Unformatted text preview: Quiz 2
ECE 816 Spring Quarter 2011
April 22th, 2011
A radar system measures backscattering at 0.5 GHz from a random medium. The radar
transmits 1 kW of power using a 5 m diameter parabolic transmitting antenna, and has
an aperture efficiency of 60% and an α illumination factor of 1.6. The random medium
exists in a thin layer between range distances of 4995 m and 5000 m from the radar,
and the radar antenna is directed toward the random medium.
The random medium is known to have:
a backscattering cross section per unit volume of ρ σ 1 10 per meter, a total scattering cross section per unit volume of ρ σ 3 10 per meter, and an absorption cross section per unit volume of ρ
Find the expected value of the power received. σ 4.9 10 per meter. Quiz 2
ECE 816 Spring Quarter 2011
April 22th, 2011
A radar system measures backscattering at 0.5 GHz from a random medium. The radar
transmits 1 kW of power using a 5 m diameter parabolic transmitting antenna, and has
an aperture efficiency of 60% and an α illumination factor of 1.6. The random medium
exists in a thin layer between range distances of 4995 m and 5000 m from the radar,
and the radar antenna is directed toward the random medium.
The random medium is known to have:
a backscattering cross section per unit volume of ρ σ 1 10 per meter, a total scattering cross section per unit volume of ρ σ 3 10 per meter, and an absorption cross section per unit volume of ρ σ 4.9 per meter. 10 Find the expected value of the power received. Solution: From the “narrow beam” approximation in page 8 of the lecture note, we have
P
P
where λ A 0.6 m, G
P
P Now approximate 2.855
4π 2.855 R 10 in integral as 10
D ρ λGθ e α 0.192 rad , we get D 1 0.192 0.192 and dR R 411 , θ 0.6 411 σ e dR e 10
R
. e dR
R dR 3.90. Final answer :
P 10 2.855 10 0.6 100 0.192 0.192 3.90 99.9 nWatts or 70.0 dB,watt. ...
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 Spring '11
 Johnson
 random medium

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