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In this article, a new method for exciting the TM11 mode to symmetrize the radiation pattern and reduce the cross‐polarization level of the conical horn antennas is presented. The main idea of this paper is to excite TM11 mode with a frequency‐dependent phase difference relative to the TE11 mode in a manner that these modes appear in phase on the radiation aperture of the antenna in the desired frequency range of 8‐8.4 GHz. Finally, the performance of the TM11 exciter and horn antenna together were simulated and after reaching the predefined goals they were fabricated. [ABSTRACT FROM AUTHOR]

In this paper, a modified broadband bow-tie antenna with low cross-polarization level and miniaturization is presented. The cross-polarization in both E- and H-planes are suppressed by defecting the antenna flares using rectangular slots. The proposed modified antenna demonstrated a cross-polarization improvement over ± 120 ° around the boresight from 2 to 5 GHz. In addition, an overall 23.5% of miniaturization compared to conventional bow-tie antenna is achieved. A tapered feed transition between microstrip-to-parallel stripline is designed to match 50 ohm SMA connector to the antenna flares. A prototype of the modified antenna is fabricated on RO4003 substrate ( ε r = 3.38, tan δ = 0.0027, h = 0.813 mm), and its performance is experimentally studied. The antenna’s characteristics including return loss, gain and radiation pattern are measured, along with the time domain characteristics, and showed reasonable agreement with the simulated results. [ABSTRACT FROM AUTHOR]

In this article, we propose several techniques for radiation characteristics improvement of a coplanar waveguide-fed monopole antenna with an asymmetric ground plane. Although utilization of an asymmetric ground plane provides wideband impedance characteristics, the cross-polarization of the monopole antenna increases, resulting from the unbalanced horizontal currents of the ground plane. The proposed techniques, which include etching a notch at the feedline, embedding a slot array in the ground plane, and adding several conducting strips on the top and bottom planes, are used to suppress cross-polarized power. From the simulated and measured results, it can be observed that the ratios of the maximum co-polarized power to the maximum cross-polarized power have been enhanced at the operating bands. The mechanisms of cross-polarization suppression are explained by using current density distributions. [ABSTRACT FROM AUTHOR]

Spin-locking and cross-polarization under magic-angle spinning are investigated for uniformly 13 C and 15 N labeled solids. In particular, the interferences from chemical shift anisotropy, and 1 H heteronuclear and 13 C homonuclear dipolar couplings are identified. The physical origin of these interferences provides guidelines for selecting the best 13 C and 15 N polarization transfer rf fields. Optimal settings for both the zero- and double-quantum cross-polarization transfer mechanisms are recommended. [ABSTRACT FROM AUTHOR]

For millimeter wave (MMW) radar system of dual polarization, this paper presents a polarization identification method of active jamming decoys. Firstly, the principle of dual polarization technique is introduced, and the characteristics of dual polarization echo of the representative radar targets and various active decoys are analyzed in detail. Secondly, some effective characteristics of active decoys and radar targets are obtained to express their polarization characteristics differences, such as polarization ratio and polarization undulation. Thirdly, an identification method based on self - adaptive constant false alarm rate (CFAR) threshold is proposed. Finally, a dual polarization test radar system is constructed to gather and analyze the experimentation echo data of buildings, vertical polarization, horizontal polarization and left-handed circular polarization active decoys, and the experimentation results prove that the dual polarization identification method of active decoys is feasible and effective. [ABSTRACT FROM AUTHOR]

ABSTRACT A compact two-channel dual trace dual column (DTDC) printed microstrip antenna array integrated with dumbbell-shaped resonator (DSR) is presented. The DSR has been integrated with DTDC array for the reduction of mutual coupling and suppression of cross-polarization (XP) level at 5.2 GHz. In this work, an omnidirectional microstrip antenna array (OMAA) is designed with five elements and then two numbers of similar arrays have been used for multiple-input multiple-output (MIMO) application. A DSR placed in between two OMAA separated by 0.54λ suppressed 12 dB mutual coupling and 7.5 dB XP level. The mutual coupling has been studied by placing DSR on the upper trace first and then in the lower trace. The mutual coupling of 11 dB is reduced when DSR is placed on the upper trace and 12 dB when it is in the lower trace of the array structure. The DTDC antenna structure exhibits maximum XP suppression when DSR in the lower trace. The antenna with compact structure based on the design has a peak gain of 12.84 dBi and band width of 250 MHz. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2182-2186, 2014 [ABSTRACT FROM AUTHOR]

