Quarter-wavelength Elements Research Articles

Wideband Vortex Beam Reflectarray Design Using Quarter-Wavelength Element

A wideband vortex beam reflectarray is designed and fabricated to generate the orbital angular momentum (OAM) waves for an $\boldsymbol{l} = 2$ mode. A quarter-wavelength element is proposed to achieve a reflection phase of 360° at the designed frequency of 6 GHz. The element consists of a loop patch, a cross-dipole patch, and four square patches. The symmetric structure of the element makes it suitable for dual polarization. It is revealed that the OAM mode purity and operational bandwidth of the reflectarray are increased by using the quarter-wavelength element. The array size is $\text{50} \times {\text{50 cm}}^2$ , which achieves measured gain of 18.98 dBi at 6 GHz and operational OAM bandwidth of 42%.

English

A compact Planar Inverted F Antenna (PIFA) as the element for dual band operation in 1.48 GHz GPS and 3.2 GHz WiMAX band is proposed. PIFAs are quarter wavelength elements. Among various possible antennas, PIFAs have the advantages of low profile, compact size and are very suitable for present-day wireless communication application. A folded slit in the top plate is used to get the dual band operation. Comparison between two different orientations for folded slit is performed. A 50% miniaturization and gain improvement is achieved when the folded slit is near to the feed with an open end. The radiation pattern and current distribution on the PIFA are also plotted.

Passive Localization of Near-Field Sources Using Cumulant

Passive source localization is one of the issues in array signal processing fields. When some source lies in the Fresnel region of the array (i.e., near-field), the wavefront of the source must be characterized by both the direction-of-arrival (DOA) and range. To localize near-field sources, some classical far-field source localization methods are modified to estimate DOA and range at the costs of array aperture, which contains two hands: (i) quarter- wavelength constraint is imposed on the intersensor spacing and (ii) fewer sources in the near-field case are localized from an array of given sensor number than those of the far-field case. In addition, it is necessary to match two separately estimated electric angles (function of DOA and range) of multiple near-field sources, i.e., encountering parameter match problem. To solve these problems, this paper develops a new cumulant-based algorithm (CBA). The key points of this paper are: (i) based on the rank-reduction idea, the nonlinear optimization problem of two-dimensional parameters is decoupled to avoid both pairing parameters and two-dimensional search; (ii) unlike some classical near-field source localization algorithms, the quarter-wavelength element spacing constraint is not required in the proposed algorithm. Simulation results are presented to validate the performance of the proposed method.

Dual-frequency and broad-band antennas with stacked quarter wavelength elements

Original lightweight, low-cost, and compact air-filled planar antennas with short-circuited elements, fed by a coaxial probe, for dual-frequency (S-antenna) and wide-band applications (E-antenna) are investigated. The two-band frequency antenna is formed of two stacked quarter-wavelength elements, short-circuited along diametrically opposed planes. This structure offers two modes with different radiation characteristics. The ratio between the two frequencies can be closely controlled within a range varying from 1.3-2. A bandwidth of 30% for a VSWR <2 is demonstrated using two stacked quarter-wavelength elements short-circuited along the same plane. Numerical simulation results are compared with experiments and a very good agreement is observed. Radiation patterns and input impedance of both structures are measured and the effects of various physical parameters are presented.

Double-resonance circuit for nuclear magnetic resonance spectroscopy

A new double-resonance probe circuit design is described. The circuit contains no quarter-wavelength elements or equivalents, yet nonetheless achieves adequate isolation between the two input channels. It contains relatively few components, and so is both compact and efficient. It has been incorporated in two solid-state nuclear magnetic resonance (NMR) probes, with excellent results.

A Design Method for Micro-Mechanical Filters with Quarter Wavelength Elements

Length expander type and thickness expander type micro-mechanical filters are proposed in this paper as attractive elements for an on-chip structure forming. The design principles have been theoretically studied by using a distributed constant circuit design theory. As the result, it is clarified that the method of inserting additional step elements in the middle of the filter is valid for solving the actualization problem of a large impedance step and a filter with the fractional bandwidth of less than 3% is realizable in a VHF and UHF band.

Application of spatial filters to DOA estimation of coherent sources

Problems associated with spatial smoothing which relate to the rate of decorrelation of correlated sources are discussed. Although a small improvement is attained, if sources have small differences in their directions-of-arrival (DOAs), they will remain highly correlated and the problem is not significantly diminished. A method which is based on the spatial filtering of an array vector is proposed. A procedure is developed that significantly reduces the correlations among sources and results in a nearly diagonal source covariance matrix. The design of the proposed spatial filters requires preliminary estimates of DOAs. This requirement, however, is not a drawback to this method, as is shown. Simulation studies are carried out for a 12-element linear array with quarter-wavelength element spacing. In all cases, 100 snapshots are used to estimate the array covariance matrix. In each case, 10 different simulations, with different noise sequences, are performed to present the variability of the resultant spectrum. The number of sources is set to 3 with -60 degrees , 30 degrees , and 40 degrees DOAs.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>