Radar Basics

Plot Combiner

The plot combiner combines primary and secondary radar plots. In this respect it has to be distinguished from the plot processor which combines only primary plots (amongst other functions).

If primary and secondary plots combine directly, then it is a good indication of the validity of the plots. It is therefore normal practice to forward combined plots directly for data transmission to the user. The plot combiner can then be designed to investigate un-combined plots in more detail.

primary and
secondary
combination

angle and
vehicle
filter

scan-to-scan
correlator

formatting
and
transmission

interface to
engineering
monitor

correlated plots

uncorrelated plots

SSR plots

primary plots

Figure 1: Block diagram of a plot combiner

It is then possible to carry out a refined angel and plot analysis. The plot density approach for the elimination of angels can be applied but based on a reduced population of plots (i.e. after plots which combine with the SSR have been removed). This improves the quality of the plot density filtering process. Plots which have low energy and exceed a prescribed density in a given sector are eliminated.

The plot combiner often incorporates a scan to scan correlator to act as final mechanism to remove false or second time around returns. Typically this involves a three point correlator (i.e. data is correlated over three scans) to eliminate false plots. In this approach the plot data is transmitted with unmodified plot positions.