Beamwidth Variation Research Articles

Effect of Number of Elements of a Reactively Loaded Ring Antenna Array on the Performance of Beamwidth Variation

We herein investigate the effect of the number of elements of a previously studied reactively loaded ring antenna array with respect to electronically variable beamwidth performance. The antenna has a unique ability to increase the effective antenna length by adding parasitic ring elements, which contributes to higher performance with respect to beamwidth variation. Monte Carlo (MC) simulations clarify that variable range of beamwidth can be improved effectively by increasing the number of ring elements M to 5. It is herein demonstrated for the case of M = 5 that the beamwidth toward the broadside direction can be controlled from 40deg to 145deg in the E plane, while maintaining the voltage standing-wave ratio (VSWR) to less than 3.0, where the antenna size is 0.32lambda times 1.32lambda. In addition, it is also confirmed that the number of estimated directions-of-arrival (DOAs) based on the reactance-domain multiple signal classification (MUSIC) algorithm can be also increased by increasing the number of ring elements.

Guassian soliton in biased photorefractive crystal

Using a variational approach, the low intensity photorefractive nonlinear Schr dinger equation is solved. The evolution properties of Guassian beam propagating in photorefractive crystal biased with positive electric field are obtained. The dynamic variation of the beam width spread or compression is investigated by analyzing the potential function description for the variation of beam width. Solutions of the low intensity Guassian beam propagating in the positively biased photorefractive crystal are obtained for the beam width, beam amplitude, and the curvature of wave front. The results show that the amplitude and width of Guassian beam will exhibit a periodical oscillatory or deconcentration behavior when propagating in the positively biased photorefractive crystal. Under certain condition, the Guassian beam can steadily propagate with invariant shape, forming a Guassian soliton. These properties have a high practical value in engineering.

Design, Simulation, Fabrication, and Characterization of a Digital Variable Optical Attenuator

In this paper, we present the design, simulation, fabrication, and some measurement and characterization of a novel 16-bit digital variable optical attenuator (VOA) that attenuates by switching individual mirror of an array as an attempt to achieve input voltage variation independence and output linearization. The design was aided by a simulation package that features coupled electrostatic and mechanical solver. The mirror array spans an area of 1500times1500 mum <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2 </sup> and contains 16 equal-length rectangular micromirrors. Each mirror is suspended by two torsion beams. Experiments on beam design and width variations are conducted. Assuming Gaussian distribution, the mirror widths computed by an iteration algorithm vary from about 40 to 250 mum. Based on silicon-on-insulator (SOI) technology, two fabrication schemes to open the backside optical entrance were investigated. A hydrofluoric (HF) acid vapor-phase-etching (VPE) setup built to release the microstructure anhydrously is the key to achieve high yield especially for fragile components. Surface flatness, resonance frequencies, and tilt angles of selected mirrors were characterized. Quartz chips patterned with aluminum electrodes and 10 mum-high SU8 spacer columns were fabricated and assembled to corresponding device chips. Optical performance adversely affected by mirror bending is believed to originate from the intrinsic stress of the SOI wafer

Application of the high-gain substrate-superstrate configuration to dielectric leaky-wave antennas

The high-gain substrate-superstrate configuration, which was proposed to increase the gain in printed circuit antennas, is applied to dielectric leaky-wave antennas (LWAs) to improve its frequency response. Analysis of a slitted suspended dielectric rectangular waveguide is carried out using a full-wave method. It is proved that the minimum values of the leakage constant of the leaky-wave mode for the suspended configuration are related to the high-gain resonance conditions. Moreover, it is found that the suspended LWA exhibits very small beamwidth variations in a large frequency bandwidth. It is well-known that inhomogeneous filled LWAs suffer from variation of beamwidth as the angle of maximum radiation is scanned with frequency. The proposed topology can be adjusted so that a flat response of the beamwidth can be obtained in a large frequency band, while maintaining the frequency-scanning behavior of the LWA.

Metamaterial-based electronically controlled transmission-line structure as a novel leaky-wave antenna with tunable radiation angle and beamwidth

