Analysis and design of rectangular microstrip antenna on two-layer substrate materials at terahertz frequency

In this paper, an effective permittivity of the two-layer dielectric substrate material has been analyzed to enhance the electrical performance of the rectangular microstrip patch antenna at terahertz frequency. The frequency dependent effective dielectric permittivity of the substrate materials has been evaluated and result has been compared with finite integral technique based CST Microwave Studio a commercially available simulator. The input impedance characteristic with electrical performance of the rectangular microstrip patch antenna on two-layer substrate materials has also been analyzed at 600 GHz. Manipulation in the input impedance characteristic of the antenna has led to a slow wave structure. This slow wave structure has been examined at 542 GHz, and improvement in the performance has been observed without increasing the overall dimension of the proposed antenna.     

Analysis and design of terahertz microstrip antenna on photonic bandgap material

In this paper, a dielectric slab with periodic implantation of the air gaps has been analyzed. An effective dielectric permittivity of the 1-D photonic bandgap substrate material (PBG material) with host material as Polytetrafluoroethylene (PTFE) has been computed at 600 GHz. Based on the extracted effective dielectric permittivity, a rectangular microstrip patch antennas on thin and thick 2-D PBG material as substrate have been designed. The electrical performances of the antennas have been simulated by using two different simulators, CST Microwave Studio based on the finite integral technique and Ansoft HFSS based on the finite element method. This proposed antenna on the PBG material as substrate shows the significant enhancement in the directivity. To validate the homogenized medium approximation, the effect of the antenna position on the substrate material has been observed. The response of antenna has been found to be independent of its position. Various electrical parameters of the proposed antennas have been compared with reported literature. In addition to this, the operating frequency of one of the antenna has been scaled down by the factor of 50 and its various results have been compared with the results obtained at 600 GHz.     

Miniaturized modified circular patch monopole antenna on ceramic-polytetrafluroethylene composite material substrate

A 0.22λ×0.29λ×0.03λ miniaturized modified circular patch monopole antenna on high permittivity ceramic-Polytetrafluoroethylene (PTFE) composite material substrate is presented. The proposed antenna is designed and investigated using 3D full wave high frequency electromagnetic simulator and fabricated using printed circuit board (PCB) prototyping machine. Impedance bandwidths (Reflection coefficient <?10 dB) of 26.76 % (5.0–6.3 GHz), 5.3 % (9.1–9.6 GHz) and 3.6 % (10.7–11 GHz) have measured. Average gains of 0.9 dBi, 3.68 dBi and 3.63 dBi measured at first, second and third band correspondingly. 87.3 %, 88.5 % and 93.1 % radiation efficiencies have achieved at three resonant frequencies 5.6 GHz, 9.5 GHz and 10.9 GHz respectively. The measured symmetric and nearly consistent radiation pattern makes the proposed antenna suitable for C band and X band applications. In this letter, the effects of dielectric properties of substrate material and design parameters have studied.     

Dual-band rectangular microstrip patch antenna at terahertz frequency for surveillance system

In this paper, a rectangular microstrip patch antenna on two-layer substrate materials has been analyzed and simulated at the terahertz frequency regime for the surveillance system. The proposed antenna has been simulated at 600 and 800 GHz frequencies by using CST Microwave Studio a commercially available simulator based on finite integral technique. This antenna structure is also simulated by using finite element method based simulator Ansoft HFSS and the results are compared with former.     

在相同相对介电常数情况下不同厚度的微带贴片天线设计与仿真验证

微带贴片天线的基板材料的相对介电常数和介质板厚度是影响天线性能的重要因素.为了验证在相同相对介电常数的情况下,改变介质基板的不同的厚度时微带矩形贴片天线的阻抗带宽的变化,通过HFSS软件设计和仿真了工作频率为1.95 GHz的4个矩形微带贴片天线,相对介电常数均为2.2,介质基板厚度分别设计为0.8、1.6、2.4、3.2 mm,比较其各自的S参数、方向图,通过仿真结果验证了相关文献所述的对于在给定的频率下,选用相同的基板材料时,厚度增大时阻抗带宽会变大的说法.     

