Hybrid lumped‐distributed loading design approach to wideband dual‐mode resonant monopole antennas

A dual‐mode resonant monopole antenna using lumped and distributed loading is proposed. The third‐order resonant mode within a monopole antenna is excited by a pair of stubs, so as wideband, dual‐mode resonant characteristic can be attained. Two lumped inductors are loaded in a certain position of the paired stubs, so as the occupied space can be shrunk to yield compact antenna size. As is experimentally validated, the hybrid lumped‐distributed loading scheme can effectively tune the third‐order resonant mode downward, with the fundamental resonant mode rarely changed. Compared to the pure distributed, stub‐loading scheme, the length of the perturbed stub can be reduced by 65%, while the impedance bandwidth is basically unchanged. The resultant dual‐mode monopole antenna can operate in a wide frequency range from 3.66 to 5.80 GHz (i.e., fractional bandwidth of 45.2%) with an omnidirectional azimuth radiation pattern as evidently validated in experiment. The advanced design approach can maintain the intrinsic linear profile of resonant monopole antennas and exhibit low configuration complexity. It may be suitable for multi‐mode resonant antennas development in space‐limited portable terminals.