Beamwidth Variation Research Articles

Directivity of horns mounted in finite enclosures: A multimodal formulation.

The beamwidth is a primary directivity metric for the design of a constant directivity horn. To date, investigations on this property have predominantly been restricted to the half-space radiation or idealized geometries. This paper examines the beamwidth behavior of an axisymmetric horn mounted in a finite cylindrical enclosure by proposing an elegant multimodal solution to the far-field directivity pattern. The variation of beamwidth is examined for the frequency, dimensions of the enclosure, and shape of the horn. At low frequencies, a fitted model is proposed to precisely depict the intrinsic beam narrowing governed by the enclosure diffraction. The asymptotic behavior of the beamwidth is explored as the flange width increases. In the high-frequency range, the horn profile is a determinant of the directivity characteristics. We report the possibility of extending the bandwidth of a constant directivity horn by leveraging the enclosure diffraction effects. The proposed analytical method is highly accurate and much faster than the finite element method for wideband analysis. It allows for an arbitrary velocity distribution at the mouth of the horn and incorporates idealized flange configurations such as an infinite baffle, a zero-thickness closed baffle, and an infinitely long enclosure as limit cases.

Clustered jamming in U-V2X communications with 3D antenna beam-width fluctuations

Jamming is the disruption of wireless communication signals, rendering them unreadable or degraded, typically caused by jamming devices. Clustered jamming in vehicular communications is a highly sophisticated attack technique characterized by the coordinated deployment of multiple jammers with the strategic intent to deliberately disrupt and incapacitate communication links, thereby presenting a formidable challenge to the reliability and security of vehicular networks. It is critical to address the intricate challenges imposed by clustered jamming in the context of vehicle-to-everything (V2X) communications augmented by unmanned aerial vehicles (UAVs), given their critical role in facilitating essential vehicle-to-vehicle and vehicle-to-UAV communication links. In this paper, we examine UAV-V2X (U-V2X) communications within the context of clustered jamming and the variations in the 3D beam-width of antennas. Also, mitigation techniques for clustered jamming in V2X communications are addressed. We consider the distribution of UAVs is governed by the Poisson point process, the distribution of vehicular-nodes (VNs) is governed by the Poisson line process, and the distribution of jammers is governed by the Matern Cluster Process. The analytical equations for the association probability and the success probability (SP) of a typical VN with the UAV and near-by VN, along with the presence of jammers and the variations of antenna beam-width are provided. Furthermore, we investigate the SP and spectral efficiency performance of the U-V2X network under different network configurations of UAVs, VNs, roads, jamming clusters, and transmit power of jamming devices. Our findings reveal that clustered jammers influence U-V2X network’s performance, further compounded by UAV beam-width fluctuations. Moreover, in low-density areas, UAVs demonstrate superior reliability for connectivity compared to VNs, despite clustered jamming. Also, lower UAV antenna fluctuations enhance UAVs’ dependability in U-V2X networks amidst clustered jamming. Specifically, for a given setup with τ= -5 dB, U-V2X link’s SP with jamming drops to one-quarter due to 2-degree beam-width fluctuations. Consequently, it is imperative to design and implement anti-jamming strategies, particularly as the number of jamming clusters and variations of antenna beam-width increase.

Clustered jamming and antenna beam-width fluctuations for UAV-assisted cellular networks

Jamming devices have the capability to deliberately disrupt legitimate communications. Clustered jamming pertains to the deployment of jammers that are concentrated within specific clusters to amplify the interference. This paper models the impact of clustered jamming interference on unmanned aerial vehicles (UAV)-assisted cellular networks, taking into account fluctuations of the 3-dimensional (3D) beam-width of low altitude platform (LAP) antennas. The distribution of UAVs and macro base station (MBS) is modeled by independent 3D and 2D homogeneous Poisson point processes, respectively, while jammers are modeled using an independent Matern cluster process. Antenna 3D beam-width fluctuations are modeled according to Normal distribution. The modeling centers on the probability of association as well as coverage and spectral efficiency for line-of-sight LAP, non-line-of-sight LAP, and MBS links. This modeling investigation is conducted under multiple jamming clusters and the antenna 3D beam-width fluctuations of UAV. Analytical expressions are derived to characterize association, coverage, and SE performance in the context of clustered jamming and UAV beam-width variation. The obtained results indicate that UAV-assisted cellular networks experience a notable decline in the proximity of clustered jammers. Furthermore, this performance degradation is significantly exacerbated when the antenna 3D beam-width exhibits fluctuations. Consequently, to enhance the performance of UAV-assisted cellular networks, it is imperative for system designers to consider the implementation of robust anti-jamming techniques.

