2.9. In target-search ground-mapping radars it is desirable to have echo power received from a target, of constant cross section, to be independent of its range. For one such application, the desirable radiation intensity of the antenna is given by U(0, 0) = 0.342 csc(0) 0° ≤ 0 < 20° 20° 0 < 60° 60° ≤ 0 ≤ 180° 0° ≤ ≤360° 0 Find the directivity (in dB) using the exact formula.