Dielectric and conductive spectra of the composite of barium titanate and LiClO/sub 4/-doped polyethylene oxide

Dielectric and conductive frequency spectra in a 10 mHz-10 GHz range have been measured for a composite consisting of barium titanate (BaTiO/sub 3/) inclusions dispersed in a LiClO/sub 4/-doped polyethylene oxide (Li-PEO) matrix with volume fraction /spl Phi/ = 0-40%. Pure Li-PEO behaves as a dielectric showing a segmental-mode dielectric relaxation at high frequencies (dielectric regime) and transfers to an ionic conductor below 10 MHz (conductive regime). BaTiO/sub 3/ is a ferroelectric having a very large dielectric permittivity and spontaneous polarization. The introduction of BaTiO/sub 3/ into Li-PEO caused a rapid increase in permittivity in the dielectric regime. In the conductive regime, the composite exhibited an additional relaxation at a frequency related to the ratio of DC conductivity of Li-PEO and the permittivity of BaTiO/sub 3/. This relaxation was attributed to accumulation of dissociated Li/sup +/ and ClO4/sup o/ns at the inclusion/matrix interface which resulted in an increase of effective permittivity and a decrease of effective conductivity. Quantitative analyses based on mixing laws for the two-phase spherical dispersion system have shown that the Bruggeman equation accurately predicted the /spl Phi/-dependence of the effective permittivity over the entire frequency range. Regarding the effective conductivity, it predicted values lower than the observed. We attributed this discrepancy to the spontaneous polarization of BaTiO/sub 3/, which induced ion trapping to reduce the DC conductivity of Li-PEO matrix.     

Analysis of a dual‐resonant multiple split‐ring patch antenna

The design and analysis of a new 0.06λ × 0.09λ compact circular polarized square‐shaped dual‐resonant multiple split‐ring patch antenna on a 1.905‐mm‐thick high‐dielectric ceramic–polytetrafluoroethylene composite is presented. The proposed antenna was designed and analyzed by using a high‐frequency electromagnetic simulator based on the finite element method and was fabricated on a printed circuit board. The measured ?10 dB return loss bandwidths were 44.44% (0.7–1.1 GHz) and 34% (2.25–3.1 GHz) at 0.9 and 2.5 GHz center frequencies, respectively. The measured radiation patterns with 5.9 and 4.0 dBi maximum gains were symmetric and steady, making the proposed antenna suitable for radio frequency identification, wireless local area network, wireless body area network, Low Rate‐Wireless Personal Area Network (LR‐WPAN), and so on. The effects of linewidth, dielectric property of the substrate materials, and number of split rings on the return loss were investigated. The surface current distribution over the radiating patch and the characteristics of the Resistance, Inductance, Capacitance (RLC) equivalent circuit of the proposed antenna were also analyzed. Copyright © 2013 John Wiley & Sons, Ltd.     

Dielectric Properties of Yttrium Vanadate Crystals from 15 K to 295 K

Yttrium Vanadate (YVO₄) is a birefringent crystal, which has similar dielectric constant as that of Sapphire. In this paper we have reported the measurement of the real part of permittivity and loss tangent of YVO₄ crystal in the temperature range 15–295 K at a frequency of 16.3 GHz. We have used the dielectric post resonator technique for the microwave characterisation of the YVO₄ dielectric rod. The multifrequency Transmission Mode Q-Factor (TMQF) technique has been used for data processing and hence precise values of permittivity and loss tangent are achieved. Easily machineable YVO₄ is characterized by low losses at microwave frequencies. At temperature of 15 K and frequency of 16.3 GHz the permittivity was 9.23 and loss tangent was 2 × 10^{− 5}. YVO₄ is identified as a potential candidate to replace expensive Sapphire in many microwave applications.     

Evaluation of the complex antenna factor of a dipole antenna by measuring the S-parameters of the balun

The complex antenna factor (CAF) of a dipole antenna with a balun is evaluated by calibrating the S parameters of the balun and calculating the effective length of the antenna element in the frequency range of 600 MHz to 2 GHz. The result is compared with that of the conventional three-antenna method. The CAF values obtained by the two methods agree in their absolute values up to 1.2 GHz. Concerning the phases of CAF, two results are close in the whole band. © 1998 Scripta Technica, Electr Eng Jpn, 123(2): 16–23, 1998     

