A frequently used planar array consists of a family of rectangular waveguides placed side by side so that neighbors share a common narrow wall. Coupling to the various waveguides in the array is often accomplished by running another waveguide underneath the array and crosswise to it, such that there is a sharing of the broad wall. The author shows a typical junction between the main line (feeding) waveguide and the branch line (array) waveguides. In this illustration, the coupling slot is centered, inclined in the common wall section, and the radiating slot is essentially a shunt element. Short circuits are placed /spl lambda//sub g//4 beyond the first and last radiating slots so as to terminate the branch line waveguide properly. On the other hand, since the tilted coupling slot is a series element, short circuits are placed /spl lambda//sub g//2 beyond the first and last coupling slots so as to terminate the feed line waveguide properly. Folded short circuits are often used in the feed line waveguide due to the limitation of available space. Sometimes the folded short is combined with a tapered waveguide section to save more space. The motivation of creating new a L-shaped series/series coupling slot is to remove the /spl lambda//sub g//2 short circuit (in other words, folded short) in the feed line waveguide.
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