Circular Polarization Mode Research Articles

Quarter-wave Pancharatnam-Berry phase gradient liquid crystal-enabled dual-polarization optical edge detection.

Here, we present a novel, to the best of our knowledge, optical edge detection scheme that can be operated in both linear and circular polarization modes, leveraging an optical spatial differentiator constructed by quarter-wave Pancharatnam-Berry (P-B) phase gradient element. After explaining the theoretical mechanism, we utilize a quarter-wave P-B phase liquid crystal polarization grating to validate the dual-polarization optical edge detection capability. We demonstrate that the orientation of linear polarization and the spin of circular polarization dictate the transition between edge and bright-field images. Besides, the linear and circular polarization modes exhibit broadband and monochromatic responsive properties, respectively. This mechanism, dependent on wavelength and polarization, holds promise for applications in color image processing, chiral sensing imaging, and polarization-entangled quantum imaging.

Polarization reconfigurable transmitarray antenna utilizing single‐layer Huygen element for Ku‐band satellite communication

SummaryThis paper introduces a concept for designing a polarization reconfigurable transmitarray (PRT). The unit cell of the transmitarray utilizes Huygen elements, with dimensions measuring 0.6 ( corresponds to a frequency of 15 GHz). An equivalent circuit model is proposed for the unit cell based on the two‐port Z‐matrix. The proposed unit cells have a very low insertion loss of 0.5 dB at 15 GHz. The PRT is illuminated by a linearly polarized (LP) microstrip‐printed Yagi antenna. The transmitarray is designed using the proposed unit cells with a two‐level phase quantization. The collimated LP radiation emitted by the transmitarray subsequently traverses a polarization reconfigurable converter (PRC). The resultant radiation from the PRC can be either LP or circularly polarized (CP), contingent on the configuration of the PIN diodes employed within the PRC. The proposed PRT demonstrates a measured gain of 16 dBi when operating in the LP mode while achieving a peak gain of 15 dBic in the CP mode. The overall size of the proposed PRT is compact owing to a small f/d ratio (0.58). The practicality of the design is validated through fabrication and measurement. This innovative antenna design holds potential applications in the realm of Ku‐band uplink satellite communication.

Metasurface-inspired circularly polarized patch antenna using DGS for sub 6-GHz applications

A novel circularly polarized metasurface inspired regular triangle patch antenna (RTPA) with enhanced gain and bandwidth is proposed in this paper. The antenna is composed of a triangular patch-driven element sandwiched between a 3×3 sub-wavelength square patch metasurface array and the ground plane. Initially, the RTPA is designed, and the ground plane is etched with fractal slots to produce degenerate modes for circular polarization. A metasurface array is used as a superstrate to improve gain and bandwidth in terms of impedance and axial ratio (AR). Another advantage of using a metasurface is the reduction of cross-polar radiation, particularly when employing a triangular-shaped patch antenna. The asymmetry of this structure leads to cross-polar components contributed by dominant modes rather than higher-order modes, and the use of a metasurface markedly diminishes these components. The proposed antenna's experimental results show a 10 dB return loss (|S11|) with a metasurface demonstrates a measured impedance bandwidth and axial ratio bandwidth of 760 and 350 MHz, respectively. The antenna exhibits right-hand circular polarization with a measured gain of 5.87 dBic at the operating frequency.

A Millimeter-Wave Broadband Multi-Mode Substrate-Integrated Gap Waveguide Traveling-Wave Antenna with Orbit Angular Momentum.

