Circularly Polarized Wave Research Articles

A wideband circularly polarized S ‐shaped slot antenna

This article introduces a simple wideband circularly polarized (CP) S-shaped slot antenna for ISM band wireless communication applications. By using a wide curve S-shaped slot patch on the top side and a T-shaped feeding line on the bottom side of the substrate, the wideband CP wave is generated. The overall size of the proposed antenna is 0.85λ × 0.85λ × 0.011λ (λ is the wavelength of the lowest operating frequency) and it has a broad impedance bandwidth of 68.1% between 1.66 and 3.44 GHz for S11 < –10 dB and a 3 dB axial-ratio bandwidth of 57.1% between 1.68 and 3.06 GHz. Within the axial-ratio bandwidth, the measured gain of the proposed antenna ranged from 2.1 to 5.4 dBic. The measured results are in good agreement with simulated results. The new type of slot antenna with wide bandwidth and simple structure is a good candidate for various RFID applications.

Dual-Loop Arrays Fed by Coplanar Parallel Lines for Wideband Circular Polarization

Using the method of moments, we analyze three types of series-fed array antennas for circular polarization. First, we present a reference antenna's radiation characteristics with symmetrical dual loops fed by balanced parallel lines. Next, we modify the symmetrical dual loops into asymmetrical ones to enhance a circularly polarized (CP) wave bandwidth. It is found that the modified antenna has a bandwidth of 35% for a 3 dB gain-drop criterion, where the axial ratio is less than 3 dB. Finally, we use unbalanced parallel lines for feeding the asymmetrical dual loops to simplify the feed system. It is revealed that the antenna shows a CP wave bandwidth of 19%, which is twice as wide as that of the reference antenna.

High-efficiency ultrathin terahertz geometric metasurface for full-space wavefront manipulation at two frequencies

It has been demonstrated that metasurfaces have the ability to manipulate the wavefront. However, most multifunctional metasurfaces reported to date only operate in either reflection or transmission mode. In this paper, a bilayer metasurface based on geometric phase is proposed to independently tailor the wavefronts of transmitted and reflected circularly polarized (CP) waves at two different terahertz frequencies. More specifically, the metasurface can transform the incident CP wave to its cross-polarization component with a high conversion coefficient of about 0.87 (0.92) after refraction (reflection) at 0.6 (1.67) THz. The full 2π phase shift can be obtained independently by varying the geometrical parameters of the unit-cell structure at two different operation modes. As proofs of concept, anomalous refraction and reflection, dual-band full-space cylindrical focusing metalens and vortex beam generation with different modes are numerically demonstrated. Our work provides an effective method to integrate two or more different functionalities into a simple metasurface-based device, and the independent phase modulation characteristic of our proposed metasurface also shows infinite potential in wavefront control of full space.

Dual Circularly Polarized Fabry–Perot Resonator Antenna Employing a Polarization Conversion Metasurface

A dual circularly polarized (CP) Fabry-Perot (FP) resonator antenna is presented in this paper. A linear to circular polarization conversion metasurface (MS) is employed as the superstrate of the FP resonator antenna. The working principle of the unit cell adopted by the MS enables it to independently control the transmission and reflection characteristics. Firstly, the MS is designed to present high reflectivity to ensure the high gain of the FP resonator antenna. Then the capability of polarization conversion is endowed to it. The square patch of the unit cell can receive two orthogonal LP waves, and the cross slot on the ground plane can also make them get through. Meanwhile, the circular patch with 45° tilted etched slot can radiate different CP waves when excited by different LP waves. Therefore, the proposed MS can combine the function of partial reflection and transmission polarization conversion. And for different LP waves, the MS can convert them into different CP waves. A dual LP microstrip patch antenna is designed to act as the feed of the resonator antenna. When the antenna is fed at different ports, different LP waves are excited in the resonant cavity and are converted into different CP waves by the MS, thus the antenna obtains dual CP radiation. The measured results indicate that the antenna can exhibit excellent dual CP radiation characteristic. Compared with other reported dual CP resonator antennas, the proposed antenna can obtain well performance with simple structure and low profile.

