A modified helical antenna having increased gain over that of a conventional axial mode helical antenna (200) without increasing the length of the antenna. The modified helical antenna (700) uses a conducting cylinder (702) placed around approximately the first two turn of the helix (716) of the antenna (700). The height of the conducting cylinder (702) should extend from a ground plane (712) to approximately 1.5 helical turns. Closely coupling the conducting cylinder (702) to the helix (716) increases the gain in the main beam (318) as energy in the side lobes (324, 326) decreases. This is true as the inside diameter of the conducting cylinder (702) approaches that of the helix (716) up to a cut-off point. For a particular application, optimization of the inside diameter (710) of the conducting cylinder (702) can be achieved empirically or through numerical analysis.