Orbit angular momentum (OAM) has been considered a new dimension for improving channel capacity in recent years. In this paper, a millimeter-wave broadband multi-mode waveguide traveling-wave antenna with OAM is proposed by innovatively utilizing the transmitted electromagnetic waves (EMWs) characteristic of substrate-integrated gap waveguides (SIGWs) to introduce phase delay, resulting in coupling to the radiate units with a phase jump. Nine "L"-shaped slot radiate elements are cut in a circular order at a certain angle on the SIGW to generate spin angular momentum (SAM) and OAM. To generate more OAM modes and match the antenna, four "Π"-shaped slot radiate units with a 90° relationship to each other are designed in this circular array. The simulation results show that the antenna operates at 28 GHz, with a -10 dB fractional bandwidth (FBW) = 35.7%, ranging from 25.50 to 35.85 GHz and a VSWR ≤ 1.5 dB from 28.60 to 32.0 GHz and 28.60 to 32.0 GHz. The antenna radiates a linear polarization (LP) mode with a gain of 9.3 dBi at 34.0~37.2 GHz, a l = 2 SAM-OAM (i.e., circular polarization OAM (CP-OAM)) mode with 8.04 dBi at 25.90~28.08 GHz, a l = 1 and l = 2 hybrid OAM mode with 5.7 dBi at 28.08~29.67 GHz, a SAM (i.e., left/right hand circular polarization (L/RHCP) mode with 4.6 dBi at 29.67~30.41 GHz, and a LP mode at 30.41~35.85 GHz. In addition, the waveguide transmits energy with a bandwidth ranging from 26.10 to 38.46 GHz. Within the in-band, only a quasi-TEM mode is transmitted with an energy transmission loss |S21| ≤ 2 dB.

A 330-GHz Radial Power Division/Combination Network Based on Circularly Polarized TE11 Mode

To compensate for severe mode interference and machining difficulties above the W-band of the traditional radial power combining scheme, a radial power division/combination network based on circularly polarized (CP) TE11 mode is designed. Firstly, the amplitude and phase distribution of the branches of a radial power divider under the excitation of CP mode are analyzed. The amplitudes of each branch are approximately equal, and the phase increases/decreases with equal differences. Therefore, a radial power divider with 16 branches based on a septum circular polarizer (SCP) is designed. An orthogonal cascade structure (OCS) and a parallel cascade structure (PCS) are proposed, and it is concluded that to obtain higher transmission efficiency, OCS and PCS should be used respectively when the phase or amplitude difference of SCP is worse. Finally, the power divider and a microstrip probe transition structure are cascaded back-to-back by using OCS, and the power division/combination network is obtained. Simulation results show that at 310-360 GHz, the amplitude difference of the branches of the power divider is less than ±0.35 dB; the combining efficiency of the power division/combination network is greater than 90%. This network has the advantages of single-mode operation, simple structure, and high combining efficiency. In addition, this article provides a feasible solution to the problem of depolarization loss caused by the cascade of SCPs.

A wideband and high-gain circularly polarized reconfigurable antenna array based on the solid-state plasma

In this paper, a wideband and high-gain circularly polarized (CP) antenna array with polarization-reconfigurable characteristics is presented based on the solid-state plasma (SSP). The proposed antenna is composed of switchable rotating radiation structures and a switchable feed network by simulating the different SSP branches. To investigate the CP operating mechanism, a reconfigurable CP element is designed through characteristic mode analysis (CMA). A switchable sequential-phase feed network is then proposed which can provide separately two rotational excitations. A spoof surface plasmon polariton (SSPP) is adopted for radiation patches to improve gain and axial ratio (AR) bandwidth. Finally, a high-gain and wideband 2 × 2 CP reconfigurable antenna array is designed. This array achieves left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP) modes when different SSP branches are excited. The array has an overlapped impedance bandwidth of 61.9 % (3.17 to 6.01 GHz) and an overlapped AR bandwidth of 40.2 % (4.01 to 6.03 GHz) in two CP states, and the peak gain is 11.68 dBic.

Performance of the merged APPLE-Knot undulator for soft x-ray beamline in medium energy ring

APPLE-Knot undulator can effectively solve the on-axis heat load problem and is proven to perform well in VUV beamline and soft x-ray beamline in high energy storage ring. However, for soft x-ray beamline in a medium energy ring, whether the APPLE-Knot undulator excels the APPLE undulator is still a question. Here, a merged APPLE-Knot undulator is studied to generate soft x-ray in a medium energy ring. Its advantages and problems are discussed. Though the on-axis heat load of the APPLE-Knot undulator is lower in linear polarization modes compared to the APPLE undulator, its flux is lower. The APPLE-Knot undulator shows no advantage when only fundamental harmonic is needed. However, in circular polarization mode, the APPLE-Knot undulator shows the ability to cover a broader energy range which can remedy the notable shortcoming of the APPLE undulator.

