Broadband Planar Monopole Antennas

Monopole antennas have several advantages but for their narrow bandwidth. Broadband planar monopole antennas have all the advantages of the monopole in terms of their cost, and ease of fabrication besides, yielding very large bandwidths. For many applications large bandwidth is required. Recently, many techniques to tailor and optimize the impedance BW of these antennas have been investigated. These include the use of bevels, slots and shorting posts. These antennas are becoming popular, and have been proposed for modern and future wideband wireless applications. The radiation performance is also shown to be acceptable over a wide range of frequency. Various planar configurations such as circular, triangular, rectangular and annular ring monopoles have been studied. Circular wire mesh monopole with peripheral strip and annular ring monopole give similar performance as compared to solid disc monopole and have light weight and less wind loading. Combinations of shorting pin and optimization of the feed point location can achieve very compact configurations. Also these antennas can provide band-notching characteristics. These antennas have been reported to provide multi band characteristics too. More recently, it has been shown that, although the square monopole (SM) provides smaller BW than the circular monopole (CM), its radiation pattern suffers less degradation within the impedance BW. Investigations on planar monopoles of different geometrical shapes, such as the ellipse, rectangle, bow tie, diamond and trapezoid have since been conducted. Until now, the achieved impedance BW for VSWR = 2:1 have usually reached about 10:1 for an elliptical planar monopole and 80% for the other planar monopoles.