Near Field Electromagnetic Ranging in Low Frequency

Near field of transmitting and receiving loop antennas exhibited a low impedance wave in low frequency, which resulted a degradation of ranging accuracy as the distance and frequency changed. A hybrid near-field electromagnetic ranging (NFER) algorithm was proposed in conjunction with the electric-magnetic field impedance and phase difference. The near-field phase-only method was derived and evaluated which showed an increasing ranging error with lower frequency and short distance. The opposite situation existed in amplitude-only method. Considering ALPHA noise distribution, the weighting coefficients were investigated using correlation operation of electric and magnetic fields. Numerical results showed that the proposed method was capable, in principle, to achieve a high accuracy under the conditions of low SNR both in a wide range and a broad bandwidth. The hybrid algorithm reached optimal ranging accuracy with the boundary coefficient 0.3 when SNR was 10dB.