Left-hand Circular Polarization Research Articles

Selective Plasmonic Responses of Chiral Metamirrors

The properties of circularly polarized light has recently been used to selectively reflect chiral metasurfaces. Here we report the more complete basic functionalities of reflectors and absorbers that display various optical phenomena under circularly polarized light at normal incidence as before. For the chiral metamirrors we designed, the circular dichroism in about 0.4 reflection is experimentally observed in visible wavelengths. The experimental results also show high reflectance for right-handed circular polarization with preserved handedness and strongly absorbed left-handed circular polarization at chiroptical resonant wavelengths. By combining a nanobrick and wire grating for our design, we find and offer a new structure to demonstrate the superposition concept of the phase in the same plane that is helpful in effectively designing chiral metamirrors, and could advance development of their ultracompact optical components.

Tunable and strong circular dichroism metamaterial absorber based on gold-VO2 hybrid structure

The existing terahertz chiral absorber faces a series of issues, including low efficiency, un-tunable absorption, and complex structure. We present a chiral metamaterial absorber integrated with gold and phase-change material vanadium dioxide (VO2) to address the issues above. Our designed metamaterial absorber’s maximum circular dichroism (CD) value, as an ideal chirality-selective meta-absorber, reaches 0.95 when VO2 behaves as a metallic state. However, when VO2 is in the insulator state, the CD value is merely 0.003. Notably, the intrinsic mechanisms of the CD effect are revealed by analyzing the difference in electromagnetic response under left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) illumination. The designed chiral metamaterial absorber supports the free switching of the CD signal between ‘on’ and ‘off’ states by continuously adjusting the conductivity of VO2 with a CD value ranging from 0 to 0.95. Moreover, the absorption performance of chiral metamaterials is affected by geometric parameters and the angle of incidence. To evaluate the capability of chiral structure in biosensing, three typical avian influenza viruses are sensed by detecting changes in their resonant frequencies and CD values. Finally, the presented chiral-selective absorber with phase-change materials has an important reference value in the terahertz range for constructing chiral light detectors, chiral thermal switching, biosensors, and tunable chiral photonics.

Reconfigurable dielectric resonator antenna and array with frequency and polarization flexibility

To implement frequency and polarization hybrid reconfiguration, a 4 × 4 array has been investigated. The radiation elements of the antenna array consist of cylindrical dielectric resonators, Wilkinson power divider, PIN diode, and dielectric substrate. The PIN diode controls the states of each branch in the Wilkinson power divider to achieve frequency and polarization reconfigurability. To verify the feasibility of the design, a fabricated sample of the proposed antenna array has been measured. The results demonstrate that the antenna array can be switched freely between its operating frequencies and polarizations. It operates within a bandwidth of 1.93 to 4.6 GHz for frequency reconfiguration, and three common polarization states—linear polarization, left-handed circular polarization, and right-handed circular polarization—can be continuously tuned from 2.96 to 3.39 GHz.

A wideband dual-circularly polarized traveling wave dielectric resonator antenna array

ABSTRACT In order to meet the demand of high capacity and high speed transmission of satellite communication system, a wideband dual-circularly polarized dielectric resonator antenna (DRA) array is proposed based on the traveling wave principle. Four DRA elements with slot-coupling excitation are sequentially placed on the ground, and the feeding network is designed to realize the two orthogonal circular polarization radiation waves. A notched copper loop (NCL) around the antenna array is adopted to improve the radiation performance. Depending on the operation of the two ports, the NCL generates the induced currents which rotates clockwise/counterclockwise, increasing the axial ratio bandwidth. In order to further improve the gain stability, the copper sheets are embedded on the top surface of each radiation element, and the copper cylinders perturb the internal field distribution of the DRA to introduce higher-order modes. The measurement results show that the left-hand circular polarization and the right-hand circular polarization operating bandwidths are 11.8% (14.97–16.85 GHz) and 12% (14.91–16.82 GHz). The antenna gain achieves 9.0 dBic. This DRA array can be applied for the vehicle mounted RF terminals in satellite communication.

