Polarization-Reconfigurable Omnidirectional Antenna Combining Dipole and Loop Radiators

This letter proposes the development of a polarization-reconfigurable omnidirectional antenna combining a dipole and a loop radiators. The omnidirectional circular polarization (CP) waves can be generated in the azimuthal plane by adopting two metal probes act as the dipole and printed spoke-like metal strips fabricated on two substrates that act as the loop. There are 48 p-i-n diodes placed on the two substrates to alter the current direction of the loop, which makes the antenna polarization reconfigurable. The polarization states of this antenna can be switched between left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP). The antenna is fed by a microstrip line, and the feeding substrate also contains a transition part and dc bias network in it. The measured -10-dB impedance bandwidth is about 18% and 14%, and the average axial ratio (AR) in the azimuthal plane is less than 3 dB for both RHCP and LHCP. The proposed antenna is designed at 1.575 GHz, such that it can be utilized for global position systems.