coherent vs. noncoherent (incoherent)

1. Summation
√ coherent summation : The relative phase of each term is included in the sum.
√ noncoherent summation : Only the magnitude of each term are summed.

2. Field

The field u(r,t) is a random function of position r and time t. Therefore we can write u as a sum of the average field <u> and the fluctuating field u_f :

 

u(r,t) = <u(r,t)> + u_f(r,t),

<u_f(r,t)> = 0

 

where the angle brackets represent the ensemble average.

 

√ coherent field : average field <u>

√ incoherent field : fluctuating field u_f

√ coherent intensity : square of the magnitude of the coherent field I_c=|<u>|²

√ incoherent intensity : average of the square of the magnitude of the incoherent field I_i =<|u_f|²>

 

The sum of I_c and I_i is the average intensity <I> :

<I>=<|u|²>= I_c+ I_i

 

[ intensity의 정의를 봤을 때 RCS에 비례하는 값이므로

 

average RCS = coherent RCS + incoherent RCS

 

(즉, incoherent RCS가 커지면 RCS계산 시 고려해야한다.)

 

 

particle의 random distribution에 의해 산란된 파는 incoherent field일 것이고 coherent field는 없을 것이다.

medium이 완벽하게 랜덤하지 않으면 산란파는 some coherent field를 포함하게 된다.

line-of-sight propagation problem에서 송신기로부터 짧은 거리에서는 거의 coherent field만 존재한다. 거리가 멀어지면 field는 덜 coherent하게 되고 더욱 incoherent하게 된다.