scholarly journals 23. Observations of discrete sources with the 22 Mc./s. Mills Cross

1957 ◽  
Vol 4 ◽  
pp. 151-153 ◽  
Author(s):  
B. F. Burke ◽  
K. L. Franklin
Keyword(s):  
Cross Section ◽  
Antenna System ◽  
Pencil Beam ◽  
Switching System ◽  
Carnegie Institution ◽  
Phase Switching ◽  
Linear Arrays ◽  
Half Wave ◽  
Carnegie Institution Of Washington ◽  
Half Power

The 22·2 Mc./s. crossed array of the Carnegie Institution of Washington has been in use since 20 July 1954. This antenna system consists of two linear arrays 2047 ft. in length, each composed of sixty-six half-wave folded dipoles. The amplitude gains of the two arrays are, in effect, multiplied together by a phase-switching system similar to that used in phase-switching interferometers (Ryle, 1952) [1]. The design differs somewhat from the arrangement first used by Mills (Mills and Little, 1953) [2] in that the arrays are arranged in the form of a slightly flattened X. The resulting pencil beam is slightly elliptical in cross-section, measuring 1°·6 by 2°·4 at half-power points, and is directed by inserting lengths of line into the feeder system of each array, phasing the dipoles such that the maximum response is at the desired zenith angle.

scholarly journals PENCIL BEAM PATTERNS OBTAINED BY PLANAR ARRAYS OF PARASITIC DIPOLES FED BY ONLY ONE ACTIVE ELEMENT

2010 ◽  
Vol 103 ◽  
pp. 419-431 ◽  
Author(s):  
M. Alvarez Folgueiras ◽  
J. A. Rodriguez Gonzalez ◽  
Francisco Jose Ares-Pena
Keyword(s):  
Active Element ◽  
Pencil Beam ◽  
Planar Arrays ◽  
Beam Patterns

scholarly journals Multiple Solutions Starting from Real Shaped Beams in Equispaced Linear Arrays

Sensors ◽  
2020 ◽  
Vol 21 (1) ◽  
pp. 62
Author(s):  
Aarón Ángel Salas-Sánchez ◽  
Camilo López-Castro ◽  
Paolo Rocca ◽  
Juan Antonio Rodríguez-González ◽  
María Elena López-Martín ◽  
...  
Keyword(s):  
Multiple Solutions ◽  
Space Vehicle ◽  
Linear Arrays ◽  
Resonant Structures ◽  
Planar Arrays ◽  
Half Wavelength ◽  
Standard Linear ◽  
Beam Patterns ◽  
Flat Top Beam

In the present work, the theoretical basis of the multiplicity of solutions obtained from an initial real symmetric distribution is derived. This initial solution is devoted to generating an equivalent pure real shaped-beam pattern for a concrete synthesis scenario. However, these new solutions are not based on real symmetric distributions; hence, not based on the generation of pure real patterns. The bandwidth performances and tolerance to errors provided by the multiple solutions in the array design are analyzed by considering different architectures, also including mutual coupling models and element factor expressions due to accuracy purposes. In addition, a technique to obtain efficient linear arrays by designing resonant structures is addressed. Examples involving both standard linear arrays of half-wavelength cylindrical dipoles and resonant linear arrays generating flat-top beam patterns are reported and discussed. Additionally, an extension to planar arrays performed by means of a generalisation of the Baklanov transformation through collapsed distribution techniques inspired in the well-known method devised by Tseng and Cheng is performed. In such a way, an analysis of the quality of solutions for generating circular and elliptical footprints with controlled both SLL and ripple which are highly interesting in the framework of space vehicle applications.

scholarly journals Synthesis of Dual-Beam Patterns by Exploiting Time-Modulation in Unequally Spaced Linear Arrays

2021 ◽  
Vol 30 (4) ◽  
pp. 646-653
Author(s):  
S. Patra ◽  
S. K. Mandal ◽  
G. K. Mahanti ◽  
N. N. Pathak
Keyword(s):  
Linear Arrays ◽  
Time Modulation ◽  
Unequally Spaced ◽  
Dual Beam ◽  
Beam Patterns

Synthesis of hexagonal planar array using swarm-based optimization algorithms

2014 ◽  
Vol 7 (2) ◽  
pp. 151-160 ◽  
Author(s):  
Anirban Chatterjee ◽  
Debasis Mandal
Keyword(s):  
Firefly Algorithm ◽  
Artificial Bee Colony ◽  
Optimization Algorithms ◽  
Corresponding States ◽  
Pencil Beam ◽  
Bounded Region ◽  
Bee Colony ◽  
Planar Array ◽  
Beam Patterns

Nature inspired optimization algorithms, namely artificial bee colony (ABC) optimization and firefly algorithm (FA), have been applied to synthesize beam patterns of a hexagonal planar array of isotropic elements. Two different cases, comprising two different beam patterns of a pencil beam and a square footprint pattern over a bounded region with lower peak sidelobe levels are presented. The pencil beam is generated by thinning the uniformly excited array and the square footprint pattern is generated by imposing optimum amplitudes, phases, and their corresponding states (“on”/“off”) to the array elements. The optimum values of the parameters for both the cases are computed using ABC and FA individually, and the superiority of FA over ABC for the proposed problem in terms of computing solutions for both the cases is established.

scholarly journals Superdirective Robust Algorithms’ Comparison for Linear Arrays

