where PD = d.c. power delivered from rectenna, PT = antenna transmit power, RT = antenna radius, Rg = rectenna radius, A, = 9.6 GW mills/kWh, K2 = 22.05 mills/kWh, K3 = 174.4 GW mills/km2 kWh, K4 = 1.31 GW mills/km2kWh. Equation 3 may be used with an optimization procedure to produce cost-efficient microwave systems constrained to preselected environmental limits. ANTENNA THEORY The SPS microwave beam characteristics are found theoretically using the Fourier transform relation between the antenna electric field and the resulting E-field pattern in the Fraunhofer region. The SPS antenna may be considered a continuous, circular aperture with near-uniform phasing, beaming energy to a circular rectenna as shown in Fig. 2. The relationship between the antenna and ground electric fields is the Fourier-Bessel (Hankel) transform and the associated power densities may be stated (6):
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