Head-and-neck multichannel B1+ mapping and RF shimming of the carotid arteries using a 7T parallel-transmit head coil.

Neurovascular MRI suffers from a rapid drop in B1 + into the neck when using transmit head coils at 7 T. One solution to improving B1 + magnitude in the major feeding arteries in the neck is to use custom RF shims on parallel-transmit head coils. However, calculating such shims requires robust multichannel B1 + maps in both the head and the neck, which is challenging due to low RF penetration into the neck, limited dynamic range of multichannel B1 + mapping techniques, and B0 sensitivity. We therefore sought a robust, large-dynamic-range, parallel-transmit field mapping protocol and tested whether RF shimming can improve carotid artery B1 + magnitude in practice. A pipeline is presented that combines B1 + mapping data acquired using circularly polarized (CP) and CP2-mode RF shims at multiple voltages. The pipeline was evaluated by comparing the predicted and measured B1 + for multiple random transmit shims, and by assessing the ability of RF shimming to increase B1 + in the carotid arteries. The proposed method achieved good agreement between predicted and measured B1 + in both the head and the neck. The B1 + magnitude in the carotid arteries can be increased by 43% using tailored RF shims or by 37% using universal RF shims, while also improving the RF homogeneity compared with CP mode. B1 + in the neck can be increased using RF shims calculated from multichannel B1 + maps in both the head and the neck. This can be achieved using universal phase-only RF shims, facilitating easy implementation in existing sequences.

Axial Ratio Improvement of Circularly Polarized Antenna Using Parasitic Elements for 5G Applications

A circular polarization (CP) antenna that can switch between right-handed circular polarization (RHCP) and left-handed circular polarization (LHCP) modes has been designed and introduced for 5G applications in the 3.5 GHz frequency band in this work. The proposed antenna comprises a crossed dipole fed by a 90° hybrid coupler. The axial ratio (AR) enhancement of 190 MHz is achieved by vertically stacking a substrate with a distance of λ / 4 from the ground plane, including an annular ring-shaped parasitic element above a circular-shaped disc. Consequently, by creating surface current rotation on the parasitic elements, the CP performance of the antenna is improved. According to the experiments, a wide impedance bandwidth of 930 MHz (3.19-4.12 GHz) and an overlapped AR bandwidth of 23.5% for both modes are achieved. The overall size of the antenna is 100 × 92.5 × 24 m m 3 , and the gain is stable across the operating frequency band with a peak value of 6.78 dBic.

An ultra‐wideband dual circularly polarized slot antenna with high isolation

SummaryAn ultra‐wideband dual circularly polarized (CP) slot antenna with high isolation is presented. Two L‐shaped probes are on the upper layer, both a ladder strip outside and a bent strip in the center on the bottom layer. The L‐shaped probes and the ladder strip result in four impedance resonance modes, and the bent strip moderates real and imaginary impedances to achieve an ultrawide impedance bandwidth. Furthermore, two L‐shaped strips on the ladder strip make two linear polarized Modes 1 and 2 into two CP modes at the low‐ and mid‐frequency bands. Meanwhile, the bent strip combined with the L‐shaped probes creates the third CP resonance mode at the high‐frequency band. The cutting corner and bent slots on the ladder strip change the amplitude and the phase of the electric fields Ex and Ey to realize ultra‐wideband CP radiation. In addition, the port–port isolation is enhanced because the currents are concentrated on the bent strip, and the coupling current path is cut off with the bent slot. The fabricated antenna achieves a −10‐dB impedance bandwidth of 111% (1.7–5.94 GHz), a 3‐dB axial ratio bandwidth of 101% (1.7–5.2 GHz), and a port–port isolation of better than 20 dB. Besides, our antenna obtains a high peak gain of 8.1 dBi and a lower profile of 0.004 λL, where λL is the lowest frequency wavelength of the operating bands in vacuum. These performances make the proposed design competitive for wireless communications.

