Paraboloid antennas

Figure 13.20 shows several practical aperture antennas. Figure 13.20(a) to Figure 13.20(d) pertain to horn types, whereas Fig. 13.20(e) is the paraboloidal antenna, which is popular with satellite television receiving systems for home use. Shown in Fig. 13.20(a) to Fig. 13.20(c) is a TEio electric field distribution. The terminology TEio implies a transverse electric field, as shown, with one-half of a cosine variation in one direction and no variation in the other direction, hence the subscript 10. In Fig. 13.20(a), it is called a... 

The paraboloidal antenna derives its name from the paraboloidal shape of the reflecting metallic surface. A source is placed at the feed point, like a horn, and the reflected wave flluminates the circular aperture. For the simplistic case of a uniform field distribution over the circular aperture, the useful parameters for this case are given in Table 13.5. 

Passivation of the surface of n-GaAs is possible with thin films of plasma-polymerized thiophene [837]. A composition containing an electrically nonconductive polymer matrix and POT can also be used in paraboloid antennas, reflectors for radar, heating systems, photoelectric devices, and electric circuits and apparatus [779]. PTs are used for manufacturing a nonlinear two-terminal device. This deviee is not asymmetrical, gives stable electrical characteristics, and is useful as a display device [838, 839], Liquid crystal display devices contain an electrically conductive polymer, e.g., PT or POT as oriented film [840-842]. PTs are also used for the production of color filters for liquid crystal displays [843]. 

The quantity h is the Bessel function of the first kind of order unity. Although a uniform distribution is not realistic, it shows the general characteristics of a paraboloidal reflector antenna. For more accuracy, it is usually assumed that there is a parabohc taper (Stutzman and Thiele, 1981) to the field distribution with the maximum being at the center and tapering to smaller values at the edge of the circular aperture. The value of the field at the edges is a function of the beamwidth of the feed antenna. 

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