Circular Polarization Pattern Research Articles

Shadows of loop quantum black holes: semi-analytical simulations of loop quantum gravity effects on Sagittarius A* and M87*

In this study, we delve into the observational implications of rotating Loop Quantum Black Holes (LQBHs) within an astrophysical framework. We employ semi-analytical General Relativistic Radiative Transfer (GRRT) computations to study the emission from the accretion flow around LQBHs. Our findings indicate that the increase of Loop Quantum Gravity (LQG) effects results in an enlargement of the rings from LQBHs, thereby causing a more circular polarization pattern in the shadow images. We make comparisons with the Event Horizon Telescope (EHT) observations of Sgr A* and M87*, which enable us to determine an upper limit for the polymetric function P in LQG. The upper limit for Sgr A* is 0.2, while for M87* it is 0.07. Both black holes exhibit a preference for a relatively high spin (a ≳ 0.5 for Sgr A* and 0.5 ≲ a ≲ 0.7 for M87*). The constraints for Sgr A* are based on black hole spin and ring diameter, whereas for M87*, the constraints are further tightened by the polarimetric pattern. In essence, our simulations provide observational constraints on the effect of LQG in supermassive black holes (SMBH), providing the most consistent comparison with observation.

A novel dual-sense polarization reconfigurable dual-band microstrip antenna

In this paper, a novel dual-band, dual-sense, polarization reconfigurable dual coupled line square microstrip patch antenna is proposed. It comprises of a diagonal edge truncated square microstrip patch with a dual coupled line structure. The dual-band operation is realized by using dual coupled lines. They also aid in generating dual-sense of circular polarization (CP) at two resonances. The diagonal edge truncated square patch consists of four PIN diodes along with the bias circuit. It realizes a dual-sense of polarization reconfiguration like right-handed circular polarization (RHCP)/left-handed circular polarization (LHCP), linear polarization (LP)/LHCP, RHCP/LP at lower resonance f1 = 2.4 GHz and higher resonance f2 = 2.6 GHz respectively for different states of the diodes. The proposed antenna is designed, simulated, fabricated, and experimentally tested for validation. The experimental results of −10 dB reflection coefficient, 3 dB axial ratio for CP, gain, and radiation pattern characteristics at the two bands are acceptable and are found to be in concurrence with simulation results in all the states. The proposed antenna would be useful for multifunctional wireless communication applications.

Revealing magnetic field structure at the surfaces of protoplanetary disks via near-infrared circular polarization

Context. Magnetic fields play a fundamental role in the dynamical evolution of protoplanetary disks, in particular via magnetically induced disk winds. The magnetic field structure at the disk surface is crucial for driving the disk winds; however, it is still poorly understood observationally. Aims. We explore a new method to probe the magnetic field structure at the disk surface using near-infrared (NIR) circular polarization. Near-infrared circular polarization arises when unpolarized stellar light is scattered by magnetically aligned grains at the disk surface. In this study, we aim to clarify to what extent the observed circular polarization pattern can be used to diagnose the magnetic field structure. Methods. We first calculated light scattering properties of aligned spheroids, and the results were then used to create expected observational images of the degree of circular polarization at a NIR wavelength. Results. Magnetically aligned grains can produce circular polarization, particularly when the field configuration deviates from a purely toroidal field. We find that disk azimuthal dependence of the degree of circular polarization tends to exhibit a double peaked profile when the field structure is favorable for driving disk winds by centrifugal force. We also find that even if the disk is spatially unresolved, a net circular polarization can possibly be nonzero. We also show that the amplitude of circular polarization is strongly dependent on grain composition and axis ratio. Conclusions. Our results suggest that circular polarization observations would be useful to study the magnetic field structure and dust properties at the disk surface.