Deep learning and genetic algorithm driven accelerated design for frequency-multiplexed complex-amplitude coding meta-hologram

Frequency-multiplexed metasurfaces represent a significant innovation in breaking the functional limitations of traditional metasurfaces, showing immense potential in multi-channel communication. However, existing frequency-multiplexed metasurfaces primarily focus on pure phase and linear polarization modulation, neglecting the modulation for complex amplitude and circularly polarized waves. Additionally, crosstalk suppression between dual-frequency channels often requires meticulous tuning of the meta-atom structure. Therefore, manually designing a set of meta-atoms that satisfies both complex amplitude modulation and low crosstalk at dual frequencies is extremely challenging and time-consuming. Here, we utilize the method of deep learning and genetic algorithm to design a kind of meta-atom capable of bi-spectral 2-bit amplitude and arbitrary phase modulation, which greatly reduces the design difficulty and achieves excellent low-crosstalk performance. This method can be easily generalized to the design of other complex meta-atoms to improve the design efficiency. Furthermore, we propose a frequency-multiplexed complex-amplitude coding meta-hologram for modulating left-handed circularly polarized (LCP) waves. When illuminated with LCP light, it can reconstruct two distinct holographic images at two different frequencies in the near field with high quality. The independent modulation capability of the metasurface for multiple degrees of freedom of frequency, amplitude and phase gives it broad application prospects in multi-channel communication, data storage and perfect holography.

Broadband polarization-adjustable antenna realized by waveguide circular polarizers.

A broadband polarization-adjustable antenna realized by two waveguide circular polarizers is proposed in this paper. The antenna consists of a rectangular-to-circular transition waveguide, two identically structured rectangular slot circular polarizers, and a conical horn, all connected in sequence. By rotating the two circular polarizers to specific angles, the antenna can switch among four polarization modes: horizontal polarization, vertical polarization, left-hand circular polarization, and right-hand circular polarization. The antenna polarization adjustment principle is thoroughly analyzed. Taking the X-band polarization-adjustable antenna as an example, simulation and optimization were performed, and a prototype was fabricated and measured. The antenna's reflection coefficient is below -18 dB across all polarization modes from 9.2 to 10GHz. In linear polarized modes, gains exceed 10.5 dBi. For circular polarized modes, the gains align with those of linear modes, with an axial ratio of less than 1 dB in the operating frequency band. The measured results are consistent with the simulation results, confirming its excellent polarization adjustment performance and potential for high power microwave applications.

An additively manufactured dual circularly polarized open‐ended waveguide antenna using outer ridges with wideband characteristic

AbstractThis paper presents a novel additively manufactured wideband dual circularly polarized (CP) open‐ended waveguide (OEW) antenna, which adopts a pair of wedge‐shaped outer ridges acting as a circular polarizer. Study found that compared to the con‐ ventional designs that employ internal polarization converting structures, such outer ridges are capable of achieving wider axial ratio bandwidth (ARBW) and better reflection coefficients. On each ridge, two rectangular slots are designed to suppress the higher order mode caused by the increased waveguide size, and further expanding the ARBW. The proposed antenna is fed by two differential ports. By switching the feeding ports, the CP states can be altered to either right‐handed CP (RHCP) or left‐handed CP (LHCP). In terms of configuration, the proposed antenna has a simple one‐piece structure and is fabricated by using dielec‐ tric 3‐D printing technology. To form the waveguide walls, its partial surfaces are coated by copper films through electroplat‐ ing. The proposed antenna features easy fabrication and light weight. Experimental results show that the proposed antenna has an impedance bandwidth of larger than 47.6% (8–13 GHz) with reflection coefficients lower than −15 dB, while the 3‐dB ARBW is 37.7% from 8.4 to 12.3 GHz.

