Terahertz microstrip array antenna with metasurface polarization conversion using silicon dioxide as dielectric layer

A circularly polarized patch array antenna with a metasurface having a polarization conversion feature at 4.975 THz frequency is proposed. The structure consists of a fully metalized grounded patch array with a metasurface on top of the antenna and separated from the array antenna by a silicon dioxide layer. The modified antenna is placed between a symmetrical surface of 11 rows of 25 fishbone-shaped gold metasurface and a ground plane. The optimal antenna structure dimensions have been examined and provided for the designed array. The performance of an array antenna has been investigated from various aspects including gain, bandwidths of impedance, and axial ratio. Placing the metasurface on the microstrip antenna array causes the radiation waves of the antenna source to be converted from the linearly polarized form to circularly polarized waves, which improves the impedance and bandwidth of the axial ratio. In addition, a transmission line model is provided to show how to achieve a suitable axial ratio, which provides a high gain as well. The overall size of the final antenna is 400 × 400 × 3.3 μm³ and provides a gain of 16 dB in the operating bandwidth of 4.71–5.2 THz (i.e., 10%).