Question

Q: (a) The antenna of a 38 cm radius dish used as a satellite receiver in the Ka-band is 25.5 GHz - It operates in the 31.5 GHz frequency band. Find out where the far-field region begins for this antenna. (b) A radar operating in monostatic configuration broadcasts at 10KW power and the receiving power of this radar sensitivity is 12 pW. The gain of the radar antenna at 12 GHz in the maximum radiation direction is 16 dB. This radar, At what far distance can the radar detect a target with a cross section 8m??

Answer 1

Qa) Given rodius of antenna (X) =38 cm Diameter CD = 20 = 76cm frequency of operation (1) = 31.5GHZ the relation, caf) 3x100 = 31.5x100 (2) in cms a=0.95cm Far field region begins at a distance (R)= ampa R=,2x67622 0.95 R=12160cm R=121.6m power Cle :lokw b) Given input minimum detectable signal, Pmin = 12 pul frequency of operation (F) = 12GHZ Gain indb = 16 G = lolog G=16 G: 1066 -34.811 Target cross section area(o) = 8m2 range equation, the range CR) is given by By Radar Hora2 1/4 RE ( en min a = 3x108 16x109 4 : 2.5cm 14 = 0.025m RE Rof 10x10°x(39.811)+x8 *(0.025)2 (47)3 * 12x152

(39.811)** 8x (0:025) = (CET 174 * 10 roseyo (40)3 x12 (3-3268101214 R 1350.65m R=1.351km let Derivation of Raxtar Range equation. transmitting antenna radiates a power 'pt throughan an antenna of gain e, the power density on target is Poll where PG ATTR2 R is the range to be determined The total power scattered by the target Ps - Pall The power density of the scattered power back at the receiving antenna is Pd2 PGO GUR22 PAW ATTE Received power Pr = Pd2xAe ,Ae = effective area of antenna Pt Go Ae Pr A et XG 411 (41722) . Pr - P+G²r2² (40139 R7 Prev22 14 ... Romax ( (4m³ Pmin
I hope everything is clear.