Polarization Purity Research Articles

X‐band, mechanically‐beam‐steerable lens antenna exploiting the Risley prism concept

This study presents a beam-steerable antenna system that uses two mechanically-rotatable, phase-shifting surfaces (PSSs) functioning like a pair of Risley prisms for beam scanning operation at X-band. One of the PSSs also acts as a lens, performing beam collimation in addition to providing a phase shift gradient. Unit cells constituting the two PSSs were co-designed to determine the distance between the two surfaces that results in high transmission coefficients and small phase errors under different beam-scanning conditions. Both simulation and measurement results have verified that the distance of 2 mm provides the best performance regarding to peak gain. Prototypes of the PSSs having circular apertures with diameters of 11.5 λ 0 at 10 GHz were fabricated and illuminated by a feed antenna to characterise the beam scanning performance. The measurement results of the proposed antenna system demonstrate the capability to steer the main beam within a ± 60 ° scanning range with a maximum gain variation of less than 3.6 dB by rotating the two PSSs with respect to each other. The fabricated prototype provides side lobe levels less than − 13.1 dB , polarisation purity higher than 20 dB, and small beam pointing errors of no more than 1 ° in all examined beam scan scenarios.

Isolation Enhancement for MIMO Patch Antennas Sharing a Common Thick Substrate: Using a Dielectric Block to Control Space-Wave Coupling to Cancel Surface-Wave Coupling

This article presents a novel and simple decoupling method to increase the isolation between two closely spaced patch antennas sharing a common thick substrate. The decoupling can be simply realized by adding a pure dielectric block (DB) above the coupled array. By means of DB to modify the space permittivity (propagation constant), the space-wave coupling can be controlled to cancel surface-wave coupling for isolation enhancement. Five benchmarks of combinations of two patch antennas with different positions or orientations are investigated to validate the decoupling concept and elaborate on the design procedure. The results show that the proposed method could provide over 20 dB isolation enhancements for patch antennas with 0.1λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> or 0.027λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> separation distances. Besides, wide isolation bandwidths and good radiation performances can be achieved for the DB-loaded antennas without reduction in total efficiency, front-to-back ratio (FBR), boresight gain, or polarization purity. Notably, the DB can be designed independently of the original array, making this method potential for some previously fabricated arrays without requiring modifying or replacing them with new ones.

Controllable laser output of high-quality cylindrical vector beam through intra-cavity mode conversion

We experimentally demonstrate the controllable laser output of cylindrical vector (CV) beams, which feature flexibility, high efficiency, and good beam quality. Particularly, the CV laser beams have negligible radial components, distinguishing themselves from the extra-cavity-generated CV beams. The output state is controlled by an intra-cavity vortex half-wave plate (VWP). By changing the topological charge (l) of VWP, we produce l = 1 and l = 2 CV beams for example. Through rotating the half-wave plate inside the cavity, the laser outputs arbitrary CV beams around the equator of the corresponding high-order Poincaré spheres. For l = 1 and l = 2 CV beams, the polarization purities are as high as 97.8% and 96.7%, the sloping efficiencies are 15.5% and 5.4%, and the beam quality factors are 2.10 and 3.31, respectively. Our result provides a reliable CV laser source for advanced applications in optical imaging and optical manipulation.

Practical design of Ku band Vivaldi antenna array

Abstract In the paper, a practical design of a Ku-band Vivaldi antenna array for compact radar system is presented. The realized gain, the beam width, polarization purity and the possible electronic beamforming in the horizontal plane were the most important requirements. Since the array was requested to show an enhanced mechanical stability, a novel geometry of elements was proposed. The Vivaldi slot was created on two substrates connected by metallic vias suppressing surface currents, and the microstrip feeder was placed in-between those substrates. Simulations are based on special approach in CST Microwave using infinite array of antenna elements, which should reduce computing time.

Theory, Design, and Verification of Dual-Circularly Polarized Dual-Beam Arrays With Independent Control of Polarization: A Generalization of Sequential Rotation Arrays

In this article, the theory, design, and validation of planar array antennas capable of producing dual-circularly-polarized (dual-CP) dual-beam radiation with a single feeding network are reported. Importantly, the properties of the formed CP beams with different handedness can be independently controlled. Such a capability is achieved by exploiting both the in-plane rotation-induced Berry phase and excitation phase for all the linearly polarized array elements, which can be regarded as a generalization of the well-known sequential rotation arrays. Microstrip patch arrays with such single-feed dual-CP dual-beam functionalities can be synthesized through a straightforward analytical approach that accurately predicts the radiation patterns for both right- and left-handed CP beams. The proposed technique and design methodology were verified by two proof-of-concept microstrip arrays consisting of 8×8 linearly polarized circular patch elements operating in the K-band, one with uniform excitation amplitudes and the other with tapered excitations for sidelobe suppression. Both arrays were fabricated and measured, experimentally achieving a joint S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> <; -10 dB, axial ratio <; 3 dB, and 3 dB gain bandwidth of more than 22.5%/20.0% and 16.7%/15.8%, respectively, for the right-and left-handed CP beams. Within this broad operational band, the beam squinting is on average within ±3°. The proposed dual-CP dual-beam arrays have fully planarized structures, low profiles, wide operational bandwidths, and high polarization purity, making them useful candidates for applications including satellite communications, point-to-multipoint communications, and so on.

