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The rectangular aperture has length l sub x and width l sub y. The aperture is excited by a uniform electric field distribution. The radiation pattern is drawn at a point, Q equals (R, theta) in the x-z plane. The point is located, at a distance of R from the aperture which makes an angle of theta with the z-axis.

The radiation pattern is drawn in the x-z plane. The x-axis represents intermediate variable gamma equals left parenthesis start fraction l sub x over lambda end fraction right parenthesis sine theta from negative 3 to 3. The z-axis represents normalized radiation intensity F of theta at nonzero integer value gamma, in d B from negative 30 to 0. The main lobe and four side lobes are drawn in the graph. The main lobe represents the maximum normalized radiation intensity. The normalized radiation intensity is maximum along the boresight direction where theta equals 0. The half-power beam width beta sub start expression x z end expression of the radiation intensity is negative 3 d B. The first side lobe level labeled, negative 13.2 d B.