Compact Dual-Polarized Filtering Dipole Antenna by Using Asymmetric Parasitic Elements

This article proposes a novel, simple design scheme for filtering dipole antennas using asymmetric parasitic elements. Traditionally, filtering dipole antenna uses a parasitic component to generate a single reflection coefficient zero and one radiation null or exploit the high-order mode of parasitic element for more reflection coefficient zeros and radiation nulls. Yet for the first time, the proposed filtering dipole antenna can simultaneously introduce two reflection coefficients zeros and two radiation nulls with only one simple parasitic element. It is theoretically proved that with electrical and magnetic couplings to the odd and even modes of the parasitic element, two radiation nulls can be introduced at both the lower and upper stopbands. This brings more freedom to filtering antenna design and yields the advantage of compact size and simple structure. To validate the idea, a dual-polarized antenna with a volume of
$0.24\times 0.24\times 0.25\,\,\lambda _{0}^{3}$
is designed and fabricated for base station applications. The measured results agree well with the simulations.