lower half of the waveguide is cut away by a length L( = 2«cota) as shown in Fig. 1(a) (1), radiation occurs in the range of Tr/2<i^<37r/2 shown in Fig. 2. If it is cut obliquely at the angle a as shown in Fig. 1(b), most of the radiation is directed into the lower-half. After reflection from the parabolic cylinder reflector whose focal axis coinsides with the waveguide axis, the electric field of each plane wave is oriented in the direction of y-axis of Figs. 2 and 3. Treated by the geometrical optics, the beam width of the stair-cut type in the E-plane is 4/and that in the H-plane is 4</cosa, where /is the focal distance of the parabolic cylinder in Fig. 2. For all of the plane waves from the aperture to be reflected by the parabolic reflector, the height of the reflector It should be equal to/ or higher. For the whole beam from the parabola not to be interrupted by the waveguide,/ should be larger than 1.5a. The field distribution in the H-plane is uniform. The E-plane field distribution is obtained as follows: The radiation power in unit angle is constant and power in Ay at A of Fig. 2 on the reflector (y=2/sint///( 1 - cost//)) is proportional to Ai/z/Ay, so that |£'(y)2<x l/|dy/dt//| and The radiation from this antenna is regarded equivalent to that from a square plane wave source (4/ X 2acosa) having the field distribution as Eq. (4) (see Fig. 4).
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