Fig. 1. Basic block diagram of backscatter imaging system

Fig. 2. Block diagram of BP inversion algorithm based on sparse induced currents

Fig. 3. Singular value spectrum of G_S matrix for different number of receiving antennas M

Fig. 4. Pareto curves composed of different regularization parameters

Fig. 5. Induced current simulation results. (a) Original object; (b) theoretical induced currents; (c) BP-based induced currents; (d) sparse induced currents

Fig. 6. Simulation imaging results. (a) Original object; (b) inversion results based on traditional BP algorithm; (c) inversion results based on improved BP algorithm

Fig. 7. Simulated results using different number of transmitting antennas. (a) Inversion results based on conventional BP algorithm using 3 Tx and 12 Rx; (b) inversion results based on improved BP algorithm using 3 Tx and 12 Rx; (c) inversion results based on conventional BP algorithm using 6 Tx and 12 Rx; (d) inversion results based on improved BP algorithm using 6 Tx and 12 Rx

Fig. 8. Experimental system of microwave imaging based on radio frequency switching network. (a) Block diagram of the system; (b) experimental photos

Fig. 9. Experimental inversion images. (a) Imaging results of traditional BP algorithm; (b) imaging results of improved BP algorithm