Circularly Polarized Wave Research Articles

Broadband and high-efficiency ultrathin wavefront manipulation based on the Pancharatnam-Berry phase principle.

A broadband and high-efficiency metasurface is proposed based on the Pancharatnam-Berry (PB) principle. The PB phase principle is analyzed using the scattering matrix approach and proposed to achieve the abrupt phase with an equal amplitude of the transmission coefficient. The abrupt phase φ has a linear relationship with the rotation angle θ, namely, φ=±2θ. A 1-D gradient metasurface was designed, and the circular polarized waves in the frequency range 8.2-10 GHz were refracted anomalously when left-handed circular polarization or right-handed circular polarization waves were irradiated vertically on the metasurface and the refraction angle of the circular polarized waves, depending on the chirality of the incident wave. Finally, a 2-D parabolic metasurface that not only converts planar circular polarized waves into spherical circular polarized waves, but also converges the parallel wave into a focus point, was designed. The focal distance of the 2-D parabolic metasurface decreases as the frequency of the incident wave decreases, and the half-maximum at full width shows the opposite trend.

Single-Layer Achiral Metasurface with Independent Amplitude-Phase Control for Both Left-Handed and Right-Handed Circular Polarizations.

Amplitude-phase control for circular polarized (CP) waves is experiencing a research upsurge in electromagnetics owing to the kaleidoscopic electromagnetic responses and promising application prospects of circular polarizations, and chiral metasurfaces are more facile to achieve a series of intriguing chiral phenomena than natural materials. However, it is difficult for most existing chiral metasurfaces to independently tailor the amplitude and phase of left-handed circular polarized and right-handed circular polarized waves at the same frequency as they suffer the drawbacks of large thickness, multiple layers, and complex structure. Herein, an innovative strategy of single-layer achiral metasurfaces of thickness 0.13λ0 is proposed to independently and simultaneously manipulate the amplitude and phase of orthogonal CP waves. As a proof of concept, an amplitude and phase controlled dual-channel meta-hologram is designed to reconstruct diverse images with high fidelity under orthogonal CP illumination, and the simulated and experimental results collectively validate the availability of our methodology. Significantly, the meta-hologram is also applicable to full polarization states according to the decomposition of electromagnetic waves. The inspiring design of single-layer achiral metasurfaces provides a simple and effective approach to explore chiral effects, and they possess enormous application potential in multitudinous microwave devices.

Wideband circularly polarized millimeter‐wave metasurface antenna array feed by SIW

A wideband millimeter-wave circularly polarized (CP) antenna based on metasurface (MS) is proposed. The antenna consists of a two-layer substrate integrated waveguide (SIW) feed structure and a layer of MS with a 2 × 2 rectangular truncated corner. As a polarization conversion structure, the MS converts the linearly polarized wave generated by the SIW into a CP wave, and four metal pins are placed in the middle to improve the impedance and the axial ratio (AR) bandwidth. Based on this antenna element, a SIW-fed 2 × 2 array using the sequentially rotating phase (SRP) feed technique is designed, which further improves the AR bandwidth and the gain level of the antenna. The results of the measurements show that the array maintains a low profile with an impedance bandwidth of 40.3% from 25.05 to 37.14 GHz, and an AR bandwidth of 31.3% from 23.14 to 32.54 GHz, and a peak gain of 14.3 dBi.

