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

Advances in wireless communications technology are currently developing very rapidly. The 900 MHz and 2.4 GHz ISM bands are widely used for a variety of applications. As an example, many laptop computers use the 900 MHz band for wireless printer and modem connections and the 2.4 GHz band for wireless LAN and Bluetooth applications. The 1.8 GHz PCS band is also under consideration for data services. As a result, the demand for a antenna operating at three bands is increasing. 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. We extend the results of the dual-band 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, July 1999, Proceedings of the XXVIth General Assembly of the International Union of Radio Science, Toronto, Canada, p.61, August 1999, and IEEE Antennas and Propagation Society International Symposium and URSI Radio Science Meeting Proceedings, Salt Lake City, Utah, vol.3, p.1302-1305, July 2000) to tri-band applications. The antenna proposed here consists of a monopole and two or four branches as shown. The branches 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. The branches on the same band have the same length. In this design, the center monopole, roughly speaking, works for the 900 MHz band, while the branches work for the 1.8 and 2.4 GHz bands.