Integrated Design of Multimode and Multifrequency Miniaturized Handset Antenna at VHF/UHF Bands

This paper presents an integrated design of a multimode and multifrequency miniaturized handset antenna working at the lower band (0.24–0.7 GHz) with linear polarization and higher band (1.98–2.01 GHz and 2.17–2.20 GHz) with circular polarization simultaneously. At the higher band, the quadrifilar helix antenna (QHA) is utilized with each arm developed into two arms of different lengths and linearly tapered widths to realize double resonance and increase the bandwidth. Moreover, a helical stub behaving as a director is introduced to improve the antenna gain. At the lower band, the outer conductor of the QHA feedline and four QHA arms are designed to constitute a monopole antenna through proper feeding and introducing four quarter-wavelength short-circuit stubs. With this radiator-sharing technique, the QHA not only works at the higher band with a circular polarization pattern but can act as a monopole antenna working at the lower band with a linear polarization pattern simultaneously. As a result, the size of the antenna can be reduced remarkably. Finally, the proposed antenna is fabricated with a total length of 228 mm and a diameter of 15 mm. At the lower band, the measured S11 is below −8 dB, and the gain is larger than 0.5 dBi. At the higher band, the measured S11 and AR are better than −13 dB and 3 dB, respectively, and the gain within the zenith angle range of 0°−35° is greater than 2.5 dBi, which demonstrates better performance.

High‐gain and wideband differentially fed circularly polarized planar aperture antenna

AbstractA novel circularly polarized (CP) planar aperture antenna that is completely self‐designed and manufactured with high gain and wideband is proposed in this paper. The antenna adopts a differential feed network so that the energy is evenly transmitted to the radiation patch. By surface current analysis, the closed loop with linearly polarized (LP) characteristics is changed into two arms of different lengths to generate CP radiation. The uniformity and symmetry of energy improve the wideband and high‐gain performance of the antenna. The fabricated antenna prototype has the characteristics of a wideband of 33.3% (28.1–39.3 GHz) and an average gain of 11.4 dBic, which could achieve 3‐dB axial ratio bandwidth of 12.4% (35.2–39.6 GHz) and a stable left‐handed CP and radiation patterns throughout the operating bandwidth with a peak gain of 15.8 dBic.

Synthesizing Circularly Polarized Multi-Beam Planar Dipole Arrays With Sidelobe and Cross-Polarization Control by Two-Step Element Rotation and Phase Optimization

In this article, a novel method is presented to synthesize multi-beam circularly polarized (CP) patterns with sidelobe level (SLL) and cross-polarization level (XPL) suppression for planar dipole arrays by optimizing both element rotations and excitation phases. Multiple sets of excitation phases are adopted as optimization variables other than the determined values according to the rotation angles in the conventional sequentially rotated technique (SRT) and the random sequentially rotated technique (RSRT), so as to improve the performance of the obtained CP multi-beam patterns. This releases many more degrees of synthesis freedom but leads to a new problem of demanding excessive computation resources for a planar rotated dipole array with multiple CP patterns. Then, a two-step rotation and phase optimization strategy is proposed to effectively solve this optimization problem. In the initial step, the common element rotations and approximated excitation phases composed of the common phase parts plus the beam focusing phase parts are found for multiple desired CP patterns with different beam directions. And then, a refining step is performed to refine the excitation phases individually for each CP beam for improved pattern performance. Four representative examples of synthesizing multi-beam patterns with both SLL and XPL suppression are provided to verify the effectiveness of the proposed method. Comparisons with the conventional SRT and RSRT are also provided to show the superiority of the proposed method.

Compact Circularly Polarized Slotted Symmetric V slits Microstrip Patch Antenna for ISM Band Applications

This paper presents a short microstrip patch antenna and analyzes its characteristics in simulation and measured ways. The proposed antenna is meant to be used from 2.4 to 2.5 GHz at the resonant frequency of 2.45 GHz Industrial, Science, and Medical (ISM) spectrum. Besides, insert a diagonal slot in the main patch, and two cutting edges with V-slit gives the antenna to propagate a circular polarization pattern. The paper aims to start learning a simple C.P. patch antenna supported the basic concept of microstrip antenna theory. A single-feed C.P., truncated corners, and slit and slot methods are employed to model the antenna apart from its parametric study. The substrate material of the developed antenna is FR-4, and it's a relative permittivity of 4.4. The antenna incorporates a compact overall size of 0.389λ0 × 0.389λ0 × 0.013λ0, where λ0 is that the corresponding free-space wavelength at 2.45 GHz. FEKO has been used for not only designing the antenna model but also analyzing its performances. Simulated and measured results have reported that the antenna can work in ISM bands (2.42-2.5 GHz) with VSWR< 2, low realized gain, and the limited 3-dB axial ratio at 2.45 GHz.