A Low-RCS and High-Gain Planar Circularly Polarized Cassegrain Meta-Antenna

Achieving highly directive radiation with broadband operation, low scattering, and thin profile for a circularly polarized (CP) antenna is particularly challenging and yet rarely reported. Here, we propose a strategy of a CP Cassegrain meta-antenna by combining a planar helical antenna, a metasurface main reflector, and a metamaterial subreflector. The main reflector is designed to achieve focusing for CP waves at 13 GHz. The subreflector is chessboard-configured chiral metamaterial slab composed of two different types of chiral meta-atoms, aiming to achieve spin- and direction-selective CP transmissions and reflections. The distance between two reflectors is half of focal length, which enables our antenna to be dubbed as a folded reflectarray. The low radar cross section (RCS) is achieved based on scattering cancellation technique by realizing near 180° reflection phase difference between two neighboring chessboard submeta-atoms. Thanks to the architecture of the two reflectors, the proposed antenna exhibits high gain and low profile simultaneously according to image theory. For verification, a planar CP Cassegrain antenna, excited by a left-handed CP (LCP) planar helical antenna, is numerically studied, fabricated, and experimentally measured. Numerical results are in good agreement with the experimental ones, showing a peak right-handed CP (RCP) gain of 26.6 dBi at 12.6 GHz. Furthermore, the backward monostatic RCS of the antenna is dramatically reduced over −10 dB in a broad bandwidth from 8.4 to 15.7 GHz when it is illuminated by an LCP planar wave. Our proposed Cassegrain antenna features simultaneously broadband, high gain, low profile, and low RCS, providing a new avenue to low-profile CP reflectarrays with invisibility.

Photonic Bandgaps of One-Dimensional Photonic Crystals Containing Anisotropic Chiral Metamaterials

Conventional photonic bandgaps (PBGs) for linear polarization waves strongly depend on the incident angle. Usually, PBGs will shift toward short wavelengths (i.e., blue-shifted gaps) as the incident angle increases, which limits their applications. In some practices, the manipulation of PBGs for circular polarization waves is also important. Here, the manipulation of PBGs for circular polarization waves is theoretically investigated. We propose one-dimensional photonic crystals (1DPCs) containing anisotropic chiral metamaterials which exhibit hyperbolic dispersion for left circular polarization (LCP) wave and elliptical dispersion for right circular polarization (RCP) wave. Based on the phase variation compensation effect between anisotropic chiral metamaterials and dielectrics, we can design arbitrary PBGs including zero-shifted and red-shifted PBGs for LCP wave. However, the PBGs remain blue-shifted for RCP wave. Therefore, we can design a high-efficiency wide-angle polarization selector based on the chiral PBGs. Our work extends the manipulation of PBGs for circular polarization waves, which has a broad range of potential applications, including omnidirectional reflection, splitting wave and enhancing photonic spin Hall effect.

High-efficiency reflective metasurfaces for terahertz vortex wave generation based on completely independent geometric phase modulations at three frequencies

One of the considerable disadvantages of a metasurface (MS) is frequency-dependent behavior, which largely restricts its practical applications. To overcome this challenge, a MS is designed to generate vortex beams at three distinct terahertz (THz) frequencies. Specifically, a unit-cell structure comprising three resonators is proposed to operate at three distinct THz frequencies. The cross-polarized reflection coefficients of the unit-cell structure are greater than 70% under circularly polarized (CP) incidence. Based on the geometric phase principle, the full 2 π phase shift can be obtained at each frequency by rotating the corresponding orientation angles of the three resonators. By carefully arranging the unit-cell structure, orbital angular momenta (OAMs) with topological charges of l = ± 1 , − 2 , and, − 3 at 0.706 THz, 1.143 THz, and 1.82 THz, respectively, can be generated for a normally incident right CP wave, and OAMs with topological charges of l = − 3 , − 2 , and − 1 can be generated for a normally incident left CP wave. The generated reflective vortex beams through the designed MS have good mode purity up to 85% at 0.706 THz, 84% at 1.143 THz, and 74.7% at 1.82 THz, respectively. Moreover, the designed reflective MS reveals a convenient and low-cost way to generate vortex beams with different/same OAM modes at three different resonance frequencies and is beneficial for potential applications in THz communication.

