Cross-polarization Properties Research Articles

A Design Method of Three-Dimensional Multireflector Quasi-Optical Systems Based on Gaussian Beam Mode Analysis

Two-dimensional (2-D) quasi-optical systems have been widely applied. However, the analysis and design of 3-D systems still need to be further developed. In this letter, an approach to rapidly analyze the performance of 3-D multireflector systems based on Gaussian beam mode analysis is proposed. The influence of reflector parameters, such as input distance, incidence angle, and so on, on the co- and cross polarization is discussed. Furthermore, a novel design method of high-performance 3-D multireflector systems is proposed. High computational efficiency is one of the advantages of this method due to the application of particle swarm optimization algorithm. 3-D systems with low cross polarization or other electromagnetic properties can be designed rapidly by this novel method. The proposed methods greatly improve the calculation efficiency, while providing calculation accuracy similar to that of physical optics (PO) in GRASP10.

Geometrical Optics-Based Advanced Design of an Open Cavity Resonant Antenna

This letter explores geometrical optics-based raytracing in combination with modal analysis to realize an open cavity structure as an advanced variant of the resonant cavity antenna (RCA). Additional ray confinement has been ensured by determining accurate phase-locking conditions as demonstrated for the first time. Its combination with the analysis of the cavity mode has also been introduced to determine the optimum design parameters, achieving improved radiation properties. With respect to a reference RCA reported earlier, the proposed approach exhibits a remarkable improvement in gain by 4-9 dB, resulting in about 17 dBi peak value consistently over the full 18% matching bandwidth. This is resultant from an increase in aperture efficiency, typically from 27% to 74%. This is achieved without any compromise with the cross-polarization property. The sidelobe level improves over the band except in higher frequency in H-plane. The proposed concept is commercially viable, showing significantly advantageous features.

편파가변 위성 방송 수신용 능동 위상 배열 안테나 개발

We herein present a study on the active phased array antenna for receiving satellite broadcasting that can electrically align its polarization to that of target transmitters in its moving condition or in the Skew angle arrangement of the broadcasting satellite receiver. Hence, we have developed an active phased array structure composed of the self-developed Vivaldi antenna and multifunction core (MFC) chip, receiving RF front end module, and control units. In particular, the new Vivaldi antenna designed in the Ku-band of 10.7–14.5 GHz to receive one desired polarization mode such as the horizontal or vertical by means of an MFC chip and other control units that can control the amplitude and phase of each antenna element. The test results verified that cross-polarization property is 20 dB or higher and the primary beam can be scanned clearly at approximately ±60°.

Analytical Models of Dual-Polarized Primary Matched Feeds for Offset Reflector Antennas With Low Cross-Polarization Properties at Both Asymmetry and Diagonal Planes

Conjugate-matched primary feeds for offset reflector antennas are reviewed and investigated for both x- and y-polarized cases. Tapered dual-mode circular waveguide feeds are analytically modeled to support a ${\rm {TE}}_{11}$ -type mode with unequal beamwidths and the ${\rm {TE}}_{21}$ -type mode for the two orthogonal polarizations. First, required mode content factors and tapering numbers of the ${\rm {TE}}_{11}$ mode are addressed for the y-polarized case in offset reflectors with different focal length-to-diameter ratios. Then, the model is appropriately tailored for the x-polarized primary feeds. It is shown that when the polarization orientation changes, the corresponding beamwidths of the ${\rm {TE}}_{11}$ mode should be swapped in the principal E- and H-planes. This is particularly important to simultaneously realize low cross-polarization levels at both asymmetry and diagonal planes, when a dual-polarized matched feed is utilized in offset reflector antennas.

Microstrip Patch With Nonproximal Symmetric Defected Ground Structure (DGS) for Improved Cross-Polarization Properties over Principal Radiation Planes

A symmetric as well as nonproximal defected ground structure has been conceived for a square microstrip patch to achieve high co- to cross-polarized (XP) isolation over the principal radiation planes. This design does not follow the thumb rule of earlier works where the defect was deployed either underneath or in close proximity to the patch boundary. The proposed configuration, therefore, appears to be ideal for some specific applications, such as dual-polarized or circularly polarized patches with improved polarization purity. A representative design in C-band has been discussed, leading to the proof of concept. Experimental verification confirms up to 8-10 dB improvement in XP level, particularly in the H-plane.

Improved Cross-Polarization Performance of a Multi-Phase-Center Parabolic Reflector Antenna

This letter addresses the cross-polarization properties of electronically controlled multi-phase-center parabolic reflector antennas, illuminated by over-moded primary feeds. Due to the presence of the higher-order modes in the primary feed, the secondary cross-polarization levels deteriorate in the case of symmetric reflector antennas. As for the offset reflectors, the primary multimode feed required to displace the phase-center location may produce a significant crosstalk in the orthogonal polarization. It is shown how one can improve the cross-polarization performances of aforementioned adaptive antennas, which are capable of providing axial beams while their phase-center locations are displaced. The conventional array technique with a simple signal processing is used for the symmetric case, whereas a trimode primary feed is employed for the offset case.

