Bow-tie Array Research Articles

Unidirectional bowtie array antenna with incision gap for digital video broadcasting‐T2 base station

This study presents a unidirectional bowtie array antenna with incision gap for a digital video broadcasting-T2 base station application. The antenna element consists of a bowtie radiator with incision gap on top of a square reflector. The element achieves a bandwidth of 82.35% for |S 11| of <−10 dB, covering a frequency range of 450–1080 MHz. The antenna array comprises of four identical antenna elements mounted vertically to form an antenna array. The simulated and measured results of the antenna array show a good impedance matching for |S 11| of <−10 dB along a frequency range of 450–1014 MHz (77.05%). The measured gains are 13.4–16.1 dBi along an operating frequency of 470–862 MHz with the narrow half-power beamwidth in the vertical plane of ∼15° ± 5° and the half-power beamwidth in the horizontal plane of ∼60° ± 5° for a frequency range of 470–666 MHz and 90.5° for 862 MHz. The radiation pattern is degraded at the frequency higher than 950 MHz.

Fano Resonance and Spectrally Modified Photoluminescence Enhancement in Monolayer MoS2 Integrated with Plasmonic Nanoantenna Array

The manipulation of light-matter interactions in two-dimensional atomically thin crystals is critical for obtaining new optoelectronic functionalities in these strongly confined materials. Here, by integrating chemically grown monolayers of MoS2 with a silver-bowtie nanoantenna array supporting narrow surface-lattice plasmonic resonances, a unique two-dimensional optical system has been achieved. The enhanced exciton-plasmon coupling enables profound changes in the emission and excitation processes leading to spectrally tunable, large photoluminescence enhancement as well as surface-enhanced Raman scattering at room temperature. Furthermore, due to the decreased damping of MoS2 excitons interacting with the plasmonic resonances of the bowtie array at low temperatures stronger exciton-plasmon coupling is achieved resulting in a Fano line shape in the reflection spectrum. The Fano line shape, which is due to the interference between the pathways involving the excitation of the exciton and plasmon, can be tuned by altering the coupling strengths between the two systems via changing the design of the bowties lattice. The ability to manipulate the optical properties of two-dimensional systems with tunable plasmonic resonators offers a new platform for the design of novel optical devices with precisely tailored responses.

On the absorption and electromagnetic field spectral shifts in plasmonic nanotriangle arrays.

The behavior of the electromagnetic field interaction with gold nanotriangles organized in bow-tie arrays is investigated. A side-by-side comparison between the measured absorbance of the array and the modelled integrated electric field resonances confined around the gold structures is presented and discussed to explain the spectral shift between both parameters. Finite difference time domain calculations and Raman measurements of gold triangles of different sizes and periodicity are systematically performed. Numerical calculations show that the spectral maximum of the electric field varies in distinct areas over the metallic structures.

Transparent and Flexible Polarization-Independent Microwave Broadband Absorber

We present an optically transparent, flexible, and polarization-independent broadband microwave absorber. It is designed to possess two spectrally overlapped resonances of a bow-tie array, which originates from the fundamental resonance mode and the coupling between the neighboring units. An Al wire gird is used to construct the bow-tie array to induce high ohmic loss and broaden the bandwidth of the resonances. As a result, the combined resonances lead to more than 90% total absorption covering a wide frequency range from 5.8 to 12.2 GHz. The transparent and flexible properties provide more flexibility for absorber applications. The optical transmittance of the whole structure is more than 62%.

A Multichannel THz Detector Using Integrated Bow-Tie Antennas

This paper presents a kind of a multichannel THz detector using lens-based bow-tie array. A hyperhemispherical silicon lens is employed to provide a focal plane; 8 bow-tie elements are arranged on the focal plane with careful design to show a performance of broadband, high gain, well compact, and easy assembling. These characteristics of the detector are preferred for detecting weak THz signal. Measured far field shows that the radiation pattern of each element is shifted angularly, by <i>&#x2248;</i>9&#xb0;, which can be used for THz imaging. Tested responsivity of the detector shows a good spectral performance from 260 to 400&#x2009;GHz: respective values were &#x2265;220&#x2009;V/W, and the best NEP is achieved at about 60&#x2009;pW/<svg style="vertical-align:-0.99644pt;width:33.099998px;" id="M1" height="17.125" version="1.1" viewBox="0 0 33.099998 17.125" width="33.099998" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,12.862)"><path id="x221A" d="M782 703l-309 -950l-231 505l-91 -47l-18 35l147 78l194 -431h2l264 810h42z" /></g> <g transform="matrix(1.25,0,0,-1.25,90,90)"> <path d="m -61.56,70.93 15.99,0" style="fill:none;stroke:#000000;stroke-width:0.68000001;stroke-linecap:butt;stroke-linejoin:miter;stroke-miterlimit:10;stroke-opacity:1;stroke-dasharray:none" /> </g> <g transform="matrix(.017,-0,0,-.017,13.05,15.825)"><path id="x48" d="M729 650v-28q-62 -5 -76 -19.5t-14 -75.5v-404q0 -62 13.5 -76t75.5 -19v-28h-268v28q65 5 79.5 19t14.5 76v199h-341v-199q0 -62 14 -76t76 -19v-28h-263v28q61 5 74.5 19t13.5 76v404q0 62 -14 76t-76 19v28h259v-28q-58 -5 -71 -19t-13 -76v-162h341v162&#xA;q0 61 -13.5 75.5t-72.5 19.5v28h261z" /></g><g transform="matrix(.017,-0,0,-.017,25.901,15.825)"><path id="x7A" d="M387 138l26 -13l-46 -125h-329l-7 15q109 161 249 388h-89q-52 0 -71.5 -13.5t-41.5 -57.5l-14 -27l-25 9q20 70 34 144h21q8 -21 55 -21h230l6 -14l-244 -390h99q54 0 78.5 16.5t55.5 64.5z" /></g> </svg>. Besides that, the proposed antenna has advantages of simple structure, easy fabrication, and low cost.

