Random phase processing for second trip echo

Second trip echoes can be a serious problem for applications that operate at a high PRF. Second trip echoes can appear separately, or can be overlaid on first trip echoes (second trip obscuration).

The random phase technique¹ separates the first and second trip echoes so that:

• In most cases, the second trip echo can be removed from the first trip, even in the case of overlapped first and second trip echoes. The benefit is a clean first trip display.
• The second trip echoes can be recovered and placed at their proper range at first trip/second trip signal ratios of up to 40 dB difference for overlapped echoes. Because of the wide dynamic range of weather echoes, this power limit is sometimes exceeded.

The technique requires that the phase of each pulse be random. Digital phase correction is applied in the processor for the first and second trips. The adaptive filter removes the echo of the other trip to increase the SNR.

Magnetron radars have a naturally random phase. For Klystron radars, a digitally controlled precision IF phase shifter is required. RVP10 provides an 8-bit RS422 output for the phase shifter.