where r=-n-RaR/AD - wave parameter, Rr - rectenna radius. The parameter t determines the rectenna radius in the u-coordinate: when r=Rr - u=2r. The coefficients Cnm can only be calculated numerically. The peak power density at the rectenna can be determined to be: The Maximum Distance Between the Antennas Using eq.(10) one can show that at the maximum distance D = Dmax the additional phase distribution is a constant function: <pa(p) = const or yn=const, n= 1...N. This statement is evident, because in this case the microwave beam has the minimum angular size - the quadratic phase distribution provides beam focusing at the rectenna centre. The additional phase distribution can only increase the beam angular size - it is necessary when the antennas are closer together. This statement gives a starting point: if one specifies amplitude distribution (coefficients z„), antenna and rectenna radii (Ra and Rr), wavelength (A), maximum distance between antennae (Dmax) and takes into account that yn=const, n=l...N, one can calculate all the systems characteristics at the maximum distance (see (1)-(13))- The Minimum Distance Between the Antennas When antennas are coming together (D < Dmax), the additional phase distribution must be maintained to obtain the desired value of the power received (Pr(Dmax)) and the peak power density at the rectenna (prmax(Dmax)). The coefficients yn must satisfy the following equations:
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