3‐D printed circularly polarized multibeam antenna array with full azimuth scanning capability and wideband characteristic for 5G millimeter‐wave applications

This paper presents a wideband circularly polarized (CP) multibeam antenna array, which is with full azimuth scanning capability and operates in Ka band for 5G applications. It adopts a circular array configuration and consists of 18 elements with a simple structure. Regarding to each element, it is fed by a 90° bent rectangular waveguide and employs a simplified single dielectric slab polarizer to produce CP waves. Within the axial ratio bandwidth (ARBW), the proposed element can achieve a stable half power beamwidth (HPBW) of 29 ± 7°, while, the 3-dB AR beamwidth is larger than the HPBW. By switching the active elements, the proposed array can realize 360° beam steering in azimuth plane, while, the HPBW and the 3-dB AR beamwidth cover the entire plane. To simplify the fabrication process, dielectric and metal 3-D printing technologies are employed for processing. Experimental results indicate that the proposed array can achieve a 40.5% 3-dB ARBW which almost covers the entire Ka band from 26.2 to 39.5 GHz and a gain of 9.9 ± 1.5 dBic. The front-to-back ratio (FBR) of each beam is higher than 19 dB. In contrast to conventional designs, the proposed antenna features wide band, simple structure, and ease of fabrication.

Terahertz Transmission‐Type Metasurface for the Linear and Circular Polarization Wavefront Manipulation

AbstractA transmission‐type metasurface (MS) based on the combined geometric and transmission phase is proposed and investigated here numerically, which can achieve independently manipulation of the circular polarization (CP) and linear polarization (LP) wavefront at terahertz (THz) region. The unit‐cell of the proposed MS is composed of the dielectric substrate sandwiched with the bilayered inner centrosymmetric‐notched‐elliptic (CNE), outer C‐shaped, and single‐split‐ring (SSR) structures. The proposed MS can convert the normal incident LP wave to its orthogonal one at the lower frequency (f1 = 0.68 THz) after transmission and left‐handed circular polarization to the transmitted right‐handed circular polarization wave or vice versa at the higher frequency (f2 = 1.34 THz). The full 2π phase shifts of the both transmitted LP and CP waves can be realized independently and simultaneously by varying the opening and orientation angles of the outer SSR structure based on the transmission phase and the orientation angle of the inner CNE structure based on geometric phase, respectively. As proofs of concept, anomalous refraction, planar focusing, and vortex beam generation for both LP and CP waves are demonstrated numerically. These findings show great potential applications in imaging and communication systems, providing new possibilities to develop multifunctional THz device for both LP and CP waves.

An Ultra-Wideband Linear-to-Circular Polarization Converter Based on a Circular, Pie-Shaped Reflective Metasurface

In this paper, we present an ultrawideband reflective metasurface with the properties of an LTC-PC, which is an orthotropic composition with two mutually orthogonal symmetric axes, v and u, and 45° rotation about the vertical y-axis. Based on the metasurface unit cell, it seems like a circular pie embedded with a rectangular patch. The converter can convert LP electromagnetic (EM) waves to CP waves over the bands from 20.18 GHz to 33.93 GHz, with a 3-dB AR bandwidth of up to 50.8% and a circular polarization wave that is RHCP (right hand CP). Moreover, the linear-to-circular PCR exceeds 98% in the frequency bands of 20–34 GHz. A comprehensive theoretical investigation was conducted to determine the fundamental cause of the LTC polarization conversion. The ∆φuv between two reflection coefficients at v- and u-polarized incidences is ±90°, which fully anticipates the axial ratio of the reflected wave. Any reflective metasurface can be used as an efficient LTC-PC if the ∆φuv is close to ±90°.