Mechanism of Circular Polarization in Giant Pulses and Fast Radio Bursts

Some giant pulses and fast radio bursts (FRBs) exhibit notable circular polarization, which remains unexplained and carries significant implications for their emission mechanisms. In this study, we identify multiple nanoshot pairs uniformly spaced by approximately 21 μs within a giant pulse emitted by the Crab pulsar. Among these pairs, a subset displays left-hand and right-hand circular polarization in two distinct nanoshots. We propose that the occurrence of such nanoshot pairs with dual circular polarizations arises from the fragmentation of a linearly polarized nanoshot along the magnetic field lines under the extreme Faraday effect, leveraging highly asymmetrical pair plasma and the ultra-intense field of nanoshots. The asymmetry in pair plasmas is likely linked to discharge activities in pulsars. Moreover, the intense field of nanoshots induces cyclotron resonance within the magnetosphere, effectively slowing down the propagation velocity of the circularly polarized mode. Our findings suggest that Crab giant pulses composing nanoshots originate in its polar cap region and escape the magnetosphere along the polar magnetic field. This mechanism can also elucidate the origin of circular polarization in some FRBs and thus lends support to their magnetospheric origin.

Generation of vectorial vortex beams by a coherently combined laser array

With the superpositions of spin and orbital angular momentum, vectorial vortex beams (VVBs) have attracted great attention in recent years. Many approaches have been developed to generate such beams, but high-power output is not supported. Here, we report the coherent beam combining (CBC) for generating VVBs that are compatible with high-power fiber amplifiers. The laser array is composed of two discrete vortex arrays with left-handed and right-handed circular polarization states. The phase and polarization of each beamlet are manipulated simultaneously. Experimentally, the phase noise in the amplifiers is compensated by the all-fiber internal phase control feedback structure. Quarter-wave plates are employed as polarization state converters. When the system is in the closed loop, a distinct and stable VVB can be obtained in the far-field. This work could provide a significant reference for the future implementation of high-power structured beams.

An inverted F-shaped slotted broadband metasurface-based circularly polarized patch antenna for 5G application

This paper presents an inverted F-shaped slotted broadband metasurface (MS)-based circularly polarized (CP) microstrip patch antenna. The host antenna comprises a truncated corner square patch with an inverted F-shaped slot, positioned on a 1.6 mm thick FR-4 substrate backed by ground plane. Concurrently, the MS layer is composed of a 4 × 4 square ring array, constructed on a separate 1.6 mm thick FR-4 substrate with net compact dimensions 0.54λo × 0.54λo × 0.027λo at 5.13 GHz, serving as a superstrate layer. The proposed antenna exhibits impressive performance, including a −10-dB impedance bandwidth from 4.40 GHz to 7.38 GHz as well as a 3-dB axial ratio (AR) bandwidth from 4.74 GHz to 5.52 GHz. Furthermore, at 5.13 GHz, it achieves a notable maximum radiation efficiency and realized gain of 85 % and 6.95 dBic respectively. Moreover, polarization of the antenna is observed as left-handed circularly polarized (LHCP). To validate the impedance response, the antenna’s equivalent circuit model has been sequentially developed, followed by the fabrication of a prototype. The measured results closely resemble with the simulated responses, indicating strong consistency between theory and experimental results. With its overall compact dimension of 0.65λo × 0.65λo × 0.027λo at 5.13 GHz, the proposed CP antenna is well-suited for 5G application.

Multi-band ultrathin reflective metasurface for linear and circular polarization conversion in Ku, K, and Ka bands

Linear polarization (LP) and circular polarization (CP) holds paramount importance in Ku, K, and Ka bands for satellite based communication, and remote sensing applications. Satellite based remote sensing applications face challenges like atmospheric attenuation, noise & interference, and signal degradation. Moreover, satellite based communication application demands CP in two distinct, non-adjacent frequency bands with orthogonal polarizations at greater oblique angles, considering the unpredictable incidence angles of electromagnetic (EM) waves. Addressing these challenges, an innovative metasurface polarization converter is proposed to operate efficiently across the Ku-band (13.5–18.0 GHz), K-band (18.0–26.5 GHz), and Ka-band (26.5–38.5 GHz) frequency ranges. The converter achieves left-handed circular polarization (LHCP) in the Ku- and Ka-bands within the frequency ranges of 14.57–15.65 GHz and 27.47–33.85 GHz for y-polarized incident EM waves. Additionally, it provides right-handed circular polarization (RHCP) in the K- and Ka-bands at 17.27–23.92 GHz and 35.87–38.32 GHz for y-polarized incident EM waves. The LP conversion ratio exceeds 95% in the frequency bands of 15.97–16.85 GHz, 24.70–26.65 GHz, and 34.37–35.45 GHz for y-polarized, LHCP, and RHCP incident EM waves, respectively. The metasurface exhibits robust performance up to incidence angles of 45 degrees under oblique conditions. Experimental validation using traditional board-circuit manufacturing demonstrates close agreement between measured co- and cross-polarized reflection coefficients and simulations in the 13.5–18 GHz, and 24–38.5 GHz frequency range. Thin metasurface with a thickness of only 0.64 = 0.013λo mm, the proposed design outperforms existing studies in the literature, establishing its competitive edge in terms of structure and performance.