A metamaterial-based electronically controlled transmission-line structure is presented and demonstrated as a novel leaky-wave (LW) antenna with tunable radiation angle and beamwidth functionalities. This structure is, in essence, a composite right/left-handed (CRLH) microstrip structure incorporating varactor diodes for fixed-frequency voltage-controlled operation. Angle scanning at a fixed frequency is achieved by modulating the capacitances of the structure by adjusting the (uniform) bias voltage applied to the varactors. Beamwidth tuning is obtained by making the structure nonuniform by application of a nonuniform bias voltage distribution of the varactors. A rigorous analysis based on an extension of the CRLH concept is proposed and the corresponding dispersion curves, obtained by equivalent-circuit formulas with LC parameters extracted from full-wave simulation, are shown. A 30-cell LW antenna structure, incorporating both series and shunt varactors for optimal impedance matching and maximal tuning range, is designed. This prototype exhibits continuous scanning capability from 50/spl deg/ to -49/spl deg/ by tuning the bias voltages from 0 to 21 V at 3.33 GHz. A maximum gain of 18 dBi at broadside is also achieved. In addition, it provides half-power beamwidth variation of up to 200% with comparison to the case of uniform biasing. The effect of intermodulation due to the nonlinearity of the varactors is shown to be negligible for antenna applications. The antenna is tested in a 10-Mb/s binary phase-shift keying transmission link and successful recovery of the baseband data is demonstrated.

Metamaterial-Based Electronically Controlled Transmission-Line Structure as a Novel Leaky-Wave Antenna With Tunable Radiation Angle and Beamwidth

A metamaterial-based electronically controlled transmission-line structure is presented and demonstrated as a novel leaky-wave (LW) antenna with tunable radiation angle and beamwidth functionalities. This structure is, in essence, a composite right/left-handed (CRLH) microstrip structure incorporating varactor diodes for fixed-frequency voltage-controlled operation. Angle scanning at a fixed frequency is achieved by modulating the capacitances of the structure by adjusting the (uniform) bias voltage applied to the varactors. Beamwidth tuning is obtained by making the structure nonuniform by application of a nonuniform bias voltage distribution of the varactors. A rigorous analysis based on an extension of the CRLH concept is proposed and the corresponding dispersion curves, obtained by equivalent-circuit formulas with LC parameters extracted from full-wave simulation, are shown. A 30-cell LW antenna structure, incorporating both series and shunt varactors for optimal impedance matching and maximal tuning range, is designed. This prototype exhibits continuous scanning capability from 50/spl deg/ to -49/spl deg/ by tuning the bias voltages from 0 to 21 V at 3.33 GHz. A maximum gain of 18 dBi at broadside is also achieved. In addition, it provides half-power beamwidth variation of up to 200% with comparison to the case of uniform biasing. The effect of intermodulation due to the nonlinearity of the varactors is shown to be negligible for antenna applications. The antenna is tested in a 10-Mb/s binary phase-shift keying transmission link and successful recovery of the baseband data is demonstrated.

Relativistic guidance of laser beams in plasmas

The authors have identified three regimes of propagation of circularly polarized laser beams in plasmas, taking into account the relativistic laser plasma interaction. An appropriate expression for the nonlinear dielectric constant has been used in the analysis of laser-beam propagation in the paraxial approximation. Three regimes of propagation in a homogeneous plasma have been identified, viz. I. In this regime the beam keeps on diverging. II. In this regime the beam travels in a guided oscillatory and diverging mode. with the width lying between the original value and a maximum value. III. In this regime the beam becomes self-focused. with the width lying between the original value and a minimum value. For a given value of ω p /ω the regimes are characterized by dimensionless power and dimensional beam width. Tthe variation of beam width with distance of propagation has also been obtained for typical values of parameters in the three regimes. The variation of beam-width parameter with distance of propagation has also been studied for inhomogeneous plasma and penetration in overdense plasmas is indicated.

Propagation of ellipitic Gaussian laser beam in a higher order non-linear medium

Using a direct variational technique involving elliptic Gaussian laser beam trial function, the combined effect of nonlinearity and diffraction on wave propagation of optical beam in a homogeneous higher order nonlinear medium is presented. Particular emphasis is put to understand the variation of beam width and longitudinal phase delay with the distance of propagation in case of lossless and lossy medium. It is also observed that stationary self-trapping is possible in lossless medium at higher laser intensity where fifth order nonlinearity becomes comparable to third order nonlinearity. The phase is also seen to be always negative.

Analysis of the existence of one-dimensional dark and gray spatial solitons in l ogarithmically nonlinear media

The existence of dark and gray spatial solitons in logarithmically nonlinear media is investigated. It is shown that both dark and gray solitons are possible in corresponding nonlinear media. The spatial width for dark solitons is analyzed .It is revealed as follows: the beam width decreases dramatically with increasing power when the peak power is much lower, exhibiting the good nonlinear effects in such cases. The variation of beam width is slow at first and then becomes constant when the peak power continuously increases .

Dynamics of self-focusing and self-phase modulation of elliptic Gaussian laser beam in a Kerr-medium

Using a direct variational technique involving elliptic Gaussian laser beam trial func- tion, the combined effect of non-linearity and diffraction on wave propagation of optical beam in a homogeneous bulk Kerr-medium is presented. Particular emphasis is put on the variation of beam width and longitudinal phase delay with the distance of propagation. It is observed that no stationary self-trapping is possible. The regularized phase is also seen to be always negative.

