Beam Tilt Research Articles

Linear Patch Array Over Substrate Integrated Waveguide for Ku-Band

A linearly polarized patch array with direct probe feed over substrate integrated waveguide (SIW) network (LP-PASIW) for Ku-band is presented. A double-stacked microstrip patch structure has been used as radiating elements. Internal SIW coupling patches are placed inside the SIW to obtain the desired radiation pattern. The internal coupling and external radiating patches are connected by means of copper vias. A mutual coupling model is also proposed to adjust the radiation and reflection properties of the array. An antenna prototype has been manufactured and measured. At 17.7 GHz, 16 dBi and 80% peak gain and efficiency values are obtained. Although a 10% reflection bandwidth (17-18.6 GHz) is achieved, the usable bandwidth is reduced to 3% due to array beam tilt dispersion.

SIW 2D PLANAR ARRAY WITH FOUR CROSS SLOTS RADIATOR AND TUNING VIAS

A Substrate Integrated Waveguide (SIW) planar array is presented using a right handed circularly polarized (RHCP) element with four crossed tilted radiating slots. In addition, a pair of metallic tuning vias is included to really improve the re∞ection of longest slots. A corporate feeding network over SIW has been designed for distributing the input signal to 128 radiating elements, divided into 8 progressive wave linear arrays of 16 elements each. The designed planar array has been manufactured and measured to verify the antenna performance. 25.5dB gain, 2.33dB axial ratio, as well as 85% radiation e-ciency values have been experimentally achieved at 17GHz. A 3% usable bandwidth (16.75{17.25GHz) is obtained due to the typical frequency main beam tilt dispersion in the elevation plane of the progressive wave arrays.

Ku-Band용 위성 배열 안테나 설계 및 제작

In this paper, a satellite array antenna operates at 12.2㎓ ∼ 12.75㎓ was designed and fabricated. The lowest height and high gain electrical beam tilt was obtained by applying backed slot and sub-reflector widening the^_@span style=color:#cccccc ^_# distance between the patch and the GND. The simulation and measurement showed good agreements, the electrica^_@/span^_#^_@span style=color:#999999 ^_# ... ^_@/span^_#^_@a href=javascript:; onclick=nodeUse('NODE02023776|147003') style=color:#999999;font-size:14px;text-decoration:underline; ^_#전체 초록 보기^_@/a^_#

Speckle-metric-optimization-based adaptive optics for laser beam projection and coherent beam combining

Maximization of a projected laser beam's power density at a remotely located extended object (speckle target) can be achieved by using an adaptive optics (AO) technique based on sensing and optimization of the target-return speckle field's statistical characteristics, referred to here as speckle metrics (SM). SM AO was demonstrated in a target-in-the-loop coherent beam combining experiment using a bistatic laser beam projection system composed of a coherent fiber-array transmitter and a power-in-the-bucket receiver. SM sensing utilized a 50 MHz rate dithering of the projected beam that provided a stair-mode approximation of the outgoing combined beam's wavefront tip and tilt with subaperture piston phases. Fiber-integrated phase shifters were used for both the dithering and SM optimization with stochastic parallel gradient descent control.

Addition of energy dispersion characteristics to the diagram of axis intercept for aberration analysis of core-lens

The diagram of axis intercept (Nishi and Takaoka [1]) is extended to consider the energy dispersion characteristic. The operating condition of core-lenses can be optimized by taking into account not only the aperture aberration but also the chromatic aberration. The diagram is applied to a typical core-lens system configured with three point charges of different polarities and is plotted as a function of the electron energy in addition to the starting angle. Near the stigmatic condition, the diagram fits the quadratic dependence on both the energy dispersion and the beam tilt angle. Then, the coefficients of aperture aberration, energy dispersion and chromatic aberration are obtained.

Reflection and refraction of an Airy beam at a dielectric interface

Reflection and refraction of a finite-power Airy beam at the interface between two dielectric media are investigated analytically and numerically. The formulation takes into account the paraxial nature of the optical beams to derive convenient field evolution equations in coordinate frames moving along Snell's refraction and reflection axes. Through numerical simulations, the self-accelerating dynamics of the Airy-like refracted and reflected beams are observed. Of special interest are the cases of critical incidence at Brewster and total-internal-reflection (TIR) angles. In the former case, we find that the reflected beam achieves self-healing, despite the severe suppression of a part of its spectrum, while, in the latter case, the beam remains nearly unaffected except for the Goos-Hänchen shift. The self-accelerating quality persists even if the beam is trapped by multiple TIRs inside a dielectric film. The grazing incidence of an Airy beam at the interface between two media with close refractive indices is also investigated, revealing that the interface can act as a filter depending on the beam scale and tilt. We finally consider reverse refraction and perfect imaging of an Airy beam into a left-handed medium.