Geometric nonlinear model and optimization of vortex-induced energy harvester with variable beam width

This paper proposes a geometric nonlinear analytical model of a vortex-induced energy harvester (VIEH) with variable beam width in order to improve the output performance. The analytic method is adopted to establish the geometric nonlinear model of VIEH. Based on the geometric nonlinear analytical model, the beam structure is then optimized to improve the output. The results show that the harvested power and average power density within a specific resistance range can be increased through the beam width variation of the VIEH. Nonlinear hardening behaviors can be observed in the outputs varied by the flow velocity of a VIEH with variable beam width.

The Effect of the Bending Beam Width Variations on the Discrepancy of the Resulting Quadrature Errors in MEMS Gyroscopes.

In this paper, we develop a new approach in order to understand the origin of the quadrature error in MEMS gyroscopes. As the width of the flexure springs is a critical parameter in the MEMS design, it is necessary to investigate the impact of the width variations on the stiffness coupling, which can generate a quadrature signal. To do so, we developed a method to determine the evolution of the stiffness matrix of the gyroscope springs with respect to the variation of the bending beams width of the springs through finite element analysis (FEA). Then, a statistical analysis permits the computation of the first two statistical moments of the quadrature error for a given beam width defect. It turns out that even small silicon etching defects can generate high quadrature level with up to a root mean square (RMS) value of for a bending beam width defect of 0.9%. Moreover, the quadrature error obtained through simulations has the same order of magnitude as the ones measured on the gyroscopes. This result constitutes a great help for designing MEMS gyroscopes, as the consideration of the bending beams width defects is needed in order to avoid high quadrature error.

The Evolution of Lateral Dose Distributions of Helium Ion Beams in Air: From Measurement and Modeling to Their Impact on Treatment Planning

To start clinical trials with the first clinical treatment planning system supporting raster-scanned helium ion therapy, a comprehensive database of beam characteristics and parameters was required for treatment room-specific beam physics modeling at the Heidelberg Ion-Beam Therapy Center (HIT). At six different positions in the air gap along the beam axis, lateral beam profiles were systematically measured for 14 initial beam energies covering the full range of available energies at HIT. The 2D-array of liquid-filled ionization chambers OCTAVIUS from PTW was irradiated by a pencil beam focused at the central axis. With a full geometric representation of HIT’s monitoring chambers and beamline elements in FLUKA, our Monte Carlo beam model matches the measured lateral beam profiles. A second set of measurements with the detector placed in a water tank was used to validate the adjustments of the initial beam parameters assumed in the FLUKA simulation. With a deviation between simulated and measured profiles below ±0.8 mm for all investigated beam energies, the simulated profiles build part of the database for the first clinical treatment planning system for helium ions. The evolution of beamwidth was also compared to similar simulations of the clinically available proton and carbon beam. This allows a choice of treatment modality based on quantitative estimates of the physical beam properties. Finally, we investigated the influence of beamwidth variation on patient treatment plans in order to estimate the relevance and necessary precision limits for lateral beam width models.

A Mechanically Rollable Reflectarray With Beam-Scanning Capabilities

A novel 1-D beam-steerable reflectarray antenna (RA) is proposed for the Ku-band. The RA aperture consists of 24×48 variable size square patch elements printed on a flexible plastic substrate. The aperture is wrapped around two cylinders to create a 12λ×12λ illumination window at the operating frequency of 14 GHz. Beam-steering is achieved by mechanically rolling the aperture. To mitigate antenna pattern degradation, an aperture phase distribution optimization technique is presented. The performance of this RA system is studied analytically using array theory. The effects of aperture size and unit-cell size are also discussed. The performance of the proposed RA is validated using simulations and measurements. The results illustrate that our design achieves 1-D beam-steering from -21∘ to +21∘ in the elevation plane while maintaining towards the broadside direction a maximum realized gain of 25.1 dBi. In this beam-scanning range, the gain variation is less than 1.5 dB, beamwidth variation is less than 1.6∘, and the side lobe level is maintained below -15 dB. In summary, the main advantage of our design is its ability to steer its high gain beam without using complicated feed networks or complex mechanical systems. Such antennas are especially needed in SmallSat and space applications.

