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1. An antenna, comprising: a plurality of stages, each stage comprising either one section or two or more adjacent sections of slotted coaxial antenna arranged in phase groups along a central vertical axis; and for each stage, an exterior feedline running parallel to the central vertical axis and radially exterior to the slotted outer layer of each section, the exterior feedline comprising a dummy portion, wherein: each section belongs to only one stage; the feedlines are space equally radially around the central vertical axis; each section comprises a cylindrical inner radiating layer with a first radius from the central vertical axis and a first height along the central vertical axis; each section comprises a cylindrical outer slotted layer with a second radius from the central vertical axis and a second height along the central vertical axis, the second radius being greater than the first radius; each outer slotted layer comprising an array of vertical slots, the array comprising a number of slots vertically and a number of slots radially, such that the number of slots per section is the product of the number of slots vertically and the number of slots radially; each phase group comprises one or more adjacent sections arranged along the central vertical axis, wherein each section belongs to only one phase group; and the antenna is driven such that a transmission phase of each phase group is separated from a transmission phase of any adjacent phase group by between 30 and 60 degrees.
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