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Unformatted text preview: 39 Antenna noise and links • In a practical application an antenna will be used to detect a specific planewave signal of interest, of, say, power density S s , in the presence of a random continuum dS ( θ, φ, f ) corresponding an some effective temperature T a . In that case, we obtain over a finite frequency band 1 Δ f containing S s , an average received power of P r = S s A ( θ s , φ s ) + Δ f dS ( θ, φ, f ) A ( θ, φ ) = S s A ( θ s , φ s ) + KT a Δ f, since Δ f dS ( θ, φ, f ) A ( θ, φ ) = Δ f 1 2 L ( θ, φ, f ) A ( θ, φ ) d Ω df = Δ f KT a λ 2 A ( θ, φ ) d Ω = KT a Δ f. • The second term of P r above is called noise power, or simply “noise”, while the first term represents the signal power, or simply the “signal”. • Since we want the “signaltonoise ratio” SNR as large as possible, we should select Δ f as small as allowed, but regrettably Δ f = 0 is not 1 A suitable Δ f is imposed by using an appropriate bandpass filter in cascade with the matched antenna termination....
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This note was uploaded on 09/27/2011 for the course ECE 450 taught by Professor Staff during the Fall '08 term at University of Illinois, Urbana Champaign.
 Fall '08
 Staff
 Electromagnet

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