Frequency-Dependent Feeding Methods for Broadband Vivaldi Arrays With Minimum Half-Power Beamwidth (HPBW) Variation

This paper reports on the design of frequency-dependent feed networks for linear antenna arrays with minimum half-power beamwidth (HPBW) variation in more than one octave of the frequency spectrum. The proposed approach is based on: i) frequency-dependent power dividers that gradually shift the RF power from the outer elements of the array to the inner ones with the increase of frequency and ii) uniformly or non-uniformly-spaced directive antenna elements. The operating principles and design trade-offs of the concept are presented through ideal simulations of four- and six-element antenna arrays shaped by isotropic or directive radiators. It is shown that by employing directive antenna elements and non-uniform spacing, minimum HPBW variation can be obtained in a broad bandwidth (BW, e.g., 3:1). For physical verification purposes, two frequency-dependent feed networks and Vivaldi antenna elements were designed, manufactured, and measured. The first network feeds a uniformly-spaced four-element array of Vivaldi antennas and demonstrates a 58% HPBW variation in a 3:1 of BW. The second network feeds a non-uniformly-spaced six-element Vivaldi array and results in a 67% HPBW variation in a 2.5:1 of BW.

Broadband Monopole Array With Reduced Half-Power Beamwidth Variation

This paper reports on the design and practical validation of monopole antenna arrays with reduced half-power beamwidth (HPBW) variation in a bandwidth (BW) greater than one octave of the RF spectrum. The HPBW variation is reduced by feeding the antenna elements with frequency-dependent feed networks. The feed networks are designed in such a way that the element power is gradually shifted from the outer elements at low frequencies to the inner elements at high frequencies. The operating principles of the proposed concept are explored through simulated examples of four-element arrays made of isotropic elements and then realistic monopole elements. Scalability of the concept to eight-element arrays is also explored using ideal simulations. For practical validation purposes, a four-element monopole antenna array and its corresponding feed network are designed and measured. The prototype resulted in a HPBW variation of 78% in a 2.6:1 BW, which is significantly reduced compared to the uniformly fed array, having a 216% variation.

Airy Beam for Free-Space Photonic Interconnection: Generation Strategy and Trajectory Manipulation

Self-accelerating beams have attracted worldwide research attentions due to their intriguingly curved trajectory with localized peak intensity and the characteristic of self-healing after obstacles. We first put forward a generation vector to analytically describe general trajectory manipulation for 2-D Airy beam. Based on the successful trajectory manipulation of 2-D Airy beam, a 100 Gbps NRZ-OOK real-time free-space photonic interconnection is experimentally demonstrated. Our results indicate that the bending trajectory can break the constraints of traditional free-space photonic interconnection where the receiver has to be set under the condition of line-of-sight. Meanwhile, by taking the power correction factor into account of the beam width variation, we propose a metric of normalized power density (NPD) in order to characterize the power density variation of beam main lobe along the free-space propagation. After calculating the 3 dB NPD range of both Airy beam and Gaussian beam, we identify that the power density of Airy beam main lobe can be maintained for a longer free-space reach than a Gaussian beam with the same minimum width.

The practical radius of a pencil beam in proton therapy

The central Gaussian shaped high dose region of a pencil beam (PB) in light ion beam therapy (LIBT) is enveloped by a low dose region causing non-negligible field size effects and impairs the dose calculation accuracy considerably if the low dose envelope is not well modeled. The purpose of this study was to calculate the practical radius, Rc, at which a PB does not influence a field more than a certain accuracy level.Lateral dose profiles of proton beams in water were simulated using GATE/Geant4. Those lateral dose profiles were integrated numerically and used to calculate field size factors (FSFs). The Rc was then determined such, that the lateral dose at radii exceeding Rc can be neglected without compromising the FSF of a 20cm×20cm field more than a desired accuracy level c. The practical radius Rc yielding c=0.5% was compared to the frequently applied concept of full width at a ratio x of the maximum (FWxM). The sensitivity to variations of the beam width was tested by increasing the initial beam width σC of the clinical beam model by 0.5 and 1mm, respectively.Neglecting the dose at radii exceeding Rc resulted in the desired FSF accuracy, whereas using the FW0.01%M cut resulted in varying accuracy. In order to yield a constant FSF accuracy, the ratio x in FWxM ranged from 0.003% to 0.065% of the maximum. In contrast to Rc, FWxM was sensitive to variations of the initial beam width. The maximum Rc over all depths was less than 7cm for the low(62.4MeV) and medium(148.2MeV) proton energy beam, which suggests that a plane parallel ionization chamber exceeding that radius is sufficient to acquire laterally integrated depth dose distributions for those energies. However, this holds not true for the highest energy (252.7MeV) or when including a range shifter (RaShi). The values of Rc are specific to our beam line configuration as the maximum Rc was depending on both, the scattering material in the Nozzle as well as the distance of the air-gap between Nozzle and phantom.

