Sense Of Circular Polarization Research Articles

Bidirectional circularly polarized antenna with defected ground structure for wideband operation

The present work proposes a wideband circularly polarized antenna with novel design to cover the operation over most of the X-band of the microwave frequencies. This antenna is planar and printed on very thin and flexible Rogers’ substrate of material RO3003 with thickness 0.13mm. The antenna structure can be viewed as composed of an elliptic open annular strip that works as the main radiator. Two symmetric parasitic elements of elliptic arc-shaped narrow strips are capacitively coupled to the elliptic strip radiator. The feeding line is coplanar waveguide with defected ground structure. The parasitic elements and the defects on the ground structures help to enhance the bandwidth of both impedance matching and circular polarization. The antenna is designed to produce bidirectional radiation patterns with opposite sense of circular polarization. The design stages to arrive at the final design of the proposed antenna are described in detail. The antenna is fabricated for experimental assessment showing high performance regarding the circular polarization, bandwidth, and efficiency. The proposed antenna has total dimensions of 30×40×0.13mm3. Both the simulation and experimental results show that the antenna impedance is matched to 50Ω over the frequency band 7.5-13.0(54%bandwidth) and the axial ratio is lower than 3 dB over the frequency band 8.85-12.35GHz(33 % bandwidth). It is shown that the antenna gain ranges from 4.5 to 5 dBi, the radiation efficiency is greater than 99 % and the total efficiency is greater than 91 % over the entire frequency band of the proposed antenna.

MULTISTABILITY IN A CHIRAL SEMICONDUCTOR MICROCAVITY

The features of the bi- and multistability effects in the semiconductor Bragg microcavity with chiral photonic crystal slab on the upper mirror are investigated theoretically. It is shown that the response of such a chiral structure under a linearly polarized coherent resonant pump demonstrates sharp multistable transitions with abrupt jumps of the exciton intensity and degree of circular polarization. It is shown that of the thresholds of bistable transitions in the system with different sense of circular polarization differ slightly, i.e. in case of a non-optimized structure, we can expect to obtain even a larger amplitude of the jumps of the degree of circular polarization of the excitonic response due to the multistability than in a specially optimized chiral structure with a high degree of circular polarization at low pump intensity.

Mechanically Tunable Terahertz Circular Polarizer with Versatile Functions

AbstractCircular polarizers that selectively transmit only one handedness of circular polarization are useful for imaging and wireless communications. Conventional circular polarizers involve 3D chiral structures, which impose fabrication challenges, while typically introducing chirality within a limited bandwidth. To overcome the limitations associated with conventional non‐planar designs, a three‐layer metasurface‐based planar circular polarizer exhibiting strong and broadband chirality is presented here. Its superiority over existing multilayer designs is derived from a systematic design procedure. Measurement results reveal that the proposed structure maintains a 15‐dB extinction ratio from 251 to 293 GHz for the preferred handedness of circular polarization, leading to a fractional bandwidth of 15.4% with a transmission efficiency above 92.7%. Furthermore, the proposed structure is mechanically tunable to alter its functionality or operation bandwidth. Specifically, through simply rotating the top or bottom metallic layer by 90°, the structure can function as a transmissive quasi‐half‐wave plate that reverses the sense of circular polarization. Moreover, the presented structure can operate at nearby frequency ranges for the aforementioned functionalities by mechanically adjusting the air gap spacings between the metallic layers. Further calculations based on the measured results of each layer suggest that the proposed structure is robust to deviations in the air gap spacings.

Demonstration of high sensitivity of microwave-induced resistance oscillations to circular polarization

We demonstrate that long-debated immunity of microwave-induced resistance oscillations (MIRO) to the sense of circular polarization is not a generic property of this phenomenon in solid-state two-dimensional electron systems. Using a large-area GaAs-based heterostructure we detect up to 30 times larger MIRO signal for the cyclotron resonance (CR) active helicity, fully consistent with the concurrently measured transmission and the deduced CR shape of the Drude absorption. We further elaborate conditions to avoid extrinsic factors capable of producing an apparent immunity of the photoresponse.