An Integrated Circularly Polarized Transmitter Active Phased-Array Antenna for Emerging Ka-Band Satellite Mobile Terminals

This paper presents the design, development, and measurement results of a low-cost integrated circularly polarized (CP) active phased-array antenna (CP-APAA) technology with sidelobe level (SLL) control, operating at $Ka$ -band, for high throughput land-mobile satellite communication. The proposed CP-APAA is comprised of ( $4\times 16$ ) 64 elements in a rectangular grid array configuration. Eight commercial monolithic monolithic microwave/millimeter-wave integrated circuit. (MMICs) with eight-RF output channels have been used to control the phase and amplitude over the antenna aperture. For simplicity, the array antenna was designed in three metal layers and fabricated by a low-cost printed circuit board (PCB) technology as a proof-of-concept for a modular and scalable $Ka$ -band PAA with a wide steering angle. Measured radiation pattern shows a right-hand CP (RHCP) pattern with an axial-ratio (AR) level < 3 dB and low pointing error ≤1.5° over a scanning angular range of 0° to ±40°. Moreover, the amplitude excitation of the CP-APAA was tapered exponentially to control and reduce the SLL from 11 to 25 dB in boresight direction. Finally, toward a multibeam array implementation, two RHCP beams have been simultaneously generated at −30° and +20° scan angles.

Near-infrared Polarimetry of the Outflow Source AFGL 6366S: Detection of Circular Polarization

Abstract We have carried out near-infrared circular and linear imaging polarimetry of the AFGL 6366S region. There is one large infrared reflection nebula associated with the AFGL 6366S cluster and one small infrared reflection nebula associated with AFGL 6366S NE. Prominent and extended polarized nebulosities over the AFGL 6366S cluster field are found to be composed of several components and local nebula peaks, and those nebulosities are illuminated by at least three sources, which is roughly consistent with a previous study. However, the detailed linear polarization patterns and their degrees differ from the earlier study. The brightest regions of the nebulae are illuminated by the IRAS/WISE source. In addition, we report the first detection of circular polarization (CP) in the reflection nebula associated with AFGL 6366S. The CP is as large as approximately 4% in the K s band, and the maximum CP extent is approximately 0.45 pc, which is comparable to that for the largest CP regions known to date, such as Orion and Mon R2, although the CP degrees are much smaller. The CP pattern is mostly quadrupolar, and its morphology resembles the shape of the C18O dense core. Therefore, the CP region is probably illuminated by the IRAS/WISE source and its polarization is amplified by the dichroic absorption of the dense core associated with the cluster. This is the ninth source whose degrees of CPs are measured to be greater than 3%, suggesting that large and extended infrared CP regions are common among mid- to high-mass young stellar objects.

Probing Twisted Magnetic Field Using Microwave Observations in an M Class Solar Flare on 11 February, 2014

This work demonstrates the possibility of magnetic field topology investigations using microwave polarimetric observations. We study a solar flare of GOES M1.7 class that occurred on 11 February, 2014. This flare revealed a clear signature of spatial inversion of the radio emission polarization sign. We show that the observed polarization pattern can be explained by nonthermal gyrosynchrotron emission from the twisted magnetic structure. Using observations of the Reuven Ramaty High Energy Solar Spectroscopic Imager, Nobeyama Radio Observatory, Radio Solar Telescope Network, and Solar Dynamics Observatory, we have determined the parameters of nonthermal electrons and thermal plasma and identified the magnetic structure where the flare energy release occurred. To reconstruct the coronal magnetic field, we use nonlinear force-free field (NLFFF) and potential magnetic field approaches. Radio emission of nonthermal electrons is simulated by the GX Simulator code using the extrapolated magnetic field and the parameters of nonthermal electrons and thermal plasma inferred from the observations; the model radio maps and spectra are compared with observations. We have found that the potential magnetic field approach fails to explain the observed circular polarization pattern; on the other hand, the Stokes $V$ map is successfully explained by assuming nonthermal electrons to be distributed along the twisted magnetic structure determined by the NLFFF extrapolation approach. Thus, we show that the radio polarization maps can be used for diagnosing the topology of the flare magnetic structures where nonthermal electrons are injected.