Simple Dual-Polarized Filtering Antenna With Enhanced Bandwidth for Base Station Applications

In this article, a simple dual-polarized antenna with filtering responses and enhanced bandwidth is proposed for base station applications. The antenna concludes three parts: dipole elements, baluns, and a ground plane, which is the same as that of a widely used traditional base-station cross-dipole antenna. By employing only two parasitic elements without using very complicated circuits, the proposed dual-polarized antenna achieves not only filtering response but also widened bandwidth. Each parasitic element produces one transmission zero at higher frequency for the polarization it is associated with, while the other parasitic element produces another transmission zero at lower frequency band for the perpendicular polarization. The two introduced radiation nulls near the passband edge are also controllable. The working mechanism for achieving filtering responses is given. To demonstrate the idea, a simple dual-polarized filtering base-station antenna element is fabricated. The proposed antenna obtains 63% (1.68–3.23 GHz) impendence bandwidth with voltage standing wave ratio (VSWR) less than 1.5. The antenna also features good isolation of more than 32 dB and stable beamwidth variation of less than ±5°. The measured gain within working band is around 8.5 dBi, while the radiation suppression level in stopband is 13 dB.

Synthesis of Linear Antenna Array with Optimal SLL and Beam Width

In many areas of wireless communications, there is a need for high directive radiating beams. To generate such a high directive beams, a linear array of antennas is preferred to that of using a single antenna. Generally a narrow beam width tends to have high directivity but specific to the applications there is also a need for wider beam widths. In case of a radar application it requires a narrow beam width when it is operating in target mode and on the other hand it requires wider beam width when it works under search mode. These optimal beam width variations can be obtained by using Optimization techniques. In this paper Biogeography based Optimization algorithm is used to generate narrow and wide beam widths for a Linear array antenna. While we try to optimize the beam widths of a linear array it will lead to an increase in the side lobe level which make it unavailable for practical applications. As a sensible antenna should always posses a very low side lobe levels a tradeoff should be made for both side lobe level and beam width. This tradeoff which has an optimal side lobe level along with directivity can be achieved by proposed fitness function optimization. The results obtained by using Genetic algorithm and Biogeography based optimization algorithm are compared.

Propagation Characteristics of Higher-Order Mixed-Pattern Solitons in Nonlinear Media

In this paper, we study the propagation and evolution of higher-order mixed-pattern solitons in nonlinear media with a strong nonlocality. The propagation analytic formula of higher-order mixed-pattern solitons is derived and discussed in detail. Taking the fourth-order mixed-pattern solitons as an example and based on numerical calculations, we present the variations of second-order moment beam width, the light intensity, and the wavefront curvature. We show that the propagation evolution exhibits unique characteristics depending on different relative factors of higher-order mixed-pattern solitons. The influence of the beam order on the propagation evolution is also discussed.

Investigation of paraxial and nonparaxial self-focusing of Gaussian beam in chalcogenide glass medium using NLSE

Variational method is used for the investigation of paraxial and nonparaxial self-focusing of Gaussian beam in bulk chalcogenide glass (Kerr media). Stationary self-focusing for paraxial Gaussian beam with distinct singularity and focusing-defocusing cycles for nonparaxial propagation of Gaussian beam is observed. Emphasis is laid on the study of variation in beam width and intensity of the beam with propagation distance.

Shape-variable four-petal Gaussian vortex breathers in strongly nonlocal nonlinear media

In this paper, we mainly investigate the propagation properties of shape-variable four-petal Gaussian vortex breathers in strongly nonlocal nonlinear media. The analytical expression of the shape-variable four-petal Gaussian vortex breather is derived in Cartesian coordinate system by means of mathematical integral method. A series of evolution properties are described analytically and numerically, such as the transverse intensity pattern, the phase distribution, the variation of the second-order moment beam width, and the on-axis light intensity. It is found that the topological charge number and the beam order of the shape-variable four-petal Gaussian vortex breather play important roles in the propagation process, and their effects on the propagation properties of the shape-variable four-petal Gaussian vortex breather are discussed graphically.