On the characterization of reflective surfaces using dual-polarization GNSS-R

Global navigation satellite systems reflectometry (GNSS-R) is a technique to extract information from reflecting surfaces by the reflected GNSS signals. GNSS-R has garnered increasing attention in the scientific literature due to its continuous global coverage and its superior spatial resolution. Moreover, operating in the L-band renders GNSS-R relatively immune to adverse weather conditions and affords high sensitivity to soil electrical properties. This work introduces a new approach with a dual-polarization antenna, left-hand circular polarized (LHCP) and right-hand circular polarized (RHCP), receiving the reflected signal from a sufficiently smooth surface so that all reflected energy arrives from the specular reflection point. The objective is to characterize the reflecting surface by extracting the relative permittivity and conductivity from the reflected signal. In contrast to other studies found in the literature, the reflection of the GNSS signal on different materials, including dielectric and conductive materials is considered. We derive a maximum likelihood estimator (MLE) for estimating the dielectric parameters of the reflective surface and other parameters of the reflected signal. We also derive the respective Cramer–Rao Lower Bound (CRLB) evaluating the performance of the MLE. The attained results are assessed based on the signal-to-noise ratio (SNR) and the angle of reflection of the reflected signal, which are the parameters that predominantly influence the proposed approach. Lower elevation angles, for instance, lead to higher estimation accuracy, while for reflective surfaces composed of metallic materials a higher SNR is needed to yield favorable estimation performance. Regarding dielectric materials, the estimation results are encouraging and thus enable diverse remote sensing applications by GNSS-R using the proposed setup.

Design of high flexible multi-band conformal printed patch antenna for sub 6 GHz 5G-based vehicular communication

ABSTRACT Vehicular communications (VCs) play a major role in intelligent transportation systems (ITS). In addition to preventing unintentional collisions and traffic jams, this system can lower fuel and energy usage in the transportation system. The Internet of Vehicles emerges by integrating the IoT with vehicles for smooth communication. In IoV, vehicular communications may be from vehicle to infrastructure (V2I), vehicle to vehicle (V2V), vehicle to pedestrian (V2P), and vehicle to network (V2N) or vehicle to roadside unit (V2R). The antenna used in vehicular communication has some problems, such as less efficiency and high return loss. The frequency response in the existing methods should not give sufficient data for selecting a better band. To avoid this kind of issue and improve the performance by selecting a better frequency band, this work presents a highly flexible multi-band conformal printed patch antenna for sub-6 GHz 5 G-based vehicular communication application. The substrate used to design the antenna is polyimide, and the microstrip patch antenna is designed with cross-shaped slots. The multi-band circularly polarised antenna is designed to operate in vehicular communication bands such as 2.4 GHz, 4.7 GHz, 5.3 GHz, and 5.9 GHz. The proposed work is simulated in HFSS, and the results of directivity, gain, reflection coefficient, Voltage Standing Wave Ratio (VSWR), radiation pattern, axial ratio, Left-Hand Circular Polarisation (LHCP), Right-Hand Circular Polarization (RHCP) and surface current distribution are evaluated for the conformal antenna.

Dielectric Sphere Oligomers as Optical Nanoantenna for Circularly Polarized Light.