Flexible CP diversity antenna for 5G cellular Vehicle-to-Everything applications

A flexible circularly polarized (CP) MIMO antenna is evaluated for Sub-6 GHz 5G and cellular-vehicle-to-everything (C-V2X) applications. The design radiates CP waves with an L-shaped feed line and a modified ground plane embedded in the slot antenna. The MIMO design resonates in the band of frequencies 3.23–6.26 GHz and radiates CP waves in the 2.95 – 6.02 GHz frequency band. This antenna model is suitable for LTE-V2X/ 5G (3.3 to 4.2 GHz), WLAN 5.2 GHz, WiMAX 5.5 GHz, and IEEE 802.11p (5.85–5.925 GHz) vehicular application bands. Here both planar and antenna conformed on foam material and a car wing mirror are investigated. Improved lowest isolation of 18.2 dB is achieved in the entire working band using the orthogonal CP arrangement of elements. The diversity functionality is tested in terms of ECC, MEG, CCL, etc. Further, the antenna radiation characteristics are tested by positioning it on the vehicle roof-top and side mirror using the Ansys savant tool.

An optically transparent circularly polarized ultrahigh‐frequency radio frequency identification reader antenna

An optically transparent circularly polarized (CP) radio frequency identification (RFID) antenna is presented in this paper. The RFID antenna consists of a coplanar-fed waveguide inverted L-shaped monopole with a dual feeding structure. The CP wave with a bidirectional radiation pattern is obtained by feeding the radiator at both ends. The transparency of the antenna is obtained by using fluorine tin oxide (FTO) coated soda-lime glass substrate. The proposed antenna operates at a Universal RFID frequency (800–1100 MHz) with circular polarization. The antenna has an impedance bandwidth of 300 MHz and an overlapped 3-dB axial ratio (AR) bandwidth of 110 MHz (860–970 MHz, 12% centered at 915 MHz). It has a peak realized gain of 1.4 dBic. The antenna with the size of 100 × 100 mm2 is designed for ultrahigh-frequency RFID reader applications.

High-gain bidirectional radiative circularly polarized antenna based on focusing metasurface

A high-gain bidirectional radiative circular polarization (CP) antenna loaded with a dual-mode focusing metasurface (MS) is proposed. The original microstrip patch antenna consists of two coaxially fed tangential patches with different sizes, enabling CP radiation at 8.15 GHz and 14.8 GHz with the gain of 5.4 dBic and 6.2 dBic, respectively. The unit-cell of the focusing MS is composed of two metallic layers separated by a dielectric substrate based on geometric phase principle, which can independently tailor the focusing effect of transmitted and reflected CP waves at 8.15 GHz and 14.8 GHz, respectively. Then, the high-gain bidirectional radiation antenna can be formed by combining the original CP microstrip antenna and focusing MS. The final designed antenna can achieve a CP radiation converge characteristic in transmission at 8.15 GHz with a peak gain of 15.9dBic, and at 14.8 GHz with a peak gain of 19.4dBic in refection, respectively. In order to verify the feasibility of the proposed design, the bidirectional radiative CP antenna with/without focusing MS were fabricated and measured, and the results are consistent basically with the simulated ones. The proposed bidirectional focusing MS antenna could provide an effective solution for dual-mode radiation and high-rate information transmission of the communication system.

Multi-functional high-efficient reflective polarization converter based on all-metal stereostructured anisotropic metamaterials at terahertz frequency

In this paper, a high-efficient reflective polarization converter based on all-metal stereostructured anisotropic metamaterials (AMMs) in terahertz (THz) region was proposed and investigated numerically. The unit-cell structure of the converteris assembled by vertical metallic double L-shaped stereostructures (DLSSs) adhered on the ground plane. The simulated results show that the proposed stereostructured AMMs can convert the incident x/y-polarized (x/y-pol.) wave into the right/left-handed circular polarization (RCP/LCP) wave, y/x-polarized (y/x-pol.) wave, and left/right-handed circular polarization (LCP/RCP) wave at 1.37 THz, 1.45 THz and 1.54 THz, respectively. Furthermore, the high-efficient polarization conversion of the proposed AMMs can be sustained within a wide incident angle from 0° to 75° for both transverse electric (TE) and transverse magnetic (TM) modes. The physical mechanisms of the observed polarization conversion are elucidated by taking advantage of surface current distributions. The further simulation results indicate that the operation frequency can be adjusted by changing the geometric parameters of the DLSSs. The proposed stereostructured AMMs-based reflective polarization converter can find potential THz applications, such as remote sensors, imaging systems, and reflector antennas.

