Shaping Electromagnetic Waves with Flexible and Continuous Control of the Beam Directions Using Holography and Convolution Theorem

Majid Karimipour,Nader Komjani,Iman Aryanian

doi:10.1038/s41598-019-48301-2

Majid Karimipour, Nader Komjani + Show 1 more

Open Access

https://doi.org/10.1038/s41598-019-48301-2

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Abstract

In this article, several versatile electromagnetic (EM) waves are presented with predefined shapes and directions based on the holography and convolution theorem. Inspiring the holography theory, a reflective interferogram is characterized by interfering the near field distributions of the object and reference waves. In this regard, the interference pattern on the hologram could be viewed as the inverse Fourier transform of the object and reference waves. Therefore, the capability of steering the EM shaped beam is realized using the convolution theorem (as an interesting property of the Fourier transform), which makes a link between the hologram impedance-pattern and far-field pattern domains. The main advantage of incorporating the holography concept and convolution theorem is realizing arbitrary shaped-beam EM waves with the possibility of flexible manipulation of the beam directions without employing any optimization algorithm and mathematical computation. It is demonstrated that the method could implement a combination of simple beams (such as collimated beams) and complex beams (such as cosecant squared, flat top, isoflux beams, etc.) with each beam possessing arbitrary direction by the same design topology. To experimentally verify the concept, a prototype of the hologram with three separate beams including two tilted cosecant squared shaped beam and one broadside pencil beam is fabricated and measured. The measured results show a significant agreement between theoretical findings.

Highlights

Be impenetrable and the reflection phase can be characterized by the impedance surface dyadic, which is generated by a dense grid of metallic particles over a grounded dielectric surface[28]
The concept of the convolution operation and its functionality for directing EM waves have been described in coding metasurfaces, in which the beam direction is limited by the periodicity of a gradient coding sequence[20,41]
In reflector-based metasurfaces corresponding to the holography theory, the interferogram is generated based on the near field data relevant to object and reference waves, which are the desired far-field radiation patterns and illuminated wave from a certain source, respectively

Summary

Introduction

Be impenetrable and the reflection phase can be characterized by the impedance surface dyadic, which is generated by a dense grid of metallic particles over a grounded dielectric surface[28]. Up to the authors’ knowledge, the most reliable method of shaping EM waves is based on optimization techniques including local and global search algorithms with iterative nature This is done by locally adjusting the phase of reflection and transmission waves in a quasi-periodic metasurface-based structure. To provide a more insightful interpretation of how holographic metasurface-base radiators work, it is necessary to explain the two-step imaging process, including the hologram formation and wave front reconstruction steps, in the microwave regime. In this fashion, some terminologies such as reference and object waves are common. A prototype of a multiple beam radiator with two tilted squared cosecant beams and one broadside beam is fabricated as a proof of concept

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