Smart antenna with reconfigurable polarization for future generation of mm-wave communication

Reconfigurable antennas with polarization agility are critical for modern millimeter-wave (mm-wave) communication systems, enabling improved link reliability, interference mitigation, and system adaptability. This paper presents a dual-band, polarization-reconfigurable microstrip antenna based on a square patch notched at two opposite corners and loaded with four PIN diodes. A defected ground structure (DGS) is introduced to enhance circular polarization purity and extend bandwidth. The antenna operates over two frequency bands: 27-29 GHz (lower band) and 32-32.6 GHz (upper band). By appropriately biasing the PIN diodes, the antenna can generate either left-hand circular polarization (LHCP) or right-hand circular polarization (RHCP) in the lower band, while maintaining linear polarization in the upper band, providing multifunctional operation within a compact design. Simulated results confirm impedance matching in the 27-29 GHz band, with a 3 dB axial ratio bandwidth of 27.42-28.22 GHz and a minimum axial ratio of 0.2 dB near 28 GHz, indicating excellent polarization purity. The antenna achieves peak gain above 6.2 dBic in both circular polarizations at the lower band and 7.2 dBi in the upper band with linear polarization. Efficiencies reach 84% at 28 GHz and over 76% at 32.3 GHz. The antenna, feed network, defected ground structure, and biasing circuits are integrated in a three-layer PCB with sub-50 μm precision traces enabled by LPKF laser prototyping, ensuring minimal parasitics. Experimental measurements show good agreement with simulations. These results validate the proposed antenna as an efficient, compact, and versatile solution for polarization-reconfigurable mm-wave communication, with advantages in adaptability, integration, and performance stability.