Transmission Phase Range Research Articles

Design and implementation of a near-field focused metasurface for microwave power transmission

In this paper, a near-field focused (NFF) metasurface composed of sub-wavelength structures for microwave power transmission is designed and implemented. Through full-wave simulations, a phase-shifting unit is proposed, which covers a transmission phase range of 360°, maintains a transmission amplitude better than −1.5 dB in most regions. Accurate design of the units at different positions in the array is achieved using phase compensation theory, forming the near-field focusing metasurface. By adjusting the transmission phase of the central unit in the metasurface to 30°, higher transmission efficiency can be achieved. Simulation results indicate that the designed near-field focused metasurface has the properties of high transmission efficiency, polarization insensitivity and distance insensitivity. To verify the transmission performance of the near-field focusing metasurface, a near-field focusing experimental platform is built and the microwave power transmission efficiency is calculated. Experimental results demonstrate that the proposed metasurface enhances the power received at the receiver, increasing the transmission efficiency by 433 %. The proposed near-field focusing metasurface holds potential for applications in high-power wireless power transfer and microwave intracavity focusing.

Scattering Mitigation Frequency Selective Surface for Unidirectional Blockage Compensation

This communication describes a concept of scattering mitigation frequency-selective surface (FSS) for unidirectional blockage compensation using a single substrate FSS without modification of the obstacle. The devised scattering mitigation FSS generates the complementary electric field to that of the blockage, enabling the blockage to become electromagnetically transparent to the antenna. Using superposition and linearity, the spatial impedance distribution of the FSS is calculated. The devised FSS consists of indented patch elements consisting of four symmetric via structures to exhibit a wide tunable transmission phase range and less than 1 dB insertion loss at the center frequency of 30.0 GHz for proof-of-concept. The proposed scattering mitigation FSS is verified in transverse magnetic (TMz)- and transverse electric (TEz)-polarized cylinder scattering scenarios. The measurement confirms the improvements of the main beam peak gain and restoration of far-field radiation patterns. The proposed investigation is expected to provide concise and practical scattering reduction solutions for blockage scenario such as vehicular communication in urban areas.

Dielectric Huygens' Metasurface Dome Antennas

This letter presents a microwave dielectric metasurface implementation comprising arrays of high permittivity pillars of varying diameter and height embedded in a lower permittivity slab. These dielectric arrays can provide a 490° transmission phase range with zero reflection and low loss and can be fabricated using additive manufacturing techniques in curved structures such as dome antennas. Full-wave simulations of a representative scan loss-reducing dome antenna agree well with analytic calculations that assume an ideal phase sheet. For simplicity, the example dome antenna is a two-dimensional (2-D) cylindrical dome; however, the dielectric metasurface implementation can be extended to 3-D dome designs.

Design and experimental demonstration of a beam scanning lens antenna.

A beam scanning antenna based on an all-metal lens is presented for high-power microwave (HPM) application in this paper. This design includes a feed antenna and two layers of different all-metal lenses, whose prototypes operating at 14.25GHz have been successfully designed and fabricated with an aperture radius of 300mm. A full transmission phase range of 360° can be achieved with a transmission efficiency of over 99% by rotating the cross-slot on the lens elements. The results of the low-power tests depict that the designed antenna can realize a beam scanning range of 120° revolving cone angle with the side lobe below -10 dB and the reflection coefficient less than -16 dB. The high-power tests demonstrate that the power handling capacity of the antenna is higher than 350MW in sulfur hexafluoride (SF6). In addition, both the designed lenses have a bandwidth of more than 100MHz. All the merits show that our designed all-metal lens antenna has a great potential to be applied in HPM systems.

3D printed metasurface for generating a Bessel beam with arbitrary focusing directions.

