Right-handed Circularly Polarized Wave Research Articles

A switchable PCM-based integrated structure with alternative radiation and stealth functions

In this work, based on the switchable polarization conversion metasurface (SPCM), the dual functions of high gain right-handed circularly polarized (RHCP) radiation and wideband 10 dB radar cross section (RCS) reduction stealth are achieved in one structure. As the key component to achieve good radiation and low RCS, the proposed SPCM unit consists of the asymmetrical Jerusalem Cross top layer and switchable metal plate bottom layer separated by an air space. Then the SPCMs are arranged in a chessboard configuration and placed above a patch array antenna with the sequentially rotated feeding network. When p-i-n diodes are on, low RCS is implemented by 180° (±37°) reflection phase differences between two neighboring SPCM cells. When p-i-ns are off, the chessboard SPCM provides a transmission window for highly directional RHCP wave radiation.

Reconfigurable Multifunctional Transmission Metasurface Polarizer Integrated with PIN Diodes Operating at Identical Frequencies

Herein, a reconfigurable multifunctional transmission metasurface polarizer, structured with double Jerusalem crosses and integrated with four PIN diodes, is presented. The bottom Jerusalem cross is rotated by 35∘ with respect to the top cross. Both numerical and experimental observations reveal that a linearly polarized (LP) outgoing wave is transmitted at approximately 4.0 GHz when subjected to a left-handed circularly polarized (LCP) or right-handed circularly polarized (RCP) incident wave. The transmission efficiency reaches -2.5 dB when all elements are in the ON state. Furthermore, active control of switchable PIN diodes operating in various statuses unequivocally demonstrates the ability to convert an incident wave polarized in the x or y direction to a LCP or RCP wave, respectively, within the identical frequency band, spanning from 3.6 GHz to 4.3 GHz. This conversion is achieved with a transmission coefficient of -3.5 dB or -4.2 dB at the peak frequency. The proposed metasurface polarizer presents a potentially dynamic method for simultaneously manipulating various polarization conversions of electromagnetic (EM) waves within a desired frequency band.

No circular birefringence exists in a chiral medium: an analysis of single-mode refraction

Optical activity is one of the most fundamental phenomena in nature. The existing theoretical description of optical activity is the circular birefringence, proposed in 1825 by Fresnel. It states that the right-handed circularly polarized (RCP) and left-handed circularly polarized (LCP) waves in a chiral medium propagate at different velocities. Here we show that this is not the case. After obtaining the refraction and reflection coefficients of any elliptically polarized wave at the surface of an isotropic chiral medium, we derive the conditions for single-mode refraction. By means of the process of single-mode refraction, we demonstrate that both the refracted RCP and the refracted LCP waves at normal incidence can be expressed as a coherent superposition of a pair of orthogonal linearly polarized waves that are rotated simultaneously. As a result, they must propagate at the same velocity as the linearly polarized waves. A physical interpretation is also given in detail. In particular, we show that the state of polarization of any elliptically polarized wave in a chiral medium is rotated with propagation. Such a rotation amounts to the rotation of polarization bases without involving the change of the Jones vector. The rotation of the RCP and LCP waves, as special cases of elliptically polarized waves, results in two opposite phases as if they propagated at different phase velocities with their polarization states transmitted unchanged. These results demonstrate that the conventional characterization of optical polarization is incomplete. A further investigation into its new features is of great significance.

Nonresonant propagation phase based metasurface design for independent manipulation of dual circularly polarized waves

Pancharatnam–Berry (PB) phase has attracted significant attentions due to its phase control characteristic for circularly polarized (CP) waves. PB phase structure usually provides equal but inverse phase shifts for the left-handed CP (LCP) and right-handed CP (RCP) waves. In this article, a method is proposed to decouple this correlation and to manipulate the wavefronts of interacting LCP and RCP waves independently and simultaneously. Nonresonant propagation phase realized through open-ended transmission line is introduced as an additional degree of freedom to achieve totally independent phase responses of the orthogonal CP waves. A metasurface is presented to shape the reflected orthogonal CP waves into vortex beam and pencil beam independently. Simulation and measurement results confirm with each other and demonstrate the proposed method.