A Ka combined horn antenna with low cross-polarization is presented in this paper. The antenna consists of an edge-slotted waveguide linear array, a metallic-grid plane in the horn throat and a horn. The effects of metallic-grid and single-ridged waveguide to the cross-polarization are analyzed. Three kinds of 62-element Taylor linear array at Ka band are fabricated and measured and the measured cross-polarization level is less than -35dB in operating bandwidth. The proposed antennas are benefit for fabrication and fixation with low cross-polarization and can be extensively used in radar and communication systems. [ABSTRACT FROM AUTHOR]

This paper presents the design and the experimental results of a dual-mode rectangular-matched feed. This type of feed cancels the unwanted high cross-polarization generated by the offset parabolic reflector antenna. In order to design this feed, higher order TE11 mode has been added in correct amplitude and phase with the fundamental TE01 mode in a rectangular structure. The proposed feed was then used as a primary feed to illuminate a linearly polarized offset parabolic reflector antenna. Through experimental results, it is verified that such a feed suppresses the undesired high cross-polarization introduced by the offset geometry of an offset reflector antenna. This kind of feed is very much suitable for monopulse tracking radar. [ABSTRACT FROM AUTHOR]

A corrugated spline-profile horn has been designed to meet the stringent specifications and constraints of a receiver for Band 1 (31.3-45 GHz) of the Atacama Large Millimeter Array (ALMA). Given the physical restrictions of the receiver, the horn will be located behind a focusing lens placed 191 mm over its aperture. After this first focusing stage, the horn must have a reflection coefficient less than −20 dB and the cross-polarization not exceeding the −30 dB level in the entire frequency range. The side-lobes should be less than −25 dB at all frequencies and its half power beamwidth must be approximately 24° at 31.3 GHz and 16° at 45 GHz. The horn has been constructed using the split-block technique and characterized in a near-field scanner setup. The results show an excellent performance complying with all the requirements. [ABSTRACT FROM AUTHOR]

Abstract: Thermodynamic limit of magnetization corresponding to the intact proton bath usually cannot be transferred in a single cross-polarization contact. This is mainly due to the finite ratio between the number densities of the high- and low-gamma nuclei, quantum–mechanical bounds on spin dynamics, and Hartmann–Hahn mismatches due to rf field inhomogeneity. Moreover, for fully hydrated membrane proteins refolded in magnetically oriented bicelles, short spin-lock relaxation times (T 1 ρ ) and rf heating can further decrease cross polarization efficiency. Here we show that multiple equilibrations-re-equilibrations of the high- and low-spin reservoirs during the preparation period yield an over twofold gain in the magnetization transfer as compared to a single-contact cross polarization (CP), and up to 45% enhancement as compared to the mismatch-optimized CP-MOIST scheme for bicelle-reconstituted membrane proteins. This enhancement is achieved by employing the differences between the spin–lattice relaxation times for the high- and low-gamma spins. The new technique is applicable to systems with short T 1 ρ ’s, and speeds up acquisition of the multidimensional solid-state NMR spectra of oriented membrane proteins for their subsequent structural and dynamic studies. [Copyright &y& Elsevier]

Abstract: The 1H→13C NMR cross-polarization (CP) was studied under magic-angle spinning at 7.5kHz in various crystal forms of the antipsychotic drug olanzapine: two polymorphs (metastable I and stable II) and eight solvates containing organic solvent and water molecules. The CP kinetics followed the non-classical I–I⁎-S model, in which CP begins in a spin cluster of proximate abundant spins I* and rare spins S, then is controlled by spin diffusion of the abundant spins I from bulk to the I* spins of the spin cluster and finally is governed by spin-lattice relaxation of the abundant spins in the rotating frame. The corresponding CP kinetics parameters were determined and analyzed. It was demonstrated that the, λ and T df values (the CP time constant, the cluster composition parameter and the 1H spin-diffusion constant, respectively) were very useful to discriminate the functional groups, especially in the 3D parameter space. In order to conveniently analyze the large amount (175) of the collected CP parameters, the number of the observed variables was reduced using the principal component (PC) analysis. The 2D plot of PC2 vs. PC1 showed adequate separation of the CH3, CH2, CH and C cases (C stands for carbons without adjacent hydrogens). It was demonstrated that those cases were located along the PC1 axis in the order of increasing 1H–13C dipolar couplings: C