Control of circularly polarized light (CPL) is important for next-generation optical communications as well as for investigating the optical properties of materials. In this study, we explore dielectric-sphere oligomers for chiral nanoantenna applications, leveraging the cathodoluminescence (CL) technique, which employs accelerated free electrons for excitation and allows mapping the optical response on the nanoscale. For a certain particle-dimers configuration, one of the spheres becomes responsible for the left-handed circular polarization of the emitted light, while right-handed circular polarization is selectively yielded when the other sphere is excited by the electron beam. Similar patterns are also observed in trimers. These phenomena are understood in terms of optical coupling between the electric and magnetic modes hosted by the dielectric spheres. Our research not only expands the understanding of CPL generation mechanisms in dielectric-sphere oligomer antennas but also underscores the potential of such structures in optical applications. We further highlight the utility of CL as a powerful analytical tool for investigating the optical properties of nanoscale structures as well as the potential of electron beams for light generation with switchable CPL parities.

Wideband circularly polarized reconfigurable metasurface antenna for 5G applications

Abstract A framework of a metasurface (MTS) – based wideband circularly polarized (CP) reconfigurable antenna for fifth generation (5G) wireless systems operating in the sub-6 GHz mid-frequency range is presented in this article. The proposed structure contains a simple patch antenna, which serves as the primary source, a shorting pin, two ring slots, and a metasurface superstrate. The shorting pin and two ring slots produce perturbation resulting in circular polarization with a narrow axial ratio (AR) bandwidth. A metasurface (MTS) superstrate composed of 4 × 4 rectangular patches stacked over the primary source antenna generates additional resonances that significantly improve the −10 dB impedance and 3 dB axial ratio (AR) bandwidth. Two PIN diodes are employed to alter the circular polarization between left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP). The prototype is made using an FR-4 epoxy substrate and has an overall size of 50 mm × 35 mm × 4.2 mm. The antenna has a −10 dB bandwidth of 44 % (4.0–6.2) and a 3 dB axial ratio bandwidth of 28 % (4.2–5.6). It also has a 3 dB beam width of 74° and 85° in the E and H planes, a gain of 7.1 dBi, cross-polar isolation of more than 15 dB, and a unidirectional radiation pattern. The simulated and measured results confirm that the implemented antenna is promising for sub-6 GHz 5G communication systems, particularly cognitive radio, wireless body area networks (WBAN), and satellite communication systems.

Multi-functional active frequency reconfigurable polarization converter using a simple DC bias circuit

A multi-functional active converter with frequency reconfiguration is proposed and experimentally verified. The unit cell is composed of two T-shaped metal patches connected with a PIN diode. Two metal vias are designed to connect the T-shaped metal to the ground. The T-shaped metal patches are slantly arranged to provide circular polarization conversion. By switching on and off the PIN diode, frequency reconfiguration can be realized. The DC bias is exerted to the PIN diode through two metal vias connecting to the ground. The ground is gracefully designed so that a very simple bias circuit is developed. It is demonstrated that three frequency bands are generated for both off and on states. An incident linear polarization can be converted to right-hand circular polarization, linear polarization, and left-hand circular polarization in these frequency bands, respectively. A circuit model is established to understand the principle of this design. It is found that circuit simulation is consistent with full wave simulation. Measurements conducted during the frequency range of 20-40 GHz shows that good agreement with simulation has been reached.

A 27 ​GHz, simple 2-bit 1×8 phased array

This study demonstrates a simple 2-bit phased array operating at 27 ​GHz that supports one-dimensional beam scanning with left-handed circular polarization (LHCP). The antenna is constructed using a compact four-layer printed circuit board (PCB) structure, consisting of a 90° phase shifter layer with microstrip structures, a ground (GND) layer, a direct current (DC) control layer, and a circularly polarized annular radiation patch layer with 1-bit phase shifting. Based on the proposed unit structure, a 1×8 array with half-wavelength inter-element spacing was designed and validated. Experimental results show that the array achieves a peak gain of 10.23 dBi and is capable of beam scanning within ±50°.

