Coupling between closely spaced back-to-back paraboloidal antennas

Using the geometrical theory of diffraction (GTD), a method of calculating the power coupling between closely spaced back-to-back paraboloidal antennas is presented. The method is illustrated by considering the coupling between two identical front-fed symmetric paraboloids, each of which is fed by a TE11mode circular waveguide.     

Capacity of MIMO systems with closely spaced antennas

Wide-band radio channel measurements at 5.2 GHz with four transmit and four receive antennas at variable element spacing are reported, aiming to evaluate the potential of compact antenna arrays at mobile terminals. We show that, for an element spacing d<0.5/spl middot//spl lambda/ (down to 0.2/spl middot//spl lambda/), the link capacity is not smaller than that for much larger d. This is explained by the observation that mutual coupling changes the radiation patterns of closely spaced antenna elements, individually. Compact multi-antenna terminals may thus become practical.     

Lowest mutual coupling between closely spaced loop antennas

The conditions for zeroing the mutual flux between two closely spaced coil antennas are examined. The analysis is expanded to examine the case of multiple linear antenna coils. Array antennas are used in many areas including magnetic resonance imaging (MRI). Theoretical and experimental results are presented and compared. Good agreement between theory and measurements has been confirmed. A two-dimensional receiving array antenna is proposed     

Nonuniformly spaced linear and planar array antennas for sidelobe reduction

The material discussed can be divided into two parts. In the first part, an iteration method is presented for calculating the distances between the elements of a symmetrical nonuniformly spaced linear array antenna for sidelobe reduction. The amplitude of the excitation is assumed to be constant. The iteration method is applied to linear array consisting of 24 elements. After a few iterations, the sidelobe-to-mainlobe power ratio was reduced to over 22 dB from its value of 13.2 dB for uniform array spacing. In the second part, several symmetrical nonuniformly spaced planar array antennas have been designed, using the nonuniform linear array spacings of part one. The planar arrays include square-shaped and circular structures, with the number of elements ranging from 284 to 576. The iteration method discussed can be applied to linear arrays with any number of elements to obtain nonuniform grid spacings for sidelobe reduction. A number of planar grid structures can be constructed using the nonuniform linear grids. The nonuniform linear and planar arrays utilize fewer radiating elements and result in desirable sidelobe structures.     

The circumferential variation of the axial component of current in closely spaced thin-wire antennas

Closely spaced thin-wire antennas are analyzed by the moment method using the piecewise-sinusoidal function to describe the current variation along the length of the wire and a Fourier series for the circumferential variation. Data are presented for the circumferential variation of the surface current density of parallel dipoles obtained by the "thin-wire" theory, wire-grid model, and the present formulation. It is found that there is substantial circumferential variation, even for dioples spaced more than several wire diameters.     

Radiation from linear antennas in a dissipative half-space

A formulation for the electromagnetic fields of finite linear antennas of arbitrary length immersed in a dissipative halfspace (such as the ocean or the earth) is presented. The electric fields in either medium can be readily evaluated once the current distribution is assumed or prescribed. The fields are given in each medium for each of the three major subdivisions of the horizontal range, the near-field range, the intermediate range, and the asymptotic range. Antenna patterns obtained from computer results using formulas derived in this paper are presented for some typical submerged linear antennas. These computer results are compared with experimental measurements performed with linear antennas submerged in the Atlantic Ocean.     

Radiation patterns of metal and dielectric wall diagonal horn antennas

The radiation patterns and gain of dielectric wall diagonal horn antennas of various thicknesses (0.15cm and 0.32 cm) and dielectric constants (? = 2.54, 2.56 and 3.03) have been experimentally studied and compared with a metal diagonal horn antenna having the same aperture at 9.418 GHz. Radiation patterns of these dielectric horn antennas when used as square horns are also presented and compared with a similar metal horn. The use and applicability of dielectric horn antennas is discussed.     

The resolution of closely spaced signals

This paper presents a method for resolving signals closely spaced in parameter space in the sense that the parameters of the signals being measured (i.e., time of arrival, frequency, etc.) are close together. A maximum-likelihood method is used to resolveMsignals inK-dimensional space, whereMmay be unknown. The resulting procedure first generates aK-dimensional cross-ambiguity function and then passes this function through aK-dimensional linear filter. The procedure effectively reduces the problem from its original form of optimally searching for a maximum in the(M times K)-dimensional space to searching forMmaxima in theK-dimensional parameter space. The method is obviously sub-optimal; its advantage lies in the relatively simple form of the detection scheme.     

Radar separation of closely spaced targets

The capability of a hypothetical radar against attacks by closely spaced aircraft may be examined in geometric terms and the results can be plotted graphically. It is seen that a pulse Doppler type radar, which provides information about target velocity as well as range and angle, is essential in this kind of environment. When the targets are so closely spaced that all else fails, then separation or at least knowledge of the number of targets present is still possible if sufficient Doppler resolution is available to permit the measurement of the small changes in velocity that will be required for the aircraft to maintain formation.     

Measured field patterns of bare and insulated linear antennas in a material medium

Apparatus designed to measure the electric field of bare and insulated linear antennas in fresh water is described. The transformation of the measured field to obtain far-zone patterns is discussed. Field patterns for bare antennas and for insulated antennas with concentric and eccentric insulation are compared, and the shaping of the pattern that can be obtained using the insulation is described. The measured field patterns are in good agreement with theoretical patterns calculated from recently developed theories.     

