Utilizing Symmetry of Planar Ultra-Wideband Antennas for Size Reduction and Enhanced Performance

With the increasingly new ultrawideband applications, antenna researchers face huge challenges in designing novel operational geometries. Monopole and quasi-monopole antennas are seen to be the most compact and easily incorporable solution for portable devices taking the advantages of printed circuit board techniques. Most antennas of such type have symmetrical structures. It is possible to attain wider operating bandwidths by meeting symmetry conditions while chopping the antenna into halves for a compact structure. However, there is no generalized way of applying such a technique. This paper addresses this issue by proposing a common feeding technique that can be applied to any antenna, which is miniaturized using its symmetrical structure. The proposed technique enables feeding the halved structure to achieve wider and better impedance matching than the reported full-size antennas. The theory of characteristic modes is applied to quasi-monopole structures to get an insight of the antennas-mechanism. The radiation patterns are also correlated with modal current distributions to understand the radiation characteristics of the modified structure. Finally, the method is implemented on some example antennas to illustrate its potential.