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The outputs of a vertical monopole and two mutually perpendicular slots in a horizontal plane can be properly combined to yield a steerable cardioid-shaped pattern for vertically polarized waves. The required weighting factors for placing the pattern null in any desired direction are presented in graphical form. The shape and the half-power beamwidth of the steerable pattern are examined. This combination antenna unit offers important advantages in direction finding and other applications, especially at microwave frequencies.
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Itoh et al. (1972) studied this question.
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