Abstract: In a PPI display type radar system wherein a sector shaped unit scanning surface is established in a scanning plane and a unit scanning surface is shifted progressively in the radial and circumferential directions to seach the received pattern for judging a target. The received pattern is identified by dividing the unit scanning surface into a plurality of annular sections derived from a plurality of concentric circles. The scanning unit for scanning surfaces having approximately the same area over the entire scanning surface is designed in such a manner that the ratio (percentage of extraction) of a number of sampled scanning beams to the number of actual scanning beams is a maximum when scanning an annular section which is located most remotely from the center. The percentage of extraction is gradually decreased toward the center so that the percentage of extraction becomes a minimum 1/n (where n is an integer) when scanning an annular section closest to the center.