Alpha-particle-induced charge transfer between closely spaced memory cells

A detailed analysis of various mechanisms involved in α-particle-induced charge transfer between two trench-type DRAM cells is reported. An analytical model has been developed to describe the charge-transfer mechanisms. The charge-collection process consists of two phases. In the first phase, funneling is tile dominant mechanism, and the axial current is calculated based on the drift component. In the second phase, the structure behaves similarly to a bipolar transistor, and both the drift and diffusion components contribute to the charge transfer. A discussion of the dependence of the charge transfer on stored charge, cell separation, charge in the α-particle track, and the substrate doping concentration is presented.     

Directional signal modulation by means of switched spaced antennas

The theory of modulation by hopping or by commutation among a number of spaced antennas is presented. The theory brings out the important considerations and criteria for determining the separation of discrete antennas in time and/or space that produces a desired modulation. In addition, antenna hopping and commutation are proposed for generating direction-dependent spread spectrum to enhance receiving system anti-interference processing gain and/or transmitted signal camouflage and LPI, as well as to provide an effective means for channel monitoring and analytical probing     

Mutual coupling in phased arrays of randomly spaced antennas

Mutual coupling effects in phased arrays with randomly located elements are studied. The network formulation of antenna arrays is found to be a convenient and useful approximation. Two main effects of coupling are separately considered. The first is the increase in the sidelobe level. A new solution for the distribution of sidelobe level has been obtained which is applicable even for small arrays. It is found that the increase in sidelobe level is noticeable only for small average spacing (e.g., less than 2.5 wavelengths). The second effect of coupling is that it causes the fluctuation of main-beam amplitude as a function of the scan angle. The probabilistic properties of these fluctuations are studied. In the uniformly spaced arrays the accumulation of coupling effects may cause "blind angles". In random arrays this accumulation is highly improbable. This method of removing blind angles is further illustrated by an experiment on diffraction gratings where Wood's anomalies and blind angles are recognized as identical phenomena. Finally, an important contribution of this investigation is the analysis by various methods of the radiation pattern of random array. The results obtained by these methods agree remarkably well with the Monte Carlo simulations.     

Radiation patterns in far field from two H-plane coupled rectangular microstrip antennas

Numerically determined far-field radiation patterns are found for H-plane mutual coupling between two rectangular microstrip antennas. A simple closed-form radiation model is used in the analysis.     

Radiation from surface-wave antennas

A recent paper by James on radiation from a dielectric antenna seems to contain some erroneous statements concerning the application of radiation formulas. These erroneous statements are pointed out and related to other theories of surface-wave antennas.     

Channel tracking for RAKE receivers in closely spaced multipathenvironments

This paper deals with the problem of channel tracking for RAKE receivers in propagation environments characterized by closely spaced multipath components. After outlining why conventional single-path channel tracking algorithms fail in such scenarios, several new estimation algorithms are developed that are tailored to channels with closely spaced multipaths. This is achieved by removing or minimizing self-interference caused by multipath components. Other interfering users are treated as noise. Both timing tracking and phasor tracking and their interaction are covered in this paper. The derived algorithms are benchmarked against perfect channel knowledge on one hand and conventional tracking algorithms on the other hand, both in a UMTS test scenario. In moderate scenarios, the use of these new algorithms leads to performance improvements of up to 2 dB, in terms of signal-to-noise ratio (SNR) at moderate bit error rates, and even manages to track the channel in conditions where conventional tracking algorithms fail completely     

Very closely spaced quadspot native-oxide confined 780-nmsemiconductor lasers

We describe the fabrication and characteristics of 7-μm spaced quadspot, independently addressable 785-nm native-oxide confined ridge waveguide laser diodes. The devices are fabricated from an Al_0.1 Ga_0.9As-Al_0.4Ga_0.6As-Al_0.5 In_0.5P quantum-well separate confinement heterostructure laser structure. Wet oxidation of the p-Al_0.5In_0.5P cladding layer is used to form a native oxide for not only ridge waveguide confinement, but also electrical insulation to allow electrical connection to laser stripes. These diodes show excellent performance: uniform threshold currents below 8 mA and differential quantum efficiencies over 35%/facet. The diodes show crosstalk less than 5%     

Fractionally spaced linear and decision-feedback detectors fortransmultiplexers

We investigate improved detectors for transmultiplexer-based high bit rate transmission over dispersive channels like telephone wires. The transmitter is based on a synthesis stage. For the receiver, we design fractionally spaced single-input/multiple-output linear detectors, possibly upgraded with a multiple-input/multiple-output decision-feedback section, for an MMSE criterion. The performance of the system is investigated for filter banks, classical DMT, and different channels. The potential of these detectors is demonstrated,     

Analysis of linear coaxial antennas

Two types of linear coaxial antennas, coaxial-colinear antennas, and slotted coaxial antennas are studied to check the possibility of using them as the base-station antenna in personal communication systems. The slot voltages and input impedance of linear coaxial antennas are obtained by using a transmission-line analysis where the radiation effect is accounted by a shunt and a serial admittance, respectively. The current distribution is obtained by solving an integral equation using the method of moments. The radiation pattern and directivity are then obtained from the current distribution and the reflection coefficient inside the coaxial cable. Factors analyzed include frequency, coaxial filling permittivity and segment number