S-Shaped Metasurface-Based Wideband Circularly Polarized Patch Antenna for C-Band Applications

This research proposed an S-shaped metasurface (MTS)-based wideband circularly polarized (CP) patch antenna for C-band uplink frequency spectrum. The proposed MTS-based CP patch antenna was of low profile and fabricated on three substrate layers: upper, middle, and lower. The upper substrate contained 4 × 4 periodic S-shaped MTS elements, the middle substrate functioned as ground plane with a rectangular-shaped slot at the center, and the lower substrate contained a coplanar waveguide with microstrip and ground. The S-shaped MTS elements converted linearly polarized (LP) into CP wave. Simulations were performed, and an antenna prototype was fabricated and experiments carried out. The measured impedance bandwidth and axial ratio bandwidth (ARBW) at the center frequency of 5.9 GHz were 43.22% (4.05 - 6.6 GHz) and 22% (5.3 - 6.6 GHz), respectively, rendering the proposed antenna suitable for satellite communication applications. The proposed antenna achieved the maximum gain of 6.16 dBic at 5.6 GHz. The novelty of this research lies in the use of S-shaped MTS elements to efficiently convert LP into CP wave and achieve wider ARBW for the C-band uplink spectrum.

Multi-beam multi-mode vortex beams generation based on metasurface in terahertz band

The generating of vortex beams in the terahertz (THz) band attracts significant attention due to their applications in high-speed communication and high-resolution imaging. In this article, a novel reflective metasurface working in the THz band is designed to generate four vortex beams with different topological charges in different directions. The unit cell is designed based on the geometric phase, and it consists of two metallic (gold) layers and one dielectric layer in between. The top layer of the unit cell includes an elliptic patch and a circular ring, and the bottom layer of the unit cell is a metallic ground. The reflection efficiency of the unit cell is very high due to the presence of metallic ground. To break through the limitations of traditional methods, the metasurface is a good choice to generate beams that carry orbital angular momentum (OAM). Using the concept of geometric phase, the reflection phase of reflective circular polarization (CP) electromagnetic waves can be controlled in an ingenious way. Owing to the property of the geometric phase, inverse phase shift can be achieved for left-handed circular polarization and right-handed circular polarization waves. By utilizing this trait of geometric phase, one can decompose a linear polarization wave into two orthogonal circular polarization waves and control their properties respectively. By rotating the top layer of the unit cell, 360-degree phase shift and the phase distribution satisfying the requirement for generating the multi-beam multi-mode vortex beam can be achieved. In order to control the direction and the topological charge of each beam, based on the geometric phase, the theory of reflectarray and the phase composition principle, the phase distribution of the reflective metasurface is calculated to provide the phase compensation to make the vortex beams point to certain directions. It is worthwhile to point out that the method presented in this paper provides a way to generate complex multi-mode vortex beams in the THz band. The simulations and measurements show that the metasurface can generate four vortex beams with topological charges &lt;i&gt;l&lt;/i&gt; = ± 1 and ± 2 in different directions in the THz band. These results also indicate that our design has great potential applications in wireless communication and high-resolution imaging.

Low-Profile Wideband Unidirectional Circularly Polarized Metasurface-Based Bowtie Slot Antenna

In this paper, the design of a wideband circularly polarized (CP) bowtie slot antenna that uses metasurfaces is presented. The antenna consists of a single-layer substrate with 4 × 4 periodic corner-truncated metasurface patches printed at the top side of the substrate and a bowtie-shaped slot etched on the ground plane. The corner-truncated metasurface patches are utilized to convert the linearly polarized wave into a CP wave. The antenna is fed by a 50-Ω coplanar waveguide. The antenna, with an overall size of 42 mm × 42 mm × 2.3 mm (0.71 λo × 0.71 λo × 0.038 λo at 5.1 GHz), was fabricated and measured. The measured reflection coefficient for |S11| < -10 dB yielded an impedance bandwidth of 3.75–6.67 GHz (55.7%), an axial ratio (AR) bandwidth of 4.38–5.98 GHz (31.37%), a 3-dB gain bandwidth of 3.75–6.0 GHz (46.88%), a peak gain of 7 dBic, and a high radiation efficiency of more than 93% within the AR bandwidth.