Cross-polarization properties of two Gaussian Schell-model beams through non-Kolmogorov turbulence

Abstract General expressions are derived for the spectral degree of cross-polarization (SDCP) of a beam generated by the superposition of two Gaussian Schell-model (GSM) beams, which illuminated with the same Gaussian Schell-mode source propagating in non-Kolmogorov turbulent atmosphere by adopting beam cross-spectral density matrix and Young's interference theory. In particular, through numerical examples based on our analytical formal the SDCP of two GSM beams is analyzed. Detailed analysis demonstrate that the SDCP is closely to the spacing of two beams on source plane as well as the strength of the atmospheric turbulent, but the fractal constant α has no affect on the SDCP.

Effect of feed phase errors on the crosspolarization of offset reflector antennas

AbstractThe impact of feed phase errors on the crosspolarization of offset reflector antennas is studied.The primary feed is assumed to be linearly polarized, with symmetrical E‐ and H‐plane patterns independent of ϕ. They are modeled by a cosnθ function, along with an extra term to account for the phase errors. Both linear and quadratic phase variations are studied. A broad range of focal length to diameter ratios, f/D from 0.5 to 1.1, are considered to investigate the crosspolarization properties in the presence of phase errors. It is shown that the reflector crosspolarization increases drastically when there is a linear phase error associated with the primary feed pattern. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:231–235, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25643

Investigation of Asymmetric Phase Errors of an Optimized Dual-Mode Primary Feed on the Cross Polarization of Offset Reflector Antennas

An analytic dual-mode primary feed is first modeled to illuminate offset reflector antennas to reduce their cross polarization. The feed is linearly polarized and includes the dominant TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> and higher order TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> modes. The phase error is then applied to the primary feed to investigate its impact on the cross polarization of offset reflector antennas. Two cases are studied in terms of which of the above-mentioned modes will be affected by the phase errors. The phase errors applying to the resultant dual-mode feed are studied as the first case. The second case includes the effect of phase error only on the higher order TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> mode resulting in different phase center locations for each mode. Asymmetric right-left phase patterns are used to conduct the study. Both linear and quadratic phase variations are studied. A broad range of focal-length-to-diameter (f/D) ratios from 0.5 to 1.1 are considered to investigate the reduced cross polarization properties in the presence of phase errors. It is shown that the reflector cross polarization increases drastically in the presence of the phase errors. In particular, the boresight-null cross polarization will no longer exist when the phase center location of the second mode is displaced from that of the dominant mode.

XPOL—the Correlation Polarimeter at the IRAM 30-m Telescope

ABSTRACTXPOL, the first correlation polarimeter at a large-millimeter telescope, uses a flexible digital correlator to measure all four Stokes parameters simultaneously, i.e., the total power I, the linear polarization components Q and U, and the circular polarization V. The versatility of the back end provides adequate bandwidth for efficient continuum observations as well as sufficient spectral resolution (40 kHz) for observations of narrow lines. We demonstrate that the polarimetry-specific calibrations are handled with sufficient precision, in particular the relative phase between the Observatory’s two orthogonally linearly polarized receivers. The many facets of instrumental polarization are studied at 3 mm wavelength in all Stokes parameters: on-axis with point sources and off-axis with beam maps. Stokes Q, which is measured as the power difference between the receivers, is affected by instrumental polarization at the 1.5% level. Stokes U and V, which are measured as cross-correlations, are very minimally affected (maximum sidelobes 0.6% [U] and 0.3% [V]). These levels critically depend on the precision of the receiver alignment. They reach these minimum levels set by small ellipticities of the feed horns when alignment is optimum (≲0.3′′). A second critical prerequisite for low polarization sidelobes turned out to be the correct orientation of the polarization splitter grid. Its cross-polarization properties are modeled in detail. XPOL observations are therefore limited only by receiver noise in Stokes U and V even for extended sources. Systematic effects set in at the 1.5% level in observations of Stokes Q. With proper precautions, this limitation can be overcome for point sources. Stokes Q observations of extended sources are the most difficult with XPOL.

Iterative least-squares synthesis methods for conformal array antennas with optimized polarization and frequency properties

An iterative least-squares synthesis technique is presented for the optimization of the element excitation in conformal array antennas. This method allows the designer to have predefined goals for the shaped radiation pattern over a selected frequency band and for the polarization properties of the array. Linear or circular polarization can be used in the synthesis. Different kinds of synthesis goals can be set, whereby the copolarization or cross-polarization properties of the array are weighted or a narrowband or wideband design is sought. The amplitudes of the element excitations can be fixed. Several synthesis examples are presented for an array on a sphere with circular polarized elements. Broad-band and low cross-polarization designs are included.

Reflection and cross-polarization properties of grooved dielectric panels

The cross-polarization and reflection properties of grooved dielectric windows are calculated. Measurements on two windows in the range 8-12 GHz are found to be in good agreement with the theory. It is shown that cross-polarization is substantially reduced if the grooves on the front and back faces of the window are orthogonal to each other.

