短路反射法测量复介电常数的研究

研究了基于波导六端口反射计系统的短路反射法测量介质材料复介电常数的测量原理,通过六端口反射计测量得到介质样品加载前后参考面的复反射系数,求得样品介质的相对介电常数和损耗正切。提出了一种新的求解复超越方程的数值解法,该方法以泰勒近似获取初值,通过梯度迭代得到最终结果,避免了复超越方程中无用多值的出现。实际测试结果表明,该方法可以快速单一地测得介质材料的相对介电常数,且精度较高。     

传输线模型介质参数校准方法研究

论述了高频信号在PCB中传输时,介质对于传输线损耗的影响。以此为基础,提出传输线介质参数校准流程,完成传输线测试板的设计,通过对测试板的仿真、测试,推导得出PCB介质的介电常数与损耗因子,提高高频传输线的仿真精度,同时验证了此流程方法的有效性。     

宽频带缝隙馈电双层贴片微带天线设计

采用矩形谐振缝隙耦合馈电的方式,在辐射贴片的上方引入寄生矩形谐振器,地板下方四分之一波长处放置反射面,两辐射贴片之间使用多层低介电常数的泡沫介质基板,设计了一款宽频带微带天线。该天线不仅频带宽,后向辐射小,而且结构简单,便于阵列集成。仿真结果表明:在电压驻波比(VSWR)小于等于2时,该天线的阻抗带宽度达到了中心频率的58.42%;在5.12~8.98 GHz的频率范围内,天线的增益大于7.1 dB,回波损耗小于-10 dB。     

液体介电常数测定装置

为方便测量各种液体的介电常数,设计平行板电容传感器探头、电容电桥式处理电路和检波滤波电路;处理电路将电容传感器的电容变化转换成与介质相对介电常数成线性变化的电压,经检波与滤波后得到直流电压,利用电压表直接显示液体的相对介电常数。进行了实验标定和实际检测,测量误差小于1%。     

基于分段涂层TDR探针的含水合物多孔介质电学参数测量仿真研究

针对海洋沉积物中天然气水合物饱和度评价需求，提出了基于分段涂层TDR探针的沉积物介电常数和电导率同步测量新方法。针对无涂层探针、全涂层探针以及分段涂层探针分别建立了模拟TDR测量响应的有限元数值模型，仿真研究了涂层参数对介电常数和电导率测量性能的影响规律，继而应用于含水合物多孔介质的测量并对误差进行了分析与校正。研究结果表明：探针涂层的厚度和介电常数直接影响采集电压信号的衰减程度，因此需根据被测介质的电学性质对其进行优化设计；在涂层厚度和介电常数已确定的条件下，通过改变涂层间隙长度可以调节探针所适用的电导率测量范围；当测量非均匀介质时，可以通过增加涂层间隙的个数来提高电导率测量的准确度；采用分段涂层探针测量含水合物多孔介质的介电常数和电导率时，需要对涂层引起的误差进行校正。     

第五代移动通信系统三重复合分形天线设计

针对第五代移动通信系统对天线的性能要求,将谢尔宾斯基分形结构、康托尔分形结构、分形折线雪花结构相融合,设计了一款三重复合分形天线,对天线性能进行了仿真分析,制作了天线样品并对其进行了测试。仿真和测试结果表明,该款天线回波损耗最小值为-21.84 d B,绝对工作带宽达到2.047 GHz,相对工作带宽达到48.51%,天线具有全向辐射特性。利用渐变介电常数介质基板设计了改进型天线结构,有效地展宽了天线的工作频段。该款天线能够完全覆盖第五代移动通信的三个候选频段,具有尺寸小、回波损耗低、工作带宽大等优点,在第五代移动通信系统中具有广阔的应用前景。     

5.8 GHz RFID标签用共面波导蝶形缝隙天线的设计

设计了一种基于5.8 GHz RFID标签应用共面波导馈电蝶形缝隙天线以满足RFID应用发展的需求.天线制作在相对介电常数为4.4的FR4介质板上.天线增益可达4.1 dBi,在回波损耗<-10 dB条件下带宽为21.7%.天线H面辐射方向图近乎全向.提出了一种天线小型化设计方案,小型化天线采用双重蝶形结构.经过小型化后的天线面积缩减了48.18%.小型化后的天线带宽也大大增加,达到51%.结果表明蝶形缝隙天线以及小型化天线都为单一平面,结构简单,适合RFID的应用.     

