360° scanning multi-beam antenna based on spoof surface plasmon polaritons

A multi-beam antenna based on spoof surface plasmon polariton (SSPP) is proposed, which is composed of 24 identical end-fire antennas rotating around the center of the circle. Thus the angle between any two end-fire antennas is 15 degrees. Every single end-fire antenna consists of feeding monopole and periodic metallic blade structure sandwiched between two identical 0.5 mm-thick F4B substrates (epsilon(r) = 2.65, tan (delta) = 0.001). And the periodic metallic blade structure can be regarded as two regions. The first region (Region I) is a double-side corrugated metallic strips with continuous gradient height, so that the SSPP has a linear propagation constant distribution on the strips. Good matching of both impedance and wave vectors between spatial wave and SSPP waveguide ensures the conversion of high-efficiency from spatial modes into SSPP modes and that of high-efficiency radiation from SSPP modes into spatial modes. The second region (Region II) is the transition part of the SSPP wave with constant blade height. Geometric parameters are optimized by using CST Microwave Studio and the dimension of the single end-fire antenna is 111 mm x 15.2 mm x 1 mm. A prototype is fabricated and tested, showing good agreement between numerical simulation and experimental results, which proves that the electromagnetic wave of the monopole is successfully coupled and nearly completely confined on the metallic blade structure, and radiated at the end of the blade, resulting in omnidirectional radiation pattern of the monopole being mediated to directive beam steering at end fire. Rotate the 24 identical antennas around the center of the circle with respect to a cylinder, namely the proposed 360 degrees. scanning multi-beam antenna in this paper. The optimized radius of the proposed antenna cylinder is set to be 128 mm. The simulated and measured results are consistent with each other and clearly indicate that the proposed multi-beam antenna shows a scanning capability over 360 degrees in the xoy plane with an average directivity of approximately 11.8 dBi and 3 dB angular width of 15 degrees in operation bandwidth 9.5-10.25 GHz. Changing the geometric parameters of the blade structure, the characteristics of the gain, bandwidth, and 3 dB angular width for multi-beam antenna will be also changed. Unlike traditional multi-beam antennas, the proposed antenna based on SSPP mode coupling is no longer limited to the principle of geometrical optics, but mediates the omnidirectional radiation pattern of the monopole to directive beam by utilizing great confinement property of SSPP, which gives high degree of freedom for designing the multi-beam antennas. Besides, derived from the characteristics of deep-subwavelength and localized field enhancement for SSPPs, the proposed multi-beam antenna obtains many advantages, such as low profile, simple structure, high realizability, and important application values.