Acoustics ◽  
2020 ◽  
Vol 2 (3) ◽  
pp. 707-718
Author(s):  
Danilo Greco ◽  
Andrea Trucco
Keyword(s):  
Underwater Acoustic Communication ◽  
Convex Minimization Problem ◽  
Experimental Conditions ◽  
Robust Algorithms ◽  
Efficient System ◽  
Linear Arrays ◽  
Frequency Responses ◽  
Quantitative Metrics ◽  
Pros And Cons ◽  
Beam Patterns

Frequency-invariant beam patterns are often required by systems using an array of sensors to process broadband signals. In some experimental conditions (small devices for underwater acoustic communication), the array spatial aperture is shorter than the involved wavelengths. In these conditions, superdirective beamforming is essential for an efficient system. We present a comparison between two methods that deal with a data-independent beamformer based on a filter-and-sum structure. Both methods (the first one numerical, the second one analytic) formulate a mathematical convex minimization problem, in which the variables to be optimized are the filters coefficients or frequency responses. The goal of the optimization is to obtain a frequency invariant superdirective beamforming with a tunable tradeoff between directivity and frequency-invariance. We compare pros and cons of both methods measured through quantitative metrics to wrap up conclusions and further proposed investigations.

Linear Arrays of Helical Polyribosomes in Cells Exposed to Antitumor Drug Vincristine Sulfate

1969 ◽  
Vol 27 ◽  
pp. 358-359
Author(s):  
Awtar Krishan
Keyword(s):  
Close Association ◽  
Annulate Lamellae ◽  
Large Array ◽  
Vincristine Sulfate ◽  
Linear Arrays ◽  
Golgi Membranes ◽  
Related Drug ◽  
Drug Leads ◽  
Lethal Doses ◽  
Vinblastine Sulfate

Earle's L-929 fibroblasts treated with mitosis-arresting but sub-lethal doses of vinblastine sulfate (VLB) show hypertrophy of the granular endoplasmic reticulum and annulate lamellae. Exposure of the cells to heavier doses of vincristine sulfate (VCR), a VLB-related drug, leads to the accumulation of large amounts of helical polyribosomes, Golgi membranes and crystals in the cytoplasm. In many of these cells a large number of helical polyribosomes are arranged in prominent linear rows, some of which may be up to 5 micrometers in length. Figure 1 shows a large array of helical polyribosomes near a crystalline mass (CRS) in an Earle's L-929 fibroblast exposed to VCR (5ϒ/ml.) for 3 hours At a higher magnification, as seen in figure 2, the helical polyribosomes are seen arranged in parallel rows. In favorably cut sections, a prominent backbone like "stalk" of finely granular material, measuring approximately 300Å in width is seen in close association with the linear rows of helical polyribosomes.

Performance and applications of a field-emission gun TEM/STEM

1992 ◽  
Vol 50 (2) ◽  
pp. 942-943
Author(s):  
Judith M. Brock ◽  
Max T. Otten ◽  
Marc. J.C. de Jong
Keyword(s):  
Field Emission ◽  
High Resolution Imaging ◽  
High Quality ◽  
Small Energy ◽  
High Brightness ◽  
Small Probe ◽  
Resolution Imaging ◽  
Convergent Beam ◽  
Beam Patterns ◽  
Beam Diffraction

A Field Emission Gun (FEG) on a TEM/STEM instrument provides a major improvement in performance relative to one equipped with a LaB6 emitter. The improvement is particularly notable for small-probe techniques: EDX and EELS microanalysis, convergent beam diffraction and scanning. The high brightness of the FEG (108 to 109 A/cm2srad), compared with that of LaB6 (∼106), makes it possible to achieve high probe currents (∼1 nA) in probes of about 1 nm, whilst the currents for similar probes with LaB6 are about 100 to 500x lower. Accordingly the small, high-intensity FEG probes make it possible, e.g., to analyse precipitates and monolayer amounts of segregation on grain boundaries in metals or ceramics (Fig. 1); obtain high-quality convergent beam patterns from heavily dislocated materials; reliably detect 1 nm immuno-gold labels in biological specimens; and perform EDX mapping at nm-scale resolution even in difficult specimens like biological tissue.The high brightness and small energy spread of the FEG also bring an advantage in high-resolution imaging by significantly improving both spatial and temporal coherence.

Structure Information From Electron Diffraction Intensities

1990 ◽  
Vol 48 (2) ◽  
pp. 516-517
Author(s):  
J. Gjønnes ◽  
N. Bøe ◽  
K. Gjønnes
Keyword(s):  
Computational Effort ◽  
Unit Cell ◽  
Small Unit ◽  
Structure Information ◽  
Dispersion Surface ◽  
Integrated Intensity ◽  
The One ◽  
Image Position ◽  
Convergent Beam ◽  
Beam Patterns

Structure information of high precision can be extracted from intentsity details in convergent beam patterns like the one reproduced in Fig 1. From low order reflections for small unit cell crystals,bonding charges, ionicities and atomic parameters can be derived, (Zuo, Spence and O’Keefe, 1988; Zuo, Spence and Høier 1989; Gjønnes, Matsuhata and Taftø, 1989) , but extension to larger unit cell ma seem difficult. The disks must then be reduced in order to avoid overlap calculations will become more complex and intensity features often less distinct Several avenues may be then explored: increased computational effort in order to handle the necessary many-parameter dynamical calculations; use of zone axis intensities at symmetry positions within the CBED disks, as in Figure 2 measurement of integrated intensity across K-line segments. In the last case measurable quantities which are well defined also from a theoretical viewpoint can be related to a two-beam like expression for the intensity profile:With as an effective Fourier potential equated to a gap at the dispersion surface, this intensity can be integrated across the line, with kinematical and dynamical limits proportional to and at low and high thickness respctively (Blackman, 1939).

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