A Novel Low Axis Ratio Double-Circularly Polarized Microstrip Antenna

This article presents a dual circular polarization (CP) microstrip antenna, emitting electromagnetic waves above and below the substrate, which is fed by the double L-probe. Selecting the L-probe feed increases the bandwidth of the antenna, and different probes control the rotation of CP. The antenna could radiate two polarized waves of the same amplitude and vertical through two square radiation patches; meanwhile, adjusting the phase difference between both waves to 90° will produce a CP wave in the far-field. The simulation and measurement results show that the antenna is in 4.3–4.8 GHz band with S11<−10 dB, S22<−10 dB, and AR<3 dB. Furthermore, a lower axis ratio could be obtained in this work compared with similar antennas of the same type.

Dual‐band double circularly polarized wide‐angle beam‐scanning antenna using planar phase gradient transmitarrays

In this article, a dual-band double circularly polarized wide-angle beam scanning transmitarrays antenna is presented. The transmitarrays antenna can convert the spherical wave into plane circular polarized wave at 20 and 30 GHz bands at the same time and same direction with wide-angle beam scanning characteristic. The unit cell consists of two kinds of Jerusalem Cross to achieve phase shift ranging from 0° to 300° at 20 GHz, from 0° to 312° at 30 GHz with acceptable loss. The fabricated antenna has a wave beam-scanning angle from 1.5° to 52.5° at 20 GHz and from 1.3° to 51.6° at 30 GHz. The maximum gains are 22.1 dBic at 20 GHz and 25.0 dBic at 30 GHz.

Quad-Band Circular Polarized Antenna for GNSS, 5G and WIFI-6E Applications

A quad-band circularly-polarized antenna, for applications of a global navigation satellite system (GNSS), 5G, and WIFI-6E, is designed, fabricated, and measured. The proposed antenna is formed by an L-shaped radiator, a rectangular frame ground with an L-shaped stub, and a rectangular strip at the opposite corner. The microstrip antenna can generate four frequency bands, covering WIFI-6E (5925–7125 MHz), 5G n77 (3300–4200 MHz), n78 (3300–3800 MHz), and the GNSS bands. This antenna generates right hand circular polarization (RHCP) waves in the low frequency band (0.95–2.11 GHz), covering GPS, BDS, GLONASS, and GALILEO applications. Moreover, an L-shaped aperture and three rectangular slits are cut on the ground to broaden the axial-ratio bandwidth at the upper band. A prototype is fabricated and measured to verify the performance of this design. It is shown that the agreement between the simulation and measurement is satisfactorily good. The measured −10 dB bandwidths for each band are 75.8% (0.95–2.11 GHz), 55.8% (3.05–5.39 GHz), 39.9% (5.84–8.19 GHz) and 10.3% (9.14–10.68 GHz), respectively. While the measured 3 dB axial-ratio bandwidths are 59.4% (1.16–2.14 GHz), 35.8% (3.23–4.64 GHz), 8.4% (5.70–6.20 GHz), and 2.6% (7.51–7.71 GHz), the measured gains are 4.56, 2.28, 4.26, and 4.30 dBi at 1.5 GHz, 3.8 GHz, 6 GHz, and 7.6 GHz, respectively.