Modified Chebyshev arrays

A class of linear arrays is introduced which, like Chebyshev arrays, have equal sidelobes in their radiation patterns. These arrays, compared to the conventional Chebyshev arrays with the same number of elements, the same size, and the same sidelobe level, provide higher directivities when the number of elements exceeds a minimum value for specified sidelobe level and element spacing. It is established that, for an arbitrary sidelobe level, the proposed arrays always provide higher saturation directivities. These arrays are synthesised using the zeros of conventional Chebyshev arrays repeatedly, and are referred to as modified Chebyshev arrays. Radiation characteristics of the proposed arrays are investigated. The influence of element spacing on the directivity difference between conventional and modified Chebyshev arrays is studied. Variations of directivity and half-power beamwidth against number of elements are examined and compared with those of conventional Chebyshev arrays.

Test of an 18-m-long suspended modecleaner cavity

Fluctuations in laser beam geometry such as lateral beam movement and beam width variation can produce perturbations in the output signal of a laser interferometer through various coupling mechanisms. In order to avoid this type of laser noise from degrading the sensitivity of interferometers designed to detect gravitational radiation, currently planned long-base-line detectors will employ resonant optical filters called modecleaners to suppress beam geometry noise. Here we describe a prototype modecleaner cavity constructed at Glasgow having an optical path length of 18 m and containing four suspended mirrors. We present results detailing various aspects of its performance.

A baffle-type directional microphone

A simple and economical directional microphone has been investigated, consisting of a plane, rectangular baffle with an omnidirectional pressure microphone placed directly on its surface. Outdoor experiments and numerical computations using the method of moments give compatible results and show useful directional properties, comparable with or superior to those of commercially available line (end-fire) or parabolic-reflector microphones of similar dimensions. Variations of beamwidth and beam shape with baffle dimensions and microphone placement are presented.

A wide-band prime-focus horn for low-noise receiver applications

A horn suitable for a prime-focus antenna requiring low cross polarization, wide bandwidth, and low spillover is described. The design is particularly suited for low-noise applications such as high-quality satellite earth-station antennas and radio telescopes. The horn has a return loss substantially better than 20 dB, a cross polar sidelobe level better than -20 dB, a beamwidth variation of 40% and negligible phase center shift. >

Investigation of planar antennas for submillimeter receivers

A frequency-scaled model of a tapered slot antenna has been investigated. The antenna consists of a dielectric substrate which serves as a carrier for a tapered slotline. The width and the shape of the slotline and the dimensions of the substrate (including the value of the permittivity) have been varied to investigate the radiation patterns. The result is a planar antenna with a symmetrical beam in the E and H planes and a beam efficiency of almost 50%. The substrate thickness is the most important limiting factor for scaling the model to submillimeter frequencies. Taking away parts of the dielectric substrate in the front area of the antenna allows a relatively large substrate thickness. The variations of the half-power beam width versus slot parameters, versus the dielectric thickness of the substrate, and versus the length and the width of the substate are presented. In addition the beam efficiency has been measured for various frequencies, and the radiation pattern has been calculated for comparison.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Accurate Field Analysis of the Propagation of Elastic Waves Through an Acoustic Microscope, Part II: Results

The results obtained by implementing the theory devel- oped in Part I are described. Attention is given to the focusing prop- erties of small-aperture lenses of gradually increasing thickness, viz, semi-angle. Instantaneous and CW field profiles of both the radial and axial field dependencies at and around the focal plane are presented. It is shown that the focus of a small aperture lens lies between the lens surface and its center of curvature and not necessarily between its cen- ter and paraxial focus. Also, the axial intensity variation shows sub- sidiary minima and maxima that ray theory fails to account for. These and other observations are made and a qualitative explanation is of- fered. Finally, the effect of a nondispersive loss on the focusing prop- erties of large-aperture small-angle lenses is investigated. HE RESULTS obtained by using the theory devel- oped in part I of this work (l) to obtain a computer simulation of the propagation of elastic waves through the components of an acoustic microscope are described. As a review, the procedure followed is to propagate the wave from the transducer to the lens aperture by finite elements and finite differences, and then use a Green's function in the liquid cell. A list of symbols used in this paper is given in (l). The theory is applied to the focusing properties of small- aperture lenses of gradually increasing thickness. The prime reason for analyzing this category is the inadequacy of other methods (see Section 111-B of (l)). A large num- ber of results are presented. These include radial and axial field variations, and instantaneous and CW field profiles. The location of the focus and the resolution there and the behavior of the field in the vicinity of the focal point are all investigated. It is concluded that the behavior of small aperture lenses is significantly different from the behavior of large aperture lenses. Finally, a section is devoted to analyzing the effect of a nondispersive loss on the focus- ing properties of large-aperture small-angle lenses. The entire package consists of two separate computer programs: the finite element and finite difference com- puter program and the Green's function program. This di- vision was found to be conducive to the efficient running of the package because there are many problems for which the finite element and finite difference computer program need only be executed once but the Green's function pro- gram many times, e.g., results are presented to show the variation of beamwidth with axial distance z. In this case, the wave must be propagated to the aperture of the lens only once, but the Green's function program must then be executed several times to obtain the radial (transverse) distribution of the field at various values of z. All the computer programs were run on a Prime 550 minicom- puter and double precision (64 bits) was used thfoughout. The package is validated by comparing the computed and analytical results for two geometries. A limiting case is then taken to show that even in this regime, the entire

