Polarization Purity Research Articles

A Circularly Polarized 1 Bit Electronically Reconfigurable Reflectarray Based on Electromagnetic Element Rotation

A circularly polarized (CP) reflectarray with 2-D electronically steerable beam is reported. The reconfigurable CP reflectarray element is realized using a circular-patch-based structure with p-i-n diodes incorporated. A new electronical phase manipulation method is proposed based on the element rotation technique and by additionally exploiting symmetries in the field distribution of the element's fundamental resonant mode. Element rotation can be equivalently achieved by altering the biasing voltage and changing the electromagnetic behavior of the reflective phasing cell. The proposed design approach brings about simplification in element configuration, leading to a reduction in the number of required diodes by a factor of one half. Practical concerns of the element and biasing complexity as well as the insertion loss are, therefore, well-handled. A fully functional 16×16 reconfigurable CP reflectarray is designed, fabricated, and tested to validate the concept. Good beam focusing and 2-D dynamic beam steering capabilities are confirmed through experiments, along with decent polarization purity and comparatively high aperture efficiency. The proposed simple and robust design could be attractive for implementing lightweight, low-cost, and large-scale 2-D reconfigurable CP reflectarrays.

Three‐port circularly polarized MIMO antenna for WLAN application with pattern and polarization diversity

AbstractIn this article, a three‐port circularly polarized (CP) multiple‐input multiple‐output (MIMO) antenna for wireless local area network (WLAN) application with pattern and polarization diversity is proposed. The proposed MIMO antenna system comprises of a broadside CP antenna element with a T‐shaped slot and two endfire CP antenna elements. Good impedance bandwidth of 16.9% and 5.5% are achieved by the broadside CP antenna and endfire CP antenna, respectively, and their corresponding axial ratio (AR) bandwidth is 7% and 10.47%. The isolation between the different antenna elements is better than 20 dB, and the polarization purity for all CP antenna is more than 25 dB along with the maximum radiation.

Physical Limitations of Phased Array Antennas

In this paper, the bounds on the Q-factor, a quantity inversely proportional to bandwidth, are derived and investigated for narrow-band phased array antennas. Arrays in free space and above a ground plane are considered. The Q-factor bound is determined by solving a minimization problem over the electric current density. The support of these current densities is on an element-enclosing region, and the bound holds for lossless antenna elements enclosed in this region. The Q-factor minimization problem is formulated as a quadratically constrained quadratic optimization problem that is solved either by a semi-definite relaxation or an eigenvalue-based method. We illustrate numerically how these bounds can be used to determine trade-off relations between the Q-factor and other design specifications: element form-factor, size, efficiency, scanning capabilities, and polarization purity.

A 256-Element Ku-Band Polarization Agile SATCOM Receive Phased Array With Wide-Angle Scanning and High Polarization Purity

This article presents a Ku-band phased-array receive tile with 256 elements. The design is based on 64 dual-polarized beamformer chips assembled on a printed circuit board (PCB) with dual-polarized antennas and an integrated Wilkinson combiner network and can operate at any polarization (linear, rotated-linear, and circular). The 256 elements are spaced $0.52\lambda $ apart at 12.7 GHz in the $x$ - and $y$ -directions. The measured patterns show near ideal patterns with a wide beam scanning range of ±70° (V- and H-pol) and a high cross-polarization rejection of 27 dB. The array has a 3-dB instantaneous scanning bandwidth of 10.6–12.5 GHz. In circular polarization mode, the measured axial ratio (AR) is 0.5 dB at 11.75 GHz for both left- and right-hand circular polarizations. The tile design is scalable to allow large-scale phased-array construction with 1024 elements or higher. Extensive measurements are presented, showing the versatility of this approach. Also, the dual-polarization feeds can be optimized to result in very low cross-polarization for circular and slanted-linear polarizations at all scan angles. The array performance, compact size, ultralightweight of 258 g, and low profile with 3.5-mm thickness make it suitable for affordable mobile Ku-band SATCOM on the move (SOTM) terminals.