A low cross-polarization center-fed microstrip reflectarray antenna is presented. The cross-polarization elimination is accomplished by a particular arrangement of the elements. Using this technique, a center-fed reflectarray antenna has been designed at center frequency of 11.7 GHz. Measurement results are compared with that of a previously reported reflectarray antenna. Both antennas are exactly the same in every aspect except for the elements arrangement. Measurement results show 1 to 12 dB reduction in cross-polarization level and a notable enhancement in the new antenna's overall gain. [ABSTRACT FROM AUTHOR]

This paper presents a novel design of Complementary-Symmetry rectangular Microstrip Antenna (CSMA) with modified ground plane for compactness, enhanced gain, bandwidth and low cross-polarization operation. A 58% size compactness is achieved when compared with the conventional rectangular microstrip antenna. The antenna operates for 18.78% of bandwidth and gives maximum of 8.21 dB gain. The cross-polar power level of --22.9 dB down is obtained with respect to co-polar. The effect of complementary-symmetry geometry and modified ground plane for improving the antenna parameters is studied and reported. The experimental results are in agreement with the simulated results. The proposed antennas may find applications in wireless communication systems. [ABSTRACT FROM AUTHOR]

Abstract: High static magnetic fields and very fast magic-angle spinning (MAS) promise to improve resolution and sensitivity of solid-state NMR experiments. The fast MAS regime has permitted the development of low-power cross-polarization schemes, such as second-order cross-polarization (SOCP), which prevent heat deposition in the sample. Those schemes are however limited in bandwidth, as weak radio-frequency (RF) fields only cover a small chemical shift range for rare nuclei (e.g. 13C). Another consideration is that the efficiency of cross-polarization is very sensitive to magnetization decay that occurs during the spin-lock pulse on the abundant nuclei (e.g. 1H). Having characterized this decay in glutamine at 60kHz MAS, we propose two complementary strategies to tailor cross-polarization to desired spectral regions at low RF power. In the case of multiple sites with small chemical shift dispersion, a larger bandwidth for SOCP is obtained by slightly increasing the RF power while avoiding recoupling conditions that lead to fast spin-lock decay. In the case of two spectral regions with large chemical shift offset, an extension of the existing low-power schemes, called MOD-CP, is introduced. It consists of a spin-lock on 1H and an amplitude-modulated spin-lock on the rare nucleus. The range of excited chemical shifts is assessed by experimental excitation profiles and numerical simulation of an I2S spin system. All SOCP-based schemes exhibit higher sensitivity than high-power CP schemes, as demonstrated on solid (glutamine) and semi-solid (hydrated, micro-crystalline ubiquitin) samples. [Copyright &y& Elsevier]

The development of a Ka-band monopulse variable polarization antenna is presented, based on polarization synthesis theory. This kind of microstrip array antenna consists of several linearly polarized subarrays of rotational symmetry, and change the polarization mode by adjusting the phase of each subarray. The circular polarization of three subarrays and four subarrays has high polarization purity with over 30 dB cross-polarization and less than 3 dB axial ratio within the half power beamwidth; and the imbalance of two peaks in difference beam is less than 1 dB, and null depth is over 30 dB. [ABSTRACT FROM AUTHOR]

Propagation of degrees of cross-polarization of a partially coherent electromagnetic beam in uniaxial crystals orthogonal to the optical axis is investigated. Based on the paraxial theory of beams, analytical propagation formulas for degrees of cross-polarization are derived and analyses are illustrated by numerical examples. It is found that values of the degree of cross-polarization in uniaxial crystals fluctuate more rapidly with larger deviation of correlation length parameters (δij - δii), but show slight variation with larger ratio of refractive index (ne/n0) or incident beam wavelength. Results also show that sources with sufficient correlation length parameters generate invariable degree of cross-polarization in uniaxial crystals. [ABSTRACT FROM AUTHOR]

