Abstract
Digital phase shifters have been applied in traditional phased array antennas to realize beam steering. However, the phase shifter deals with the phase of the induced current; hence, it has to be in the path of each element of the antenna array, making the phased array antennas very expensive. Metamaterials and/or metasurfaces enable the direct modulation of electromagnetic waves by designing subwavelength structures, which opens a new way to control the beam scanning. Here, we present a direct digital mechanism to control the scattered electromagnetic waves using coding metasurface, in which each unit cell loads a pin diode to produce binary coding states of “1” and “0”. Through data lines, the instant communications are established between the coding metasurface and the internal memory of field-programmable gate arrays (FPGA). Thus, we realize the digital modulation of electromagnetic waves, from which we present the field-programmable reflective antenna with good measurement performance. The proposed mechanism and functional device have great application potential in new-concept radar and communication systems.
Highlights
From the coding metasurface are steerable at the same frequency by varying the lattice size of the chessboard configuration
We have presented a field-programmable reflective antenna based on the coding metasurface in the microwave frequency, in which the binary units are realized by loading pin diodes to subwavelength artificial structures
By switching the pin diodes, the binary units possess opposite phases, which are represented by codes “1” and “0”
Summary
If only the phase differences between the coding lattices “1” and “0” are considered, the pattern function of the whole coding metasurface, when illuminated by plane waves, can be written as MN. We observe that the perfect binary state occurs at 8.9 GHz, where the states “on” and “off ” possess identical reflective amplitude and opposite reflective phases These working states satisfy the assumptions in Eq (2), and the presented units can be used to produce the programmable coding metasurface. In this case, the scattered electric field intensity of each lattice can be expressed as exp(−jk0rm,n) rm,n exp(−jk0r′m,n) . Between the source and each unit structure are fixed It only needs switching the pin diodes to change the binary codes. Except for some divergences which should be resulted from the non-uniformity of the field intensity on the metasurface, the main lobes appear around the predicted directions
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