A Dual Circularly-Polarized Multilayer Reflective Surface Based on Loaded Ring Slots

In this paper, a dual circularly-polarized multilayer reflective surface (MRS) based on loaded ring-slots for reflectarray applications is presented. The MRS comprises a wideband multilayer circular polarizer cascaded with a multilayer reflective screen with independent phase shifting properties for the two orthogonal linearly polarized components. The first polarization conversion is accomplished by a four-layer polarizer based on periodic arrays of bisected split rings that converts two incident circularly-polarized waves, one left-handed (LHCPW) and other right-handed (RHCPW), into two linearly polarized waves with orthogonal polarization planes. These two waves can be phase-shifted independently by a periodic two-layer array of specially designed reflective elements. Each element consists of a ring-slot resonator loaded with two pairs of reactances orthogonally located that can be varied to obtain two linear reflection phase tapers along the array. These reflected waves are then transformed back by the polarizer into two circularly polarized waves traveling into the desired directions. To validate the proposed approach, a six-layer prototype operating at 32 GHz that provides reflection elevation and azimuthal angles for the RHCPW at 22° and 180°, respectively, and reflection elevation and azimuthal angles for the LHCPW at 18° and 0°, respectively, has been designed, fabricated, and experimentally verified.

The Sensitive Element of Acoustic Sensor on Circular Polarized Waves: From Theoretical Considerations towards Perspective Rotation Rate Sensors Design.

In this paper, the perspectives of using the features of acoustic wave propagation to design rotation rate sensors (RRS) are discussed. The possibility of developing the solid-state sensitive elements (SE) of RRS on acoustic waves of circular polarization is shown. The theoretical basis of bulk acoustic wave propagation under rotation is given. The direct excitation of circularly polarized acoustic wave (CPAW) is considered, the design of the CPAW emitting transducer is offered. The results of experimental studies that indicated the circular nature of the particle motions in the radiated wave are discussed. The principally new concept of the RRS SE design on CPAW, being able to operate under high vibration and acceleration, is proposed. The experimental results revealed a high correlation with theoretical and numerical predictions and confirmed RRS on CPAW operability.

Plasma concept for generating circularly polarized electromagnetic waves with relativistic amplitude

Propagation features of circularly polarized (CP) electromagnetic waves in magnetized plasmas are determined by the plasma density and the magnetic field strength. This property can be applied to design a unique plasma photonic device for intense short-pulse lasers. We have demonstrated by numerical simulations that a thin plasma foil under an external magnetic field works as a polarizing plate to separate a linearly polarized laser into two CP waves traveling in the opposite direction. This plasma photonic device has an advantage for generating intense CP waves even with a relativistic amplitude. For various research purposes, intense CP lights are strongly required to create high energy density plasmas in the laboratory.

Design of a Broadband Circularly Polarized Antenna by Using Axial Ratio Contour

A novel method of using axial ratio (AR) contour to design a broadband circularly polarized (CP) antenna is presented in this letter. By resolving a radiated CP wave into two orthogonal far-field components, the resulted AR will be determined by the radiated power and phase differences between the two orthogonal components. Therefore, a series of AR contours can be obtained for different AR values of the radiated wave. In the AR contour, details of phase advance, phase lag, power advance, and power lag can be simultaneously observed along with the resulted AR. Based on these analyses, the AR contour is first utilized to directly design a broadband CP antenna instead of using the traditional AR versus frequency curve to achieve optimal AR bandwidth. Compared to the traditional AR curve, the method of using AR contour to design CP antenna is more effective and informative. The designed broadband CP antenna was also fabricated and measured for the final performance verification.

Wide-Angle Circular Polarization Converter Based on a Metasurface of Z-Shaped Unit Cells

Since it’s designable, metasurface was widely used in various fields, especially the design of polarization converters. However, most of the polarization converters currently designed can only work under normal incidence or small angle incidence, which hugely limits the application of the device. In this paper, a chiral metasurface based on the z-shaped unit cell which can manipulate circular polarization wave is proposed. The simulation result shows that this converter can maintain the polarization state of circular polarization after reflection from 8.18 to 13.988GHz with a polarization conversion ratio more than 90%. Moreover, the structure is insensitive to incidence angle，which can keep a stable performance both for left-handed circularly polarized wave and right-handed circularly polarized waves as the incident angle increase to 75°. The proposed metasurface with simple structure, angular stability can be used in communication and polarization manipulating devices.

