The design and analysis of miniaturized planar monopoles

The design and analysis of miniaturized planar monopoles is presented for bow-tie and reverse bow-tie monopoles. A genetic algorithm (GA) approach is used to generate reduced size planar monopoles as small as 0.12λ. Through an analysis of the GA designs, design guidelines for antenna miniaturization are deduced. The resonant frequency of the antenna can be reduced by making the element edge more ragged, and further reduced by placing long notches along the sides of the element. These notches improve the impedance matching of small antennas by increasing the radiation resistance and adding inductive reactance to tune the antenna. These techniques do not significantly reduce the high radiation efficiency characteristic of the planar monopole. A numerical analysis comparing the NEC and WIPL-D simulation results to measurements shows that WIPL-D can predict the performance of the GA designs more accurately.