Additively Manufactured Metal-Only Millimeter-Wave Dual Circularly Polarized Reflectarray Antenna With Independent Control of Polarizations

This communication proposes an additively manufactured metal-only millimeter-wave dual circularly polarized (CP) reflectarray with independent control of polarizations. A metal-only right-hand CP (RHCP) antenna is designed and used as the reflectarray’s phase-shifting unit cell (UC). The RHCP UC is immune to the LHCP incidence, and the UC directly reflects the LHCP incidence into free space. Thus, the phase shifting of the LHCP wave solely depends on the rotation angle of the UC. For the RHCP incidence, it is received by the RHCP UC first and induced into the metal waveguide. Then, the energy is reflected by the ground of the metal waveguide and reradiated into free space with RHCP. Thus, the phase shifting of the RHCP wave is determined by the rotation angle of the UC and the length of the metal waveguide. By properly selecting the rotation angle of the UC and the length of the metal waveguide, RHCP and LHCP can be independently manipulated. To demonstrate, two reflectarray antennas with different LHCP and RHCP beam directions are fabricated using additive manufacturing and experimentally verified.

Newton-ADE-FDTD Method for Oblique Incident Magnetized Time-varying Plasma

In this paper, the Newtonian equation of motion describing the movement of electrons when electromagnetic waves propagate in a magnetized plasma is combined with the traditional auxiliary differential equation finite difference time domain (ADE-FDTD) method. The FDTD iterative formulas of transverse magnetic (TM) wave and transverse electric (TE) wave of the electromagnetic wave obliquely incident on the magnetized time-varying plasma plate are derived. The biggest difference between this method and the ordinary ADE-FDTD algorithm is the addition of the logarithmic derivative of the time-varying plasma electron density to calculate the current density, which is called the Newton-ADE-FDTD method. Through Example 1, the reflection coefficient of electromagnetic wave incident on the magnetization time-varying plasma plate was calculated, and the correctness of the improved algorithm was verified. At the same time, the Newton-ADE-FDTD algorithm is used to calculate the reflection coefficient of electromagnetic waves incident on the magnetized plasma-dielectric photonic crystal. The results show that different incident angles have a greater impact on the reflection coefficients of left-handed circularly polarized wave (LCP) and right-handed circularly polarizedwave (RCP).

Simultaneously Achieving Circular‐To‐Linear Polarization Conversion and Electromagnetically Induced Transparency by Utilizing a Metasurface

AbstractIn this work, the simultaneous realization of circular‐to‐linear polarization conversion (PC) and electromagnetically induced transparency (EIT) is theoretically reported in terahertz (THz) range by utilizing a metasurface when left‐handed circularly polarized (LCP) waves are incident. The metasurface is composed of two kinds of via‐coupled modules (VCMs). Each module can realize the same EIT phenomenon by the destructive interference during the bright and dark modes due to the symmetry‐broken rotation operation of the structure instead of the near‐field coupling. The VCMs can simultaneously respond to the incident LCP waves and are identically converted into LCP and right‐handed circularly polarized (RCP) waves, which own the same amplitudes and phase shifts. Therefore, the LCP and RCP waves can generate a resultant linearly polarized (LP) wave. The EIT transparent windows have emerged in 0.729–1.051 THz during the transmission of the LCP waves and the conversion of LCP to RCP. The values of maximum group delays both are 358 ps. The operating frequency band of the PC is located in 0.65–1.10 THz, and relative bandwidth reaches 51.4%. Optimal relative conversion efficiency reaches 93.2% at 0.921 THz. The EIT behavior has been investigated by the two‐oscillator model to further confirm the consistency of the simulation results.

All-dielectric transmission type three-frequency linearly polarized to circularly polarized converter

In this article, a transmissive three-frequency linearly polarized (LP) wave to circularly polarized (CP) wave metasurface is designed using all-dielectric materials. The structure is composed of a cross-shaped bar resonator and a split circular ring resonator. Numerical simulations results show that when the LP wave is incident on the device, it will be converted into nearly perfect right-handed circularly polarized (RHCP), left-handed circularly polarized and RHCP waves at 2.2146, 2.2467 and 2.3144 THz. The distribution of the conduct current, electric field and magnetic field are investigated to explain the physical mechanism. And the influence of the structural parameters and different incident angles for the structure are also studied in the end.

Coplanar Waveguide-Fed Bidirectional Same-Sense Circularly Polarized Metasurface-Based Antenna

This paper presents the design of a bidirectional same-sense circularly polarized (CP) antenna that uses metasurfaces. The antenna consists of two metasurfaces, each comprising an array of 2 × 4 corner truncated patches placed back-to-back on the top and bottom of the antenna. In addition, a ground plane with an etched slot is sandwiched between the substrates at the front and back, and the feed line is a 50 Ω coplanar waveguide. The antenna radiates same-sense right-handed CP waves in both the front and back directions and has overall dimensions of 48 mm × 24 mm × 3.048 mm (0.91λo × 0.45λo × 0.05λo at 5.7 GHz). The measured reflection coefficient for |S11| < -10 dB yields an impedance bandwidth of 5.21–6.26 GHz (18.4%) and an axial ratio (AR) bandwidth of 5.36–6 GHz (11.2%) for both front and back directions. The antenna gain is 3–5.29 dBic for both directions and has a radiation efficiency of >96% within its AR bandwidth.

