In this paper, for the first time, a new generation of ultrafast reprogrammable multi-mission bias encoded metasurface is proposed for dynamic terahertz wavefront engineering by employing VO2 reversible and fast monoclinic to tetragonal phase transition. the multi-functionality of our designed VO2 based coding metasurface (VBCM) was guaranteed by elaborately designed meta-atom comprising three-patterned VO2 thin films whose operational statuses can be dynamically tuned among four states of "00"-"11" by merely changing the biasing voltage controlled by an external Field-programmable gate array platform. Capitalizing on such meta-atom design and by driving VBCM with different spiral-like and spiral-parabola-like coding sequences, single vortex beam and focused vortex beam with interchangeable orbital angular momentum modes were satisfactorily generated respectively. Additionally, by adopting superposition theorem and convolution operation, symmetric/asymmetric multiple beams and arbitrarily-oriented multiple vortex beams in pre-demined directions with different topological charges are realized. Several illustrative examples successfully have clarified that the proposed VBCM is a promising candidate for solving crucial terahertz challenges such as high data rate wireless communication where ultrafast switching between several missions is required. In recent years, the scope of THz science and technologies has reached a maturity and attracted massive attention due to their potential applications like biomedicine 1 , security checking and high data rate transmit through wireless communication 2-4. However, as the key technique, manipulating EM waves reveals the necessity of employing metasurfaces as the two-dimensional analogous of more general volumetric metamaterials to furnish an inspiring groundwork for realizing some rich diverse applications such as, but not limited to, invisibility cloaks 5,6 , negative refraction 7 , optical illusion 8 and epsilon near zero behaviors 9,10. Recently, T. Cui et al. has revolutionary introduced the concept of digital metasurfaces as a link between the physical and digital worlds, making it possible to revisit metamaterials from the viewpoint of information science where manipulation of EM waves with different functionalities can be realized by controlling sequences of digital coding states "0" and "1" with opposite phase responses 11. Due to the lower weight and being easier to design and fabricate, digital metasurfaces have experienced rapid development compared to traditional wave manipulation 12. By purposefully distributing coding particles over a 2D plane in a periodic or aperiodic manner, a variety of exquisite physics phenomena and innovative EM devices have been created 13-17. However, in most of these strategies, the metasurfaces are designed for a specific application and their functionalities remain fixed once they are constructed. For example, Shao et al. proposed a dielectric 2-bit coding metasurface with distinct functionalities from anomalous reflection to vortex b...

Recent years have witnessed an extraordinary spurt in attention toward the wave-manipulating strategies revealed by phase–amplitude metasurfaces. Recently, it has been shown that, when two different phase-encoded metasurfaces responsible for doing separate missions are added together based on the superposition theorem, the mixed digital phase distribution will realize both missions at the same time. In this paper, via a semi-analytical procedure, we demonstrate that such a theorem is not necessarily valid when using phase-only metasurfaces or ignoring the element pattern functions. We introduce the concept of asymmetric spatial power divider (ASPD) with arbitrary power ratio levels in which modulating both amplitude and phase of the meta-atoms is inevitable to fully control the power intensity pattern of a reflective metasurface. Numerical simulations illustrate that the proposed ASPD designed by proper phase and amplitude distribution over the surface can directly generate a desired number of beams with predetermined orientations and power budgets. The C-shaped Pancharatnam–Berry meta-atoms locally realize the optimal phase and amplitude distribution in each case, and the good conformity between simulations and theoretical predictions verifies the presented formalism. A prototype of our ASPD designs is also fabricated and measured, and the experimental results corroborate well our numerical and semi-analytical predictions. Our findings not only offer possibilities to realize arbitrary spatial power dividers over subwavelength scale but also reveal an economical and simple alternative for a beamforming array antenna.

Abstract-In the present paper a simple model has been given to simulate the signal propagation through two cross orthogonal microstrip lines in two different layers of the PCB board. First the structure has been analyzed using full wave software like HFSS, then a simple and suitable lumped equivalent circuit is proposed for the cross talk region and its parameters are obtained. Finally the sparameters of this equivalent circuit compared with the results of full wave simulations. The results show good agreement up to some GHz.

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