CPW‐fed compact thin‐film UWB antenna with dual band‐notched characteristics

This paper presents a new compact thin‐film ultrawideband (UWB) antenna with dual band‐notched characteristics. The antenna contains a rectangular slot with a fork‐like tuning stub. To achieve the dual band‐notched characteristics, narrow and U‐shaped slots are inserted on the radiator. This antenna is printed on a Mylar film substrate of 0.3 mm thickness with a dielectric constant of 3.2. The antenna has compact dimensions of 34.5 × 27.3 mm². It operates in the frequency range 2.9–11.3 GHz with impedance matching covering the entire bandwidth and reasonable radiation properties. It also exhibits dual band‐notched characteristics. One of the notched frequencies is in the range 3.3–3.7 GHz (WiMAX band) and the other in the range 5.1–5.8 GHz (WLAN band). The antenna is designed and simulated by using the commercial IE3D software, which is based on the method of moments. The antenna was fabricated and measured using Agilent E363B PNA network analyzers. The characteristics of the fabricated antenna show high correlation with those obtained from the simulation. The results confirm that the proposed antenna can achieve notch performance for WLAN and WiMAX communication systems and is also suitable for various portable UWB applications. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

基于HFSS的Hilbert分形天线分导线段设计

对采集变压器局部放电超高频信号的四阶Hilbert分形天线进行重新建模和设计,以达到更好的效果。首先分析天线的三种导线段在采集信号过程中的作用,并以导线段为单元,基于HFSS对天线重新建立模型,将三种导线段长度、介质厚度、介电常数和导线宽度六个变量应用SNLP算法优化。优化结果显示,0.3 GHz~3 GHz超高频范围内,谐振频率点达到四个,并将0.3 GHz~1 GHz范围内的通频带拓宽整合为超过500 MHz宽带,1 GHz以上的三个通频带也均超过450 MHz,且方向性良好,增益参数也有了很大程度的改善。所述特性经过试验验证。天线尺寸较小,可以置于变压器箱体内,能很好地应用于油浸式变压器局部放电超高频信号的采集。     

Influence of water absorption on high‐frequency characteristics of insulation layers of printed circuit boards

The influence of water absorption on complex permittivities of various insulating materials used for printed circuit boards was investigated in the frequency range of K‐band (18–26 GHz). Experimental results revealed that the influence of water absorption on complex permittivity, the dielectric loss factor tanδ, in particular, was considerably high. For example, the dielectric loss of polyimide film at 85°C, 85% RH became 10 times larger than that at room temperature and humidity. Since the complex permittivities, however, retained the initial values when the specimens are dried, the water in the specimen should exist freely at the internal interfaces of the materials. The increase of permittivity directly affects the performance of printed circuit boards at high frequencies, so that it is important to clarify the influence of water on dielectric properties of insulations. Copyright © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

NON DESTRUCTIVE DIELECTRIC CHARACTERIZATION OF THIN FERROELECTRIC FILMS MATERIALS USING COPLANAR LINE STRUCTURE

ABSTRACT

This paper presents a nouvelle and non-destructive Broadband characterization method which uses a coplanar line for the measurement of the complex permittivity of linear dielectric materials and precisely, that of ferroelectric thin films. The method uses the transmission coefficient and the quasi-TEM analysis to find the effective permittivity of the multilayer system, and then the coplanar conformal mapping technique is employed to extract the relative permittivity of the thin layer. Comparing our results to those of cavity resonator method at 12 GHz shows a good agreement. The measurement is done in the microwave frequency band (45 MHz–20 GHz).     

Properties of Ferroelectric Liquid Crystal/Multiwall Carbon Nanotube Doped Composite

Carbon nanotubes-ferroelectric liquid crystal composites have been prepared and studied. Doping of carbon nanotubes into ferroelectric liquid crystal in varying concentration has been investigated in thin cells in the frequency range of 50 Hz–1 MHz. Decrease in the dielectric permittivity and dielectric strength is found with the doping of carbon nanotubes, however ～32% increase in the relaxation frequency has been observed in higher concentration carbon nanotubes doped ferroelectric liquid crystal composite than pure ferroelectric liquid crystal sample. A decrease in conductivity has also been noticed after doping.     

Fabrication and properties of 2D EBGs by moulding/demoulding with high permittivity ceramics

Two-dimensional electromagnetic bandgap structures (2D EBGs) are designed and fabricated by moulding/demoulding. A high permittivity and low dielectric loss microwave material, Bi₂O₃-ZnO-Nb₂O₅ (BZN) was used. The impacts of high permittivity on the 2D EBGs’ properties are investigated. As the experiments showed, wide electromagnetic band gap is found in the frequency ranges from 5.6 to 10.6 GHz, and 12.6 to 16.6 GHz. The first gap is greater than 60% of the gap center frequency, while the second gap is 25% of the center frequency. The interval between the two gaps is larger than 2 GHz, and the return loss of both gaps is as large as ?40 dB. This interesting phenomenon of multi band gaps is very useful for diplexers, multi-mode tunable dielectric antennas and resonators. Based on these, expansive applications may be exploited in the future. The experimental results are in good agreement with the simulations’.     

