Rotating Permanent Magnet Antenna Array Based on Near-Field Polarization Modulation

As a new type of low-frequency magnetic antenna, the rotating permanent magnet antenna (RPMA) has great application potential in underwater and underground communication. An RPMA array based on near-field polarization modulation is presented in this letter. The near-field polarization modulation is proposed because the RPMA can radiate circularly polarized magnetic fields in the direction of the rotation axis. Since the RPMA is intrinsically an electrically small antenna, it can only work in the near-field area where the field decays with the third power of the distance. The 1 × 2 array, which can enhance the field strength, is manufactured and tested. The measured results of the axial ratio and phase difference show that the proposed method is effective when the offset angle is not greater than 5.7°. A communication experiment is also carried out, and the results show that the RPMA array can achieve a transmission rate of 2 bps.