基于内部阵列电极的电容层析成像系统

为了研究电容层析成像系统在测量高介电常数流体中的应用,设计了一套具有内部阵列电极的电容层析成像传感器,改善了传统传感器的灵敏度和非线性特性,拓宽了系统的测量范围。用蒸馏水作为连续相介质进行了数据采集和图像重建,并进一步研究了介质电导率对系统成像的影响。实验表明,该系统可以实现高介电常数介质的测量,并且可用来测量具有微弱导电能力的物体。     

基于边缘效应的圆环式电容传感器电场仿真分析

介绍了圆环式电容传感器的工作原理,即电容边缘效应,通过Hybrid-Trefftz算法建立了有限元模型,利用有限元软件ANSYS对不同传感器模型进行了电场分析与仿真计算,得出了最优结构组合,并以最优结构组合为例,给出了介电常数与电场强度的关系。仿真结果表明:圆环式电容传感器设计中,影响传感器测量性能的最直接和最重要的2个参数是两极板间距和极板长度;被测介质的介电常数越小,电场强度就越大。该仿真对后续产品的设计具有很好的理论指导作用。     

填充介质倒梯形脊波导衰减特性的有限元分析

脊波导在传播电磁波的过程中伴随有能量损耗,为了研究填充介质脊波导的衰减特性,本文采用有限元法借助Matlab软件计算了TE模式下部分填充介质倒梯形对称双脊波导的衰减常数和功率容量.分析了脊波导衰减常数和功率容量与脊波导尺寸、工作频率、填充介质相对介电常数之间的关系,给出关系曲线图.这些结果将丰富现有的填充非均匀介质脊波导的数据,为填充介质脊波导的设计和优化提供有价值的依据.     

A compact filtering antenna using dielectric strip resonator and parallel microstrip feed line

A filtering antenna using dielectric strip resonator and parallel microstrip feed line is proposed to achieve compact dielectric size and filtering response without gain reduction. The compact dielectric size is contributed by the dielectric strip resonator with high permittivity operated in the TM_δ1 cavity mode, whose electric field distribution along the short side is far less than half‐wavelength distribution. Therefore, the size of the proposed dielectric strip resonator is smaller than the traditional dielectric patch resonator operated in the TM₁₁ cavity mode. Additionally, the parallel placed microstrip line not only can excite the dielectric strip resonator for filtering response without gain reduction, but also can provide one upper‐edge radiation null for frequency selectivity enhancement. Compared with the reported filtering dielectric antennas, the proposed design exhibits the features of compact dielectric size, simple structure and wide stopband. For demonstration, one prototype operating at 4.9 GHz is fabricated, achieves the dielectric size of 0.00078 λ3 0 (λ₀ is the wavelength in the free space at the center frequency), the measured peak gain of 7.1 dBi, the 10‐dB impedance matching bandwidth of 4%, the stopband (> 16 dB) up to 1.84 f₀, and the cross‐polarization level of 20 dB within 3‐dB beam range.     

CAD oriented frequency,temperature, and DC bias dependent small‐signal,scalable circuit model of parallel‐plate paraelectric varactors

Simple, CAD compatible small‐signal scalable circuit model for the thin film parallel‐plate ferroelectric varactors is reported. It is based on the measured permittivity and loss tangent of the ferroelectric films along with the fundamental theoretical relationships of ferroelectrics in paraelectric phase. The model makes use of the measured DC field (voltage) at the inflection point of the C‐V curve where the nonlinearity (dC/dV) and the tunability are maximum. Both the capacitance and the equivalent loss resistance (dielectric losses) in the ferroelectric film take into account the low permittivity layers at the boundaries of the nano‐columns of the film. The frequency dependent losses in the top and bottom plates of the varactors and the parasitic inductance of the plates are also taken into account. The model is valid for ferroelectric films having columnar structure. It is useful in wide temperature, DC field, and frequency ranges. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.     

Dielectric property improvement of polymer-nanosized strontium titanate-composites for applications in microelectronics

With respect to applications in microelectronics the frequency and temperature dependent dielectric properties of a series of polymer-based composites, consisting of a thermally curable unsaturated polyester-styrene resin and nanosized strontium titanate filler, have been characterized. Following earlier investigations targeting an improvement of dielectric properties the impact of a thermal treatment of the dielectric filler on the resulting composite properties was determined. In case of composites containing 55 wt% strontium titanate heat treatment at 1,000°C increases the permittivity by almost 25% and lowers the loss factor value by a factor of almost 10 due to grain growth and larger crystallite sizes.     

一种新的介质滤波器设计方法

分析并设计了新型介质滤波器结构,提高了滤波器的性能,减小了体积.同时使用HFSS电磁仿真软件对所设计的谐振器进行仿真.同时设计了新型的滤波器耦合矩阵综合和优化方法,大大提高了耦合矩阵综合与优化的性能和计算速度.     

