Reconfigurable Circularly Polarized Cross-Dipole Antenna

This letter introduces a reconfigurable circularly polarized (CP) cross-dipole antenna fabricated on a double-layered printed circuit board (PCB) substrate for 2.45GHz ISM band wireless communications. Unlike conventional cross-dipole antennas, the proposed cross dipole is designed with wide open ends such that both impedance and axial-ratio (AR) bandwidths are enhanced. In addition, to excite the CP radiation effectively, a curved-delay line providing an orthogonal phase difference among the cross-dipole elements is attached at the corners of the sequentially rotated elements. By choosing a proper radius of the curved-delay line, a wide input impedance of the antenna can be realized. In order to achieve polarization reconfiguration, diodes are added to the curved-delay line. The phase difference between the two orthogonal dipoles can be changed by controlling the current on the diode. The antenna is center-fed by a 50- coaxial cable and is placed above a square reflector to obtain a directional CP radiation pattern. With the advantage of centered feed, symmetric CP radiation patterns can be achieved across the entire operating bandwidth. An impedance bandwidth of about 43% (2.08GHz~3.22GHz) when the antenna operates in the left-hand circular polarization state, and simulated results of the impedance bandwidth of about45% (2.06GHz~3.2GHz). The AR bandwidth of about 31.1% (2.28GHz~3.12GHz). An impedance bandwidth of about 44% (2.1GHz~3.3GHz) when the antenna operates in the righthand circular polarization state, and simulated results of the impedance bandwidth of about47% (2.07GHz~3.35GHz). The AR bandwidth of about28.5% (2.35GHz~3.13GHz).