Theoretical study of two-element array of equilateral triangular patch microstrip antenna on ferrite substrate

The radiation characteristics of a two-element array of equilateral triangular patch microstrip antenna on a ferrite substrate are studied theoretically by considering the presence of bias magnetic field in the direction of propagation of electromagnetic waves. It is found that the natural modes of propagation in the direction of magnetic field are left- and right-circularly polarized waves and these modes have different propagation constants. In loss-less isotropic warm plasma, this array antenna geometry excites both electromagnetic (EM) and electroacoustic plasma (P) waves in addition to a nonradiating surface wave. In the absence of an external magnetic field, the EM- and P-waves can be decoupled into two independent modes, the electroacoustic mode is longitudinal while the electromagnetic mode is transverse. The far-zone EM-mode and P-mode radiation fields are derived using vector wave function techniques and pattern multiplication approaches. The results are obtained in both plasma medium and free space. Some important antenna parameters such as radiation conductance, directivity and quality factor are plotted for different values of plasma-to-source frequency.     

Theoretical study of 2 X 2 element planar array of equilateral triangular patch microstrip antenna in plasma medium

The radiation properties of 2 X 2 element planar array of equilateral triangular patch microstrip antenna in plasma medium are studied. The array factor and far-zone EM-mode and P-mode radiation fields of the array geometry are derived using vector wave function techniques and pattern multiplication approaches. The total field patterns and various characteristics of pattern such as half power beam width (HPBW), first null beam width (FNBW) and direction of maximum radiation are computed for two different values of progressive phase excitation difference between the elements. The results of this array geometry are obtained both in plasma medium and in free space and compared with those of single element equilateral triangular patch microstrip antenna.     

Radiation from a small spheroidal antenna with plasma shell

We construct and study an analytical solution of the boundary-value problem for the radiation field of a small spheroidal antenna located in free space and surrounded by a thin shell of cold homogeneous isotropic plasma. Conditions for a resonant increase in the field in free space as a function of the plasma-shell thickness with the variation in the spheroidal-antenna shape are studied. It is shown that the plasma shell has the largest effect on the radiation field of a strongly prolate spheroidal antenna. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 3, pp. 246–257, March 2006.     

基于纳观域碳纳米管的太赫兹波天线研究

基于碳纳米管独特的结构特点建立了以其为基础的Pocklington积分方程,并设计了一种全新的碳纳米管太赫兹(THz)波天线.数值仿真和理论计算结果表明,碳纳米管能够产生高频THz电磁辐射,半波长为60μm、半径为2.712nm的单壁碳纳米管偶极天线在-10dB反射系数以下可以实现2.5THz与7.6THz的双频带工作,带宽分别为8.4%与2.7%,由其构成的纳米管天线阵可以获得10.3dB的高增益特性.所得结果有助于在纳观域开展高频THz波辐射源及天线的研究与设计. 关键词： 太赫兹波 碳纳米管 天线 辐射源     

Negative luminescence and thermal radiation in semiconductor planar resonator structures

We present the results of theoretical and experimental investigation of interference effects of negative luminescence (NL) in planar resonator structures with an optically thin active semiconductor layer, as well as association of those effects with thermal radiation (TR) from such structures. The conditions are studied at which one can determine the NL characteristics of a structure with equilibrium electrons and holes by measuring its TR. We investigated the spectra and angular dependence of NL in the planar structures where active element is a Pb_0.8Sn_0.2Te film on a transparent BaF₂ substrate coated with aluminium. It is shown that, for such structures, NL efficiency in the interference peaks may be close to unity, and the antenna effect appears in the radiation pattern at some fixed wavelength. Both radiation intensity and the near-field energy in the vicinity of NL source energy are studied.     

钻孔雷达全向天线的设计与分析

根据钻孔雷达全向天线的设计要求,为减少天线的结构尺寸增加带宽,设计了一种新型电阻加载全向天线。通过理论分析和数值优化,选择了较优的结构尺寸,得到了较佳方向图和带宽。天线外径为65 mm,使用10 mm厚天线罩封装后外径为85 mm;天线的S11小于-10 dB频带为70~260 MHz,带宽约190 MHz。该天线的带宽超过100 MHz,中心频率处增益大于-3 dB,辐射电场脉冲波形拖尾小于主峰幅度1/5,方向图在H面为全向。基于矢量网络分析仪的天线特性测量结果与数值计算结果基本一致,结果表明设计的天线能够满足钻孔测井雷达系统小尺寸宽带的要求。     

