ICs operating at millimeter-scale wavelengths are critical to 5G. But those technologies have also led to the development of scalable phased array architectures, which are useful for sensing and imaging.
Along those lines, Princeton University has announced that a team of their researchers at Princeton University, led by Kaushik Sengupta, Associate Professor of P.U.’s Electrical and Computer Engineering, took this architecture to a new level. In their paper, the researchers describe a new type of antenna array based on the art of origami. Their metasurface array, called waterbomb, is designed like a folded paper box and allows the creation of a reconfigurable radar imaging surface.
The origami structure enables engineers to quickly shift arrays of antennas, thereby increasing their capabilities. Image used courtesy of Princeton University
To achieve such an arrangement, the researchers installed a new class of broadband metasurface antennas on flat antenna panels. They then connected these panels to form an origami surface with an offset checkerboard pattern.
They report that their reconfigurable antenna can change its shape to curves or spheres to alter the electromagnetic waves in calibrated waves, allowing the surface to process information from a broader wave spectrum. This ability expands the capability of antennae for imaging and sensing applications.
Benefits of a Reconfigurable Antenna Array
The properties of imaging surfaces, such as signal-to-noise ratio and resolution heavily depend on the diversity of electromagnetic waves the surface can synthesize. However, one feature of the mm-wave systems is that they are predominantly planar. Planar systems are preferred because of their simplicity and ease of design.
On the other hand, frequency and spatial diversity are limited in planar imaging arrays. Therefore, there is a significant interest in changing surface topologies for high control over the synthesis of radio waves.
Princeton researchers say that their reconfigurable system combines the simplicity of planar arrays and the ability to radiate frequency-dependent orthogonal field projections. Moreover, the origami-based antenna array allows for large physical apertures required to image complex scattering scenes with a wider field of view.
Metasurface Antennas as a Building Block
Metasurface antennas have gained considerable attention from researchers as they can be designed to achieve unusual transmission and reflection properties to modify the dispersion characteristics of surface reflection waves. Recently, metamaterials have been used to miniaturize antennas, such as complementary split ring resonator (CSRR) loaded antennas.
Though each resonator is not a good radiator, an array of these elements could provide excellent radiation characteristics, gives a high degree of freedom for controlling the magnitude and phase of the current over the large metasurface, and provides good impedance matching due to inter-element coupling.
Princeton researchers combined these metasurface tiles that radiate frequency-dependent nearly orthogonal projection with origami electromagnetic surface, resulting in a better field of view.
Realizing the Concept of Origami Design
There were several constraints researchers had to meet to mount rigid metasurface antennas on a variable structure. The design required flexible hinges in the fabrication process that keep the antenna planar to each other with a relatively high fill factor. Also, the range of possible fold patterns depends on the rigid foldability and hinges.
Illustration of the origami structure with metasurface antenna tiles and how they help with limited field of view. Image used courtesy of Sengupta and co-authors. (Click image to enlarge)
Princeton researchers easily achieved the first three deformations: planar, x-cylinder, and y-cylinder. However, a spherical surface required some curvature. They used a well-known folding pattern called waterbomb tessellation, which allows for curvatures. They then inserted square tiles in this pattern using a technique called grafting to keep the individual metasurface tiles conformal to the desired plane, cylinder or sphere.
Surface designs for imaging array. Illustration of the origami structure with metasurface antenna tiles and how they help with limited field of view. Image used courtesy of Sengupta and co-authors. (Click image to enlarge)
The team attached 22 active metasurface panels that radiate near orthogonal modes across 17 GHz – 27 GHz to a reconfigurable waterbomb surface, demonstrating the surface’s capability to image complex 3D objects in full detail.
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