In this Letter, a metasurface combined with emerging 3D printing technology is proposed. The proposed metasurface regards the simple cube as the unit cell, and the height of the cube is the only variable. A nearly linear transmission phase range covering 360° operating at 20 GHz is obtained when the height is regulated in [2.26 mm, 11.20 mm]. Therefore, the proposed unit cell can be adopted to any metasurface with various functions. Taking the generation of a non-diffractive Bessel beam as an example, two metasurfaces composed of 30×30 units with different focusing directions are designed based on non-diffractive theory and the generalized law of refraction. Two prototypes are 3D printed and measured by a near-field scanning system. The measured results validate our design with satisfactory focusing and beam deflection performance. Additionally, the 3D printed metasurface has lower cost and a shorter processing cycle, and avoids metal loss. Therefore, a 3D printed metasurface is an excellent candidate that can be applied in millimeter wave or even higher frequency bands.

A Circularly Polarized 3-D Printed Dielectric Transmitarray Antenna at Millimeter-Wave Band

In this letter, a novel elliptical cylinder dielectric resonator (ECDR) is proposed. By combining a square substrate and two symmetrical ECDRs, an ECDR element is formed, which can effectively achieve the transformation from the linearly polarized incident wave to the circularly polarized (CP) transmitted wave. By adjusting the height of the element, a linear transmission phase range over 360° can be obtained, which can reduce the fabrication difficulty and cost through a 3-D printed technology significantly. Meanwhile, the ECDR element has a low conductor loss in high frequency. Additionally, a CP 3-D printed dielectric transmitarray antenna at the millimeter-wave band is designed by employing the ECDR elements. It is found that the aperture efficiency is up to 40.3%, the 3 dB axial ratio bandwidth is 17%, and the 1 dB gain bandwidth is 13.3%, respectively. The measured results are in good agreement with the simulated ones. This may be the first time that a CP 3-D printed dielectric transmitarray antenna has been reported.

Compact Double-Layer FR4-Based Focusing Lens Using High-Efficiency Huygens' Metasurface Unit Cells.

High transmission efficiency metasurface unit cells have been designed based on surface electric and magnetic impedances derived from Huygens’ principle. However, unit cells for low transmission loss (<1 dB) over a wide transmission phase range require at least three metallic layers, which complicates the unit cell design process. In this paper, we introduce high-efficiency Huygens’ metasurface unit cell topologies in double-layer FR4 printed circuit board (PCB) by implementing surface electric and magnetic current using the top and bottom metallic patterns and via drills. Eleven unit cells were optimized for wide phase coverage (−150° to 150°) with a low average transmission loss of −0.82 dB at 10 GHz. To demonstrate the high-efficiency of the designed unit cells, we designed and fabricated two focusing lenses with dimensions of near 150 × 150 mm (5λ × 5λ) to focus a spherical beam radiated from short focal distances (f = 100 and 60 mm). The fabricated focusing lens showed 12.87 and 13.58 dB focusing gain for f = 100 and 60 mm at 10 GHz, respectively, with a 1 dB fractional gain bandwidth of near 10%. We expect that the proposed focusing lens based on high-efficiency double-layer metasurface unit cells can help realize compact and high-gain focusing lens-integrated antenna systems.

Wideband Frequency Selective Surface Based Transmitarray Antenna at X-Band

In this paper, a wideband multilayer transmitarray antenna is designed for Ku frequency band. The unit cell is designed at 12GHz using frequency selective surface structure. Double square ring with center patch based multilayer unit cell is simulated. The effect of substrate thickness variation on transmission coefficient magnitude and phase range is discussed. The horn antenna designed at X-band will be used as feed source for transmitarray antenna. Transmitarray simulation results show wide impedance bandwidth from 10 to 13GHz. Wide gain bandwidth of 1.975GHz with peak gain of 18.96dB is achieved. The proposed transmitarray design will find applications in high gain, directional, low profile antennas for X-band communication systems.