Bilayer split-ring chiral metamaterial based reconfigurable antenna for polarization conversion

Abstract A bilayer split-ring chiral metamaterial converts the linearly polarized wave, into a nearly perfect left or right-handed circularly polarized wave. The proposed antenna is intended to operate at center frequency of 5.80 GHz with switchable polarization capability. The polarization re-configurability is achieved by electronically switching of two PIN-diode pairs, which are embedded into bilayer split-ring Chiral Metamaterial. The optimized length of rectangular patch is 16 mm and width is 12.1 mm. Two types of radiation characteristics offered by the proposed antenna; left hand circularly polarized in mode 1 and right hand circularly polarized in mode 2. Measured results show that its impedance bandwidth is 155 MHz from 5.70 to 5.855 GHz for both mode 1 and mode 2. The measured axial-ratio bandwidth is 100 MHz from 5.75 to 5.85 GHz for mode 1 and 110 MHz from 5.73 to 5.84 GHz for mode 2. Antenna has LHCP gain of 2.52 dBi and RHCP gain of −23 dBi in mode 1. RHCP gain of 2 dBi and polarization purity of about −20 dBi is obtained in mode 2. The proposed antenna has simple structure, low cost and it has potential application in field of wireless communication (i.e., WiMax, WLAN etc.).

A chemically etched corrugated feedhorn array for D-band CMB observations

We present the design, manufacturing, and testing of a 37-element array of corrugated feedhorns for Cosmic Microwave Background CMB) measurements between 140 and 170 GHz. The array was designed to be coupled to Kinetic Inductance Detector arrays, either directly (for total power measurements) or through an orthomode transducer (for polarization measurements). We manufactured the array in platelets by chemically etching aluminum plates of 0.3 mm and 0.4 mm thickness. The process is fast, low-cost, scalable, and yields high-performance antennas compared to other techniques in the same frequency range. Room temperature electromagnetic measurements show excellent repeatability with an average cross polarization level about − 20 dB, return loss about − 25 dB, first sidelobes below − 25 dB and far sidelobes below − 35 dB. Our results qualify this process as a valid candidate for state-of-the-art CMB experiments, where large detector arrays with high sensitivity and polarization purity are of paramount importance in the quest for the discovery of CMB polarization B-modes.

Enhancement of polarization purity in square dielectric resonator antenna using coaxial feed with metal strip loading for point-to-point communication applications

In this paper, a simple technique to enhance the polarization purity in a square dielectric resonator antenna (SDRA) using metal strip loading on the probe feed is presented for point-to-point communication applications. Coaxial feed placed at the commonly used offset location adjacent to the DRA has been studied in this regard. Cross polarized (XP) fields scattered from the feed into the air are found to be one of the reasons behind the deterioration of polarization purity in SDRA. When a thin metal strip is loaded on the probe feed using liquid solder to control these XP fields, the measured result shows an XP isolation of 47 dB at the boresight, 42 dB and 29 dB at the angular region of ±30°in the E-plane and H-plane, respectively. The proposed technique helps to overcome many unavoidable fabrication errors associated with complex machining and drilling processes involved in contemporary DRA designs for XP suppression. The proposed SDRA design offering good XP isolation performance and simple fabrication technique is highly suitable for low cost and high precision applications.

Compact Pattern Diversity Antenna with 3-D Printed All-dielectric Superstrate for WLAN Access Points

ABSTRACT This paper presents a four-port pattern diversity antenna with a 3-D printed all-dielectric superstrate for 5.2 GHz Wireless Local Area Network (WLAN) access points. The topology of four-port coaxial-fed circular patch antennas provides a beam tilt of ±45° and ±15° with an angular coverage of ±60°. The beam tilt is obtained through this unique topology, without the need for any additional phase shifting circuits. Then, a low-cost 3-D printed dielectric superstrate is designed to enhance and equalize the gain without compromising on the beam tilt and polarization purity of the antennas. The antenna module has an impedance bandwidth of 80 MHz (5.16 GHz–5.24 GHz), covering the IEEE 802.11ac band, for a gain of 9 dBi throughout the band and across the ports. The dielectric superstrate provides a gain enhancement of 3.8 dB for antennas 1 and 4, and 5.4 dB gain enhancement for antennas 2 and 3, respectively.

Compact Dual-Polarized Vivaldi Antenna with High Gain and High Polarization Purity for GPR Applications

A compact ultra-wideband dual-polarized Vivaldi antenna is proposed for full polarimetric ground-penetrating radar (GPR) applications. A shared-aperture configuration comprising four Vivaldi elements for orthogonal polarizations is designed to reduce the low-end operating frequency and improve the port isolation with a compact antenna size. The directivity of the antenna is enhanced by the oblique position of the radiators and the implementation of a square loop reflector. Experimental results demonstrate that the antenna has very good impedance matching, port isolation, and dual-polarized radiation performance, with low dispersion characteristics across band of interest from 0.4 GHz to 3.0 GHz. GPR measurements with the designed antenna show that the antenna maintains good detection capability even for objects buried in a highly conductive soil.

