Cross-polarization Effects Research Articles

Ultrawide Bandwidth Umbrella-Shaped Microstrip Monopole Antenna Using Spiral Artificial Magnetic Conductor (SAMC)

The design and characterization of a compact ultrawideband (UWB) antenna is presented in this letter. The bases for achieving such an UWB operation are through using semicircular microstrip monopole antenna and introducing a metamaterial as an artificial magnetic conductor (AMC). The AMC reduced antenna size, enhanced antenna gain and bandwidth, and decreased the cross-polarization effect. A spiral artificial magnetic conductor (SAMC) is used as a ground plane with one and four arms to further improve the antenna performance. Furthermore, to reduce surface wave propagation and decrease bandwidth discontinuity, holes surrounding the antenna structure are drilled in the substrate. The new antenna provides an impedance bandwidth of more than 35 GHz with S11 < -10 ± 0.5 dB. The SAMC antenna has a wide frequency range for practical applications ranging from all required wireless communication bands, i.e., GSM 900 MHz, ISM band, Bluetooth, wireless LAN and S-band, to new medical applications. Details of the proposed antenna design are described, and experimental results are presented.

Free space measurement of the cross-polarized transmission band of a bianisotropic left-handed metamaterial

A left-handed metamaterial based on a bianisotropic S-ring resonator is fabricated. By shorting some of the horizontal arms of the paired S-rings, net electric (magnetic) dipoles accumulate under certain magnetic (electric) field induction, which results in a magnetoelectric coupling effect. Free space experimental measurements are carried out and the experimental results demonstrate the cross polarization effect around the left-handed pass band of the metamaterial. The simple planar configuration of the structure also indicates the superiority of this inclusion in the realization of bianisotropic left-handed metamaterials.

Effect of cross-polarization of electromagnetic source on the degree of polarization of generated beam

In this paper we study the degree of cross-polarization of a beam-like field whose cross-spectral density matrix is symmetric with respect to the permutation of its spatial arguments. Formulas were derived expressing the degree of cross-polarization in terms of the generalized Stokes parameters. With the help of an uniformly polarized quasi-homogeneous model source, the effect of degree of cross-polarization of a source on the degree of polarization of the radiated beam was demonstrated, that, two sources with same spectral degrees of coherence and polarization but with different degrees of cross-polarization can generate beams that have different spectral degrees of polarization in the far field.

Negative refraction and cross polarization effects in metamaterial realized with bianisotropic S-ring resonator

The refraction and propagation properties of left-handed materials with bianisotropic effects are investigated. We show that the dispersion relation of the material is strongly influenced by the inclusion of chirality; therefore, different refraction behaviors are observed corresponding to different values of the chirality. A realization of the bianisotropic left-handed material based on the structure of S-ring resonators is further proposed. By subtly shorting some horizontal metallic strips inside of the ring, magnetoelectric coupling is raised, leading to a bianisotropic effect in this artificial medium. The structure is theoretically analyzed from a microscopic viewpoint, and then the macroscopic constitutive parameters are presented, where a nonzero chirality component is clearly shown. Numerical simulation shows that there exists strong cross polarization effects when waves are incident onto a slab of this material, further confirming the results predicted by our theoretical analysis.

COMPACT ARTIFICIAL MAGNETIC CONDUCTOR DESIGNS USING PLANAR SQUARE SPIRAL GEOMETRIES

Compact spiral artificial magnetic conductors (AMC) have been investigatedin this paper. First, single andd ouble spirals are examinedto achieve an in-phase reflection at a lower frequency comparedto a conventional patch element of the same size. However, these two designs generate a large cross polarization. The cross polarization affects the operating frequency and bandwidth. In order to eliminate the cross polarization effect, a four-arm spiral element is introduced. This geometry does not generate a cross polarization, and an operating frequency that is 49.45% lower than the reference patch element has been achieved.

Cross-polarisation method for improvement of 14N NQR signal detectability

This is a study of the cross-polarization effects in the case of 14N quadrupolar spin-system with a long spin–lattice relaxation time. Two important benefits of the cross-polarization technique were demonstrated for PETN: (i) a polarization transfer resulting in increased NQR single shot signal response and (ii) a dynamic reduction in recovery time of the NQR system allowing scan repetition on a much shorter timescale. It was proved that this technique can reduce the optimal waiting time between pulse sequences up to 60 times through a significant reduction of the relaxation time of the quadrupolar spin-system. All experiments were carried out at room temperature using spin-locking multi-pulse sequences and small external magnetic field.

A model to characterize the effect of cross phase modulation on polarization in an optical fiber transmission system

This paper presents a model that described the process of inter-influence between cross phase modulation (XPM) and polarization effects such as polarization mode dispersion (PMD) and polarization dependant loss (PDL) in an optical fiber communication system. Previous papers have discussed PMD–PDL and PMD–XPM effects in separate models, but in this work we developed a model that is capable of characterizing and evaluating PMD, PDL and XPM simultaneously. From the model, we found that PMD and PDL can be affected by XPM. The presence of XPM changed the vector directions of PMD and PDL in Stokes space.