Analysis and design of optically transparent antenna on photonic band gap structures

An optically transparent microstrip patch antenna is designed on photonic bandgap structures and its radiation characteristics are computed and analyzed in the visible spectrum region. The proposed antenna consists of indium tin oxide, a transparent conducting material used both as a radiating patch and a ground plane separated by the 5 μm thin glass substrate. The introduction of periodic cylindrical air cavity structures in the glass substrate leads to the formation of photonic band gap. The patch thickness is carefully selected based on the analysis of the optical transmission coefficient with respect to patch thickness. The effective dielectric constant of the photonic band gap loaded glass substrate is computed using the effective medium approach. The refractive index of the proposed antenna is presented and discussed. The radiation efficiency of the antenna is shown to improve significantly due to insertion of proposed photonic band gap structures. The proposed design has yielded a bandwidth of 2–2.3 THz for a return loss (S₁₁) of less than −15dB and achieved a peak gain of 4.97dB at 2.27 THz.     

Experimental Simulation of a Warm-Plasma Medium

A warm-plasma medium is simulated using two rodded media. The E- and H-plane radiation patterns of an X-band horn antenna in the presence of such a medium are studied experimentally at 9.5 GHz and are compared with the theoretical patterns.     

A novel flat lens horn antenna designed based on zero refraction principle of metamaterials

In this paper, a horn antenna filled with a metamaterial structure as lens inner the aperture is presented. Unlike conventional curve lenses, the lens is designed in the present work using a fully flat structure, which results in a great improvement for the directivity of the horn antenna based on the zero refraction characteristics of the metamaterial. In this structure, a periodic-structure metamaterial with three-layer metal grids is designed using the CST Microwave Studio for optimization and its zero refraction property is validated. For the characterization of the antenna, the electric-field distribution in radiation area, reflection parameter (S₁₁), gain and radiation pattern are calculated. The results show that the gain of a wide flare angle horn antenna is enhanced with over 2 dB between 16.10–17.30 GHz after the metamaterial is utilized. Therefore, the metamaterial lens horn structure results in a miniaturized antenna design approach compared to the optimum conventional horn of the same aperture size and gain in the interested frequency band. PACS 78.70.Gq; 81.05.Zx; 84.40.Ba     

Radiation patterns of electric dipole antenna in the presence of a biisotropic sphere

Analytic expressions of the dyadic Green's function of an arbitrary electric current source embedded in a general biisotropic sphere are presented at first, and the radiation characteristics of an electric dipole antenna placed on the surface of a biisotropic sphere lens are examined. The effects of the electric-and the magnetic-coefficients ( _e and _m ) of biisotropic medium on the radiation patterns of electric dipole antenna are investigated in detail.     

Receiving Antenna in a Magnetoplasma in the Resonance Frequency Band

We find the rms voltage on a receiving dipole antenna in the electromagnetic field of a quasipotential-wave packet in a magnetoplasma in the resonance frequency band. It is shown that this voltage can be determined as a product of the electromagnetic-field amplitude of the incident wave by the effective length L_eff of the receiving antenna. For a short dipole whose length is much smaller than the electromagnetic-mode wavelength, the antenna effective length is proportional to the product of the dipole effective length in free space by the excitation coefficient of quasielectrostatic waves (non-normalized electric-field pattern of a dipole). In the case where the receiving antenna is located in proximity to the resonance cone on the lighted side, this excitation coefficient is much greater than unity. Therefore, the determined voltage differs significantly from the conventional estimate which is based on formulas valid for antennas in free space. We perform our derivations using the reciprocity theorem and the fluctuation-dissipation theorem applied to a regular electromagnetic field and a receiving antenna, which constitute the special case of a system which is not in equilibrium but allows an equilibrium (stationary state) to be reached between the incident radiation field and the electromagnetic field reemitted by the antenna. The emphasis is placed on the universal nature of the applied calculation procedure which is valid for arbitrary antennas and matters.     

A conical microstrip antenna with uniform substrate

A novel conical microstrip antenna with uniform substrate is investigated. The far field radiation patterns of wraparound microstrip antennas mounted on such a structure are studied theoretically. Results for a wraparound antenna of half-wavelength in width excited by TM₀₁ are given, which are verified accurate and efficient by the ones of wraparound cylindrical antennas when the cone angle is very small.     

