Differential-Fed Circularly Polarized Reconfigurable SIW Antenna by Using Liquid Metal

In this letter, we present a novel differential-fed circularly polarized reconfigurable substrate integrated waveguide (SIW) antenna based on liquid metal (LM). The antenna consists of four quarter-mode substrate integrated waveguide (QMSIW) cavities, where select metallized vias are removed between the cavities to create coupling windows for inductive coupling. This coupling mechanism generates a 90° phase difference, enabling circularly polarized radiation. The width of the coupling windows allows precise control over the strength of the coupling. Furthermore, polarization reconfigurability is achieved by adjusting the filling position of the LM, thereby modifying the location of the coupling windows. To facilitate reconfiguration conditions, containers realized through the 3D printing technique are loaded on the top and bottom of the antenna. The proposed antenna demonstrates impressive radiation gain with 9.9 dBic in the left-handed circular polarization (LHCP) state and 10 dBic in the right-handed circular polarization (RHCP) state. With its features including polarization reconfigurability, differential feeding, and high gain performance, this antenna design offers a unique solution.