Random phase second trip processing

Second trip echoes can be a serious problem for applications when the radar is operated at high PRF (for example, >500 Hz). Second trip echoes are caused by the range aliasing of targets. They appear as false echoes on the display, usually elongated in the radial direction. On Klystron systems they have valid Doppler velocities. On magnetron systems, the Doppler velocities are not valid, but the noise from the 2nd trip echoes can obscure valid first trip velocity information.

RVP10 has optional random phase processing for the filtering and recovery of second trip echoes. While details of the technique are proprietary to Vaisala, we describe the general principle and the configuration options to optimize the algorithm performance.

The information that is used to separate the first and second trip echoes is the phase.

Magnetron radars

For a magnetron radar, the phase of each pulse is different. When 1st and 2nd trip echoes are received simultaneously, the phase of the first trip return is different from the phase of the second trip return. RVP10 measures the phase of the transmitted pulse and the phase locking is done digitally.

Klystron radars

For a Klystron radar, the phase is controlled by RVP10 through a digital phase shifter that is precisely calibrated. Typically, the Klystron Stalo is phase shifted so that each transmit pulse has a different phase.

The sequencing is controlled by RVP10.