Efficacy of a wideband flexible antenna on a multilayer polymeric nanocomposites Fe3O4-PDMS substrate for wearable applications

The recently introduced polymeric nanocomposites substrate layer technology is used in the design of a flexible antenna array for wearable applications. This new technology allows a considerable widening of the bandwidth of classical microstrip topologies. This means that a relatively wide band can be combined with a full ground plane in a very simple structure, which is an ideal combination in wearable applications. The wideband and flexible features enabled the antenna to mitigate body-detuning effects. The proposed antenna prototype consists of a 2 × 2 array of rectangular patch elements with dimensions of 70 × 70 × 4.2 mm³. The measurements are performed in free space, and on-body under bent conditions. The antenna working within the frequency band of 5 GHz–8.2 GHz, with a fractional impedance (FBW) bandwidth of 50.34%. The antenna demonstrates a maximum radiation efficiency of 60%, and 9.8 dB of realized gain. Since this antenna is intended for on body-centric wireless communication application, the specific absorption rate is evaluated when the antenna is placed on the right arm of a realistic human phantom. The performances and features of the proposed antenna paved the way for off-body connections in a WBAN and wearable applications including WiFi, telemedicine and Vehicle-to-Everything (V2X).     

基于等离子体的定向天线阵理论与实验研究

当前国内学者对等离子体天线的研究主要集中于柱状天线和反射面天线, 而在国外已有学者以等离子体阵列结构设计了功能多样的智能天线系统. 为了较系统地了解这一新的设计思路, 基于等离子体散射理论对中心单元激励的圆形定向天线阵进行了理论和实验研究. 设计了一个16元等离子体无源振子的圆形天线阵, 实现了天线电磁波单波束和多波束的定向辐射. 通过理论计算和分析, 阐述了天线电磁波单波束和多波束辐射的原理. 通过建立实验系统, 测试了圆形天线阵的定向辐射特性. 实验结果和理论值接近, 说明该等离子体圆形天线阵可以实现天线电磁波的定向辐射和多波束辐射. 另外, 该天线阵还具有快速切换辐射方向、参数快速重构、雷达隐身性良好的优点. 关键词： 等离子体 定向天线阵 单波束 多波束     

Perturbation Analysis for a New Omni-Directional Antenna Consisted of Circular Rod Corrugations Gloved with a DNG Shell

A new omni-directional leaky-wave antenna is proposed in the paper, which is consisted of circular rod corrugations gloved with a Double-negative (DNG) shell. The leaky characteristics of the new antenna are analyzed by improved perturbation method. The electromagnetic fields are described in terms of a radial transmission-line network, which tremendously simplifies the analysis procedure with good calculation accuracy and brings considerable physical insight into the overall behavior of the dielectric grating antenna. The case where the n = −1 space harmonic of TE₀₁ mode radiating into the space is carefully investigated, it is demonstrated that the gloved cylindrical DNG shell greatly enhances the leaky strength of the antenna. As a result, the dimension of the antenna could be largely reduced keeping the radiation efficiency unchanged, which is of practical significance for some applications.     

Simultaneous solution of Kompaneets equation and radiative transfer equation in the photon energy range 1-125 keV

Radiative transfer equation in plane parallel geometry and Kompaneets equation is solved simultaneously to obtain theoretical spectrum of 1-125 keV photon energy range. Diffuse radiation field are calculated using time-independent radiative transfer equation in plane parallel geometry, which is developed using discrete space theory (DST) of radiative transfer in a homogeneous medium for different optical depths. We assumed free-free emission and absorption and emission due to electron gas to be operating in the medium. The three terms n, n² and (∂n/∂x_k) where n is photon phase density and x_k=(hν/kT_e), in Kompaneets equation and those due to free-free emission are utilized to calculate the change in the photon phase density in a hot electron gas. Two types of incident radiation are considered: (1) isotropic radiation with the modified black body radiation I^MB[1] and (2) anisotropic radiation which is angle dependent. The emergent radiation at τ=0 and reflected radiation τ=τ_max are calculated by using the diffuse radiation from the medium. The emergent and reflected radiation contain the free-free emission and emission from the hot electron gas. Kompaneets equation gives the changes in photon phase densities in different types of media. Although the initial spectrum is angle dependent, the Kompaneets equation gives a spectrum which is angle independent after several Compton scattering times.     