A Reconfigurable Dual-Band Dual-Circularly Polarized Antenna for Vehicle Global Navigation Satellite System Application

A simple and novel reconfigurable dual-band dual-circularly polarized (CP) cavity backed high-gain antenna for vehicle global navigation satellite system (GNSS) is first reported in this paper. This design consists of a simple planar printed monopole with four branches, four pin-diodes and a modified cavity. Four pin-diodes are used to control the length of these four branches. By asymmetrically changing the states of these four diodes, this antenna can resonate both right-hand circular polarization (RHCP) wave and left-hand circular polarization (LHCP) wave at two bands. An elliptical cavity with a metal step is adopted to realize unidirectional radiation. To verify the concept, one prototype is fabricated and measured. The measured impedance bandwidths (|S11| < −10 dB) are 22.69% (1.055-1.325 GHz) and 5.68% (1.54-1.63 GHz), and the 3-dB axial ratio (AR) bandwidths are 7.4% (1.211-1.304 GHz) and 3.91% (1.554-1.616 GHz) with only 1.261 center frequency-ratio (CFR). The proposed antenna has advantages of simple structure, reconfigurability, higher gain, and smaller CFR.

Fabry–Pérot-Based Compound All-Dielectric Huygens’ Structure for Circularly Polarized Millimeter-Wave Beamforming

An all-dielectric Fabry–Perot compound Huygens’ structure is proposed for beam-forming at the millimeter-wave (mm-wave) band for circularly polarized (CP) waves. The proposed structure is based on a symmetric unit cell in the plane of the structure, which allows for CP wave transmission, and is demonstrated in the near field of a 60 GHz right-hand CP slot array antenna. Full-wave demonstration of a uniform structure shows a negligible effect on the reflection and radiation of the antenna from 59 to 62 GHz. Full-wave simulations were further used to demonstrate a phase-gradient structure for beam-steering from 59 to 61 GHz. Finally, a difference-pattern structure was fabricated and experimentally demonstrated for operation from 61 to 62 GHz, exhibiting low reflection and good axial ratio (AR) performance across the bandwidth.

Broadband switchable terahertz half-/quarter-wave plate based on metal-VO2 metamaterials.

We propose a metal-vanadium dioxide (VO2) metamaterial with broadband and functionality-switchable polarization conversion in the terahertz regime. Simulation results show that the function of the proposed metamaterial can be switched from a half-wave plate (HWP) to a quarter-wave plate (QWP) over a broad bandwidth of 0.66-1.40 THz, corresponding to a relative bandwidth of 71.8%. The HWP obtained when VO2 is in the insulating state has reflection of 90% and linear polarization conversion ratio exceeding 98% over the bandwidth of 0.58-1.40 THz. By transiting the phase of VO2 into the conducting state, the obtained QWP can convert the incident linearly-polarized wave to circularly-polarized wave with an ellipticity of 0.99 over 0.66-1.60 THz. Additionally, results show that the proposed broadband switchable HWP/QWP has a large angular tolerance. We expect that this broadband and switchable multi-functional wave plate will find applications in polarization-dependent terahertz systems including sensing, imaging, and telecommunications.

Planar Achiral Metasurfaces-Induced Anomalous Chiroptical Effect of Optical Spin Isolation.

Planar chiral structures respond differently for oppositely handed incident light, and thus can produce extraordinary chiroptical effects such as circular conversion dichroism (CCD) and asymmetric transmission (AT). Such chiroptical effects are powerful tools to realize the fundamental principle of optical spin isolation, which leads to a plethora of applications such as optical conversion diodes, chiral imaging, and sensing. Here, we demonstrate the chiroptical effects of simultaneous CCD and AT through meticulously designed single-layered achiral nanofins. Our metamolecule consists of four achiral hydrogenated amorphous silicon (a-Si:H) nanofins that are carefully oriented and optimized to exhibit considerable CCD and AT. The device demonstrates a circular conversion dichroism of 55% and an asymmetric transmission of 58% at a wavelength of 633 nm. Right-hand circularly polarized light (RHCP) is completely absorbed, while left-hand circularly polarized light (LHCP) is transmitted with a polarization conversion, making it a perfect circular polarization wave isolator with negligible backscattering (due to low reflectance). This unique design and its underlying working mechanism are described comprehensively with three different techniques. These methods validate the proposed design and its methodology. For practical applications such as imaging, the proposed design realizes the Pancharatnam-Berry (PB) phase, achieving a 0-2π phase coverage for transmitted circular polarization. For the proof of concept, a metahologram is designed and demonstrated by employing the achieved full-phase control. The measured response of the fabricated metadevice not only validates the CCD and AT but also exhibits a simulated polarization conversion efficiency of up to 71% and measured efficiency up to 52%, comparable to state-of-the-art metahologram demonstrations.