XFEL beamline design for vacuum birefringence experiment

The station of extreme light (SEL) at Shanghai High repetition rate XFEL and Extreme light facility (SHINE) combines 100 PW laser pulse and an X-ray free electron laser (XFEL) beam, which provides possible experimental conditions for observing the effect of vacuum birefringence. We have designed the XFEL beamline of SEL with X-ray energy of 12.914 keV aiming for vacuum birefringence experiment. Ultra-high polarization purity of the X-ray beam at the level of 10−10 is required before colliding with a 100 PW laser pulse. An X-ray polarizer is set at the end of the designed beamline to avoid the potential risk of depolarization induced by any other X-ray component. The designed beamline provides a focal X-ray beam FWHM size of 6.35μm and total transmission of 3.5%. Further calculation indicates that 333 shots are needed to reach 5σ confidence level for the vacuum birefringence experiment under optimal conditions with present design parameters of 100 PW laser pulse and XFEL beam in SEL. Moreover, potential radiation damage, and proposed engineering stability requirements and system’s adjustment capabilities of X-ray beamline have been discussed.

Nonlinear Compton scattering of polarized photons in plane-wave backgrounds

We investigate the phenomenology of nonlinear Compton scattering of polarized photons by unpolarized electrons in plane-wave backgrounds. The energy and angular spectra of polarized photons are calculated for linearly and circularly polarized pulses, monochromatic fields and constant crossed field backgrounds. When the field intensity is in the weakly nonlinear regime, photons in different polarization states are predicted to possess very different energies and angular distributions. We explain this difference by calculating the spectrum for nonlinear Thomson scattering in a linearly polarized monochromatic background and projecting the electron's trajectory onto the different polarization directions. Finally, we calculate a scenario for multi-GeV electrons and, by considering the energy and angular-resolved photon polarization purity, find one can achieve a GeV-photon beam with polarization purities of over $90%$.

High-brightness broad-area diode lasers with enhanced self-aligned lateral structure

Broad-area diode lasers with increased brightness and efficiency are presented, which are fabricated using an enhanced self-aligned lateral structure by means of a two-step epitaxial growth process with an intermediate etching step. In this structure, current-blocking layers in the device edges ensure current confinement under the central stripe, which can limit the detrimental effects of current spreading and lateral carrier accumulation on beam quality. It also minimizes losses at stripe edges, thus lowering the lasing threshold and increasing conversion efficiency, while maintaining high polarization purity. In the first realization of this structure, the current block is integrated within an extreme-triple-asymmetric epitaxial design with a thin p-doped side, meaning that the distance between the current block and the active zone can be minimized without added process complexity. Using this configuration, enhanced self-aligned structure devices with 90 µm stripe width and 4 mm resonator length show up to 20% lower threshold current, 21% narrower beam waist, and slightly higher (1.03×) peak efficiency in comparison to reference devices with the same dimensions, while slope, divergence angle and polarization purity remain almost unchanged. These results correspond to an increase in brightness by up to 25%, and measurement results of devices with varying stripe widths follow the same trend.

Hollow-core design provides polarization purity

The finding that hollow-core optical fibres can preserve the state of linearly polarized light over hundreds of metres with exceptional purity could benefit applications in sensing, gyroscopes and quantum optics.

A blind source separation jamming suppression method based on channel ratio function

ABSTRACT In order to counteract the main lobe multi-false target jamming of radar, a blind source separation jamming suppression method based on channel ratio function is proposed. The cross-polarised auxiliary antenna is used to expand the receiving channel, and the blind signal processing method is used to separate the jamming from the target echo. This method utilises the statistical characteristics of channel ratio function and chooses the time unit with only jamming to process. And it realises jamming suppression and echo extraction. The simulation results show that the proposed method has good jamming suppression performance and is not affected by channel noise and polarisation purity of auxiliary antenna.