Bi-Band Bow-Tie Antennas Array Design Using a Simple Equivalent Transmission Line Model

In this paper we propose a simple equivalent and accurate transmission line model for bi-band bow-tie antennas array design over a band of frequencies for satellite communications. This model uses the resistance of a square element that appears at the edges of the antenna (radiating slots). To test this model, two antennas array were simulated and results were compared with those obtained by a rigorous method (moment’s method) of the simulator ADS/Momentum. Using this transmission line approach the resonant frequency, return loss, VSWR, reflected phase, input impedance can be determined simultaneously. The results confirm the validity of the proposed model.

Corporate-Feed Multilayer Bow-Tie Antenna Array Design Using a Simple Transmission Line Model

A transmission line model is used to design corporate-fed multilayered bow-tie antennas arrays; the simulated antennas arrays are designed to resonate at the frequencies 2.4 GHz, 5 GHz, and 8 GHz corresponding to RFID, WIFI, and radars applications. The contribution of this paper consists of modeling multilayer bow-tie antenna array fed through an aperture using transmission line model. The transmission line model is simple and precise and allows taking into account the whole geometrical, electrical, and technological characteristics of the antennas arrays. The proposed transmission line model showed its interest in the design of different multilayered bow-tie antennas and predicted the correct resonance frequency for different applications in telecommunications. To validate the proposed transmission line model, the simulation results obtained are compared with those obtained by the method of moments. The results of simulations are presented and discussed. Using this transmission line approach, the resonant frequency, input impedance, and return loss can be determined simultaneously. The paper reports several simulation results that confirm the validity of the developed model. The obtained results are then presented and discussed.

Extraordinary Nonlinear Absorption in 3D Bowtie Nanoantennas

This paper reports that arrays of three-dimensional (3D), bowtie-shaped Au nanoparticle dimers can exhibit extremely high nonlinear absorption. Near-field interactions across the gap of the 3D bowties at the localized surface plasmon resonance wavelengths resulted in an increase of more than 4 orders of magnitude in local field intensity. The imaginary part of the third-order nonlinear susceptibility (Im χ((3))) for the 3D bowtie arrays embedded in a dielectric material was measured to be 10(-4) esu, more than 2 orders of magnitude higher than reported for other metal nanoparticle-dielectric composites. Moreover, 3D dimers with increased nanoscale structure (such as folding) exhibited increased optical nonlinearity. These 3D nanoantennas can be used as critical elements for nanoscale nonlinear optical devices.

UWB 통신용 대수 주기 보우타이 다이폴 배열 안테나

In this paper, a log periodic bow-tie dipole array (LPBDA) antenna for UWB communications is investigated. Bow-tie shaped dipole elements are used instead of general dipole elements for LPDA antennas and the input reflection coefficient and realized gain characteristics of the LPBDA as a function of a flare angle are analyzed. It turns out that as the flare angle of the bow-tie dipole elements is increased, the lowest operating frequency is shifted toward lower frequency and the operating frequency band is increased, but the average gain is decreased. However, the gain variation of the LPBDA is much decreased and the front-back ratio is improved compared to the LPDA. Standard LPDA and LPBDA with a flare angle of 13 degrees are fabricated on an FR4 substrate with a dielectric constant of 4.4 and a thickness of 1.6 mm. Measured gain for the LPDA ranges from 4 to 6.5 dBi at 3.1 to 10.6 GHz band, while that for the LPBDA is in the range of 4.2 to 5 dBi.

Resonance modes, cavity field enhancements, and long-range collective photonic effects in periodic bowtie nanostructures

The discovery of single-molecule sensitivity via surface-enhanced Raman scattering on resonantly excited noble metal nanoparticles has brought an increasing interest in its applications to the molecule detection and identification. Periodic gold bowtie nanostructures have recently been shown to give a large enhancement factor sufficient for single molecule detection. In this work, we simulate the plasmon resonance for periodic gold bowtie nanostructures. The difference between the dipole and the quadrupole resonances is described by examining the magnitude and phase of electric field, the bound surface charge, and the polarization. The gap size dependence of the field enhancement can be interpreted by considering cavity field enhancement. Also, additional enhancement is obtained through the long-range collective photonic effect when the bowtie array periodicity matches the resonance wavelength.