Bispectral Circular Dichroic Coding Metasurfaces

AbstractThe frequency‐dependent circular dichroism is proposed to extend the wave manipulating capability of coding metasurfaces. As a proof of concept, the bispectral circular dichroic coding metasurfaces (CDCMs) are realized using circular dichroism resonators (CDRs) implemented via introducing loss resistors into the circular polarization conversion resonators. The CDRs are distinguished into left‐handed CDRs and right‐handed CDRs. Left‐handed CDRs absorb left‐handed circularly polarized (LCP) wave and convert right‐handed circularly polarized (RCP) wave into LCP wave. Conversely, they are defined as right‐handed CDRs. Two bispectral CDRs are designed with the left‐handed (right‐handed) and right‐handed (left‐handed) working bands in 7–8.5 and 22.2–22.5 GHz, respectively. And then, 1 bit bispectral CDCM with 0101…/1010… coding sequence is designed. Simulated results indicate that the designed CDCM strongly absorb the incident LCP (RCP) waves in the frequency region 7–8.5 GHz (22.2–22.5 GHz), but the incident RCP (LCP) waves are anomalously reflected into four beams of the LCP (RCP) waves with high efficiency. The measured results agree well with the simulations. The results in this work may provide an effective solution for the inverse and helicity‐dependent manipulation of the electromagnetic waves in two distinct frequency regions.

A right-handed circularly polarized wave generated by a waveguide-fed holographic metasurface

We propose a novel method superposed two linearly polarized components to generate a right-handed circularly polarized (RCP) wave by using a holographic waveguide-fed metasurface. Combining with the holography principle and the polarizable particles based method, the expected RCP wave can be steered flexibly only by changing the slot state of each unit cell. A prototype generating a RCP wave at boresight direction is simulated, fabricated and measured, respectively. Both simulation and experiment results verify the good capability of the proposed metasurface. Applying this method, the resultant metasurface does not need a complex feeding network and can be easily extended to a reconfigurable CP metasurface. Therefore, the proposal has a huge potential in reconfigurable multifunctional CP devices.

Absorbers with spin-selection based on metasurface

In recent years, due to their features nonexistent in natural matirials, the perfect absorbers based on metasurfaces have become a hot research point. Although great progress has been made, the absorbers with spin-selection are rarely reported. However, the absorbers with spin-selection have more widespread applications in chiral sensors and satellite communication. Therefore, a spin-selection absorber based on the metasurface with modified square split-ring structure is proposed. Firstly, the theoretical conditions for generating the spin-selection absorption are analyzed theoretically, and then the qualified metasurface unit cell is designed under the guidance of the theory. We design an asymmetric modified square split-ring resonator to break both the <i>n</i>-fold (<i>n</i>>2) rotational symmetry and mirror symmetry. The unit cell is composed of three layers, i.e. the top layer, which is a modified square split-ring, the middle layer, which is an FR4 dielectric plate with a thickness of 4 mm, and the bottom layer, which is an all-metal plate acting as the reflecting incident wave. In order to obtain the optimal performance, the designed meta-atom is optimized by CST Microwave Studio, a well-known commercial full wave simulation software.The numerical simulation results show that the unit cell can selectively absorb the right-handed circularly polarized waves and reflect left-handed circularly polarized waves at 7.2 GHz. A maximum absorption rate for the absorption of right-handed circularly polarized (RCP) waves reaches a value higher than 90%, while the absorption rate of the other spin state is kept lower than 19%. In addition, to meet the need of practical applications, the absorption performance is also further investigated under different oblique incident angles, with the wave vectors confined in the <i>x-z</i> plane and <i>y-z</i> plane, respectively. Finally, to further understand the mechanism of spin-selection absorber, the surface current distributions are also simulated for LCP and RCP wave, respectively. The different surface current distributions are obtained for incident LCP and RCP wave, which is a solid evidence for spin-selection absorption. This paper offers a reference for the generation of spin-selection absorber. The proposed method not only is suitable for microwave region, but also can be extended to higher frequencies, and hopefully it can be widely used in the field of communication.

