Reconfigurable metasurface achieved dynamic beam control and information modulation of L-band beams

In this paper, a method of designing broadband reconfigurable polarization-converting metasurface operating in L-band is proposed. This method can also be used to directly modulate the information by using two modulation modes: binary amplitude shift keying (BASK) and binary phase shift keying (BPSK). Switching the ON/OFF state of PIN diode can be used to modify the amplitude and phase responses of the cross-polarized reflection of the element in a frequency band of 1.17–1.66 GHz, thereby creating a 1-bit digital coding meta-atom. By changing the real-time coding patterns of amplitude and phase, the reconfigurable metasurface can control beams and information modulation. Simulation results show that by changing the coding patterns of the metasurface, twin-beams and four-beams with different reflection angles can be obtained which fully validates the control ability of dynamic far-field beam. As an experimental verification, a reconfigurable metasurface consisting of 10×10 meta-atoms is fabricated, and its beam control and information modulation functions are tested. The far-field patterns of the metasurface with different coding phase distributions are measured. Furthermore, modulation signals of varying high/low voltage levels and rates are loaded onto the metasurface, in order to control its modulation mode and rate. The modulated signals reflected from metasurface are captured by a high-speed radio-frequency (RF) oscilloscope at varying rates and reflection angles, and then demodulated so as to recover the original information. On this basis, a metasurface wireless communication system based on BASK and BPSK is constructed to transmit digital image information in a real-world environment. In the experiment, the image is first represented by a sequence of 0 bit and 1 bit, corresponding to the operational state sequence of the metasurface used for transmitting information. The field programmable gate array (FPGA) is then used to generate signals with high and low voltage levels in real time according to the sequence of working states of the metasurface, and to modulate the carrier signal irradiated onto the metasurface. Therefore, the signal is converted into a modulated signal and received by the antenna. Finally, the signal is demodulated by the universal software radio peripheral (USRP) and transmitted to the terminal equipment, yielding the constellation diagrams and enabling the recovering of the images. The image information recovered under both modulation schemes verifies that the system can achieve real-time modulation and transmission of digital information. The proposed metasurface and the design method may be used in many fields, such as satellite communications and digital broadcasting.