Accurate Field Analysis of the Propagation of Elastic Waves Through an Acoustic Microscope, Part I: Theory

The results obtained by implementing the theory devel- oped in Part I are described. Attention is given to the focusing prop- erties of small-aperture lenses of gradually increasing thickness, viz, semi-angle. Instantaneous and CW field profiles of both the radial and axial field dependencies at and around the focal plane are presented. It is shown that the focus of a small aperture lens lies between the lens surface and its center of curvature and not necessarily between its cen- ter and paraxial focus. Also, the axial intensity variation shows sub- sidiary minima and maxima that ray theory fails to account for. These and other observations are made and a qualitative explanation is of- fered. Finally, the effect of a nondispersive loss on the focusing prop- erties of large-aperture small-angle lenses is investigated. HE RESULTS obtained by using the theory devel- oped in part I of this work (l) to obtain a computer simulation of the propagation of elastic waves through the components of an acoustic microscope are described. As a review, the procedure followed is to propagate the wave from the transducer to the lens aperture by finite elements and finite differences, and then use a Green's function in the liquid cell. A list of symbols used in this paper is given in (l). The theory is applied to the focusing properties of small- aperture lenses of gradually increasing thickness. The prime reason for analyzing this category is the inadequacy of other methods (see Section 111-B of (l)). A large num- ber of results are presented. These include radial and axial field variations, and instantaneous and CW field profiles. The location of the focus and the resolution there and the behavior of the field in the vicinity of the focal point are all investigated. It is concluded that the behavior of small aperture lenses is significantly different from the behavior of large aperture lenses. Finally, a section is devoted to analyzing the effect of a nondispersive loss on the focus- ing properties of large-aperture small-angle lenses. The entire package consists of two separate computer programs: the finite element and finite difference com- puter program and the Green's function program. This di- vision was found to be conducive to the efficient running of the package because there are many problems for which the finite element and finite difference computer program need only be executed once but the Green's function pro- gram many times, e.g., results are presented to show the variation of beamwidth with axial distance z. In this case, the wave must be propagated to the aperture of the lens only once, but the Green's function program must then be executed several times to obtain the radial (transverse) distribution of the field at various values of z. All the computer programs were run on a Prime 550 minicom- puter and double precision (64 bits) was used thfoughout. The package is validated by comparing the computed and analytical results for two geometries. A limiting case is then taken to show that even in this regime, the entire

Nonlinear distortion of hypertubular light beams

The author analyzes the thermal and Kerr self-action of hypertubular light beams and pulses. On the basis of the numerical modeling and integral description of a beam's behavior in both a thick and a thin nonlinear layer it is shown that shaping the beam leads to a substantial decrease of its radius and displacement of its centroid. The obtained integrals and integral relations permit one to follow the dynamics of the propagation of these beams. Using the methods from similarity theory, the variations of the optimal beam width with nonlinear medium and target distance are determined.

Beamwidth and Useable Bandwidth of Delay-Steered Microphone Arrays

Automatic delay steering of microphone arrays improves sound pickup in large rooms. But steering to wave-arrival directions away from broadside degrades the acuity of the beam and diminishes the useable bandwidth of the array. This paper derives quantitative relations for the variation in beamwidth and bandwidth for one-dimensional, uniform, unweighted arrays composed of (2N + 1) receivers spaced by distance d. The results show how the upper and lower useful frequencies and the beam acuity are conditioned not only by receiver spacing and frequency, but also by wave-arrival direction and steering direction. The relations developed permit detailed design of steerable arrays for specified frequency range and spatial coverage.

Quantitative Volume Backscatter Imaging

A conventional ultrasonic B-scan image is converted into a volume backscatter image by accounting for four propagation effects: dispersion of transmitted energy, beam width and beam intensity variations, inhomogeneous attenuation of ultrasonic energy, and signals resulting from specular reflections at interfaces. These images are a two-dimensional map of backscatter efficiency, are independent of details of the measurement system, and are quantitative images of an intrinsic property of tissue and other materials.