Switchable T-Slot for Dual-Circularly-Polarized Slot-Array Antennas in Ka-Band

This letter presents two slotted array antennas working in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ka</i> -band with switchable circular polarization capability. The first prototype is a series-fed slotted-waveguide linear array composed of ten T-shaped slots. The second antenna is a 2-D array with 2 × 2 T-shaped slots fed by a corporate distribution network. In both cases, a reflection coefficient below <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 10 dB has been experimentally observed within the targeted frequency band between 29.5 and 30.5 GHz. Good polarization purity is achieved for both polarization senses and in both prototypes. The fundamental contribution of this letter is to propose a simple mechanism to switch the circular polarization sense in a low-cost, low-profile, and high-efficient antenna. The design and experimental results confirm that the solution is suitable for both one- and two-dimensional arrays in the millimeter-wave band.

Discovery of Two-Dimensional Electromagnetic Plasma Waves

We report the experimental discovery of "superluminal" electromagnetic 2D plasma waves in the electromagnetic response of a high-quality GaAs/AlGaAs two-dimensional electron system on a dielectric substrate. We measure the plasma wave spectrum on samples with different electron density. It is established that, at large two-dimensional densities, there is a strong hybridization between the plasma and the Fabry-Perot light modes. In the presence of a perpendicular magnetic field, the plasma resonance is shown to split into two modes, each corresponding to a particular sense of circular polarization. Experimental results are found to be in good agreement with the theory.

Radio Measurements of the Magnetic Field in the Solar Chromosphere and the Corona

The structure of the upper solar atmosphere, on all observable scales, is intimately governed by the magnetic field. The same holds for a variety of solar phenomena that constitute solar activity, from tiny transient brightening to huge Coronal Mass Ejections. Due to inherent difficulties in measuring magnetic field effects on atoms (Zeeman and Hanle effects) in the corona, radio methods sensitive to electrons are of primary importance in obtaining quantitative information about its magnetic field. In this review we explore these methods and point out their advantages and limitations. After a brief presentation of the magneto-ionic theory of wave propagation in cold, collisionless plasmas, we discuss how the magnetic field affects the radio emission produced by incoherent emission mechanisms (free-free, gyroresonance, and gyrosynchrotron processes) and give examples of measurements of magnetic filed parameters in the quiet sun, active regions and radio CMEs. We proceed by discussing how the inversion of the sense of circular polarization can be used to measure the field above active regions. Subsequently we pass to coherent emission mechanisms and present results of measurements from fiber bursts, zebra patterns, and type II burst emission. We close this review with a discussion of the variation of the magnetic field, deduced by radio measurements, from the low corona up to ~ 10 solar radii and with some thoughts about future work.

Bistatic radar observations of near-earth asteroid (163899) 2003 SD220 from the southern hemisphere

We report results of Canberra-ATCA Doppler-only continuous wave (CW) radar observations of near-Earth asteroid (163899) 2003 SD220 at a receiving frequency of 7159 MHz (4.19 cm) on 2018 December 20, 21, and 22 during its close approach within 0.019 au (7.4 lunar distances). Echo power spectra provide evidence that the shape is significantly elongated, asymmetric, and has at least one relatively large concavity. An average spectrum per track yields an OC (opposite sense of circular polarization) radar cross section of 0.39, 0.27, and 0.25 km2, respectively, with an uncertainty of 35%. Variations by roughly a factor of two in the limb-to-limb bandwidth over the three days indicate rotation of an elongated object. We obtain a circular polarization ratio of 0.21 ± 0.07 that is consistent with, but somewhat lower than, the average among other S-class near-Earth asteroids observed by radar.

Interactions Remove the Quantization of the Chiral Photocurrent at Weyl Points.

