Directional Modulation Retrodirective Array-Enabled Physical Layer Secured Transponder for Protected Wireless Data Acquisition

A time-modulated retrodirective array (RDA) is proposed to achieve directional modulation (DM) for physical layer (PHY) security in wireless communication. The designed and fabricated RDA is based on the phase conjugation technique, in which the retransmitted signal is time-modulated by using pin diodes as RF switches. By feeding proper periodic sequences to the pin diodes-based switches, the resulting harmonic signals can be suppressed in the desired secure angle, while their levels rise and distort the retransmitted signal in other unwanted angles, thereby enabling PHY security. Measured bit-error-rate (BER) results by injecting an orthogonal frequency-division multiplexing (OFDM) signal to the LO port of the PHY secured RDA verify better security performance in comparison with a conventional RDA without time modulation.