Wideband Circularly Polarized Antenna Array Using Three-Layer Segmented Patches for Q-Band Application

A compact wideband circularly polarized (CP) millimeter-wave (mm-wave) antenna array using three-layer segmented patches (SEP) element is presented in this letter. To achieve miniaturization and wideband feature, three-layer SEP with four <i>L</i>-shaped branches are first designed to generate three CP modes (AR minimum points) within a compact size. With the three CP modes, a broad AR bandwidth of 31.7&#x0025; is achieved by the proposed CP element. Then, four metallic vias and an <i>L</i>-shaped feeding line are used to improve impedance matching. As a result, a wide impedance bandwidth of 33.1&#x0025; is also obtained by the proposed CP element. Based on the proposed wideband CP element, a compact 4&#x00D7;4 CP antenna array fed by a simple full-incorporate microstrip network is designed. Measured results of the array show a 3 dB AR bandwidth of 29.7&#x0025; from 30.1-40.6 GHz, an impedance bandwidth of 36.1&#x0025; from 29.15-42.0 GHz, and a peak gain of 18.2 dBic, which is well suited for Q-band satellite communications.

Characteristic Mode Inspired Broadband Circularly Polarized Folded Transmitarray Antenna

The circularly polarized (CP) antennas with high gains have gained growing interest due to their significant advantages, but the existing works usually suffer from narrow bandwidths. In this work, a novel circularly polarized folded transmitarray antenna (CPFTA) inspired by the characteristic mode analysis (CMA) method is proposed to achieve a broadband and high-gain CP radiation. The proposed CPFTA consists of a top-layer multifunctional metasurface (MTS), a bottom-layer polarization conversion metasurface (PCM) integrated with a linearly polarized (LP) microstrip feed source. Enabled by the CMA, the unit cell etched with an asymmetric U-slot of the MTS is optimized to generate two pairs of CP modes to broaden the bandwidth of the CPFTA. Moreover, a modified broadband E-shaped LP microstrip antenna is integrated with the PCM, resulting in a compact profile. A CPFTA prototype is fabricated and characterized to verify the effectiveness of the design. The measured results show that the fabricated antenna could obtain an impedance bandwidth of 31.7%, a 3 dB axial ratio (AR) bandwidth of 36.5%, and a 3 dB gain bandwidth of 30.1% with a peak gain of 22.35 dBic at 9.55 GHz.

Subwavelength-Cavity High-Gain Circularly Polarized Antenna with Planar Metamaterials

We present a specific subwavelength-cavity high-gain circularly polarized ultra-thin antenna made of planar metamaterials. The antenna is designed to operate at 2.80 GHz with a fixed thickness of approximately 1/6 of the operating wavelength in free space. The asymmetric unit cells of the metamaterial antenna exhibit two characteristics, namely, negative permeability and polarization selection. A linear-polarization micro-strip patch, which can realize circular polarization without a complicated feeding network, is embedded in the cavity as a feed. The circular polarization mode of the antenna can be changed by simply rotating the planar metamaterial horizontally. Simulations and experiments conducted on this antenna yielded results that are in good agreement with each other. This new subwavelength planar antenna can have potentially important applications in communication, early warning systems, and radio observation.