The chiral photocurrent or circular photogalvanic effect (CPGE) is a photocurrent that depends on the sense of circular polarization. In a disorder-free, noninteracting chiral Weyl semimetal, the magnitude of the effect is approximately quantized with a material-independent quantum e^{3}/h^{2} for reasons of band topology. We study the first-order corrections due to the Coulomb and Hubbatrd interactions in a continuum model of a Weyl semimetal in which known corrections from other bands are absent. We find that the inclusion of interactions generically breaks the quantization. The corrections are similar but larger in magnitude than previously studied interaction corrections to the (nontopological) linear optical conductivity of graphene, and have a potentially observable frequency dependence. We conclude that, unlike the quantum Hall effect in gapped phases or the chiral anomaly in field theories, the quantization of the CPGE in Weyl semimetals is not protected but has perturbative corrections in interaction strength.

Implementation of Spatial/Polarization Diversity for Improved-Performance Circularly Polarized Multiple-Input-Multiple-Output Ultra-Wideband Antenna

In this paper, spatial and polarization diversities are simultaneously implemented in an ultra-wideband (UWB) multiple-input-multiple-output (MIMO) antenna to reduce the correlation between the parallel-placed radiators. The keystone of the antenna is systematically modified coplanar ground planes that enable excitation of circular polarization (CP). To realize one sense of circular polarization as well as ultra-wideband operation, an extended rectangular slot is etched on the left-hand-side of the coplanar waveguide (CPW) feed. This is combined with the asymmetrical ground plane geometry on the right-hand-side of the feeding line. The current flowing on the slotted ground plane forms a quasi-loop and generates CP, whereas the combination of the vertical current on the feedline and the horizontal current on the asymmetric ground plane adds to the axial ratio (AR) bandwidth. To implement the MIMO design with polarization and spatial diversity, the position of the coplanar ground planes is switched with respect to the feedline, and placed in a parallel formation with the edge-to-edge distance of $0.29\lambda _{0}$ . All geometrical parameters are optimized at the full-wave level of description before prototyping and experimental characterization. Simulation and measured results indicate that the proposed MIMO antenna features approximately 82% impedance bandwidth from 2.9 GHz to 7.1 GHz and 68.5% (3.1 GHz- 6.35 GHz) AR bandwidth. Moreover, the peak envelop correlation coefficient (ECC) is below 0.003, which corresponds to almost no correlation between the radiators. The antenna can be operated with either bidirectional or unidirectional characteristics, covering multiple commercial application bands including WLAN and WiMax.

Microscopic model for radiation-induced magnetoresistance oscillations excited by circularly polarized radiation

We develop a microscopic model to explain the striking result of immunity to the sense of circularly polarized radiation of the photo-excited resistance oscillations in high-mobility 2D electron systems. Our model is based on the radiation-driven electron orbit model, previously developed to explain the photo-induced resistance oscillations and zero resistance states in these systems. According to it, the guiding center of the Landau states when irradiated by circularly polarized radiation performs a circular path driven by radiation. In principle, in an infinite sample, this path is different according to the the sense of circular polarization (left or right). However, the limited size of the sample with the essential role of the edges and the concurrent presence of the Hall electric field tend to quench the displacement of the driven guiding center making nearly equal both trajectories. In the end and in the presence of scattering, the longitudinal irradiated magnetoresistance turns out nearly the same irrespective of the sense of circular radiation.

A Miniaturized Broadband High-Impedance Surface With Flexible Circular Polarization Sense

This communication presents a miniaturized ( $0.084\lambda _{0} \times 0.044\lambda _{0}$ ) dual-layered broadband polarization-dependent high-impedance surface (PDHIS). The unit-cell (UC) structure consists of periodic narrow horizontal patch arrays and vertical meander lines on the top and bottom layers of a thin substrate ( $0.012\lambda _{0}$ ), respectively. Using this arrangement, the phase difference between the orthogonal polarization’s of the reflector is enhanced to 180° ± 30° over a wide range of frequencies. The UC of the proposed PDHIS is 88.7% smaller and the measured 3-dB axial-ratio bandwidth is 168.27% broader than a conventional anisotropic HIS. Also, the proposed PDHIS is polarization agile and the circular polarization sense can be easily controlled by changing the alignment of the reflector with respect to the incident plane wave. An equivalent circuit model of the dual-layered anisotropic HIS is presented and the proposed structure is validated using simulations and measurements.

