Dual-band omnidirectional coupled-fed monopolar filtering antenna

A dual-band omnidirectional coupled-fed monopolar filtering antenna is designed in this paper. The pro-posed filtering antenna consists of three stacked circular substrates. A via-loaded annular ring and an annu-lar ring are fabricated on the top of bottom and middle substrates respectively. Four adjustable resonant modes are introduced by this way, which are combined in pairs to generate two independently controllable operating bands. Meanwhile, each resonant mode can produce corresponding omnidirectional radiation, making the proposed filtering antenna have omnidirectional radiation function. There are four adjustable radiation nulls (RNs) located at the both sides of two passbands realized by the coupled-fed via-loaded annular ring and the circular patch printed on the uppermost substrate. Hence, high skirt selectivity can be obtained. The proposed dual-band filtering antenna is simulated, fabricated and measured. The simula-tion and measurement are in excellent agreements. It is proved that the proposed filtering antenna realizes a stable omnidirectional radiation pattern in the azimuth plane with the cross-polarization level of lower than 20 dB. Additionally, the measured results display that the 10-dB impedance bandwidths are 6.3 % (2.47-2.63 GHz) and 6 % (5.38-5.71 GHz), respectively. The maximum realized gains are 2.6 and 5.2 dBi for two working bands with the out-of-band suppression of more than 15 dB.(c) 2022 Karabuk University. Publishing services by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).