Wideband and low profile multipolarization reconfigurable antenna based on metasurface

AbstractIn this letter, a wideband and low‐profile multipolarization reconfigurable antenna based on metasurface (MTS) is proposed. The antenna mainly contains two parts, an upper layer of MTS and a bottom layer of circular slot antenna. The MTS acts as a polarization controller, by mechanically rotating the MTS layer at a proper angle while keeping the circular slot antenna remain stationary, the polarization mode of the antenna can be switched to linear polarization (LP), left‐hand circular polarization (LHCP), and right‐hand circular polarization (RHCP). The experimented −10 dB impedance bandwidth of 37.8% and 54% for LP and circular polarization (CP) modes, respectively. The measured overlapped 3‐dB AR bandwidth is 22.2% for both CP modes, covering from 3.2 to 4 GHz. Moreover, the measured peak gain of the presented antenna reaches 9 dBi and 8 dBic for LP and CP modes, with a lower profile of 0.05 λ0.

A Circularly Polarized Hybrid Dielectric Resonator Antenna With Wide Bandwidth and Compact Size

A circularly polarized (CP) hybrid dielectric resonator antenna (DRA) with wide bandwidth and compact size is proposed in this letter. Three CP modes can be combined together for broadband operation, which are the cross-slot mode, the DR mode, and the distributed patch mode, respectively. The cross-slot functions as both a radiator and part of the feeding structure, providing the first CP mode and excites the other two CP modes, respectively. The 2 × 2 distributed patch is inserted inside the DR. The DR and the patch can generate another two CP modes without enlarging the DR size. Through optimization, these three CP modes can be combined to achieve a wide operating bandwidth with a compact size of 0.39 × 0.39 × 0.14 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the free-space wavelength at the center frequency of 3.5 GHz). A prototype was fabricated and measured for demonstration. It has an impedance bandwidth of 38.9% (2.9–4.3 GHz), an axial ratio bandwidth of 34.3% (2.9–4.1 GHz), and a realized gain between 5.6 and 6.7 dBi.

Gravitational wave constraints on spatial covariant gravities

The direct discovery of gravitational waves (GWs) from the coalescence of compact binary components by the LIGO/Virgo/KAGRA Collaboration provides an unprecedented opportunity for exploring the underlying theory of gravity that drives the coalescence process in the strong and highly dynamical field regime of gravity. In this paper, we consider the observational effects of spatial covariant gravities on the propagation of GWs in the cosmological background and obtain the observational constraints on coupling coefficients in the action of spatial covariant gravities from GW observations. We first decompose the GWs into the left- and right-hand circular polarization modes and derive the effects of the spatial covariant gravities on the propagation equation of GWs. We find that these effects can be divided into three classes: 1) frequency-independent effects on GW speed and friction, 2) parity-violating amplitude and velocity birefringences, and 3) a Lorentz-violating damping rate and dispersion of GWs. With these effects, we calculate the corresponding modified waveform of GWs generated by the coalescence of compact binaries. By comparing these new effects with the publicly available posterior samples or results from various tests of gravities with LIGO/Virgo/KAGRA data in the literature, we derive the observational constraints on coupling coefficients of the spatial covariant gravities. These results represent the most comprehensive constraints on the spatial covariant gravities in the literature.

Efficient optimization of chemical exchange saturation transfer MRI at 7 T using universal pulses and virtual observation points.

To optimize the homogeneity of the presaturation module in a Chemical Exchange Saturation Transfer (CEST) acquisition at 7 T using parallel transmission (pTx). An optimized pTx-CEST presaturation scheme based on precomputed universal pulses was designed. The optimization was performed by minimizing the L2-norm between the effective and a given target while imposing energy constraints under virtual observation points (VOPs) supervision. The proposed method was evaluated through simulations and experimentally, both in vitro, on a realistic human head phantom, and in vivo, on healthy volunteers. The results were compared with circular polarization (CP) presaturation and other pTx approaches previously proposed. All experiments were conducted on a 7 T MRI scanner using a commercial 8Tx/32Rx head coil. The simulations show that the proposed pTx strategy boosted with VOPs is superior to the CP mode and existent pTx approaches. While the best results are obtained with subject specific pulses, the gain provided by the use of VOPs renders the universal pulses superior to tailored pulses optimized under vendor provided SpecificAbsorptionRate(SAR) management. In the phantom, the glucose map was significantly more homogeneous than with CP (root mean square error [RMSE] 17% vs. 30%). The efficiency of the method for in vivo hydroxyl, glutamate and rNOE weighted CEST acquisitions was also demonstrated. The use of a pTx presaturation scheme based on universal pulses optimized under VOP SAR management is significantly benefiting CEST imaging at high magnetic field.

