3. Results of Computer Simulation The computer program has been used to generate data for the system study. Figure 3 shows the overall efficiency as a function of frequency for a transmission range of 50 km. The antenna sizes are a 10 m radius for the transmitting antenna and a 20 m radius for the receiving rectenna. The simulation assumed that the DC to RF conversion efficiency falls off linearly from 85% at 1 GHz to 80% at 35 GHz, and the RF to DC efficiency drops from 80% at 1 GHz to 75% at 35 GHz. The antenna size was selected such that the system operates in the far field region. From Fig. 3, it can be seen that at the reference system point, of 35 GHz and 50 km, the overall system efficiency is approximately 50%. Slightly higher efficiencies can be attained by increasing the value of U] in Equation (4) to increase the collection efficiency. To operate at the same frequency, this would require a larger antenna or a shorter transmission range. Figure 4 shows the efficiency versus transmission range at the operating frequency of 35 GHz. It can be seen that the efficiency drops rapidly when the range exceeds 50 km. Longer transmission distance or higher efficiencies require larger transmitting antennas as shown in Fig. 5.
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