Pattern reconfigurable UHF RFID universal reader antenna array

In response to the rising demand for adaptable and versatile RFID reader antenna, this paper presents an integrated reader system featuring an array of four antennas. The primary objective is to design four identical, circularly polarized, high-gain, wide-band antennas that cover the 860–960 MHz UHF RFID band. Each antenna consists of three layers, the radiator and director layers, designed as patch antennas with trimmed edges and a central slot, while the reflector layer is constructed from a copper material. These layers are assembled with four Teflon spacers, and a coaxial connector is utilized for feeding the antenna. An open-circuit stub is used to improve impedance matching. CST Microwave Studio was employed for design optimization. The four sector antennas achieve a 150 MHz bandwidth (833–983 MHz) and a maximum gain of 8.4 dBi. When combined with a four-port RFID reader (ThingMagic M6E), the antenna system generates four electronically switchable beams in the azimuth plane. The proposed antenna exhibits left-hand circular polarization (LHCP) within the RFID ISM band, maintaining an axial ratio (AR) between 1 dB and 3 dB. The antenna array, including the reader and control unit, measures 255 × 255 × 210 mm. Simulation and measurement results confirm the system's performance and functionality.

Compact dual-band dual sense circularly polarized flexible antenna with polarization rotation metasurface for off-body communications

ABSTRACT A dual-band dual circularly polarised flexible antenna, operating at 3.5 GHz for WiMAX and 5.8 GHz for industrial, scientific, and medical (ISM) bands, is proposed for wearable applications. The antenna design integrates a wideband comb-shaped slotted monopole antenna with a polarisation rotation metasurface (PRMF). The PRMF unit cell consists of a nested split square ring in the corner and a square ring in the centre, where the split square rings facilitate polarisation conversion and the centre square ring enhances the axial ratio. The PRMF integration helps achieve dual circular polarisation (CP) radiation, with left-handed CP in the WiMAX band and right-handed CP in the ISM band. The proposed monopole antenna and PRMF are printed on a conformal polyimide substrate, with a total footprint of 48 × 48 mm2 (0.31λo2). The proposed antenna has a 10 dB impedance bandwidth of 24.9% (3.2 to 4.2 GHz) and 18.9% (5.3 to 6.43 GHz), a 3-dB axial ratio bandwidth of 11.1% and 21.4%, and a peak gain of 6.4 and 6.7 dBic in both bands. Numerical and measured results demonstrate that the antenna performs well in the presence of human body and structural deformations. These attributes make the proposed design highly suitable for off-body wearable applications.

Ultra-Thin Metasurface Polarization Converter with Linear and Circular Polarization Features for RCS Applications

AbstractIn this study, an attractive ultra-thin metasurface (MS) converter is proposed for both K-band (18–27 GHz) and Ka-band (27–40 GHz) having the superior performance of the linear-to-linear polarization (LP-LP) conversion and the linear-to-circular polarization (LP-CP) conversion. Its operating bandwidth for the LP-LP conversion is approximately over 18.6–26.7 GHz (lower part of the K-band) with a conversion efficiency of more than 90% and over 19.55–24.8 GHz (upper part of the K-band) with a polarization conversion ratio (PCR) value of more than 99%. In addition, its operating bandwidth for the LP-CP conversion (a left-handed circular polarization (LHCP)) is nearly between 31.8 and 40.5 GHz (Ka-band) with a PCR value of more than 99%. The converter can achieve a PCR value greater than 90% for both the LP-LP and LP-CP conversions for an oblique incidence wave with an incidence angle up to $$ 40^\circ $$ 40 ∘ . The design also provides mono-static radar cross section for the 18.6–26.7 GHz frequency range, where the LP-LP conversion is provided. The proposed structure can be considered to be ultra-thin having a thickness of 1 mm corresponding to 0.075$$\lambda $$ λ in the LP-LP and 0.12$$\lambda $$ λ in the LP-CP cases concerning the center frequency. The cost-effective bandwidths (BWCEs) are 210 and 34 for the LP-LP and LP-CP conversions, respectively. Free-space experiments were carried out at X-band and Ku-band to validate our design.