Fourier-Domain Phase Retardation Vortex Measurement

Optical vortices have found a wide range of applications thanks to their helical phase topology allowing to carry the orbital angular momentum. In this work, self-interfering vortex beams are utilized in a new single-shot holographic method for the circular phase retardation measurement. The vortices carrying information about the phase retardation introduced between two orthogonal circular polarization modes are generated by the spin to orbital angular momentum conversion. The phase retardation is stored in off-axis holographic records acquired in a common-path setup using a geometric-phase grating. In the proposed method, the circular phase retardation is reconstructed in the Fourier domain, surpassing the measurement precision provided by methods restoring the retardation from the rotation of a Double-Helix Point Spread Function (DH PSF). The developed method can be adapted for application to polarimetry, orientation imaging and diagnostics of nano-emitters.

Application of Waves with Circular Polarization in Magnetotelluric Sounding

Abstract—We consider the possibility of using circular polarizations, which make the field vector in a wave rotate clockwise or counterclockwise, as independent polarizations of the primary wave during magnetotelluric sounding (MTS). This approach has been proposed for the first time to search for possible manifestations of the Hall effect under natural conditions during MTS; in this case, if the effect is small, waves with circular polarization become normal modes in a horizontally layered medium located in the constant magnetic field of the Earth. Standard impedance relations are replaced by the corresponding apparent resistance impedances and curves for waves with circular polarization (mode). In the search for manifestations of the Hall effect during MTS, it becomes necessary to determine differences in the mode apparent resistivity curves due to the presence of lateral inhomogeneities of the medium. This study deals with the specific features of MTS in the case of representing the primary source field by circular polarization waves. Results of the theoretical analysis of mode impedances are demonstrated. Numerical simulation is used to investigate the differences in the mode impedances and curves depending on the nature of the distribution of lateral inhomogeneities in the medium. Mode apparent resistivity curves obtained by processing the experimental data of the MTS in Gorny Altai are presented. It is shown that, in comparison with standard curves, mode curves are subject to less distortion by lateral inhomogeneities of the medium owing to the specific features of distributions of the charges and currents excited by circular polarization waves in them.

Design of a Novel Circularly Polarized MIMO Antenna with Enhanced Isolation for Ultra-wideband Communication

In this paper, we propose a circularly polarized (CP) ultra-wideband (UWB) MIMO antenna. Compared with common linearly polarized (LP) UWB antenna, the proposed antenna can excite circular polarization (CP) mode for WLAN communication and its impedance bandwidth can also fully cover UWB spectrum. It consists of identical circularly polarized antennas. Each unit adopts circular monopole with extended orthogonal rectangle patch to realize broadband and symmetrical rectangular ground with slot in the diagonal of each antenna unit to achieve circular polarization for WLAN band. It has a very compact size and the dimension is 25 × 51 × 0.8 mm3. The impedance bandwidth of the proposed antenna is from 3.1 GHz to 13.5 GHz, with average gain of 4 dBi, fully covering UWB bandwidth and enhanced by 38%. At the same time, circular polarization is achieved by embedding two symmetrical rectangular slot structures in the two opposite corners of every antenna unit. The extended orthogonal rectangle patch is introduced to enhance impedance bandwidth and broaden axial ratio (AR) bandwidth. The measured 3 dB axial ratio (AR) bandwidth is 1.8 GHz (4.7-6.5 GHz), fully covering WLAN band. Meanwhile, the slit slot between antenna units and rectangular openings are introduced to achieve high isolation. The proposed antenna keeps ECC (envelope correlation coefficient) below 0.01, which showing good isolation and diversity characteristics. The proposed antenna can simultaneously operate in the UWB spectrum and exhibit circularly polarized (CP) radiation characteristic in WLAN.