Circularly Polarized Antenna With Reconfigurable Broadside and Conical Beams Facilitated by a Mode Switchable Feed Network

A pattern-reconfigurable slot-augmented patch antenna is reported that radiates circularly polarized (CP) fields and is switchable between a broadside and a conical radiating mode. Two novel design strategies were adopted to realize these advantageous performance characteristics. First, a mode switchable feed network which includes a set of eight L-probes was developed that facilitates the proper excitation of either the patch’s TM11 or TM21 mode and yields symmetric radiation patterns. Second, their operating bands were made to overlap by augmenting this patch with an annular slot. Consequently, the radiation pattern is easily switched between the broadside and the conical modes within the overlapping operational bandwidths. A prototype was fabricated and tested. The measured results are in good agreement with their simulated values, verifying the design concepts. The measured operating bandwidth, 7.8% from 2.45 to 2.65 GHz, was determined from the overlap of the impedance and axial ratio bandwidths for both modes. The measured realized gain values are stable for both radiating states within this operational bandwidth, the broadside (conical) peak value being 8.5 dBic (5.8 dBic). The CP pattern reconfigurability of this antenna with its favorable performance characteristics makes it an ideal candidate for many RFID and satellite communication applications.

Analytic study on CP enhancement of millimeter wave DR and patch subarray antennas

This article presents a comparative analysis for the performance of single, 2 × 2, and 4 × 4 dielectric resonator (DR) and patch circularly polarized (CP) antenna subarrays at 30 GHz. In order to enhance the CP bandwidth, the subarray elements are fed by two kinds of sequential feeding techniques using parallel and hybrid ring feeds. The 4 × 4 patch antenna subarrays fed by parallel and hybrid ring feeding networks are fabricated and tested. Measurements show acceptable agreement with simulation results. The experimental results show a bandwidth of 36.9% for both (−10 dB) impedance matching and (3 dB) axial ratio CP patterns for the patch subarray antenna with hybrid ring feeding. For the parallel feeding, the corresponding bandwidth is 28.81%. The proposed antennas combine desirable features such as wide impedance and AR bandwidths, low profile, and easiness of fabrication and therefore is a good candidate for millimeter wave systems around 30 GHz.

Wideband Omnidirectional Circularly Polarized Antenna Based on Tilted Dipoles

A wideband omnidirectional circularly polarized (CP) antenna is developed. The omnidirectional CP antenna includes four tilted dipoles that are wrapped around a cylinder for omnidirectional CP pattern. Each tilted dipole is coupled with a parasitic element for bandwidth enhancement. It is shown that the wideband omnidirectional CP antenna achieves an axial ratio (AR) bandwidth of 44% (1.69–2.64 GHz) for $\text{AR} and an impedance bandwidth of 61% (1.35–2.54 GHz) for ${\text{return loss}} > 10\;\text{dB}$ . The antenna gain is around 1 dBi with an omnidirectionality of less than 1.5 dB.

A Hemispherical 3-D Null Steering Antenna for Circular Polarization

In this letter, a compact three-dimensional (3-D) null steering antenna is presented for circular polarization. Two high-isolated circularly polarized (CP) pattern modes, the broadside and the conical CP pattern modes, are synthesized for 3-D null steering in the upper hemisphere. The broadside CP pattern mode is generated by a corner-truncated patch, and the conical CP pattern mode is generated by four rotationally symmetric strips. By controlling the exciting power ratio and the relative phase delay of the two modes, continuous null steering is achieved in the elevation plane and the azimuth plane, respectively. A prototype of the proposed antenna operating at 1.575 GHz is fabricated and tested for the global position system (GPS) applications. The simulated and measured results verify the null steering performance of the proposed design.

NEAR-INFRARED CIRCULAR POLARIZATION SURVEY IN STAR-FORMING REGIONS: CORRELATIONS AND TRENDS

We have conducted a systematic near-infrared circular polarization (CP) survey in star-forming regions, covering high-mass, intermediate-mass, and low-mass young stellar objects. All the observations were made using the SIRPOL imaging polarimeter on the Infrared Survey Facility 1.4 m telescope at the South African Astronomical Observatory. We present the polarization properties of ten sub-regions in six star-forming regions. The polarization patterns, extents, and maximum degrees of linear and circular polarizations are used to determine the prevalence and origin of CP in the star-forming regions. Our results show that the CP pattern is quadrupolar in general, the CP regions are extensive, up to 0.65 pc, the CP degrees are high, up to 20 %, and the CP degrees decrease systematically from high- to low-mass young stellar objects. The results are consistent with dichroic extinction mechanisms generating the high degrees of CP in star forming regions.

