New display for frequency-modulated continuous-wave radars

In the system proposed, the transmission consists of an unmodulated carrier, c.w. with negative linear f.m. and c.w. with positive f.m. The display in baaed on the range-velocity plane and the position of a target in thin plane is identified with the triple intersection of loci derived from the returns from the three types of transmission, denoted A, B and C respectively. The locus of an A return is a vertical line displaced from the range axis by an amount corresponding to the Doppler frequency shift. A type B response has as locus a line with a negative slope and a type C response gives a line with a positive slope. By superposing the three rasters the target-identifying triple intersections are obtained. The signals are obtained from three filter banks, one for each mode. The C. R.t, scan is synchronized with the filter sampling. With the simple system described, triple intersection is possible only over a small portion of the range-velocity plane if the number of filters in each bank is limited. It in shown that maximum coverage is obtained if the B and C banks each have 50% more filters than the A bank. The system thus gives sector coverage, and the sector can be moved anywhere in the plane by means of variable-frequency heterodyning oscillators for range and velocity. Magnified sector displays can be obtained by means of fast sweeps triggered by tracking markers. Among future developments mentioned are the suppression of excess lines, leaving only the triple intersections, and automatic readout of target co-ordinates, with adjustable persistence enabling the co-ordinate point to be displayed as a track.