Let D = the diameter of the ARA. Unless the transmission lines follow very circuitous routes, []. For most transmission lines, [] If [] — L — — 10^3 m, This is certainly small enough to justify the approximation where [] is the radial velocity of the kth element at time []. Similarly, From (All) we see that the phase difference, [] , between the signals arriving at r = 0 at time t consists of two terms.
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