Polarization-Reconfigurable and Frequency-Tunable Dipole Antenna Using Active AMC Structures

A polarization-reconfigurable and frequency-tunable mechanism based on an active artificial magnetic conductor (AMC) structure is proposed. The active AMC unit cell consists of a four-corner-cut inner patch and four triangles loaded with four varactors, and it can realize polarization-reconfigurable and frequency-tunable reflection characteristics by adjusting the capacitance of the varactors. By employing it as a ground plane of a pair of linearly-polarized dipole antennas, a multi-functional antenna can be well designed with polarization reconfigurability and frequency-tuning capability. By controlling the DC bias of the varactors accordingly, the three polarization states of right-/left-handed circular polarization (R/LHCP) and linear polarization (LP) can be switched, respectively, while the operating frequency of each polarization can be flexibly tuned. The measured tuning frequency ratio for the LP state (|S
₁₁
| <; -10dB) can reach 1.56:1, while the ratio for either the LHCP or RHCP state (axial ratio<; 3dB) is about 1.28:1. Moreover, a large bandwidth for each polarization state can be obtained, where the bandwidths are up to 17.1% and 8.7%, respectively, for the LP and CP states. Besides, it is more flexible for the CP states since the bandwidth can be adjusted. For a demonstration, one prototype of the proposed antenna is fabricated and measured. The agreement between the theoretical and measured results indicates good performances of the proposed antenna.