1-Bit Transmissive Meta-surface with Low Sidelobe Level by Periodic Phase Modulation

A novel method to decease the side lobe level (SLL) of the 1-bit transmissive meta-surface is proposed and verified by periodic phase modulation. Because the unit of the transmissive meta-surface can only generate phase shifts of 0° and 180°, its SLL is rather high, which limits its applications in radars and military communications. With the periodic phase modulation, the 1-bit transmissive unit can be equal to multiple bits to generate more refined phase shifts. Therefore, the high SLL caused by less phase quantization of the transmissive unit can be restrained. Theory analysis and numeric simulations are provided to verify the proposed idea, and a C-band 1-bit transmissive meta-surface is fabricated and test to examine its effectiveness. The fabricated meta-surface includes 20 × 20 units arranged uniformly in a square with the element spacing 2 cm. The unit of the transmissive meta-surface acquires phase shifts through element current inversion, which works at 7.5 GHz with the relative bandwidth about 10%. The feed of the surface is a horn antenna, whose distance to the surface is 20 cm. A FPGA board controls the phase states of each unit, which makes the generated beam point to different directions. Array patterns are measured when the generated beam points to the normal direction of the meta-surface. Compared to the conventional 1-bit transmissive meta-surface, the SLLs of the modulated one decrease about 8 dB.