Frequency and circular‐polarization switchable microstrip antenna for dynamic spectrum allocation

AbstractThis article presents a novel frequency‐reconfigurable microstrip antenna supported with an opposite circular polarization sense for dynamic spectrum allocation. The degenerate TM10 and TM01 frequencies are designed by using the distinctly separated electrical delay depending on the H‐shaped slot along the feeding positions for generating circularly polarized waves. In addition, the circularly polarization sense is controlled by changing the status of the pin diode because the switched vertical path affects only TM10 frequency without changing horizontal TM01 frequency. To verify the feasibility of the proposed antenna, the conceptual equivalent circuit is established and the experimental validation is carried out. The implemented antenna successfully demonstrates frequency‐reconfigurable capability with opposite circular polarizations and shows a good agreement with the simulation results.

The polarization mode of the auroral radio emission from the early-type star HD 142301

ABSTRACT We report the detection of the auroral radio emission from the early-type magnetic star HD 142301. New VLA observations of HD 142301 detected highly polarized amplified emission occurring at fixed stellar orientations. The coherent emission mechanism responsible for the stellar auroral radio emission amplifies the radiation within a narrow beam, making the star where this phenomenon occurs similar to a radio lighthouse. The elementary emission process responsible for the auroral radiation mainly amplifies one of the two magneto-ionic modes of the electromagnetic wave. This explains why the auroral pulses are highly circularly polarized. The auroral radio emission of HD 142301 is characterized by a reversal of the sense of polarization as the star rotates. The effective magnetic field curve of HD 142301 is also available making it possible to correlate the transition from the left to the right-hand circular polarization sense (and vice versa) of the auroral pulses with the known orientation of the stellar magnetic field. The results presented in this letter have implications for the estimation of the dominant magneto-ionic mode amplified within the HD 142301 magnetosphere.

Flare SOL2012-07-06: On the Origin of the Circular Polarization Reversal Between 17 GHz and 34 GHz

The new generations of multiwavelength radioheliographs with high spatial resolution will employ microwave imaging spectropolarimetry to recover flare topology and plasma parameters in the flare sources and along the wave propagation paths. The recorded polarization depends on the emission mechanism and emission regime (optically thick or thin), the emitting particle properties, and propagation effects. Here, we report an unusual flare, SOL2012-07-06T01:37, whose optically thin gyrosynchrotron emission of the main source displays an apparently ordinary mode sense of polarization in contrast to the classical theory that favors the extraordinary mode. This flare produced copious nonthermal emission in hard X-rays and in high-frequency microwaves up to 80 GHz. It is found that the main flare source corresponds to an interaction site of two loops with greatly different sizes. We have investigated the three possible known reasons of the circular polarization sense reversal - mode coupling, positron contribution, and the effect of beamed angular distribution. We excluded polarization reversal due to contribution of positrons because there was no relevant response in the X-ray emission. We find that a beam-like electron distribution can produce the observed polarization behavior, but the source thermal density must be much higher than the estimate from to the X-ray data. We conclude that the apparent ordinary wave emission in the optically thin mode is due to radio wave propagation across the quasi-transverse (QT) layer. The abnormally high transition frequency (above 35 GHz) can be achieved reasonably low in the corona where the magnetic field value is high and transverse to the line of sight. This places the microwave source below this QT layer, i.e. very low in the corona.

Quantized circular photogalvanic effect in Weyl semimetals

The circular photogalvanic effect (CPGE) is the part of a photocurrent that switches depending on the sense of circular polarization of the incident light. It has been consistently observed in systems without inversion symmetry and depends on non-universal material details. Here we find that in a class of Weyl semimetals (for example, SrSi2) and three-dimensional Rashba materials (for example, doped Te) without inversion and mirror symmetries, the injection contribution to the CPGE trace is effectively quantized in terms of the fundamental constants e, h, c and with no material-dependent parameters. This is so because the CPGE directly measures the topological charge of Weyl points, and non-quantized corrections from disorder and additional bands can be small over a significant range of incident frequencies. Moreover, the magnitude of the CPGE induced by a Weyl node is relatively large, which enables the direct detection of the monopole charge with current techniques.

