A mmWave Microstrip Patch Antenna with Diode-Loaded Tuning Stub for Frequency and Polarization Reconfigurability

This study introduces a frequency and polarization reconfigurable antenna designed for 5G mm-wave applications. The antenna functions under reconfigurable conditions, toggling between linear and circular polarization modes with simple DC biasing circuit, while also supporting dual-frequency operation and providing flexibility for different communication situations. The proposed antenna, measuring $11\times 12\times 0.8128\text{mm}^{3}$ and using a Rogers RO 4003C substrate, whose permittivity is 3.38, is incorporated rectangular slots to achieve more circular polarization at resonance frequency. In circular polarization mode, the antenna supports both left-hand circular polarization (LHCP) and linear polarization, depending on the biasing state. The antenna achieves an axial ratio of 0.88 dB, ensuring outstanding polarization purity. The antenna shows a return loss of −35.94 dB at 28.16 GHz, demonstrating effective impedance matching, and also exhibits a return loss of −15.00 dB at 31.44 GHz, indicating satisfactory performance over a broader frequency range. This frequency shift between the ON state (28.16 GHz and 31.44 GHz) and OFF state (30.84 GHz) demonstrates the antenna's frequency reconfigurability, complementing its polarization re-configurability. This explicit framing of dual-frequency operation as frequency reconfigurability enhances clarity and precision in describing the antenna's versatile capabilities. In addition, it maintains a gain exceeding 5.5 dBi throughout the operating bandwidth, positioning it as a strong option for high-performance mm-wave wireless systems. The peak gain is approximately 7.1 dBi.