Investigation of intense sheet electron beam transport using the macroscopic cold-fluid model and the single-particle orbit theory

The focusing and the stable transport of an intense elliptic sheet electron beam in a uniform magnetic field are investigated thoroughly by using the macroscopic cold-fluid model and the single-particle orbit theory. The results indicate that the envelopes and the tilted angles of the sheet electron beam obtained by the two theories are consistent. The single-particle orbit theory is more accurate due to its treatment of the space-charge fields in a rectangular drift tube. The macroscopic cold-fluid model describes the collective transport process in order to provide detailed information about the beam dynamics, such as beam shape, density, and velocity profile. The tilt of the elliptic sheet beam in a uniform magnetic field is carefully studied and demonstrated. The results presented in this paper provide two complete theories for systemically discussing the transport of the sheet beam and are useful for understanding and guiding the practical engineering design of electron optics systems in high power vacuum electronic devices.

Local symmetry breaking of a thin crystal structure of -Si3N4 as revealed by spherical aberration corrected high-resolution transmission electron microscopy images

This report is an extension of the study for structural imaging of 5-6 nm thick β-Si(3)N(4) [0001] crystal with a spherical aberration corrected transmission electron microscope by Zhang and Kaiser [2009. Structure imaging of β-Si(3)N(4) by spherical aberration-corrected high-resolution transmission electron microscopy. Ultramicroscopy 109, 1114-1120]. In this work, a local symmetry breaking with an uneven resolution of dumbbells in the six-membered rings revealed in the reported images in the study of Zhang and Kaiser has been analyzed in detail. It is found that this local asymmetry in the image basically is not relevant to a slight mistilt of the specimen and/or a beam tilt (coma). Rather the certain variation of the tetrahedral bond length of Si-N(4) in the crystal structure is found to be responsible for the uneven resolution with a local structural variation from region to region. This characteristic of the variation is also supposed to give a distorted lattice of apparently 2°-2.5° deviations from the perfect hexagonal unit cell as observed in the reported image in the work of Zhang and Kaiser. It is discussed that this variation may prevail only in a thin specimen with a thickness ranging ~≤ 5-6 nm. At the same time, it is noted that the average of the bond length variation is close to the fixed length known in a bulk crystal of β-Si(3)N(4).

A Method for Gyrotron Beam Coupling into a Corrugated Waveguide

In the radio-frequency (rf) power transmission system of an electron cyclotron heating and current drive (EC H&CD) system, the gyrotron power should couple with the fundamental mode of the corrugated waveguide (HE11 mode) because unwanted higher-order modes affect the beam radiation characteristics, which is a problem in the quasi-optical launcher design. To achieve high HE11 mode purity, a beam coupling method that measures the transmission mode in the waveguide was examined using a 170-GHz high-power gyrotron for the first time. In beam coupling, the offset and tilt angle of the input beam at the waveguide inlet were minimized by controlling the angles of the mirrors in the matching optical unit (MOU) to minimize unwanted LP11 modes in the waveguide. The rf field profile in free space after 1.3 m of the waveguide from the MOU was measured, and the transmission mode content was analyzed. According to the analyzed mode content, the HE11 mode content was optimized by remote adjustment of the mirror angles with a digital controller. The optimization procedure of beam coupling achieved 95% of HE11 mode purity at the entrance of transmission line, which is the first demonstration that meets the criteria of the ITER EC H&CD system.

A 76 GHz Multi-Layered Phased Array Antenna Using a Non-Metal Contact Metamaterial Waveguide

A 76 GHz phased array antenna (PAA) using waffle-iron ridge waveguides with non-metal contacts has been developed. The non-metal contact technology has the advantage of avoiding losses due to imperfect metal contacts, and also facilitates the fabrication of small-size and multi-layer stacked structures. The principle and results of the developed phase shifter, radiator and feed network are presented. For the feed network, it is shown that the phase differences between adjacent radiators are the same, which confirms the validity of the fundamental operation of the PAA. A PAA combining the feed network and 16 radiators with a size of 62 mm × 62 mm × 25 mm was realized. The characteristic of the PAA was evaluated by calculating the directivity using measured data from the radiator and the feed network. From these considerations, the PAA was found to have the capability of providing a beam tilt angle of ±18° while maintaining a gain of more than 32 dBi.

