Broadband planar aperture-coupled antenna array for WLAN and ITS beam-steering applications

A broadband multilayer beam-steering antenna array with a modified mushroom-like radiating element is introduced. The two-layer aperture-coupled array consists of four equal sets of mushroom-like elements, each of which is made of 16 unit cells in a 4 × 4 configuration. The feeding network is a modified quasi-Butler matrix, which benefits from improved double-box branch line couplers. The network has an isolation bandwidth between 4 and 7.9 GHz (65%) and a transmission bandwidth from 4.8 to 7.1 GHz (39%), which operates acceptably in most of the C-band, especially at wireless local area network and Intelligent Transport Systems (ITS). A broadband Butler matrix uses broadband 3 dB couplers and a middle network. The geometry of the element and feeding network is utilized in array form to enhance the impedance bandwidth and radiation efficiency of the antenna. The results show that the antenna impedance bandwidth covers 3.82 to 8.2 GHz (port 1) and 3.8 to 8.28 GHz (port 2) for Snn ≤ −10 dB, which covers the C-band fully (4–8 GHz). Moreover, it has a 3 dB gain-bandwidth of 2.25 GHz that extends from 4.65 to 6.9 GHz with a peak value of 13.65 dBi. The antenna array has a 3 dB axial ratio bandwidth of 1.65 GHz that extends from 4.9 to 6.55 GHz and involves wireless local area network (5.15–5.825 GHz) and ITS (5.795–6.400 GHz). The radiation efficiency of the array for both port excitations is in excess of 75% when circular polarization is achieved. Two firing beams at elevation angles of 20° and −35° are obtained for ports 1 and 2 upon excitation, respectively.