In-Band Scattering Control of Ultra-Wideband Tightly Coupled Dipole Arrays Based on Polarization-Selective Metamaterial Absorber

With the polarization-selective metamaterial absorber (PSMA), a unique approach for reducing the in-band radar cross section (RCS) while preserving the radiation performance of a tightly coupled dipole array (TCDA) is proposed. The proposed PSMA structure is comprised of resistive films, dielectric layers, and polarization gates. In detail, the resistive films are loaded on the surface of a TCDA, and the polarization gates are utilized to broaden the absorption bandwidth of PSMA as well as to improve the polarization purity of the array. Moreover, the process of the co-design of the phased array with PSMA is presented. The designed infinite array is able to achieve a 3:1 bandwidth from 6 to 18 GHz with the active VSWR $10 \times 10$ single-polarized prototype array is fabricated and measured. Measured results are in good agreement with simulated ones, thus demonstrating that the PSMA structure is able to reduce the scattering significantly throughout the operating band of the array under normal and oblique incidence.

A Crossed Dipole Phased Array Antenna Architecture With Enhanced Polarization and Isolation Characteristics

A dual-polarized planar phased array antenna with enhanced polarization and isolation characteristics for multifunction applications is presented. A bent crossed dipole is selected as the element of the array antenna. The bend angle is optimized to widen the E-plane active element pattern of the dipole resulting in a pair of matched co-polar patterns. Contrary to common patch array antennas, this design does not require a continuous grounded substrate. This diminishes the surface wave propagation along the ground plane. Efficient techniques, applied to the element design, isolate the two polarizations from each other. Higher than 40 dB port isolation is achieved within the entire frequency range of 2.7–3.0 GHz in principal plane scanning. In order to preserve the symmetry of the array antenna, a mirrored arrangement in both orthogonal directions is applied to the array configuration. This enhances the co- to cross-polarization levels to better than 45 dB in scanning up to ±45° in the principal planes. The proposed phased array antenna with enhanced polarization purity can potentially improve polarimetric performance.

Circularly‐polarised end‐fire antenna and arrays for 5G millimetre‐wave beam‐steering systems

This study presents a circularly-polarised substrate-integrated waveguide end-fire antenna and four-antenna arrays for 5G beam-steering mobile devices at 28 GHz. Polarisation is achieved through implementation of a substrate-integrated waveguide notched-septum polariser. It is then loaded with a dielectric lens to improve gain, axial ratio bandwidth, and circular polarisation (CP) purity. To suppress the mutual coupling between array elements, vias are extended on either side of the lens. It also improves the single-element axial ratio and front-to-back ratio. The antenna's performance is found to be resilient to typical manufacturing tolerances for the lens and via extensions. The element and arrays are manufactured and measured. The prototypes demonstrated an impedance bandwidth of 11.4% with a maximum array gain of 10.5 dBi and a steering range of up to ± 35 ° (with reduced performance when steered to ± 45 ° ). Within this range, the antenna array demonstrates a gain variation of up to 3 dB and very good CP purity within the radiation half-power beamwidths (HPBWs). A wide single-element elevation HPBW of 95 ° is also demonstrated. Given its performance and ease of manufacture in a printed circuit board process, the proposed antenna could be a strong candidate for 5G millimetre-wave beam-steering systems.

Exceptional polarization purity in antiresonant hollow-core optical fibres

High-performance interferometers, gyroscopes, frequency combs, quantum information experiments and optical clocks rely on the transmission of light beams with the highest possible spatial and polarization purity. Free-space propagation in vacuum unlocks the ultimate performance but becomes impractical at even modest length scales. Glass optical fibres offer a more pragmatic alternative, but degrade polarization purity and suffer from detrimental nonlinear effects. Hollow-core fibres have been heralded for years as the ideal compromise between the two, but achieving high modal purity in both spatial and polarization domains has proved elusive thus far. Here, we show that carefully designed, low-nonlinearity hollow-core antiresonant fibres can transmit a single pair of orthogonal polarization modes with cross-coupling on the scale of 10–10 m–1; that is, orders of magnitude lower than any other solution. This free-space-like optical guidance can immediately provide a leap in performance for photonics-enabled sensors and instruments. Carefully designed hollow-core antiresonant fibres support a pair of orthogonal polarization modes with a level of purity and cross-coupling that is orders of magnitude lower than other fibre designs and beyond the fundamental Rayleigh scattering limit of glass core fibres.

