Question

9. (6 points) An antenna engineer is asked to design a X/2 dipole antenna to operate at 450 MHz. (a) Calculate the length of the antenna if it is located in free space. (b) Calculate the magnetic field intensity, H, at a distance of 400km, polar position 0 = 30 degrees and current I = 2A (c) What value of the current I is needed for the total radiated power to equal 100 mW. (d) Determine the length of the antenna if it is located under seawater (e = 81e0, = Ho, 0 =4 S/m)

Answer 1

Answex! Given hat length of antepn a isk/ foesueny 5 Pe450 H 150KloHz The fomula lenyth is 4ave eshere c i5 the velooty of P5 Poegueny 3 X108 450 x106 O66m The antenn a len gth is l &-0.33m

Given distan ce 4o oKm 400 xD e = 30 The propagation onstant , = 2x 0.66 B=9.52 Yad/ The foomula magnetic Aeld inten sity s Ce 5 52) (oom) (2x) (400K10 in 30 2 0.174o.98)

iven The fotal xadafed power 5 equ a to l0omw Nexthe total adialed Powes halp oale dipole 73 73 looKio axlooxio3 73 5a.3mA E-8160 The wave wloGty 5, ME

MX810 85 V 33.3 X o ms lenath anterhna is The wave 33.3X1o6 450xlo6 There Pose length of antenna 5, L-0.037