Wide-band sleeve-cage and sleeve-helical antennas

A sleeve-cage monopole has parasitic wire elements that form a sleeve around the driven cage antenna. Appropriate placement and dimensions of the wire parasites lead to bandwidth enhancement. Genetic algorithms and an integral equation solver are employed to determine the position and lengths of the parasitic wires in order to minimize voltage standing wave ratio (VSWR) over a band. The cage is replaced by a normal-mode quadrifilar helix for height reduction and the resulting structure is referred to as a sleeve helix. Measured VSWR and input impedance data are in good agreement with computed data. A fabricated sleeve-cage monopole has a bandwidth ratio of 4.4:1 and a sleeve helix has a bandwidth ratio of 3.5:1 for measured VSWR less than 3.5.