Foldover

Range Foldover and Earth s Rotation 3.1 Range Foldover Phenomenon... 

Total Range Foldover. Radar transmits pulses every Tr seconds and for high PRF situations, following (24), the distance Ar between range ambiguities on the ground (distance between consecutive pulse... 

To compute the total number of range foldovers for the entire range, we can make use of Fig. 16. In Fig. 16, the point of interest (D) is within the mainbeam, and the return of the radar pulse from there represents the main clutter. However because of the 2-D antenna pattern, previous pulse returns returning from adjacent range ambiguities points — both... 

As we have seen in Section 3.1 the range foldover phenomenon — clutter returns that correspond to previous radar pulses — contributes to the SBR clutter. Another important phenomenon that affects the... 

SINR With/Without Earth s Rotation and Range Foldover... 

No range foldover, no earth s rotation (ideal case) ... 

Figure 22. SINR loss with/without range foldover and earth s rotation as a function of range and Doppler...

Range foldover present, earth s rotation present. 

Fig. 22 shows the SINR loss for the four cases above as a function of range and Doppler for an SBR located at height 506 km above the ground. The PRF is 500 Hz and 6az = 90°. The output is normalized with respect to the noise only case. The performance is significantly degraded when both range foldover and earth s rotation are present at the same time. 

Fig. 23 shows the SINR loss for two different ranges. The SINR loss is on the order of 20-40 dB when both range foldover and earth s rotation are present, depending on the actual range. The performance in terms of clutter nulling is inferior when these two effects are present. 

Thus, having both range foldover and earth s rotation at the same time results in unacceptable performance degradation as shown in Fig. 23 whereas when either one is present separately, the effect can be rectified. 

Waveform diversity can be used on the sequence of transmitted radar pulses to realize the above goal by suppressing the range foldover returns. In ordinary practice, a set of identical pulses are transmitted. To suppress returns due to range foldover, for example, individual pulses... 

The foldover design for the Plackett-Burman design in Table 14.9. 

An 11-factor Plackett-Burman design with foldover. 

Hint row 8 of this design and row 8 of the saturated fractional factorial design in Table 14.7 suggest that the reflection or foldover must be carried out first. Repetitions of switching one row with another, and switching one column with another, will eventually yield the desired result. Retain the identities of the rows and columns. 

Linear effects 3-8 Prediction over limited region. Estimate linear effects and interactions only. 2" Full and fractional factorial, PB with foldover... 

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