Nonlinear resonance effects in atomic gases—spontaneous and stimulated electronic Raman scattering of Na atoms excited resonantly atDlines by a tunable dye laser

A report is given of the first quantitative study of the spontaneous and stimulated electronic Raman scattering by a resonance doublet of the sodium atom excited resonantly at the D1 and D2 lines by a tunable dye laser. Theoretical and experimental analyses of the differential scattering cross section and polarization properties at the Stokes and anti-Stokes frequencies show that the observed scattering is due to a nearly resonant process involving the ground state 3S1/2 as the dominant intermediate state. The stimulated Stokes and anti-Stokes scattering lines, which are shifted from the D1 and D2 lines by an amount corresponding to the frequency separation between lowest-lying excited doublets 3P1/2 and 3P3/2, are observed by exciting a sodium vapor cell with a passively mode-locked dye laser.

A Proposed Multiple-Beam Microwave Antenna for Earth Stations and Satellites

An offset Cassegrainian antenna with essentially zero aperture blockage is expected to support closely spaced well-isolated beams suitable for earth stations and satellites. Each beam is fed with a separate small-flare-angle corrugated horn and has good area efficiency over a 1.75:1 bandwidth. Each beam also has good cross-polarization properties. The antenna is compact, and the design appears practical for a 4- and 6-GHz earth station, a 20- and 30-GHz earth station, and a 20- and 30-GHz satellite.

Depolarization properties of offset reflector antennas

The cross polarized radiation for linearly polarized excitation and the beam displacement for circularly polarized excitation have been investigated for offset reflector antennas. Numerical calculations are given to illustrate the dependence upon the angle <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\theta_{0}</tex> between the feed axis and the reflector axis as well as upon the half-angle <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\theta_{c}</tex> subtended at the focus by the reflector. In the case <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\theta_{0} = \theta_{c} = 45\deg</tex> , measured results have been obtained for both linearly and circularly polarized excitations with a dual mode feed illuminating an offset paraboloid. The cross polarized radiation of horn reflector and open Cassegrainian antennas rises sharply to rather high values off the beam axis; however, in general, the maximum cross polarized radiation of offset reflector antennas can be made small by using a small angle between the feed and reflector axes. The cross polarization caused by offset is compared with that caused by an unbalanced feed pattern. The effect of the longitudinal current distribution and of departure of the surface from a paraboloid on cross polarization are also examined. The clarification of these cross polarization properties is found to be valuable in the design of reflector antennas.

Spin-Orbit Coupling forΛ−He4Scattering Using a One-Boson-Exchange Model for theΛNInteraction

The polarization and cross sections for $\ensuremath{\Lambda}\ensuremath{-}^{4}\mathrm{He}$ elastic scattering are calculated for $\ensuremath{\Lambda}$ incident energies 1-20 MeV. A $\ensuremath{\Lambda}\ensuremath{-}^{4}\mathrm{He}$ potential is constructed using a phenomenological $\ensuremath{\Lambda}N$ Gaussian central potential and the empirical shape for $^{4}\mathrm{He}$, and a spin-orbit potential obtained from a one-boson-exchange (OBE) model for the $\ensuremath{\Lambda}N$ interaction. As indicated recently by Downs, the OBE model for $\ensuremath{\Lambda}N$ forces leads to strong antisymmetric spin-orbit terms due to vector-meson exchange. This means that the $\ensuremath{\Lambda}\ensuremath{-}^{4}\mathrm{He}$ potential depends only on part of the $\ensuremath{\Lambda}N$ spin-orbit interaction, since it results from summing the latter interaction over the nucleon spin states. Parameters from three quite different OBE calculations are used to predict the $\ensuremath{\Lambda}\ensuremath{-}^{4}\mathrm{He}$ scattering, and these three sets of OBE parameters lead to remarkably similar predictions concerning the cross sections and polarization properties for this energy range. However, no $\ensuremath{\Lambda}\ensuremath{-}^{4}\mathrm{He}$ resonances are predicted, in contrast to recent Hartree-Fock calculations of $\ensuremath{\Lambda}\ensuremath{-}^{4}\mathrm{He}$ scattering. The polarization effects predicted are large, and experimental data concerning them would have interesting consequences for our knowledge of the origin of spin-orbit forces in the baryon-baryon system.

Polarization Correlations of the Gamma-Rays ofCs134and of Annihilation Radiation

The polarization correlation of the antiparallel cascade gamma-rays of ${\mathrm{Cs}}^{134}$ has been observed. The well-known cross-polarization property of the annihilation radiation has been utilized to determine the effective geometry of the polarimeters. The observed ratio of coincidences in perpendicular and parallel orientations is 0.91\ifmmode\pm\else\textpm\fi{}0.08. This ratio is not in disagreement with previous assignments of spin and parities to the excited states of the daughter nucleus, ${\mathrm{Ba}}^{134}$.