Dual-Layer Transmitarray Antenna With High Transmission Efficiency

In contrast to traditional multilayer transmitarray designs, a novel dual-layer transmitarray antenna, consisting of two metallic layers printed on opposite sides of a single dielectric substrate, is proposed to achieve high transmission efficiency. First, it is theoretically derived that a dual-layer element, using the circular polarization conversion approach, can achieve a high transmission magnitude and a full transmission phase coverage. Next, a split-ring element has been designed as an example to demonstrate the theoretical analysis, where a full 360 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> transmission phase range with better than -1.0 dB transmission magnitude has been obtained. To experimentally validate the proposed concept and design, a circular transmitarray prototype is designed, simulated, fabricated, and tested at Ka-band. The diameter of the circular aperture is 405 mm (27λ), and the thickness of the transmission surface is 3.18 mm (0.2λ). The measured peak gain of the designed transmitarray is 36.1 dBic at 19.4 GHz with the aperture efficiency of 60.2%, while the measured 1 dB gain bandwidth is 9.5% (19.0-20.9 GHz).

Design of a beam scanning metamaterial antenna with polarization transform for high‐power microwave application

AbstractAn all‐metal beam scanning metamaterial antenna with polarization transform based on the concept of Risley prism is presented in this paper. The antenna is composed of a feed source and three different all‐metal metamaterial lenses. Each lens consists of numerous cross‐slot metamaterial elements. A full transmission phase range of 360° can be achieved for a transmission efficiency over 99% at 14.25 GHz by rotating the cross‐slot on the element. Mechanically rotating the three lenses along the same axis can steer the radiation beam in both azimuth and elevation planes. The simulation results agree well with the theoretical analysis which indicates that the metamaterial antenna can realize a beam scanning range of 120° revolving cone angle with the side lobe better than −13 dB. During the scanning, the directivity of the antenna varies from 34.82 dBi to 37.84 dBi, with the aperture efficiency in the range of 38%‐76%. For the radiated circular polarized (CP) plane wave beam, the beam width remains below 4° and the axial ratio is basically better than −5 dB. Furthermore, the power handling capacity of the metamaterial antenna in this paper is gigawatt (GW) class, which can be applied in the field of high‐power microwave (HPM).

Design of a wideband square slot bandpass frequency‐selective surface using phase range analysis

This article presents the design of a wideband bandpass frequency‐selective surface (FSS). The structure is designed using the analysis of the generalized scattering matrix (GSM)‐based transmission phase range. A relationship between the transmission phase range and the bandpass fractional bandwidth (FBW) is developed. The analysis reveals that the FBW of the FSS unit‐cell is proportional to the phase range. Based on the interpretation of results, a design curve has been drawn, and using this curve, a simple square slot FSS on a low‐cost FR‐4 substrate has been fabricated and measured. Using the design curve, a 53% FBW has been predicted. The simulated results show a 52% FBW with the 3.52‐GHz center frequency (fo). The response for the transverse electric (TE) and transverse magnetic (TM) modes has been measured. The structure has a bandpass FBW equal to 50% and 53.3% in TE and TM modes, respectively. The method presented in this article may be used to increase the bandpass response of different FSS topologies.

A wideband quad-layer transmitarray antenna with double cross slot rings elements

This paper introduces and studies a multi-layer frequency selective surface structure as a new unit-cell to design a wideband quad-layer transmitarray antenna. The proposed unit-cell consists of a double cross slot rings (DCSRs) on a rectangular patch. This unit-cell supports the transmission phase range response about 400° with magnitude better than −3 dB at 10 GHz and its sensitivity to the feed incident angle, up to 30°, is very low. To validate the design approach, a quad-layer transmitarray antenna, which each layer contains 169-element, is designed at 10 GHz and then fabricated and measured. The measured results show 1-dB gain bandwidth of 25% (9.75–12.53 GHz) with 23.34 dB maximum gain and 38.3% aperture efficiency at 10.3 GHz. Moreover, the 2-dB and 3-dB gain bandwidth are 31% (9.45–12.92 GHz) and 36% (9.30–13.35 GHz), respectively. As a result, the proposed element has the broadband performance and therefore can be a proper candidate to design wideband transmitarray antennas.

