b. The Transmitting Antenna The transmitting antenna has a diameter of 1000 meters. Each square meter of surface is fed by one Amplitron. The noise radiated from this area can be considered as coherent, and at the design frequency the area has a gain of where K has a value which varies with frequency and has a peak value of about 0.83 at the design frequency and is lower the farther away one goes from 3300 MHz. This is due to many factors, including a decrease in efficiency of slot coupling, an increase in standing wave ratio, and other factors which are inherent in the antenna design. A typical curve of G versus frequency is shown in Figure 77. This curve can be approximated by the expression c. The Filtering System As in the case of the Amplitron, the filtering system also consists of two separate cases: Case (a), which is realizable at present, and Case (b), which is designated as the design goal or that which is achievable in the future as the result of further study. Case (a) is divided into two parts, a2 and a4, which designate a two-section and a four-section filter, respectively. Each filter section has a half 3 dB width of 100 MHz from the fundamental. It follows the law of -6 dB per octave (of 100 MHz) per section.* Figure 78 shows a straight line curve which is a good representation of the filter performance. Figure 78 is really the resultant noise power/MHz input to the transmitting antenna, considering both the Amplitron design and the external filter design.
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