LEARNING EVENT 13: CASSEGRAINIAN ANTENNA WITH POLYROD FEED
The polyrod feed system can also be used in conjunction with the cassegrainian antenna to obtain a highly
efficient low-noise antenna system as shown in Figure 2-12. The polyrod feed guides the electromagnetic
energy to the hyperboloid subreflector. The polyrod's dielectric material is tapered toward the waveguide horn
so that the dielectric material can provide a uniform illumination of the hyperboloid subreflector. By using the
combined polyrod feed and the cassegrainian antenna instead of the conventional cassegrainian feed and
antenna system, the overall antenna size can be reduced by approximately 40 percent.
Figure 2-12. Cassegrainian antenna with polyrod feed.
SECTION III. MODULATOR ANALYSIS
LEARNING EVENT 14: MODULATORS
The primary purpose of the modulator is to convert a baseband input from the terminal equipment to an angle-
modulated signal. Angle modulation is a modulation category that includes both frequency modulation and
phase modulation. The baseband input usually consists of FDM signals from the teletypewriter/voice
multiplexing equipment.
SS0031
2-12
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