Design and qualification of Ku-band-radiating chains for receive active array antennas of flexible telecommunication satellites

AbstractAirbus Italia recently developed enhanced passive components as key elements for its telecommunication Ku-band antenna product lines, tailored to reconfigurable payloads. This paper describes the design and qualification of a dual linear polarization Ku-band-radiating chain, developed for the DRA receive (Rx) active antennas embarked on the Eutelsat Quantum satellite. The feed chain covers the entire Ku-band frequency range allocated for fixed satellite services providing receive functionality and embedding sharp rejection features over the adjacent transmit band. The proposed design provides high radiation efficiency (&gt;90%) and polarization purity (XPD &gt; 33 dB), together with low RF losses and flat group-delay variation over a 13% fractional bandwidth, keeping a compact size and reduced axial length. The unit has been optimized for high reproducibility in high volume productions, typical of large DRA applications, for which stringent mass and dimensional constraints, as well as excellent amplitude and phase tracking among similar units, are key features. Details of the feed chain design and an overview of RF and environmental qualification test results are presented.

Study of Dual-Frequency Polarizer for Electron Cyclotron Resonance Heating Systems of 105 and 140 GHz

In electron cyclotron resonance heating (ECRH) systems, the desired polarization is achieved by using two polarizers, a linear polarizer and an elliptical polarizer. These two polarizers serve as an important part of a 63.5-mm corrugated metallic waveguide transmission line for the ECRH. The dual-frequency polarizers (DPs) for the 105- and 140-GHz systems were designed in the present article by using the optimization of the phase difference method. The linear polarizer of 105-GHz shared an optimized polarizer with an elliptical polarizer of 140 GHz. The elliptical polarizer of 105-GHz shared another optimized polarizer with a linear polarizer of 140 GHz. The polarization characteristics of the single-frequency and DPs at the frequencies of 105 and 140 GHz were analyzed and compared. The polarization purity of the combination of the two polarizers was also calculated. The results indicated that arbitrary polarization state could be successfully achieved with the use of the designed DPs.

Microwave shielding with far-from-circular polarization

Ultracold polar molecules can be shielded from fast collisional losses using microwaves, but achieving the required polarization purity is technically challenging. Here, we propose a scheme for shielding using microwaves with polarization that is far from circular. The setup relies on a modest static electric field, and is robust against imperfections in its orientation.

Tangentially and radially polarized Nd:YAG hollow lasers with two pairs of axicons

We present a novel method for generating tangentially and radially polarized laser radiations by using two pairs of positive and negative axicons. Tangentially and radially polarized diode-pumped Nd:YAG hollow lasers were demonstrated respectively. At an incident pump power of 17.8 W, the output power of tangentially and radially polarized laser beam is 6.9 W and 8.6 W, respectively. Polarization purity of tangentially and radially polarized laser beam is 99.2% and 98.7%, respectively. The experimental results reveal that tangentially and radially polarized laser beams with high polarization purity can be generated by resonator cavity consisting of only axicons. To the best of our knowledge, this is the first time that the cylindrical vector laser beam was realized only by axicons.

Common-path generation of stable cylindrical perfect vector vortex beams of arbitrary order

A highly flexible and efficient method of generating stable radially and azimuthally polarized perfect optical vortex beams and all higher order cylindrical perfect vector vortex beams is proposed and demonstrated. The method is the most convenient implementation of the coherent superposition of two orthogonally circularly polarized optical vortex beams of arbitrary integer topological charges. The proposed method employs a spatial light modulator to control the relative phase between the vertical and horizontal polarization components of an input perfect vortex beam in a common-path configuration to generate arbitrary ordered cylindrical perfect vector vortex beams by changing the reference gray-level value. Calibration curve of relative phase vs grayscale of the phase function on the spatial light modulator is obtained to facilitate the determination of required phase-offset using pre-calculated grayscale color-map. The generated beams consist of high mode purity and states of polarization, as obtained from measured spatially resolved Stokes parameter, are uniformly distributed throughout the beam cross-section. The interference pattern of the two beams in a projected linear polarization state also give the cylindrically symmetric petal beams with a control over the number and orientation of petals.

A compact triple band circularly polarized planar antenna for wireless application

AbstractA compact planar triple band circularly polarized (CP) antenna loaded with parasitic elements is proposed for wireless applications. For achieving circular polarization 2 inverted L‐shaped strips are added to the longer arm of dual band monopole and ground plane. A rectangular patch and a U shaped radiator are added to increase the impedance bandwidth as well as polarization purity. Electrical size of the antenna is 0.32λ × 0.32λ, where λ is the free space wavelength at its lowest CP frequency that is, 2.4 GHz. The structure shows an impedance bandwidths (│S11│ ≤ –10 dB) of 870 MHz (1.83‐2.7 GHz), 1.17 GHz (3.27‐4.44 GHz), and 400 MHz (4.75‐5.15 GHz). The 3‐dB axial ratio bandwidths of the proposed structure are 12.2%, 5.3%, and 4.28% at 2.375, 3.47, and 4.9 GHz of center frequencies respectively. The proposed structure is fabricated and its parameters are measured. Measured results nearly match with the simulated results and it shows satisfactory gain in all the three operating CP bands.