In the case of the obliquely-cut type, cut at the angle a,/'can be made as short as a. From this aperture, some of the plane waves are radiated upwards, and the equivalent plane wave source is not square but spreads infinitely in width as shown in Fig. 5. The field distribution is expressed by Eq. (4), most of the power being concentrated around the center of the reflector. So even a reflector with height h = f can catch about 82% of the power. For // = 2/, 3/, and 4/, the efficiency is as large as 91%, 94%, 96%, respectively (Fig. 6). This efficiency t? is derived from the ratio of the reflected power to the whole power. Using a variable t = y/lf, the reflected power from the parabolic reflector with height /t(=/to) is calculated as
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