Graphene-based metamaterial transmitarray antenna design for the generation of tunable orbital angular momentum vortex electromagnetic waves

A graphene-based metamaterial transmitarray antenna is proposed to generate tunable orbital angular momentum (OAM) vortex waves in terahertz. Theoretical design of the transmitarray antenna has been developed by using the transmission line network model, and a multilayer graphene-based metamaterial element has been designed. By changing the chemical potentials of the graphene sheets, the 360° transmission phase range of the element is achieved in a broad band from 4.2 THz to 5.6 THz. By arranging the metamaterial element into a transmitarray, the OAM waves with tunable modes including l = 0, ±1, ±2 and the mode purity greater than 0.96 are generated. Simulation results are given to demonstrate good performance of the proposed design, which provides a feasible way to the efficient generation and manipulation of the OAM vortex waves in terahertz.

Beam Steering Conformal Transmitarray Employing Ultra-Thin Triple-Layer Slot Elements

A novel conformal transmitarray with beam steering ability is presented. First, an ultra-thin transmitarray element consisting of three layers of identical square ring slots is developed. The element has a thickness of 0.508 mm (0.04 wavelength in the free space at 25 GHz), achieving a transmission phase range of 330° with a maximum 3.6 dB loss. The element is then applied to a curved transmitarray conformal to a cylindrical surface fed by a standard gain horn with about a 10-dBi gain. A prototype is fabricated radiating a boresight beam with a peak measured gain of 19.6 dBi and an aperture efficiency of 25.1%. Second, when the transmitting surface of the above array is divided into two parts from the middle with different main beam directions, the combined beam can be radiated to an oblique angle with respect to the boresight direction. Using this method, a mechanical beam scanning conformal transmitarray antenna is designed. Its size is about 2.5 times larger than the fixed-beam one and consists of six transmitting surfaces with main beams directed to different angles. By rotating the feed horn to different positions, the main beam of the array can be switched to ±15°, ±10°, ±5°, and 0°. A prototype is fabricated with a stable gain of about 18.7 dBi at all beam angles.

Wideband and low-profile transmitarray antenna using transmissive metasurface

Based on the Pancharatnam-Berry phase principle, a wideband low-profile transmissive metasurface was designed and applied to a transmitarray antenna (TA). While a full transmission phase range of 360° was achieved by rotating the proposed unit cell, the transmission coefficient was always close to 1 in the frequency range of 10.4–11.6 GHz. Hence, a TA comprised of 20 × 20 unit cells of size 180 mm × 180 mm was designed and fabricated. The simulated results agreed well with the experimental data, validating the excellent performance of the proposed metasurface structure. The measured peak gain of the TA was 21.64 dB at 11 GHz, resulting in an aperture efficiency of 34%. In addition, we attained a 12% 1-dB gain bandwidth (10.2–11.5 GHz) and an 18% 3-dB axial ratio bandwidth (10–12 GHz) for the TA. The proposed metasurface exhibits distinct performance benefits in terms of having wide bandwidth, low-profile, and high-efficiency, as well as represents a promising design option for a high-performance TA.

Wideband Phase-Gradient Metasurface Antenna With Focused Beams

A transmitting lens antenna with focused beams by employing four-layer phase-gradient metasurface (PGMS) is proposed. A wideband slot-coupled antenna is mounted close to the focal position of the PGMS acting as a feed. The electromagnetic wave radiated through the feed source is transformed to plane wave within a wide frequency covering from 9.4 to 10.6 GHz. The in-band measured gain is from 16.7 to 19.4 dBi and a 3-dB gain bandwidth of around 10% is achieved, which demonstrates that the proposed four-layer PGMS still has the ability to focus electromagnetic wave within a wide frequency band efficiently though its transmission phase range at some specific frequency bands does not meet 360°.