Beam Tilting Slot Antenna Elements with a Forced Resonance by Reactance Loading

This paper presents the basic characteristics of a beam tilting slot antenna element whose forced resonance is realized by reactance loading; its structure complements that of a dipole antenna element. The radiation pattern is tilted using a properly determined driving point position; a single loading reactance is used to obtain the forced resonance without great changes in the tilt angle. Numerical results show that the reactance element needs to be loaded near the driving point in order to obtain the forced resonance of the antenna and the minimum changes in the beam tilt angle at the same time. When the proposed forced resonant beam tilting slot antenna with a 0.8λ length is driven at -0.2λ from the center, the main beam tilt angle of 57.7 degrees and the highest power gain of 3.8dB are obtained. This slot element has a broad bandwidth, unlike the complementary dipole element.

Low-Profile 77-GHz Lens Antenna With Array Feeder

A 77-GHz lens antenna for automotive radar applications is presented. It consists of a feeder in the form of a 2×2 patch array etched from a single layer on a 100-μm-thick substrate and a commercially available dielectric lens. Compared to previously published lens antennas, the presented design has the advantages of excellent electrical performance and a low profile in combination with a thin lens. Measurements of port impedance match and radiation patterns are presented. Beam tilt by lateral offset of the lens is demonstrated experimentally.

An accurate multislice method for low-energy transmission electron microscopy

The conventional multislice method (CMS), originally proposed by Cowley and Moodie (1957), is an important algorithm for image and electron diffraction calculations in transmission electron microscopy. Nevertheless, this method is based on the so-called high-energy approximation, which neglects the second differential term ∂ 2 φ( r)/∂ z 2 to greatly simplify the calculation without severe loss of accuracy. In the current study, we show that for low-energy transmission electron microscopy (LE-TEM) (<100 kV), the high-energy approximation error becomes large and the accurate multislice method, proposed by Chen and Van Dyck (1997), can be used as an alternative method to obtain more accurate calculations. The accurate multislice method, called the revised real space method (RRS) in this paper, can be realized by treating the propagation and scattering as an entirety in real space. A detailed comparison of the numerical results of the RRS and CMS at different accelerating voltages, Debye–Waller factors, and beam tilts is performed. Results show that for image and diffraction simulations in LE-TEM, CMS is no longer sufficiently accurate and the RRS procedure can be used as an alternative method with reasonable computing time.

Repulsion and total reflection with mismatched three-wave interaction of noncollinear optical beams in quadratic media

The phenomenon of the total reflection of a weak signal beam from a high-power reference beam due to noncollinear mismatched parametric interaction in a quadratic medium is demonstrated. In a planar geometry the conditions of the signal beam reflection from the optical inhomogeneity induced by the reference beam are found. The analytical expression for the critical value of the signal beam tilt is obtained, and it is shown that total reflection occurs if the initial tilt is less than the critical value. The influence of the walk-off and the reference beam focusing on interaction dynamics are discussed. It is shown that in a bulk medium the beam reflection turns into scattering by an induced inhomogeneity. If reflection conditions are fulfilled, the cylindrical reference beam acts as a convex mirror and lunate distortions of the reflected beam profile occur.

Limiting factors in atomic resolution cryo electron microscopy: no simple tricks.

To bring cryo electron microscopy (cryoEM) of large biological complexes to atomic resolution, several factors--in both cryoEM image acquisition and 3D reconstruction--that may be neglected at low resolution become significantly limiting. Here we present thorough analyses of four limiting factors: (a) electron-beam tilt, (b) inaccurate determination of defocus values, (c) focus gradient through particles, and (d) particularly for large particles, dynamic (multiple) scattering of electrons. We also propose strategies to cope with these factors: (a) the divergence and direction tilt components of electron-beam tilt could be reduced by maintaining parallel illumination and by using a coma-free alignment procedure, respectively. Moreover, the effect of all beam tilt components, including spiral tilt, could be eliminated by use of a spherical aberration corrector. (b) More accurate measurement of defocus value could be obtained by imaging areas adjacent to the target area at high electron dose and by measuring the image shift induced by tilting the electron beam. (c) Each known Fourier coefficient in the Fourier transform of a cryoEM image is the sum of two Fourier coefficients of the 3D structure, one on each of two curved 'characteristic surfaces' in 3D Fourier space. We describe a simple model-based iterative method that could recover these two Fourier coefficients on the two characteristic surfaces. (d) The effect of dynamic scattering could be corrected by deconvolution of a transfer function. These analyses and our proposed strategies offer useful guidance for future experimental designs targeting atomic resolution cryoEM reconstruction.

