Dual pattern antenna for portable communications devices

A dual pattern antenna (FIG. 1, 20) functions as a bi-filar or quadrifilar helical antenna depending of the location of the feed element (FIG. 4, 120). When the feed element (120), within the hollow dielectric tube (FIG. 4, 140), is used to feed the antenna (20) at a distal end portion (FIG. 4, 142) the antenna functions as a bi-filar helical antenna and exhibits a relatively omnidirectional radiation pattern (FIG. 3, 70). When the feed element is used to feed the antenna at a proximal end portion (FIG. 4, 141), the antenna (20) functions as a quadrifilar helical antenna having a radiation pattern which exhibits desirable gain properties in the area above the antenna (FIG. 4, 40). The use of capacitive coupling allows the feed element (120) to slide within the hollow dielectric tube (140) so that the pattern of the antenna can be quickly changed, thus making the antenna well-suited for portable communications devices such as satellite cellular telephones.