Broadband high-efficiency 3-bit coding metasurface in transmission mode based on the polarization conversion technique.

The main drawback of the transmissive focusing metasurface (TFM) is its low operational bandwidth and aperture efficiency. Increasing both of these radiation characteristics simultaneously is a major challenge for these structures. This paper introduces a novel multi-state coding metasurface that utilizes system-level and element-level synthesis approaches to enhance frequency bandwidth and aperture efficiency. Unlike most of the TFMs proposed in this field, the proposed novel element consists of only two dielectric layers. The multi-frequency phase synthesis (MFPS) approach, a well-established broadband technique, is utilized for the system-level synthesis approach. An optimization algorithm is utilized to balance the phase error in the whole band in terms of gain variations and aperture efficiency. At the element design level, a PCT-based wideband technology is utilized and implemented by a subwavelength non-resonant element. The element is composed of three C-shaped metallic patterns, and the metal layers are printed on both sides of two identical dielectric layers without using any metalized via in the configuration. By simply changing the angle of arc curves in all layers, eight states of phase quantization are achieved. The amplitude of the transmitted wave with rotated polarization is larger than 0.9 from 12.3 to 16.5 GHz, except for state 4, which has an amplitude greater than 0.5 at the beginning of the band. A 25 [Formula: see text] 25-element TFM was designed, fabricated, and tested using the aforementioned broadband technique (MFPS along with PCT-based wideband technology). The measurement results show that the 1-dB gain bandwidth of the antenna is 12.3-16.5 GHz, which is equivalent to 29%. The maximum measured aperture efficiency is 53.6%, occurring at 12.8 GHz. The proposed metasurface is classified in the group of broadband high-efficiency TFMs.

High-efficiency dual-polarized broadband reflecting metasurface using continuous polarization conversion technique and element with multi degree of freedom.

In this study, two effective approaches are combined which are implemented at the element design level and system design level to simultaneously improve the frequency bandwidth and aperture efficiency of a dual-polarized single-layer reflecting metasurface. At the element design level, a broadband behavior is realized by using the polarization conversion technique (PCT) which is a novel technique to enhance the bandwidth of the element. To this end, an anisotropic metasurface with the I-shaped metal patch is proposed for rotating the polarization of the wave emitted from a point source by 90[Formula: see text] and making a continuous phase shift in a full range of 360[Formula: see text] within 8-18 GHz. Therefore, a completely equiphase aperture is achieved leading to enhancing the metasurface performance such as directivity and aperture efficiency and reducing the sidelobe level compared to reflecting metasurface developed by 1-bit phase quantization technique. At the system design level, the three-frequency phase synthesis (TFPS) method, which is based on determining the best constant reference phase for the aperture, is used and the corresponding constant reference phases are optimized to minimize the phase error in the whole band. The combination of TFPS and PCT enhances the effectiveness of the TFPS method considerably. An 841 element reflecting metasurface with aperture dimensions of 290 cm [Formula: see text] 290 cm is designed, simulated, and fabricated in Ku-band to verify the concept. The measurement results show that the 1-dB gain bandwidth before and after combining PCT and TFPS techniques are 17.47% (14.1-16.8 GHz) and 30.3% (14-19 GHz), respectively. In addition, the maximum aperture efficiency of the proposed metasurface is 63.62% which occurs at 14.5 GHz.

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

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.