Handbook of Antenna Technologies
The focus of UWB antenna research activity has matured in recent years and currently mainly concentrates on applications such as biomedicine and security. Early UWB antenna designs were driven by the FCC allocation of spectrum in 2002 and focussed on obtaining wide impedance bandwidths with reasonable group delay characteristics. Many of these were simple planar monopoles antennas with canonical geometries. The emergence of new applications channelled the emphasis towards miniaturisation and integration into devices. This required optimisation of the antenna geometries to ensure that good system performance is achieved from the integrated antenna. Many optimisation techniques are available including the spline technique to generate the outline of the antenna element and ground plane. Simple methods based on genetic algorithms are employed and evolutionary algorithms which are capable of optimising for multiple goals are beneficial when multiple antenna parameters are simultaneously investigated. These techniques have proven advantageous especially when time-domain performance is critical and provide solutions for both single-ended and differential feed arrangements. The main applications using UWB channels in the 3.1 GHz −10.6 GHz spectrum are localization and tracking applications, mainly employing impulse radio UWB imaging, and generally using linear polarization. However circularly-polarized UWB antennas have been developed, both directional and omnidirectional and are being investigated across various systems.