Progress of ITER equatorial electron cyclotron launcher design for physics optimization and toward final design

The design of the equatorial electron cyclotron (EC) launcher has advanced toward a more reliable and manufacturable final design. The modification to quasi-optical layout of the millimeter wave transmission line leads to the launcher design being reliable and more realistic toward the final design and the cost reduction. It is proposed that one of three beam rows of the launcher is flipped so that the EC power enables to contribute the counter-EC current drive based on the ITER physics requirement. In addition, a poloidal beam tilt angle of 5° has been introduced in the top and bottom beam row so that all beams can access from on axis to near mid-radius. These design modifications render the EC system more flexible to adapt the needs of advanced ITER physics experiments. It is preliminarily estimated that the nuclear shielding capability of the present modified design satisfies the neutron flux criterion, but the shut down dose rate of γ-ray is slightly higher than the criterion.

Measuring acetabular dysplasia in plain radiographs

Several radiologic parameters have been used to qualify an acetabular coverage in studies determining whether an association exists between acetabular dysplasia and osteoarthritis of hip. However, it is not known which parameter is optimum for these epidemiologic studies. We evaluate the reliability, validity, and robustness of the radiologic parameters of acetabular coverage used in these studies. Center-edge angle (CEA), acetabular depth (AD), acetabular angle (AA), acetabular roof obliquity (ARO), and roof angle (RA) were evaluated. The components of intra- and interobserver reliability were tested. The correlations between each parameter were used to depict convergent validity. The robustness of the parameters to different projection (urogram), different definitions of the lateral acetabular margin, and a differing pelvic tilt were evaluated. The intra- and interobserver reliabilities of CEA, AD and AA ranged from 0.777 to 0.925. The CEA, AD and AA showed acceptable validity in the correlation. The AD on the urograms was 22.0% higher than those on the standing hip radiographs (P < 0.001). When the osteophyte was included in the definition of lateral acetabular margin, the CEA and AD increased significantly (P < 0.001). In simulating pelvic tilting, the AD increased significantly with the anterior pelvic tilt (P < 0.001). The ARO and RA showed poor clinical relevance. When measuring acetabular dysplasia, the AD is unsuitable for use, because it is not robust to different projection of beam and different pelvic tilts. Furthermore, one should consider that the CEA and AA are significantly influenced by different definitions of lateral acetabular margin.

High-impedance surface-based square loop antenna with RF-absorber

A beam steerable square loop antenna is presented over a high impedance surface with RF-absorber. For a test frequency of 5.0 GHz, the proposed antenna is 4.69-mm thick and has an impedance bandwidth of 700 MHz and a gain of 7.93 dB. When compared with a recent published steerable square loop antenna over hybrid high impedance surface, the new antenna offers near equivalent performance but with a much simpler design and a cheaper fabrication process. The absorber's permittivity is found to control the antenna's beam tilt and sidelobe level. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:481–485, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25777

Coplanar Patch Antenna with Tilted-Beam Radiation for Pattern Steerable Applications

A design of generating tilted beam radiation from microstrip antennas is described in this paper. The antenna has a coplanar annular patch, and it is excited by a top-loaded probe through gap coupling. When the antenna is operated at the TM02 mode of the ring patch, its radiation pattern can be changed from a uniform conical beam to a tilted beam by moving the feed point from the antenna center. The direction and directivity of the tilted beam are related to the feed position and the offset distance, respectively. Experimental results indicate that the directivity of the tilted beam is 2 dB higher than that of the original uniform conical beam, and they have good agreements with simulated results carried out with HFSS.

Zero tilt omnidirectional collinear array antenna with coplanar feed

An innovative approach to the design of a centre-fed omnidirectional collinear array for use in the 900 MHz band is presented. The coplanar printed circuit realisation using a combination of the CPW and coplanar strips is shown to be very effective in eliminating beam tilt with change in frequency. Both measured and simulated results confirm less than 1.5° of beam tilt in the omnidirectional pattern with an azimuth ripple of approximately +/−0.7 dB, over an impedance bandwidth of greater than 10%.