Broadband low-profile transmitarray antenna using three-dimensional cross dipole elements

This article presents a novel transmitarray antenna using three-dimensional frequency selective structures as the radiating elements. The proposed unit cell, which consists of two cascaded cross dipoles, has a thickness of 0.22λ0 and provides a 310° transmission phase range with transmission magnitude equal or better than −0.8 dB. Compared with those conventional transmitarray antennas, the proposed one can realize greater flexibility in the installation with less manufacturing complexity. For the purpose of validation, a transmitarray prototype using the proposed elements has been manufactured and tested at X-band. The peak gain of 25.5 dB is achieved at the frequency of 10 GHz, resulting in an aperture efficiency of 64%. Besides, antenna bandwidth of 10% for 1-dB gain is achieved in this design.

Transmitarray Design With Enhanced Aperture Efficiency Using Small Frequency Selective Surface Cells and Discrete Jones Matrix Analysis

We present a four-layer transmitarray antenna using small and dense frequency selective surface (FSS) cells and a horn antenna operated in a Ku band satellite downlink (10.7 to 12.75 GHz in Europe). The FSS offers a full transmission phase range of 360° and low loss between the incident and the transmitted waves: the magnitudes of the transmitted waves were equal to or better than −3.5 dB for incident transverse electric and transverse magnetic waves up to 30° in oblique angle. The transmitarray was fabricated using FR-4 boards with a loss tangent of about 0.02. FR-4 boards with lower loss tangents at the operating Ku band were not used because of the requirement for low cost. We also present the design of the horn antenna used to illuminate the transmitarray. The design applies discrete Jones matrix analysis; the final full transmitarray (333 unit cells) with the horn antenna were co-simulated using a full-wave simulation tool. The measured and simulation results are in excellent agreement. With a cell pitch of 0.39 $\lambda _{0}$ , the transmitarray achieves a dynamic range of 20 dB. The measured gain of the transmitarray prototype is 26.2 dB at a center frequency of 11.7 GHz, resulting in an aperture efficiency of about 62%. The measured results were achieved with a very small transmitarray (backpack-fit versus truck-carried). The −1 dB gain bandwidth of the transmitarray antenna is 12.6% at the center frequency (11.7 GHz).

Control of Beam Direction for Substrate-Integrated Waveguide Slot Array Antenna Using Metasurface

The method to control the aperture phase distribution of antenna using a metasurface is proposed to point the antenna beam to desired directions. A $1\times 10$ substrate-integrated waveguide (SIW) slot array antenna directly integrated with the metasurface of double-layer miniaturized framed Jerusalem crosses is, for example, designed to achieve the oblique radiation beam in 30° at $Ka$ -bands. In order to achieve a full 360° transmission phase range, part of SIW slots are inverted to obtain additional 180° phase shift so that more than 400° phase shift range is realized. The measured results show that the beam directions are within 29.3 ± 1° from 34.25 to 35.75 GHz with a return loss better than 15 dB. The measured maximum gain is 12.1 dBi at 34.75 GHz. The combination of the array antenna and the metasurface features a low profile, simple structure, and flexible design for oblique beam application.

High-Efficient Wideband Transmitarray Antenna

A new structure for transmitarray antennas is presented. The proposed semiplanar transmitarray keeps certain geometrical curvature, that the required transmission phase range is reduced significantly from 360°, causing an increase in bandwidth and efficiency. The proposed antenna structure has varied element thickness—the central element being the thinnest and elements growing in thickness as we move toward the edges. To evaluate the new model, an X-band prototype antenna is fabricated with the number of layers for the elements growing from 2 to 5 from center to the edges of the aperture. The required phase range for the elements was reduced from 360° to 51.5°. Measurement results show that proposed antenna with aperture size of ${\text{21.8}}\lambda _{0}^{2}$ has 22.3 dBi maximum gain at 10.3 GHz. In addition, the proposed design achieves a 24.27% 1 dB gain bandwidth and 62% efficiency.