Resonance and Cross-Polarization Effects in Conventional and Complementary Split Ring Resonator Periodic Screens

The behavior of periodic plane arrays of split ring resonators (SRRs) and of complementary split ring resonators (CSRRs) when they are illuminated by a plane wave is analyzed. The effects of the angle of incidence and polarization are considered. A surface admittance approach is used for the analysis. Experimental results in free space are provided in order to check the theory. Good qualitative agreement is observed between theory and experiment, although some quantitative disagreements still remain and need explanation. Application of the studied devices as frequency selective surfaces and polarization converters can be envisaged as a consequence of the high variety of the reported resonant and cross-polarization effects

Excitation and cancellation of higher-order beam modes at isotropic interfaces

The phenomenon of excitation and cancellation of higher-order elegant Hermite-Gaussian and Laguerre-Gaussian three-dimensional beams, induced at a dielectric isotropic interface by cross-polarization coupling, is analysed. The cross-polarization effect depends quantitatively on interrelations between beam field spatial distribution and beam polarization. These relations are derived for two basic cases of linear and circular polarization and confirmed by numerical simulations.

On the performance of telemedicine system using 17-GHz orthogonally polarized microwave links under the influence of heavy rainfall

This paper describes the design of a telemedicine system based on next-generation wireless local area networks (WLANs) operating at 17 GHz. Seventeen gigahertz is proposed for next-generation WLAN services offering numerous advantages over traditional IEEE 802.11 networks that operate in the range of 2.4-5 GHz. Orthogonal polarization is often used to increase spectrum efficiency by utilizing signal paths of horizontal and vertical polarization. Radio waves exceeding 10 GHz are particularly vulnerable to signal degradation under the influence of rain which causes an effective reduction in isolation between polarized signal paths. This paper investigates the influence of heavy rain in a tropical region on wide-band microwave signals at 17 GHz using two links provided by a fixed broad-band wireless access system for two-way data exchange between paramedics attending an accident scene and the hospital via microwave equipment installed in the ambulance. We also study the effects of cross polarization and phase rotation due to persistent heavy rainfall in tropical regions.

Virtual channel space-time processing with dual-polarization discrete lens antenna arrays

This paper discusses channel capacity improvements with optimal multiantenna wireless communications using a discrete lens array (DLA) at the analog front end. It is first shown that optimal signaling over multiantenna channels via virtual spatial models (VSMs) has a direct hardware correspondence in a multibeam spatially fed antenna architecture. A multibeam dual-polarized DLA is designed and characterized, and the effects of measured antenna radiation patterns on calculated capacity are quantified. In particular, the paper examines: 1) effects of cross-polarization for a dual-polarized multibeam array; 2) effects of beam overlap in a multibeam array; and 3) effects of gain variations for different scan angles. It is demonstrated that adding an ideal dual-polarized array achieves a capacity improvement of up to 88% compared to the single-polarization case. In practice, the two polarizations are weakly coupled, and the measured cross-polarization level of -14 dB decreases the capacity of the system by less than 2%. Furthermore, it is shown that a dual-polarized multibeam DLA is nearly insensitive to polarization rotation in a rich scattering environment, whereas single-polarized antennas incur a capacity degradation of up to 24%. Finally, capacity decrease due to measured nonuniform amplitudes on the antenna aperture is shown to be less than 10%.

Cross-polarization effects of light beams at interfaces of isotropic media

Polarization aspects of the three-dimensional optical beam reflection and refraction at dielectric interfaces are analyzed within the framework of the aberrationless approach. The power and the transversal beam profile of the cross-polarized beam are determined in the paraxial approximation. The cross-polarization phenomenon is experimentally demonstrated. Based on the theoretical and experimental results, a simple new method using an appropriate dielectric mirror is proposed for the generation of radially polarized light beams.

Undulator-induced transparency of magnetized plasma: new approach to electromagnetic energy compression

It is well known that circularly polarized electromagnetic waves propagating along the magnetic field in the plasma are strongly absorbed when the wave frequency matches the electron cyclotron frequency. This absorption can be eliminated by adding a weak magnetic undulator, leading to the undulator-induced transparency (UIT) of the plasma. Moreover, the group velocity of the waves in the plasma is strongly reduced, resulting in the extreme compression of the wave energy in the plasma. Compressed waves are polarized along the propagation direction and can be used for synchronous electron or ion acceleration. Numerical simulations reveal yet another interesting property of the electromagnetic waves in UIT plasma: strong coupling and conversion between two circular wave polarizations. Depending on how important this cross-polarization effect is, several propagation regimes have been identified and explored by fluid and particle-in-cell simulations.

Ab initioanalysis of frequency selective surfaces based on conventional and complementary split ring resonators

Frequency selective surfaces (FSSs) made up of periodic arrays of split ring resonators (SRRs) are analysed. This analysis includes complementary screens, or complementary SRR-FSSs (CSRR-FSSs). It is shown that these FSSs show a dual behaviour, with a stop/pass band behaviour at the frequency of resonance of the SRRs/CSRRs. Cross-polarization effects in the SRR and the CSRR are considered, and it is shown that they permit resonance to occur for normally incident plane wave excitation. This latter property of SRRs and CSRRs also implies that the FSSs considered may act as polarizers and polarization converters as well. An analytical theory, valid for perfectly conducting and infinitely thin screens, is proposed for the SRR-FSSs and CSRR-FSSs. These approximations are valid in the microwave and millimetre-wave range, and up to the terahertz range.

