Branch number and height effects on the multi-branch dual-band monopole antenna

Dual-band antennas with one feed have some advantages over multi-feed antennas and were proposed for cellular applications. These antennas can also be used for dual-band ISM applications. The antenna, proposed by Liu (see IEEE Antennas and Propagation Society International Symposium and URSI Radio Science Meeting Proceedings, Orlando, Florida, vol.3, p.1578-81, 1999) consists of a monopole and one or more branches as shown. The branches have an equal length and are circumferentially connected to the monopole a short distance away from the monopole feed point. The branches are parallel to and a small distance away from the monopole. In this design, the center monopole, roughly speaking, works for the low band, while the branches work for the high band. We study the effects of the number of branches and the branch height on the antenna performance. The method of moments is used to find the input impedance of the antenna, while the genetic algorithm is used for searching the resonating monopole and branch lengths for a given number of branches, branch height and the distance between the monopole and the branches.