The Effect of Sea State on the Polarization of Reflected Beidou B1 Signals

Background: Oceanographic buoys generally employ satellites for positioning and data transmission. However, sea surface conditions can affect these signals. The Signal to Noise Ratio (SNR) of small observation buoys can be improved by exploiting polarization diversity. Methods: This paper discusses the effect of sea surface conditions on the polarization and reflection loss of Beidou B1 reflected signals for the purposes of exploiting polarization diversity. The Rayleigh roughness criterion is used to assess the roughness of the sea surface. The Fresnel reflection coefficients are derived to analyze the polarization and reflection loss of the Beidou B1 reflected signals with different sea surface states. Results: The results obtained show that for the Beidou B1 signals, the sea surface is considered rough for most sea surface states and incident angles. For smooth sea surfaces, the Beidou B1 reflected signals are mainly Left Hand Circularly Polarized (LHCP) waves, but Right Hand Circularly Polarized (RHCP) waves dominate when the incident angles are larger than the Brewster angle. The reflected loss is between -2 dB to -3.4 dB. In rough sea surfaces and the signals propagation is dominated by diffuse reflection. The reflection loss decreases with the incident angle and there is a fluctuation when the incident angle is around 49 degrees. The specular reflection signal has a significant amplitude when the angle of incidence is large. RHCP waves are the main component of the reflected signals, and the reflection loss is relatively small which can be employed for polarization diversity or marine remote sensing. Conclusion: polarization diversity is only useful with good sea conditions, and the corresponding gain decreases with the deterioration of the sea surface conditions.

Two-port dual-band circularly polarized dielectric resonator-based MIMO antenna with polarization diversity

ABSTRACT In this communication, dielectric resonator based two-port Multi Input Multi Output (MIMO) antenna is structured and examined. L-shaped microstrip line with a serial step impedance transformer is used to excite moon-shaped aperture, which in turn stimulates ring-shaped dielectric resonator antenna. Some of the important features of the proposed MIMO radiator are: (i) alteration of cylindrical to ring-shaped dielectric resonator is supportive to give wide-impedance bandwidth; (ii) aperture excites dual orthogonal hybrid ( and ) mode inside the ring dielectric resonator antenna, which aids to get dual-band circular polarization waves; and (iii) use of polarization diversity concept is helpful to give lesser mutual coupling (less than −20 dB) between the ports. After doing experimental confirmation, the proposed radiator is working over the frequency range 2.4–3.88 GHz. It also supports 3-dB axial ratio in dual-frequency range, i.e., 2.44–2.64 GHz and 3.4–3.65 GHz, respectively. Right-handed circular polarization and good value of diversity parameters make the proposed antenna employable for WLAN (2.5 GHz) and WiMAX (3.3 GHz) applications.

Helicity-dependent metasurfaces employing receiver-transmitter meta-atoms for full-space wavefront manipulation

Manipulating orthogonal circularly polarized (CP) waves independently in both reflection and transmission modes in a single metasurface is pivotal. However, independently controlling CP waves with different polarizations is difficult especially for both reflection and transmission modes. Here, we designed a receiver-transmitter metasurface with helicity-dependent reflection and transmission properties. Our design breaks the fixed phases of the geometry metasurface-carrying Pancharatnam-Berry operators by combining the receive and transmit antennas. To verify the effectiveness of the modulation, we designed three linear deflectors with: (a) reflection phase gradient, (b) transmission phase gradient, and (c) both of gradients to achieve anomalous reflection, anomalous refraction, and simultaneous anomalous reflection and refraction, respectively. As proof of the concept, a bifunctional meta-device with functions of anomalous reflection and focusing transmission for different incident CP waves was simulated and measured. Our findings offer an easy strategy for achieving arbitrary bifunctional CP devices.

A review of high-efficiency Pancharatnam–Berry metasurfaces

Manipulating circularly polarized (CP) electromagnetic waves as desired is important for a wide range of applications ranging from chiral-molecule manipulations to optical communication, but conventional natural-materials-based devices suffer from bulky configuration and low efficiencies. Recently, Pancharatnam–Berry (PB) metasurfaces have demonstrated strong capabilities to control CP waves in different frequency domains. In this article, we present a concise review on PB metasurfaces for CP light manipulations, focusing mainly on the research works done by our own group. After briefly introducing the working principles of PB metasurfaces, we separately discuss how to construct high-efficiency PB metasurfaces in reflection and transmission geometries, and how to utilize them to control CP waves in different frequency domains, including meta-lensing, meta-hologram, and surface couplers. Finally, we conclude this review with our perspectives on future developments of PB metasurfaces.