T-MATRIX ANALYSIS OF MULTIPLE SCATTERING FROM PARALLEL SEMI-CIRCULAR CHANNELS FILLED WITH CHIRAL MEDIA IN A CONDUCTING PLANE

The T-matrix method is used to model semicircular channels filled with chiral materials in a conducting plane. The coupling of both TM and TE polarizations is represented explicitly. Addition theorems in half space are derived and used to take account of the multiple scattering of parallel channels. The boundary conditions are checked for chiral channels to verify the algorithm proposed. Coand cross-polarization effects of chiral materials are investigated by varying several physical and geometrical parameters of the parallel channels.

Corrugated waveguide band edge filters for CMB experiments in the far infrared

Millimetre wave corrugated waveguide-horn structures are used as both single-moded and multi-moded bolometer feeds in a number of cosmic microwave background (CMB) experiments (e.g. PLANCK, Archeops, QUaD). Such horns tend to be employed over a relatively wide bandwidth and for single-moded horns the waveguide acts as the high pass filter. In this paper we report on our investigation on how the waveguide details determine the exact location of the low frequency band edge of such corrugated horns. A sharp step-like band edge, below which there is negligible propagation, is ideally required. Furthermore any leakage below the expected cut-off, possible in corrugated guides, could lead to non-idealised cross-polar effects. Typically deeper corrugations are required in the waveguide filter than at the horn aperture for wide bandwidth operation, thus necessitating a transition section over which the corrugation depth smoothly varies. An electromagnetic mode matching technique and a surface impedance hybrid mode model are used to compute the horn transmission characteristics. We have also undertaken laboratory measurements of the band edge of prototype corrugated horns in order to test the models.

Generalized ellipsometry for materials characterization

Ellipsometry experiments normally measure two to four parameters, which are converted to the ellipsometric parameters ψ and Δ. This is usually sufficient for many samples, but more complicated situations (such as anisotropic or depolarizing samples) require more sophisticated measurements. Over the last 7 years, we have developed the two-modulator generalized ellipsometer (2-MGE), which measures eight elements of the sample Mueller matrix simultaneously either in reflection or transmission. In reflection, the 2-MGE totally characterizes light reflection from anisotropic samples, measuring the normal ellipsometry parameters, as well as the cross-polarization and depolarization effects. Applications include the determination of the spectroscopic optical functions of uniaxial materials (such as TiO 2 and ZnO), and the measurement of cross-polarization from diffractive structures. In transmission, the 2-MGE completely characterizes a general linear diattenuator and retarder. Applications include the measurement of the retardation and diattenuation of film polarizers and internal electric fields in LiNbO 3 and CdZnTe under bias.

Coalescence Production of Broad Near-Threshold Resonances

Several cases are discussed when an amplitude of resonance production is a sharply varying function of the resonance mass, leading to considerable differences between true and visible resonance parameters. The case of production is considered in more details. As all non-trivial features are caused by the peculiarities of the triangle graphs (threshold and proper-moving complex singularities near physical region), the possible methods of their visualization in inclusive cross sections and polarization effects are also studied.

The effect of precipitation on microwave LMDS networks-performance analysis using a physical raincell model

This article proposes an application of the EXCELL model to microwave local multipoint distribution systems. With EXCELL, validated in many years of observations with a meteorological radar, rain is modeled by a population of exponentially-profiled raincells. Their statistics can be made to honor any given rainfall cumulative distribution function. It is, thus, possible to simulate synthetic precipitation events so that rain effects on various radio link topologies (point-to-point or multipoint) can be evaluated on each event. Both copolar and crosspolar effects were modeled, and the C/I and C/N statistics were evaluated for a large number of events.

The future of diffraction at RHIC

The future of diffraction program at the Relativistic Heavy Ion Collider (RHIC) is discussed. Most of the program is associated with an approved experiment Total and Differential Cross Sections and Polarization Effects in pp Elastic Scattering at RHIC, PP2PP experiment. In the medium | t| range, diffractive region, with four momenta transferred 0.006 < | t| < 1.3 (GeV/ c) 2, the experiment will address one of the main, unsolved problems in particle and nuclear physics: long-range QCD and confinement. In the small | t| range, Coulomb Nuclear Interference (CNI), 0.0004 < | t| < 0.12 (GeV/ c) 2, the experiment will, in a model-independent way, test general analytical properties of scattering amplitudes: analyticity, unitarity, and crossing symmetry. In addition, by measuring single spin asymmetries such as A N , double spin correlation parameter A NN , and cross section difference Δσ T = σ tot (↑,↓) − σ tot (↑,↑), we will be able to determine the helicity amplitudes φ i . Those amplitudes are not well known now, so their systematic study at RHIC will help to understand the spin structure of the nucleon and of the exchanged mediators of the force, Pomeron and Odderon.