Dielectric properties of liquid crystals for display and sensor applications

Temperature dependence of dielectric properties of nematic liquid crystals are investigated for two types of devices: wide temperature range liquid crystal (LC) displays and capacitor temperature sensor. Both real and imaginary components of the dielectric constant have been measured in wide frequency and temperature range including t < 0 °C as well as versus the angle θ between the directions of both magnetic and electric field in the measuring scheme. Some physical parameters of the nematic LC (NLC) dielectric relaxation have been determined. Effective values of the LC dielectric permittivity with different values of the LC pretilt angles in different parts of a complex LC cell have been simulated.     

A thin‐layer dielectric and metamaterial unit‐cell stack loaded miniaturized SRR‐based antenna for triple narrow band 4G‐LTE applications

This article presents the design of a miniaturized dual‐band antenna for long‐term evolution (LTE) application is presented. In the basic antenna design, split ring resonator was loaded in the radiating plane of the patch and frequency of resonance was further modified with the help of E‐shaped stub. The antenna has been fabricated using FR‐4 substrate and the measured dual bands at 2.11 and 2.665 GHz are found in a close match with the simulated data. By placing a thin dielectric resonator of permittivity ε _r = 10.2 and thickness of 1.27 mm, two closely spaced narrow bands are obtained at 2.217 and 2.28 GHz. A novel metamaterial unit‐cell having near‐zero refractive index is designed and mounted above the dielectric resonator. This stack configuration generates triple narrow frequency band in the LTE 2 GHz spectrum range. The overall size of the proposed antenna is 20 × 25 mm².     

1800MHz同轴谐振微波介质滤波器的结构设计及其仿真

研究18 0 0MHz的微波介质滤波器的设计原理和计算方法,同时使用高频结构仿真软件对所设计的滤波器进行了仿真分析。所要求的滤波器的参数指标为:中心频率f0 =180 0MHz ,插入损耗IL <2 .5dB ,3dB带宽BW =4 5MHz ,带内波动Ap<1.5dB ,10 0MHz处带外抑制As>2 5dB。     

Electromagnetic design of microwave filters using the finite element method

We present two complex microwave filter designs using the finite element method (FEM). A metallic cavity, loaded by low-loss dielectric plates is first optimized to obtain a high unloaded quality factor resonator. An original synthesis approach is then proposed to design a three-pole dielectric loaded cavity filter. The FEM is also applied to characterize a filter element, a dielectric resonator (DR) coupled on a whispering gallery mode (WGM) to two microstrip lines. A generalized [S] matrix is computed. Different elements are then put together to generate complex filtering responses. © 1997 John Wiley & Sons, Inc. Int J Microwave Millimeter-Wave CAE 7: 167–179, 1997.     

Dielectric resonator based two‐port dual band antenna for MIMO applications

This article investigates a dual band multiple input multiple output (MIMO) cylindrical dielectric resonator antenna (cDRA) for WLAN and WiMAX applications. It consists of two symmetrical orthogonally placed radiators. Each radiator is excited through a narrow rectangular aperture with the help of a microstrip line. For higher mode excitation, the proposed structure uses dual segment DRA which apparently looks like stacked geometry. The aperture fed dielectric resonator works as a feed for upper cDRA to generate higher order mode. The presented radiator covers the band between 3.3‐3.8 GHz and 5‐5.7 GHz. The measured isolation is better than 20 dB in the desired band. The average gain and radiation efficiency achieved for the proposed antenna is 6.0 dBi and 85%, respectively at the operating frequency band. In the proposed geometry, broadside radiation patterns are achieved by exciting HEM_11δ and HEM_12δ modes in a stacked geometry. Different MIMO performance parameters (ECC, DG, MEG, and CCL) are also estimated and analyzed. The prototype of proposed antenna is fabricated and tested. The measured outcomes are in good accord with the simulated one.     

Dielectric characterization and voltage holding ratio of blue-phase cells

The phase behaviors of a blue-phase (BP) liquid crystal in a planar-aligned cell were investigated by means of temperature-dependent dielectric spectroscopy. With auxiliary observations of optical transmission spectra and birefringent textures, we found that the transition temperatures of two adjacent mesophases, including the cholesteric-to-BPI, the BPI-to-BPII, and the BPII-to-isotropic, can clearly be distinguished by the first and second derivatives of the real-part dielectric permittivity function to the temperature at a specific frequency. Furthermore, an attempt to evaluate the device performance of a polymer-stabilized BP, derived from the photopolymerization of two monomers (RM257 and TMPTA), was achieved with a new circuital design for the voltage-holding-ratio (VHR) measurement. Preliminary results of the VHRs of samples at 180 Hz and their temperature dependence were obtained accordingly.