Influence of sense rotation of circularly polarized laser pulse on the wake-field acceleration in magnetized plasma

The present paper investigates the effect of different sense rotations of circularly polarized (CP) Gaussian laser pulse on wake-field generation and electron acceleration when there is an axial static magnetic field. The nonlinear equation, which explains the interaction of intense CP laser beam with magnetized plasma in the quasi static approximation, is derived. The numerical analysis of our results indicates that the amplitude of plasma wake for both sense of circular polarization is similar, but affected by propagation direction of exterior magnetic field. It is found that the dephasing length is increased for the left-hand polarized laser fields, while decreased for the right-hand ones, which is reinforced as the enhancement of the forward exterior magnetic field. It is shown that the right-hand polarization laser pulse with reversed exterior magnetic field could leads to much larger electron energy (about 2.4GeV) than that of other cases.

Dual-Frequency Reflectarray Based on Split-Ring Slots

This letter presents a dual-frequency reflectarray (RA). This RA is capable of forming two differently oriented main lobes with the same sense of circular polarization in the directions determined by the reflection elevation angles $\theta _{01}$ and $\theta _{02}$ at two closely spaced frequencies. The RA element contains a pair of concentric split-ring slots with different angular rotations. The geometry of the element was modified and optimized to suppress a mutual coupling between the concentric rings. To validate the operation principle, 317-element offset RAs $\text{RA}\_0\_20$ , $\text{RA}\_20\_0$ , $\text{RA}\_30\_40$ , and $\text{RA}\_40\_30$ were designed to operate at 34.5 and 38.5 GHz for the pairs of elevation angles ( $\theta _{01}$ , $\theta _{02}$ ) equal to (0 $^\circ$ , 20 $^\circ$ ), (20 $^\circ$ , 0 $^\circ$ ), (30 $^\circ$ , 40 $^\circ$ ), and (40 $^\circ$ , 30 $^\circ$ ), respectively. Then, these RAs were fabricated and tested. The highest measured aperture efficiency of 0.45 was observed for $\text{RA}\_0\_20$ and $\text{RA}\_20\_0$ at 34.2 GHz, whereas the $\text{RA}\_30\_40$ demonstrated the lowest aperture efficiency of 0.25 at 38.2 GHz.

Dual Circularly Polarized Series-Fed Microstrip Patch Array With Coplanar Proximity Coupling

We demonstrate a concept of compact and highly efficient circular traveling wave series-fed microstrip patch array working at 10 GHz. The patch elements are excited by a microstrip line through coplanar proximity coupling. A dual-port feeding allows us to select the direction of the traveling waves and, consequently, the sense of circular polarization of the patches. Simultaneous feeding to both ports with proper amplitude and phase difference can result in radiated waves of arbitrary polarization. Owing to the circular array arrangement and the strong proximity coupling, the antenna exhibits a compact structure and achieves a high antenna efficiency of 90% with seven patches. Based on reciprocity, the antenna can readily be also utilized for polarimetry applications for which the signal amplitude at each port is proportional to the amplitude of each individual sense of polarization. Measured results of an antenna prototype successfully validate the concept.

Cascaded circular‐polarisation‐selective surface based on bisected split rings

A cascaded circular-polarisation-selective surface (CPSS) based on bisected split rings is presented. The proposed CPSS allows the transmission of one sense of circular polarisation while reflecting the other sense. To validate the proposed design, a nine-layer prototype that operates in the Ka band has been designed, fabricated and tested. Experimental results show that transmission coefficients higher than −1 dB and axial ratios lower than 3 dB are obtained for one sense of circular polarisation, whereas transmission coefficients lower than −20 dB are obtained for the opposite sense over the frequency band from 26.39 to 35.43 GHz.