On the Fundamental Limitations of Ultra-Wideband Antennas

An electrodynamic limitation on the characteristics of antennas with a semi-infinite range as the limiting case of ultra-wideband (UWB) antennas is found. This limitation relates the directivity, the input reflection coefficient, the lowest operating frequency, and the overall size of the antenna and takes into account its geometric shape. An expression for estimating the lowest operating frequency of antennas with a given size and shape is obtained. Expressions for estimating the minimum achievable size and lowest operating frequency of rectangular printed UWB antennas with linear polarization are derived.