DIELECTRIC BEHAVIOUR OF A NANOGRAIN PMN POWDERS

ABSTRACT

Dielectric permittivity of 150 nm mean grain size Pb(Mn_1/3Nb_2/3)O₃ (PMN) nanopowder has been investigated by dielectric spectroscopy in the 20 Hz–1 MHz frequency range and 100 K–400 K temperature range. The broad and diffused dielectric dispersion has been observed, but the dispersion region and the maximum of the real part of dielectric permittivity is shifted to lower temperatures compare to PMN single crystal and ceramics. The mean relaxation time, obtained from fits of the frequency dependences of the dielectric permittivity with Cole-Cole formula, changes according to the Vogel-Fulcher law with the freezing temperature T ₀ = 88 K which is much lower than in bulk PMN materials.     

Measurement of permittivity and dielectric loss in 2,4-dimethyl substituted pyridine using microwave cavity spectrometer and time domain reflectometer

Microwave cavity spectrometer and time domain reflectometer is used to measure the permittivity and dielectric loss at different temperatures in 2,4-dimethyl substituted pyridine. The observed data of the width of resonance profile and the shift in the resonance frequency have been analyzed using Slater perturbation equations for cavity spectrometer. The dielectric parameters measured from the time domain reflectometer as a function of time at different temperatures have been transformed to frequency domain to obtain the permittivity and dielectric loss. The observed values of the permittivity and dielectric loss at 9.0 GHz are fitted in Slater's perturbation equations to obtain the form factor, which represents interactions. The relaxation time has been evaluated at different temperatures using the ratio of width and twice of frequency shift and thermodynamical parameters have been determined. This experimental study provides fruitful information about the bulk properties of 2,4-dimethyl substituted pyridine.     

Gain enhancement and broadband RCS reduction of a circularly polarized aperture-coupled annular-slot antenna using metasurface

A circularly polarized microstrip slot antenna with low radar cross-section (RCS) and high gain was designed using a metasurface composed of a \(6 \times 6\) array of corner-truncated square patches placed on top of the upper substrate. By optimizing the geometry of the metasurface patches and L-shaped feed of the proposed antenna, broadband RCS reduction and improved overall antenna performance were achieved. A prototype antenna was fabricated, and the results showed that the proposed antenna exhibited an impedance bandwidth of 29.08 % in the frequency band of 4.29–5.75 GHz. The designed antenna achieved good 3-dB axial ratio (AR) bandwidth of about 30.18 % with center frequency of 5.3 GHz, and gain in the broadside direction of 9.9 dBi. Using the designed metasurface, remarkable monostatic RCS reduction was obtained in the frequency range from 4 to 13 GHz.     

一种新型宽带单面异向介质结构的分析与设计

提出一种在4—7GHz频率范围内可实现双负特性的新型宽带单面异向介质结构,其有效相对带宽为54．5％,中心频率电尺寸为0．051。通过对比分析了粒子型异向介质与传输线型异向介质的优缺点,将两者结合起来,并基于电磁波入射到异向介质平板的传输和反射数据,根据NRW方法从中提取出该新型结构的有效介电常数和磁导率。结果表明：本文所提出的新型异向介质结构在特定频段范围内表现出双负特性;根据计算频率为5GHz时电磁波传播的相速,证明该新型宽带单面异向介质结构具有后向波特性。     

Dielectric,impedance and modulus spectroscopy of BaBi2Nb2O9

Barium Bismuth Niobate (BaBi₂Nb₂O₉) has been synthesized by solid state reaction method. The X-ray diffraction study confirms the formation of compound. Morphological analysis has been carried out from the scanning electron microscopy images and the elemental analysis from the energy dispersive spectroscopy profiles. Investigation of dielectric and ferroelectric properties of the sample was done by varying the temperature from 25 °C - 500 °C in a frequency range of 1 kHz- 1 MHz. At 100 kHz, the phase transition was observed at 214.02°C. Further, this ferroelectric bi-layered perovskite exhibits an interesting relaxor behavior with a strong dispersion of the dielectric permittivity. A detailed study on the impedance spectroscopy over a wide range of temperature and frequency exhibits the contribution of grain ad grain boundary on different electrical parameters. From modulus spectroscopy, the presence of non-Debye type of relaxation in the material has been manifested. The complex modulus plots support the negative temperature coefficient of resistance (NTCR) type behavior of the material.