Study of polarization strategy with two elliptical grating polarizers for ECRH systems

• The polarization strategy for ECRH systems with two elliptical grating polarizers was studied. • The polarization purity of the polarization strategy was analyzed. • The elliptical polarizer was tested at the low power experiment. The grating polarizer is a critical component in the millimeter-wave transmission line in an electron cyclotron resonance heating (ECRH) system, the main function of which is to change the polarization characteristics of the millimeter-wave. This paper presents an optimal polarization strategy for the millimeter-wave transmission line in an ECRH system. With two identical sinusoidal-groove elliptical grating polarizers, an arbitrary polarization can be realized. A special elliptical grating polarizer has thus been designed and its performance has been tested on a low power test bed. The results of the low power experiments agree well with the theoretical calculation values. The purity of the polarization achieved via the polarization strategy developed in this work has also been calculated and is found to be no less than 99.98 %. The analysis indicates that almost all the polarization states can be obtained by this polarization strategy.

Polarization studies on Rayleigh scattering of hard x rays by closed-shell atoms

We present a theoretical study on the elastic Rayleigh scattering of x-ray photons by closed-shell atoms. Special attention is paid to the transfer of linear polarization from the incident to the outgoing photons. To study this process, we apply the density-matrix formalism combined with the relativistic perturbation theory. This formalism enables us to find general relations between the Stokes parameters of the incident and scattered photons. By using these expressions, we revisit the recent proposal to use Rayleigh scattering for the analysis of the polarization purity of synchrotron radiation. We show that this analysis can be performed without any need for the theoretically calculated scattering amplitudes, if the linear polarization of the scattered light is measured simultaneously at the azimuthal angles ${0}^{\ensuremath{\circ}}$ and ${45}^{\ensuremath{\circ}}$ with respect to the plane of the synchrotron. To illustrate our approach, we present detailed calculations for scattering of 145 keV photons by lead atoms.

Performance of Partially Deployed Spaceborne Ultra-Wideband Miura-Ori Apertures

Reconfigurable and deployable antenna arrays are required communications and remote sensing onboard small satellites/CubeSats. There is also a need for packing before launch due to the limited payload space for exo-atmospheric deployments. In this context, origami-based aperture packing and unpacking is relevant and attractive for low-volume storage. However, after several physical morphing cycles, origami apertures may not maintain the performance exhibited by fixed apertures. That is, origami-based antenna arrays are likely to suffer from reduced gain and polarization purity. Therefore, physical effects caused by origami folding should be analytically incorporated into the design. This paper proposes a statistical analysis to study the gain performance of deployable ultra-wideband Miura-ori apertures by including geometrical errors inherent to a partially deployed state. A closed-form expression of the gain degradation is derived and verified using full-wave simulations.

High field X-ray laser physics

High field X-ray laser physics

Advanced X-ray polarimeter design for nuclear resonant scattering.

This work presents the improvements in the design and testing of polarimeters based on channel-cut crystals for nuclear resonant scattering experiments at the 14.4 keV resonance of 57Fe. By using four asymmetric reflections at asymmetry angles of α1 = -28°, α2 = 28°, α3 = -28° and α4 = 28°, the degree of polarization purity could be improved to 2.2 × 10-9. For users, an advanced polarimeter without beam offset is now available at beamline P01 of the storage ring PETRAIII.

Miniature tri‐polarized MIMO slit‐postwall step impedance resonator slot antenna array

A miniaturized tri-polarized MIMO slot antenna loaded with slit-postwall-slot step impedance resonator (SIR) is proposed. The SIR, which shortens the length of radiation slot for the miniature purpose, consist of two slit-slot lines with high impedance and a slit-postwall-slot line with low impedance, because the postwall can decrease the characteristic impedance of slit-slot line. Meanwhile, the slits can improve the polarization purity and isolation of the antenna array effectively. Compared with the conventional slot antenna array, the measured results of proposed antenna array shows that the cross-polarization ratio has improved 2 dB on H plane and 3 dB on E plane at 2.45 GHz, while the lengths of ground plane and slot are shortened 77.8% and 77%, respectively. Furthermore, the proposed antenna array operates at dual band and the isolation are −22 dB at 2.45 GHz and -27 dB at 4 GHz. The performance and structure of the proposed antenna array can be applied for the condition of high polarization purity and demanding volume.

