Answer:
a) 915 m
b) 0.15 W/[tex]m^{2}[/tex]
Explanation:
solution:
a) The wavelength of the microwaves electromagnetic wave is:
λ=[tex]\frac{c}{f}[/tex]=[tex]\frac{3*10^{8} }{12*10^{9}}[/tex]=0.025 m
the circular radar antenna acts like a circular aperture of diameter D will have a bright central maximum of diameter:
w=2.44λL/D
so at 30 km screen:
w=2.44λL/w
=2.44*0.025*30*10^3/2
=915 m
b)
The area of a beam at 30 km is:
A=[tex]\pi r^{2}[/tex]=[tex]\pi (\frac{w}{2} )^2[/tex]=[tex]\pi (\frac{915}{2} )^2[/tex]=[tex]657*10^{3} m^{2}[/tex]
the average microwave intensity is equal to the ratio of the power of the antenna and area of the beam:
I=P/A
So at 30 km:
I=100*10^3/657*10^3
=0.15 W/[tex]m^{2}[/tex]