An Electronically-Switched Frequency-Agile Hybrid Dielectric Resonator Antenna With a Fixed Reconfigurable Circularly Polarized Band

In this article, an electronically-controlled frequency-agile hybrid dielectric resonator antenna is presented that also produces a reconfigurable circularly polarized (CP) wave over a specific frequency range. Two L-shaped metallic strips are placed adjacent to a partial ground plane that can be shorted/detached in four combinations using two PIN diodes (D1 and D2). Frequency reconfigurability is achieved by switching from both OFF to at least one ON state to yield a single and dual-band responses for the former and latter, respectively. The Eigen mode simulation reveals that the upper-band is mainly attributed to the quasi-TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">δ21</sub> mode of the rectangular dielectric resonator. The lower-band in one and two ON-states arises due to the dielectric-loaded monopole antenna and the strip-loaded partial ground plane, respectively. The ON-OFF state produces a right-handed CP wave at the lower band that can be reconfigured to a left-handed CP wave by switching to OFF-ON state. A fabricated sample is measured and simulation results are validated. The measured -10 dB impedance bandwidths for OFF-OFF, ON-ON, OFF-ON, and ON-OFF are 13.31% (4.42-5.05 GHz), 11.30% (2.17-2.43 GHz)/27.43% (3.68-4.85 GHz), 30.64% (2.46-3.35 GHz)/17.94% (4.16-4.98 GHz), and 26.57% (2.48-3.24 GHz)/18.7% (4.12-4.97 GHz), respectively. The measured 3 dB axial ratio bandwidths are 12.20% (2.54-2.87 GHz) and 10.95% (2.59-2.89 GHz) when D1 and D2 are turned-ON alternatively.

Theoretical Investigation of Radiation in the Normal Direction for a Metaloop Antenna

Radiation in the normal direction for a metaloop antenna is discussed. First, the radiation field generated from an N-type current distributed along a loop, E N , is investigated. The investigation clarifies the behavior of the unbalance between the left-handed circularly polarized (LHCP) component of E N at frequency f (-) and the right-handed circularly polarized (RHCP) component of EN at frequency f (+) , where the loop circumference at these frequencies is one guided wavelength. Secondly, the radiation field generated from a C-type current, E C , is investigated. The second investigation, when combined with the first investigation, leads to an inference that balanced radiation (and hence balanced gain) will be obtained when the N-type current over a certain region of the loop is replaced with a C-type current. Thirdly, to check this inference, a radiation field generated from a composite of the N-type and C-type currents, E NC , is formulated. Using this formulation, the ratio of the gain for an LHCP wave to the gain for an RHCP wave, G r , is derived. Fourthly, a metaloop antenna simulation model that has a balanced gain is created using practical N-type and C-type metaatoms that realize the composite current. Finally, a metaloop antenna is fabricated on the basis of the antenna simulation model. Measurements confirm that the fabricated metaloop antenna has a balanced gain in the normal direction. As supplementary data, the radiation pattern and VSWR of the fabricated metaloop antenna are also presented, together with the radiation efficiency and some comments.

Chirality selective metamaterial absorber with dual bands.

In this paper, a sensitive chirality selective metamaterial absorber (CSMA) is constructed by using 'I-shaped' resonator with asymmetric twisted metallic wires. Absorption of 95.18% and 91.77% at two resonant frequencies can be achieved for left-handed circularly polarized (LCP) incident wave, with little loss of right-handed circularly polarized (RCP) incident wave, which results in significant absorptive circular dichroism. Not only can the CSMA intensely absorb LCP illumination with dual bands, but also circularly polarized (CP) conversion for RCP wave is achieved over a broad bandwidth. The spin-dependent absorption, closely linked to chiral symmetry breaking, is investigated through oblique incidence, power loss distribution and scanning parameters optimization. The proposed strategy is further demonstrated in mid-infrared band which could advance the applications in polarization manipulation to circularly polarized detectors/lasers, chiral sensing/bolometers, and molecular spectroscopy.

A Linearly Polarized Patch Antenna With a Continuously Reconfigurable Polarization Plane

A linearly polarized (LP) wave with an arbitrary polarization plane is generated by combining left-handed circularly polarized (LHCP) and right-handed circularly polarized (RHCP) waves radiated from a dual-circularly polarized patch antenna. The polarization plane of the LP wave is continuously controlled by changing the phase difference between the LHCP and RHCP waves by using variable phase shifters composed of a quadrature hybrid and varactor diodes. Experimental results show that the polarization plane rotates continuously from −95° to 107° with a cross-polarization discrimination kept better than 22 dB in the boresight direction at 5.2 GHz.