Near‐constant beamwidth quadruple bandwidth double‐ridged horn antenna design

It is well known that the beamwidths of horn antennas are inversely proportional to frequency. Previous studies point to minimum ±12% beamwidth stability within a maximum of 2.5:1 bandwidth (BW) ratio. To extend this BW, a design methodology for broadband double-ridged horn antenna (DRHA) is proposed and applied to 4.5-18 GHz frequency band. Firstly, a conventional DRHA is designed and studied to compare the beamwidth variation of wideband horn antennas. By explicitly addressing the shortcomings of conventional DRHA, DRHA is redesigned and near-constant beamwidth DRHA is proposed using the modifications implemented on the sidewalls. The antenna utilises ridges to extend the frequency band, unlike other wideband constant beamwidth horns. The authors show that ridged horns, whose dimensions are appropriately designed and modified, can have stable beamwidths. Then, properly positioned curved pinwalls are designed to provide considerable improvement in H -plane beamwidth constancy. Broadband double-ridged waveguide-to-coaxial adapter is also designed for 50 Ω reference. The prototype is manufactured, and the measured antenna exhibits wideband characteristics with 30.9° ± 2.7° half power beamwidth in H -plane over 4:1 BW ratio. This variation corresponds to ±8.7% beamwidth stability along with the target frequency band.

Design of 2-18 GHz balanced antipodal Vivaldi antennas using substrate-integrated lenses

ABSTRACTConventional balanced antipodal Vivaldi antennas (BAVAs) normally have deep ripple levels in E-plane mainlobe region and significant H-plane beamwidth variation over upper frequency band, which are drawbacks for ultra-wideband (UWB) applications. To overcome these issues, this paper introduces two types of lens configurations in front of BAVA. A gradient-index semi-cylindrical lens and a cylindrical lens are employed to improve ripples depth of E-plane mainlobe and broaden H-plane beamwidth, respectively. Both these lenses and BAVA are integrated on the same substrate and the desired refractive indexes of lenses are realized by a combination of a set of air-filled holes in the substrate. Prototypes of the modified BAVA with lenses (BAVA-Ls) are designed, fabricated and experimentally investigated as well. Measured results show close agreement with simulation. The proposed BAVA-Ls exhibit promising performances such as smaller ripple levels in E-plane mainlobe, wider H-plane beamwidth, higher aperture efficiency, and excellent group delay, while maintaining good bandwidth characteristics over 2–18 GHz.

An evaluation of computed tomography dose index measurements using a pencil ionisation chamber and small detectors

The aim of this study was to compare the values of the computed tomography dose index 100 (CTDI100) obtained using two small detectors (i.e. a small ionisation chamber and a small solid state detector) with those obtained from a 100 mm pencil ionisation chamber for various input CT parameters: beam width, kVp, mAs, pitch, and head-body phantom variation. The measurement of CTDI100 using the 100 mm pencil chamber was carried out in a single rotation of axial mode, while the measurement using small detectors was carried out in helical mode. The differences of CTDI100 values obtained with two small detectors were about 7% for all variations. The differences of CTDI100 values obtained with small detectors and a 100 mm pencil ionisation chamber for beam widths of more than 4 mm were within 40%. However, for the narrowest beam widths (4 mm), the difference between them was very large (about 150%).

Modified probabilistic laser sensor model to reduce the effect of the mixed pixel for robust autonomous mobile robot navigation

The reliable performance of the autonomous mobile robot depends upon the accuracy and reliability of the sensors. Mixed pixel problem is the consequence of the effects caused by diverse intrinsic and extrinsic parameters, impulse noise, variation in incident angle and beam width that reduce the reliability of the laser scanner that leads to generate uncertainty in sensory information. The objective of this study is to modify the laser sensor model by reducing the effect of the mixed pixel problem corresponding to incident angles and intensity by a newly designed algorithm - Edge Detection Technique (EDT) for laser scanner to generate an efficient mobile robot mapping for the robust autonomous navigation. Various real-world experiments have been performed to check the reliability of the proposed EDT algorithm linked with probabilistic laser sensor model fitted on a mobile robot and the obtained results are validated through qualitative and quantitative analysis corresponding to conventional approaches.