Compact wideband antenna above a wideband non-uniform artificial magnetic conductor

A compact wideband antenna place above a non-uniform artificial magnetic conductor (AMC) is presented. The antenna is composed of a wideband coplanar waveguide fed antenna, with wideband harmonic suppression characteristic using non-uniform defected ground structure. Besides, a non-uniform wideband AMC is designed. The AMC unit cell is composed of a square patch into which a four arms spiral shape is etched. It exhibits a wider ±90° bandwidth than the spiral unit cell and a smaller size than the square patch unit cell. The antenna is placed above the proposed AMC structure formed by 6 × 5 unit cells. The overall dimensions of the complete structure are 0.7 × 0.6 λ ₀ ² , where λ ₀ is the free-space wavelength at the lowest frequency. It offers a low-profile configuration with a total thickness of λ ₀/14.3, and it is matched between 2.5 and 5.4 GHz (73.5 %). Furthermore, it has a stable main lobe radiation pattern in the E- and H-planes within the operating frequency band. Moreover, compared with the antenna without AMC, the broadside realized gain is significantly increased. A prototype has been realized, and there is a good agreement between simulated and measured results. Furthermore, the proposed structure presents a size reduction of about 34 %, and better radiation characteristics in comparison with the conventional square AMC.     

Convective model of a microwave discharge in a gas at atmospheric pressure in the form of a spatially localized plasma

Experiments and a theoretical model consistent with them are presented which show that a stationary microwave discharge in a gas at atmospheric pressure under the action of free convection due to the action of the buoyant force on the heated air can be spatially localized, taking a spheroidal shape. Vortex motion inside the spheroid gives this localized plasma formation some of the properties of a material body which are manifested in a distinct material isolation from the surrounding space, in the formation of a narrow thermal boundary layer and flow separation, and in the formation of secondary vortices in the wake region. The characteristic radius of the stationary localized plasma is governed mainly by the wavelength of the microwave radiation a∼0.137λ. Energy balance is established to a significant degree by convective cooling of the microwave-heated structure. Zh. éksp. Teor. Fiz. 112, 877–893 (September 1997)     

Simulation of the electromagnetic characters of a Faraday-shielded antenna in a helicon wave plasma source

In this article, a structure that employs a Faraday shield between the Shoji antenna and the dielectric tube, which aims to reduce the dielectric wall sputtering, is investigated for the helicon wave plasma (HWP) sources. Faraday shield is usually used between the antenna and the reaction chamber to reduce the radiation from the high electromagnetic field generation, as well as to prevent the sputtering of the antenna material from polluting the reaction chamber during the discharge. Here, the influence of the Faraday shield on the longitudinal and radial electric field of the antenna is analysed through COMSOL Multiphysics^TM. Significant attenuations of both the longitudinal and radial fields are observed in the presence of the shield. In addition, by comparing the electric field distribution under two different shielding parameters, it is found that the shielding effects are not the same. Therefore, a detailed study of two kinds of design (pitch and gap) for the shield was carried out. The results show that the pitch has a little impact on the overall shielding effect when the gap is unaltered. The best shielding performance appears when we set the pitch at T of 8 and 10. In addition, the shielding effect also becomes worse as the gap increases while the pitch remains unchanged. A relatively good shielding effect can be produced by setting the gap to the value of 4–8 mm (a gap/pitch ratio of 2/15–4/15). This work provides a theoretical basis for designing a Faraday shield structure between the antenna and the dielectric tube, which is helpful to realize stable and controllable HWP discharges.     

Purcell effect in triangular plasmonic nanopatch antennas with three-layer colloidal quantum dots

A model describing a plasmonic nanopatch antenna based on triangular silver nanoprisms and multilayer cadmium chalcogenide quantum dots is introduced. Electromagnetic-field distributions in nanopatch antennas with different orientations of the quantum-dot dipoles are calculated for the first time with the finite element method for numerical electrodynamics simulations. The energy flux through the surface of an emitting quantum dot is calculated for the configurations with the dot in free space, on an aluminum substrate, and in a nanopatch antenna. It is shown that the radiative part of the Purcell factor is as large as 1.7 × 10₂ The calculated photoluminescence lifetimes of a CdSe/CdS/ZnS colloidal quantum dot in a nanopatch antenna based on a silver nanoprism agree well with the experimental results.