change on neutral particle concentration as was the condition in the "F" region. As the ionosphere drifts out of the heated region, the temperature will almost instantaneously decrease to normal (within a few milliseconds) but the time required for the density to return to normal will be longer (10-to 20-minutes). There should be no change in solar ray absorption by the ionosphere since the neutral particles rather than the electrons and ions, absorb solar radiation. As mentioned previously, the density of the neutral particles remains constant in the hole region. The main problems associated with nonlinear heating and hole creation are possible disruptions in HF, VHF communication systems, and VLF navigation systems due to additional RFI and multipath degradations. The power density levels at which nonlinear effects in the ionosphere begin to occur have not been measured at S-band frequencies and can only be speculated upon. There are a number of possible ground-based tests which can provide information on the nonlinear effects and determine at what power levels these effects actually occur. However, for the model configuration the 23mw/cm2 was taken as the upper bound for the power density level and consequently, was a factor in selecting 5GW as the output DC power. IV.A.2(c) NOMINAL EFFICIENCIES FOR SYSTEM SIZING After the DC output power at the rectenna and the transmit array size are selected, then representative values for efficiencies for each of the subsystems in the SPS are determined. The nominal system efficiency from the RF radiated output of the transmit antenna to the collected DC power at the rectenna is specified to be 76%. Using this efficiency and the 5GW DC output power, the RF power radiated from the transmit antenna is 6.5GW. The microwave system performance curves given in this report are all based upon 6.5GW radiated RF power. The nominal efficiencies for the microwave subsystems and their associated power levels are given in Figure IV.A.2-6. The total microwave system efficiency (nominal) from the DC output of the rotary joint to the collected DC output of the rectenna is 63%. Details on the efficiency tolerances for the total SPS system are given later in the text. IV.A. (d) FREQUENCY SELECTION A frequency of 2.45 GHz was chosen for the JSC system, which is the same as that used in the Raytheon/Lewis studies (ref. 1,2). The 2.45 GHz is at the center of a 100 MHz band reserved for government and non-government indistrial, scientific, and medical use. This band has the advantage in that any radio communication services operating within the 2450 + 50 MHz limits must accept any harmful interference that may be experienced from the operation of industrial, scientific and medical equipment. That is, as long as the microwave energy is confined to this frequency band, there will be no interference problems. Other advantages of this frequency include low atmospheric attenuation even in the presence
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