Wideband Omnidirectional Circularly Polarized Antenna for Millimeter-Wave Applications Using Conformal Artificial Anisotropic Polarizer

A wideband omnidirectional circularly polarized (CP) antenna using a conformal artificial anisotropic polarizer is proposed for millimeter-wave applications. The antenna consists of three parts: an omnidirectional linearly polarized (LP) radiator, an annular hyperbolic lens, and a conformal anisotropic polarizer. The annular hyperbolic lens regulates the spherical wavefront from the LP radiator into a cylindrical shape prior to propagating into the conformal artificial anisotropic polarizer. Each curved slab of the polarizer is conformally tilted 45° to the incident electric field. Therefore, the conformal polarizer is the three-dimensionalization of the 2-D planar artificial anisotropic polarizer. The polarizer designing methodology is the first of its kind to generate wideband CP wave omnidirectionally. The hyperbolic lens and the conformal polarizer are fabricated together using stereolithography (SLA) 3-D printing technology. The measurement results show that the antenna has a wide operating bandwidth of 45% (from 24 to 38 GHz), which completely covers potential 5G 28 GHz spectra. The proposed design has a low fabrication complexity and brings possibilities for high-speed wireless communications using circular polarization.

Novel circularly polarized slot array antennas with a wide 3-dB axial ratio bandwidth based on a spindle-shaped radiating cavity

AbstractA novel wide 3-dB axial ratio (AR) circularly polarized 2 × 2 array antenna is proposed in this paper. The spindle-shaped coupling cavity with tilted waveguide is capable of generating circular polarization waves from incident linear waves, which improves the AR bandwidth (ARBW) of the antenna. With this structure, a similar amplitude of the two orthogonal transmitted wave components and a stable phase difference of nearly 90° can be generated. The circularly polarized antenna proposed herein has been fabricated. According to the measurement results, the operating bandwidth from 5.32 to 6.13 GHz is <−10 dB. In addition, the measured ARBW, which is below 3 dB, can cover the range of 5.41–6.02 GHz. The maximum gain of the antenna can attain 15.65 dBi, and the efficiency is better than 80%.

Lightweight switchable bifunctional metasurface based on VO2: High-efficiency absorption and ultra-wideband circular polarization conversion

Switchable multi-function metasurfaces have received much attention due to their excellent performance of manipulating electromagnetic waves. In this paper, we present a novel design that can realize a high-efficiency absorber and an ultra-wideband circular polarization converter based on an anisotropic metasurface through the phase transition of vanadium dioxide (VO2). At room temperature, the metasurface acts an ultra-wideband circular polarization converter with the VO2 film maintains an insulating state, the theoretical analysis and numerical simulation show that the polarization conversion ratio reaches more than 90% in an ultra-wide band (6.3–15.0 THz) and even reaches almost 100% at two peaks, the relative bandwidth is 82%. When the temperature increases to 68 ℃, the metasurface becomes a high-efficiency absorber with VO2 film in metallic state. Numerical calculations show that the absorber has over 90% high-efficiency absorption of X-linearly polarized wave in the 10.8–13.2 THz frequency range and over 90% high-efficiency absorption of left-handed circular polarization wave in the 10.8–14.4 THz frequency range, both are angle insensitivity for small incident angles from 0° to 20°. The physical mechanisms of the two functions based on our structure are discussed. Our novel design has potential significance in future terahertz medical imaging, non-destructive detectors, polarization converters, and THz communication system.

Corrections to “Multiband Chiral Metasurface for Asymmetric Reflection and Transmission of Circularly Polarized Waves” [Jan 22 178-182

In [1], there was a typo in the transmission coefficient matrix presented in (2). The correct equation is as follows: \begin{align*} &\hspace{-12pt}\left({\begin{array}{cccc} {{T_{rr}}}&{{T_{rl}}}\\ {{T_{lr}}}&{{T_{ll}}} \end{array}} \right) \\ &\hspace{-12pt}=\! \frac{1}{2}\!\left(\! {\begin{array}{cccc} {{T_{xx}} + {T_{yy}} + i({T_{xy}} - {T_{yx}})}&{{T_{xx}} - {T_{yy}} + i({T_{xy}} + {T_{yx}})}\\ {{T_{xx}} - {T_{yy}} - i({T_{xy}} + {T_{yx}})}&{{T_{xx}} + {T_{yy}} - i({T_{xy}} - {T_{yx}})} \end{array}} \!\right)\!. \tag{2} \end{align*}