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This paper presents an aperture coupled circularly polarized antenna element working in the 26GHz millimeter wave band. The antenna element is fed by four groups of coupling aperture, and composed of parasitic patch, primary patch, coupling apertures, feeding network and square equivalent shield cavity. To satisfy the demand of wide-angle scanning phased array antenna, the overall dimension of the antenna element is 0.5λ, λ refers to the wavelength at the center frequency. The four groups of coupling apertures are designed with the π-shape to implement miniaturization, moreover, eliminate the energy that coupled to the feed network below. The feeding network is a one-four power divider composed of cascaded one-two Wilkinson power dividers, and in form of stripline. The four output ports of the feed network successively provide signals with equal amplitude and phase difference of 90º to the coupling apertures to realize circularly polarization. The one-four divider feed network is arranged in the outer space of the π-shaped apertures, and completed in one layer of the multilayers PCB, which reduce the number of the layers and simplify the design of the PCB stack. This antenna is designed based on the technology of stacked multilayer dielectric substrates and AIP architecture. The RF chip mounted on the back surface of the multilayer board, and connect with the antenna that designed in the upper part of the multilayer board by the metallic via-holes. By adopting the multi-point feeding technology and π-shaped coupling aperture, the axial ratio of the circularly polarized antenna improved significantly. The simulated results show that the proposed antenna has good performance within the whole working bandwidth 24.25~27.5GHz with VSWR<1.15, AR<1dB, the average radiation efficiency exceeds 80%, and can be a promising candidate for millimeter-wave phased array antenna.
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