Three-dimensional folded antenna with ultra-wideband performance, directional radiation and compact size

A compact ultra-wideband (UWB) antenna with directional radiation is presented. The antenna has a low profile and does not need a large ground for its performance. The antenna is based on using a three-dimensional folded structure that is modified using semi-circular slots on bowtie-shaped elements. The antenna´s mechanism, its design guidelines and its optimisation are described thoroughly. A prototype of the antenna is fabricated and measured for performance verification. The prototype shows 77% fractional bandwidth (centred at 2 GHz) based on 10 dB return loss reference. The equivalent overall size of the prototype is (λ_eff/3) × (λ_eff/4) × 0.07λ_eff (λ_eff = effective wavelength at the lowest resonant frequency), which proves the compactness of the antenna. The antenna shows unidirectional radiation pattern with around 15 dB front-to-back ratio, -20 dB cross-polarisation in the two principle planes and around 5 dBi gain. The antenna is prescribed for compact UWB applications that use the low 1-3 GHz frequency band.