A high-resolution channel sounding technique has been used to investigate the cross-polarization of electromagnetic waves in the 5-6 GHz band. Experiments were performed in two non-line-of-sight indoor locations, and it was found that there is a strong dependency of the cross-polarization of multipath components on the elevation angle-of-arrival. For a vertically polarized transmitting antenna, clusters of co-polarized multipath components were confined predominantly to the region around the horizontal plane that contains the virtual line-of-sight between transmitter and receiver. In contrast, cross-polarized signals were detected for a variety of elevation angles with considerable power levels. The surroundings of the receiver were identified as the principal source of depolarized signals. In addition, time dispersion analysis of the multipath signals led to the determination of the AoAs where there is a strong correspondence between co- and cross-polarized signals as a consequence of the partial depolarization of MPCs. This work supports the exploitation of the joint space and polarization diversities in indoor propagation scenarios to improve the system performance. [ABSTRACT FROM PUBLISHER]

A novel compact electromagnetic band-gap (EBG) structure in a spiral shape is presented and investigated. This structure significantly enlarges the capacitance between neighboring elements. The simulations and experimental results have proved that the size of the spiral structure is only 30.9% of the conventional EBG structure. Two applications have been shown, including patch antenna with the spiral EBG structure and a double-element microstrip antenna array with low mutual coupling. The measured results show that a gain improvement over 3 dB and a significant reduction of cross polarization in H-plane are obtained. A 6 dB reduction of mutual coupling is achieved in a double-element EBG microstrip antenna array. [ABSTRACT FROM AUTHOR]

Structural information can be extracted from one-bond residual dipolar couplings (RDC) measured in NMR spectra of systems in field-ordered media. RDC can be on the order ofJ-couplings if the anisotropy of alignment is ~ 10-2, 10-fold stronger than that typically used for structural studies of water-soluble proteins. In such systems the performance of1H?15N polarization transfer methods of the INEPT type is not satisfactory. In this study we show the effectiveness of adiabatic-passage cross-polarization (APCP) in transferring the1H?15N polarization in the bicelle-associated peptide Leucine Enkephalin (Lenk). APCP is efficient both in static samples and in samples spun at the magic angle (MAS) or any other angle of the spinning axis to the magnetic field (variable-angle spinning, VAS). The anisotropic spectrum of an aligned static sample and the isotropic spectrum of the sample under MAS provide a set of possible values for the1H-15N RDC of phospholipid-associated Lenk. The unambiguous determination of the1H-15N RDC was accomplished by means of VAS experiments. [ABSTRACT FROM AUTHOR]

Using enhancement of the 27Al central-transition magnetization by applying RAPT prior to 27Al → 29Si cross-polarization, we demonstrate fast acquisition of 29Si one-dimensional MAS and two-dimensional 27Al–29Si HETCOR spectra on a new sialon phase Ba2Al3Si9N13O5. [Copyright &y& Elsevier]

Hertz's vector potential is used to compute the co- and cross-polarized scattered fields due to simple targets like an arbitrarily oriented wire, an arbitrarily oriented loop of wire, and an infinite cylinder. The monostatic cross-polarization properties of these targets are studied with different radar and target parameters. Important conclusions are summarized. It is found that under certain combinations of parameters, the cross-polarization radiation is significant even for simple targets. [ABSTRACT FROM AUTHOR]

In this paper, the design of a broadband dual-polarized microstrip patch antenna with excellent polarization purity is investigated theoretically and experimentally. Based on cavity-model theoretical analysis, a test dual-polarized microstrip patch antenna fed by double slot-coupled feeds with a 180° phase shift and a coplanar microstrip feed is presented. The simulated and measured results show that this antenna achieves a high isolation (< -41 dB) across the entire operating frequency and low cross-polarization level (< -30 dB). © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 329–331, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20625 [ABSTRACT FROM AUTHOR]