A Circularly Polarized Pattern Diversity Antenna for Hemispherical Coverage

In this communication, a circularly polarized (CP) antenna is proposed for satellite communication applications. The proposed antenna consists of two parts. One part is in-phase-fed folded monopoles with omnidirectional CP radiation pattern, and the other part is sequential-fed L-shaped monopoles with broadside CP radiation pattern. By combining the two parts as a pattern diversity antenna, upper hemispherical coverage with left-handed circular polarization (LHCP) is achieved in a small volume of 0.38λ×0.38λ×0.071λ ( λ is the free-space wavelength). A prototype of the proposed antenna operating at 1.575 GHz has been built and tested. The measured overlapping bandwidth for both the two patterns with -10-dB impedance bandwidth and 3-dB axial-ratio (AR) is 6.7% (1.515-1.62 GHz), also with high port isolation. In addition, the AR and gain coverage over the upper hemisphere is discussed in detail.

Design of a half-ring type dipole antenna for WLAN communications

In this article, a novel and compact printed half-ring dipole antenna for WLAN communications is proposed. The proposed dipole antenna consists of a tapered balun and a pair of half-ring dipole which have both the modified microstrip half-ring with a feed line and the modified microstrip half-ring with the tapered balun on the ground plane. The proposed antenna has a decreased physical size and radiates an omnidirectional pattern compared with conventional dipole antenna because of the proposed ring dipole antenna uses a circular-type dipole. Prototypes of the proposed antenna for the 4.9–6 GHz bands are constructed and tested. The proposed antenna obtains a measured peak gain of about 5.8 dBi at 5.32 GHz, and an appeared circular polarization pattern at 5.04 GHz. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1832–1836, 2014

NOVEL MODELING AND DESIGN OF CIRCULARLY POLARIZED DIELECTRIC RESONATOR ANTENNA ARRAY

This paper presents a design of circularly polarized dielectric resonator antenna (DRA) array. The dielectric resonators (DRs) were excited by rectangular aperture coupling slots feed with a linear microstrip. The slot positions were determined based on the characteristic of standing wave ratio over a short ended microstrip to deliver the maximum amount of coupling power to the DRs, in order to improve the array gain Each DR element was rotated 45 - with respect to the sides of the exciting slot to generate circular polarization pattern. The DRA array was modeled and simulated as a parallel RLC input impedance component using Agilent (ADS) software, since that will ensure the resonant frequency of the antenna as primary design step before simulating in (CST) software and doing the measurements. The results of the return loss, gain radiation and pattern axial ratio are shown. The gain of the proposed array in X band was about 8.5dBi, while the 3dB axial ratio bandwidth started from 8.14 to 8.24GHz. The impedance bandwidths started from 8.14GHz to 8.26GHz. The proposed DRA exhibited an enhancement of the gain in comparison to a single pellet DRA. The size of the whole antenna structure is about 40mm £ 50mm and can potentially be used in wireless systems.

DESIGN OF BROADBAND CIRCULARLY POLARIZED SQUARE SLOT ANTENNA WITH A COMPACT SIZE

This paper proposes a newly designed compact coplanar- waveguide-fed wideband circularly polarized (CP) printed square slot antenna (PSSA), in the square slot of which are a halberd-shaped feeding signal line and a square ring patch. By placing a specially designed metal re∞ector behind the bidirectional CP PSSA, one can obtain unidirectional CP patterns with a associated 3-dB axial-ratio bandwidth (ARBW) almost the same as that of the bidirectional antenna. The bidirectional L- and S-band PSSAs designed on FR4 substrates have 3-dB ARBWs as large as 25.3% and 29.1%, respectively. For the L-band antennas, the unidirectional design yields a 3-dB ARBW of 25.7% and a gain of about 3dB higher than that of the bidirectional counterpart. In all these 3-dB axial- ratio bands, impedance matching with VSWR • 2 is also achieved. Most importantly, the design concepts, procedures, and rules for the proposed antenna are presented in detail.

A low profile single dipole antenna radiating circularly polarized waves

A low profile single dipole antenna that can generate circularly polarized (CP) radiation patterns is proposed in this paper. The CP patterns and low profile configuration are achieved using a specially designed artificial ground plane: a thin grounded slab loaded with periodic rectangular patches. The artificial ground plane exhibits in-phase reflection coefficients with polarization-dependent feature. The radiation mechanism of the antenna is described, and experimental results verify the antenna concept.