A Wideband Water-Based 3D-Printed Reflect–Transmit Antenna Array Toward mmWave Positioning Applications

This paper presents a water-based reflect-transmit antenna (WBRTA) array for millimeter-wave (mm-wave) applications. The WBRTA array incorporates the low-permittivity polylactic acid (PLA)- and high-permittivity water-based unit cells. The low permittivity PLA unit cells provide better transmission, whereas the water-based unit cell offers good reflections due to a very high permittivity. Therefore, the WBRTA enables simultaneous beam splitting in reflection and transmission modes across a wider bandwidth. In addition, depending on the distribution and configuration of the water- and PLA-based unit cells, the WBRTA enables beam tilting of up to 45° in the reflection and transmission modes simultaneously. The proposed WBRTA offers peak gains of 25.2 dBi in transmission and 24 dBi in reflection at the central frequency. The corresponding sidelobe levels (SLLs) are -22 dB for transmission and -17 dB for reflection, while cross-polarization (x-pol) levels remain below -81 dB. In addition, the wide operational bandwidth, low sidelobe levels, and high polarization purity make the proposed WBRTA relevant as an enabling antenna structure for positioning-oriented sensing functions in future mmWave wireless systems.