Analysis and Design of Dual-Modal Filtenna for Dismountable Aperture-Shared Array

In multiband aperture-shared base station arrays, low-band (LB) antennas block the radiation of high-band (HB) antennas, causing cross-band scattering effects and thus degrading HB radiation patterns. Meanwhile, the cross-band mutual coupling between LB and HB antennas deteriorates the port-to-port isolation. In this article, an LB antenna is proposed to simultaneously suppress cross-band scattering and coupling at HB, which is called a dual-modal filtenna. The LB filtenna comprises slot-etched dipole and capacitive surfaces. It is studied through equivalent circuits operating in two modals, namely spatial modal and self-excited one. In the spatial modal, the LB radiator is illuminated by an HB-radiated wave and realizes a bandpass filtering response to pass the HB electromagnetic (EM) wave. Moreover, in the self-excited modal, the radiator is excited by the fed network and generates a radiation null at HB to improve the out-of-band rejection. On the LB radiator, slots forming parallel resonances are etched to suppress scattering and coupling. However, the suppression frequencies of scattering and coupling cannot simultaneously operate at HB. Then, capacitive surfaces are designed to manipulate the two suppression frequencies to HB. For validation, a dismountable dual-band array is designed. The array consists of the proposed LB (1.7–2.3 GHz) element, a
$2\times 2$
HB (2.5–2.7 GHz) array. A frequency-selective surface (FSS) is placed between them to make the array dismountable. The simulated and measured results show that the HB radiation pattern is rarely affected. Besides, the performance of the LB element is maintained. The cross-band isolations are better than 27 dB.