An integrated portable Raman sensor with nanofabricated gold bowtie array substrates for energetics detection

An integrated field-portable surface enhanced Raman scattering (SERS) sensing system has been developed and evaluated for quantitative analysis of energetics such as perchlorate (ClO(4)(-)) and trinitrotoluene (TNT) at environmentally relevant concentrations and conditions. The detection system consists of a portable Raman spectrometer equipped with an optical fiber probe that is coupled with novel elevated gold bowtie nanostructural arrays as a sensitive and reproducible SERS substrate. Using the standard addition technique, we show that ClO(4)(-) and TNT can be quantified at concentrations as low as 0.66 mg L(-1) (or ~6.6 µM) and 0.20 mg L(-1) (~0.9 µM), respectively, in groundwater samples collected from selected military sites. This research represents the first step toward the development of a field SERS sensor which may permit rapid, in situ screening and analysis for various applications including national security, chemical, biological and environmental detection.

Optical guiding properties of high-brightness parabolic bow-tie laser arrays

This paper presents the characteristics of parabolic bow-tie laser arrays (PBTLAs) which are a novel category of laser diodes specially designed to achieve high power with high brightness at 980 nm. Output powers in excess of 2.8 W/facet have been measured from five-element PBTLAs with output beam less than twice the diffraction limit, achieving high brightness of 275 MWcm/sup -2/srad/sup -1/ at 3 A (pulsed) injection current (=22 times the threshold). Changes in the achievable brightness due to changes in the optical cavity geometry and in the lateral optical guiding strength are discussed in detail, using the coupled-mode theory to interpret the experimental results. At threshold all devices operate in the highest (double lobed) array mode. At higher currents the arrays of tapered lasers change to quasi-in-phase operation when the modal gain of the fundamental array mode dominates because of the combined effect of carrier hole burning and spatial filtering from the narrow stripe central section of the device. Similar trends have been observed under continuous-wave operation. The reduction of lateral optical guiding strength is deleterious for the operational characteristics of PBTLAs and linear bow-tie arrays, and it leads to filamentation in gain-guided devices even at low currents. Theoretical results presented in this paper show that scalability is in principle possible; however, changes in the lateral gain profile due to hole-burning can significantly increase the modal gain of higher order modes and, therefore, strongly influence the optical output profile.

High Brightness Index-Guided Parabolic Bow-Tie Laser Arrays

This letter describes a novel 980-nm parabolic bow-tie laser array (PBTLA) that is suitable for high-power and high-brightness operation. Output powers in excess of 2.5 W/facet pulsed in a 1/spl deg/ (lateral) beam, less than twice the diffraction limit, corresponding to 275 MW/spl middot/cm/sup -2//spl middot/sr/sup -1/ brightness, have been measured without the use of external lenses from uncoated PBTLAs fabricated in-house (top metal contact surface area/spl sim/0.1 mm/sup 2/). Experimental results presented in this letter indicate that coherence effects are significant in the operation of such devices. Theoretical models based on the simple diffraction theory and on the coupled-mode theory have been used to interpret the experimental results.

Electron beam lithography of microbowtie structures for next-generation optical probe

The development of microbowtie structures for a next- generation optical probe called the Wave Interrogated Near-Field Array (WINFA) is presented. The WINFA combines the sensitivity of near-field detection with the speed of optical scanning. The microbowties are de- signed to act as resonant elements to provide spatial resolution well below the diffraction limit with a transmission efficiency approaching unity. Following an introduction of the concept and background informa- tion, the design of the microbowtie is presented. A numerical electromag- netic scattering model is developed and used for better designs of the bowtie structures. The electron-beam lithography process is then used to fabricate the final designed bowties structure. Special fabrication proce- dures have been developed to cope with the charge dissipation problem that arises when lithographing an insulating substrate as is required in the present probe design. Two types of substrates and two types of resists are considered in the present study. The fabricated microstruc- tures have 40 nm bowtie gaps that are more than 200 000 times smaller than the one built previously. All fabricated bowtie microstructures are examined and the results are compared. It has been found that, in addi- tion to the relative ease in fabrication, the bowties on indium-tin-oxide coated glass substrate can not only minimize the charge accumulation in a glass substrate, but also satisfy the functional requirement of optical transparency to the incident wave. Recommendations for making a bowtie structure in the even smaller bowtie array are also included.

Microwave modeling of 2-D active grid antenna arrays

A new measurement technique for determining the broadband driving point impedance of large two-dimensional active grid arrays is presented. The active array radiates a plane wave in the broadside direction when all elements are locked in phase. For analysis, the array is reduced to a single unit cell by exploiting the array symmetries. The driving point impedance of the unit cell is determined by using the dielectric waveguide measurement method (DWM). The approximations of the method are discussed, and the method is compared with other measurement techniques. Results are presented for four square arrays: dipole, bow-tie, double-vee and slot array. The measurement method is verified by comparing it to the full-wave theory in the whole range. It is shown that all four antenna arrays can be represented by very simple circuits that use only transmission lines as circuit elements. The bow-tie array is found to represent the best choice for broadband operation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>