The development of a novel ultra-wideband (UWB) antenna is reported. The antenna, based on a microstrip transmission line, forms a quasi-horn and possesses an extremely wide bandwidth of many decades with relatively high gain. It does not require a balun or transition at the input port and is inherently matched. Two such antennas, when used as transmit and receive elements, have a high isolation between them, even when they are placed next to each other and no absorbing material is used. Measured results show a return loss of better than 10 dB from 0.2 to more than 20 GHz, gain from 7.5 dBi at 2.6 GHz to 17.6 dBi at 18 GHz, and good radiation patterns. Although not measured, the antenna should also perform well at much higher frequencies than 18 GHz. With proper size and shape, the antenna can achieve a relatively flat gain response over an extremely wide bandwidth. Calculated and measured radiation patterns also agree reasonably well.
