An Orthogonal Quad-Beam Scanning Antenna Using 1-Bit Dielectric Modulation in Plasmonic Metamaterial Transmission Line for Traffic Monitoring Applications

In this paper, a novel orthogonal quad-beam scanning antenna using 1-bit dielectric modulation in a planar plasmonic metamaterial transmission line (PMTL) is proposed. The PMTL is realized by incorporating periodic subwavelength grooves along both sides of a single-conductor strip, facilitating a surface even-mode with slow-wave properties. The dispersion characteristics of this mode can be flexibly controlled by tuning the structural parameters of the PMTL. To generate a distinctive radiating mode from the slow-wave PMTL, a novel 1-bit dielectric modulation method utilizing the rectangular dielectric structure (RDS) is proposed. This approach is implemented by periodically loading RDS units along the PMTL without altering the metallic structure, enabling the phase constant in the propagation direction to alternate between two discrete states, coded as ‘0’ and ‘1’. This design method not only offers significant advantages in simplicity and flexibility but also creatively enables the one-dimensional leaky-wave antenna to achieve orthogonal quad-beam scanning capability. Furthermore, by adjusting the thickness of the RDS, both the sidelobe level and radiation efficiency of the antenna can be effectively improved. A prototype of the designed antenna is fabricated and measured to validate its performance. Experimental results demonstrate that the proposed antenna achieves continuous quad-beam scanning over 60° across two orthogonal planes within the frequency range of 7.7-10.2 GHz, while maintaining a high peak gain. These advantages make the proposed orthogonal quad-beam scanning antenna highly promising for intelligent traffic monitoring applications, especially at intersections.