Highly efficient Yb:YAG microchip laser for direct generation of radially polarized vector vortices

High beam quality, highly efficient radially polarized vector vortex beam has been generated in a Yb:YAG microchip laser pumped with an annular beam formed with a hollow focus lens. The output power of 2.15 W has been achieved at the absorbed pump power of 3.53 W. The optical-to-optical efficiency is 60.9%. The radially polarized vector vortex lasers working at 1030 nm, 1050 nm, 1030/1050 nm dual-wavelength depending on applied pump power. High polarization purity with degree of polarization of over 91% has been achieved for radially polarized vector vortex lasers. Our work provides an effective method for developing compact wavelength tunable, radially polarized vector vortex lasers.

A highly sensitive imaging polarimeter in the x-ray regime

We report on the development of a highly sensitive imaging polarimeter that allows for the investigation of polarization changing properties of materials in the x-ray regime. By combining a microfocus rotating anode, collimating multilayer mirrors, and two germanium polarizer crystals, we achieved a polarization purity of the two orthogonal linear polarization states of 8 × 10−8. This enables the detection of an ellipticity on the same order or a rotation of the polarization plane of 6 arcsec. The high sensitivity combined with the imaging techniques allows us to study the microcrystalline structure of materials. As an example, we investigated beryllium sheets of different grades, which are commonly used for fabricating x-ray lenses, with a spatial resolution of 200 μm, and observed a strong degradation of the polarization purity due to the polycrystalline nature of beryllium. This makes x-ray lenses made of beryllium unsuitable for imaging polarimeter with higher spatial resolution. The results are important for the development of x-ray optical instruments that combine high spatial resolution and high sensitivity to polarization.

A Compact Substrate Integrated Waveguide Notched-Septum Polarizer for 5G Mobile Devices

In this letter, a compact substrate-integrated waveguide (SIW) notched-septum polarizer is designed, manufactured, and tested. Metalized slots are used instead of vias in proximity to the notches to improve polarization purity. An impedance matching bandwidth of 7.9% at 29 GHz and transmission coefficient of better than $-$ 1.6 dB are demonstrated. The axial ratio is less than 3 dB over a bandwidth of 4.5% at 29 GHz (sufficient for 5G). An implementation of the polarizer in an array antenna was measured to validate its reliability in antenna applications. Given its performance and small form-factor (length of $\lambda _o$ /7 at 29 GHz), the proposed polarizer may be a good option for SIW circularly polarized endfire antennas in 5G mobile devices.

On the Design of Dual-Polarised Linear Antenna Arrays with Enhanced Port-to-Port Isolation.

The paper describes the process of designing a dual-polarised linear antenna array with enhanced port-to-port isolation, with the example of a four-element array with isolation better than 60 dB for the U-NII 5.15–5.925 GHz band. As a single antenna, dual-polarised electromagnetically coupled microstrip antennas were used with port-to-port isolation not exceeding 25 dB. A significant improvement in the isolation of the array was achieved thanks to the application of a dedicated feeding network. On the basis of theoretical analysis, a mathematical model describing port-to-port isolation was developed. Circuit and full-wave simulations were carried out to show the influence of electromagnetic couplings between antennas and/or the microstrip lines of the feeding network and the selection of phase shifters/power dividers on the isolation. The fabricated prototype is characterised by a gain of about 14 dBi, polarisation purity of at least −27 dB within the main lobe and close to expectations isolation better than 57 dB within the whole operational band.

Generation of Pure OAM Beams with a Single State of Polarization by Antenna-Decorated Microdisk Resonators

We report waveguide-addressed plasmonic-photonic resonators that generate beams of controlled orbital angular momentum and spin angular momentum content upon driving through a waveguide. From phase-gradient metasurfaces, we borrow the idea of carefully combining multiple nanoscale resonators in a repeat unit, from which we build periodic rings that decorate microdisk resonators. We describe the general mode structure of microdisk cavities perturbed by antenna arrays on the basis of a quasinormal mode formalism and present a strategy to simultaneously control the orbital and spin angular momentum content of light outcoupled to the far field. We propose a realization that uses silicon nitride disks and aluminum nanorod antennas. We find excellent polarization and orbital angular momentum (OAM) purity, as benchmarked by polarization-resolved interferometric Fourier microscopy on single devices.