an area of footprint overlapping, measurement is performed synchronously.

In this paper, several pulse patterns are designed for the GPM by adopting variable pulse repetition frequency (VPRF). To cope with large variance in range from a satellite, which is caused by the beam swing and the Earth oblateness, a systematic algorithm is proposed, increasing sampling rates. In addition, issues on hardware implementations and designs are also discussed.