Ultra-wideband quasi-circular monopole antennas with rectangular and trapezoidal grounds

Two planar quasi-circular monopole antennas with rectangular and trapezoidal grounds are presented. The impedance bandwidths of the two antennas, defined by measured return loss better than 10 dB, are from 1.3 to 18.4 GHz and from 1.1 to 13.5 GHz, respectively. Both numerical and experimental results show that the proposed antenna with trapezoidal ground has significantly improved radiation performance, compared with the one with rectangular ground. Parameters and design considerations of the trapezoidal ground are discussed in detail. These novel monopole antennas have very wide impedance bandwidth, compact size and low fabrication cost, which are suitable for various broadband applications.