Study of Terahertz Radiation Generation by Two Laser Beams in an Axial Magnetized Rippled Density Plasma

This paper presents a scheme to achieve terahertz radiation by the beating of top-hat lasers in a rippled density collisional magnetized plasma. The nonlinear current at terahertz frequency arises on account of nonlinear ponderomotive force as a result of beating of the two lasers. A uniform static magnetic field which is considered parallel to the direction of lasers leads to, depending on the phase-matching conditions, propagation of right-hand circularly polarized (RCP) or left-hand circularly polarized (LCP) waves in plasma. It is found that, terahertz amplitude of RCP wave for high values of beating frequency is slightly larger than LCP wave. The contribution of magnetic field, laser index and collision frequency are discussed for the efficient terahertz radiation generation. With the optimization of these parameters, the efficiency of order of 25 percent can be achieved in the present scheme.

Design and experimental verification of single-layer high-efficiency transmissive phase-gradient metasurface

Polarization characteristic is an important feature of electromagnetic (EM) wave. Manipulating polarization state and controlling propagation direction of EM wave by phase-gradient metasurface (PGM) have become a research hotspot in recent years. However, using transmissive PGM for polarization manipulation often suffers a low efficiency. To alleviate this problem, multilayered structure was utilized. However, it often suffered bulky volume and design complexity. Therefore, engineering a thin high-efficiency transmissive PGM with polarization manipulation is a pressing and challenging issue. In this paper, a single-layer high-efficiency transmissive PGM with cross-polarization conversion and anomalous refraction is designed. To illustrate the working mechanism, the PGM is comprehensively investigated through theoretical analysis, EM simulations and experimental measurements. The unit cell evolving from an electric-field-coupled resonator is carefully designed to exhibit a Pancharatnam-Berry phase gradient. Each rotated element irradiated separately by the normally-incident left-handed circularly polarized (LHCP)and right-handed circularly polarized (RHCP) waves is simulated in CST microwave studio. The results show that the cross-polarization transmission magnitude keeps over 0.9 and does not change as the rotation angle varies. Moreover, the phase shift is twice the rotation angles and the direction of refracted beam is opposite under the above two different polarizations. In addition, the cross-polarization conversion ratio is above 0.9 from 14 GHz to 15.8 GHz. On the premise of high transmission magnitude, the phase of the cross-polarized transmission can be freely manipulated via varying axis orientation. By spatially arranging six unit cells in rotation angle steps of 30, a PGM with a phase difference of 60 between adjacent unit cells is designed. As is well known, linearly-polarized (LP) EM waves can be decomposed into LHCP and RHCP waves with equal amplitudes. Therefore, an LP wave through the PGM will be separated into two counterpropagating CP waves. The high-efficiency anomalous refraction of the PGM is verified from simulated near-field electric field distributions and far field normalized power patterns. The simulated refracted angle is 33.5, which is in accordance with the theoretical designed value (33.75). Moreover, the transmissive power intensity spectrum under the normally-incident LP waves is simulated and measured. The simulated and measured results are in good agreement with each other, showing that the transmitted wave is perfectly split into two counterpropagating waves from 14.9 GHz to 15.3 GHz. Compared with the available transmissive PGMs, our proposed PGM features high efficiency and thin structure with only single layer, making the proposed PGM a promising alternative to manipulating propagation and polarization of EM waves.

Metamaterial Spiral Antenna

Conventional spiral antennas radiate either a left-handed circularly polarized (CP) wave or a right-handed CP wave in a specific direction (single CP radiation). This letter presents a novel spiral antenna, designated as the metamaterial spiral, which radiates a dual CP wave. First, the principle for left-handed CP radiation and right-handed CP radiation is explained using “current bands.” Second, based on this principle, a prediction for dual CP radiation is made for a spiral structure. Third, for confirming this prediction, spiral arms are constructed using numerous straight filaments, each having a left-handed property with an inherent right-handed property. Numerical simulation confirms the predicted dual CP radiation. The gain and radiation pattern are discussed.

The efficient inject of high microwave powers into the overdense magnetoactive plasma in the waveguide

On the boundary vacuum — a dense magnetoactive plasma, an incident RHCP (right hand circularly polarized) wave is strongly reflected ifω 0 2 /ω 2 ≫ 1 andω ce/ω > 1;ω, ω 0,ω ce are the ncident wave frequency, the plasma frequency and the electron cyclotron frequency, respectively. This reflection strongly lowers the efficiency of the plasma heating by microwaves. Our experimental study shows that a suitable matching system consisting of dielectric plates, placed in front of the plasma, can ensure practically complete transfer of the RHCP wave energy into a dense plasma. The experiment was carried out in the S band waveguide (λ=12·7 cm) with the power of the order of l kW.