New Methods of Dielectric Measurements in the Millimeter-Wave Band

A heterodyne interferometer was constructed in the V-band at 60GHz to measure the phase difference associated with the material. This phase difference is then used to calculate the real part of the dielectric constant from the index of refraction. Measuring equipment for monitoring the permittivity and loss of a medium in the millimeter-wave band (gamma = 3.5 mm) is developed. The measurement error of the equipment using the reflection method is less than 2%. A new spectrometer for the precision measurement of dielectric permittivity and loss tangent, which is capable of providing high resolution data for the first time over an extended W-band (68-118GHz) frequency for specimens with a large range of absorption values, including highly absorbing specimens that otherwise would not be possible.     

Measurement of Low-Loss Dielectric Materials Using Dielectric Rod Resonator

To obtain the complex permittivity of low-loss dielectric materials at 60 GHz, a measurement method is developed. Using a dielectric rod resonator excited by a dielectric waveguide, effective conductivity of conducting plates for short circuiting the resonator is determined. The complex permittivity of the dielectric rod is determined by the resonant frequency and unloaded quality factor of the TE_0m1-mode resonator. Moreover, the complex permittivity of single crystal sapphire, polycrystalline ceramics, and cordierite has been investigated in virtue of numerical simulation. For all the measured specimens in this study, the proposed method is seen to provide much better accuracy for values.     

Ultra-Low Loss Microwave Dielectric Ceramic Li<Subscript>2</Subscript>Mg<Subscript>2</Subscript>TiO<Subscript>5</Subscript> and Low-Temperature Firing Via B<Subscript>2</Subscript>O<Subscript>3</Subscript> Addition

Li₂Mg₂TiO₅, a rock-salt structured ceramic fabricated by a solid-state sintering technique, was characterized at the microwave frequency band. As a result, a microwave dielectric permittivity (ε_r) of 13.4, a quality factor of 95,000 GHz (at 11.3 GHz), and a temperature coefficient of resonance frequency (τ_f) of ? 32.5 ppm/°C have been obtained at 1320°C. Li₂Mg₂TiO₅ ceramics have low permittivity, a broad processing temperature region, and a low loss, making them potential applications in millimeter-wave devices. Furthermore, B₂O₃ addition efficiently lowered the sintering temperature of Li₂Mg₂TiO₅ to 900°C, which opens up their possible applications in low-temperature co-fired ceramics (LTCC) technology.     

Microwave sintered Mg-Cd ferrite substrates for microstrip patch antennas in X-band

The ferrites with chemical formulae MgFe₂O₄, Mg_0.6Cd_0.4Fe₂O₄ and Mg_0.2Cd_0.8Fe₂O₄ specified with Ferrite S1, S2 and S3 were prepared by the oxalate co-precipitation method using AR grade sulphates under microwave sintering technique. The single phase cubic spinel structure formation of all the ferrites was confirmed by XRD and FTIR techniques. The dielectric parameters such as permittivity (ε_r), dielectric loss tangent (tan δ_e), permeability (µ_r) and magnetic loss tangent (tan δ_m) were determined from parameters S₁₁ and S₂₁ by using material measurement software with VNA. The synthesized ferrites S1, S2 and S3 with determined dielectric parameters were used as substrate to design rectangular microstrip patch antenna by simulation using Ansoft Designer SV 2.2. The designed antennas were fabricated by using screen printing technique. The return loss (RL), 10 dB % bandwidth and VSWR of these fabricated antennas were measured on vector network analyzer. The simulated and measured values of resonating frequency, return loss (RL), 10 dB % bandwidth and VSWR were nearly matched with each other. Mg_0.2Cd_0.8Fe₂O₄ (Ferrite S3) can be used as substrate of antenna for better results.     

Analysis of high frequency properties of multilayer structures for multichip modules

The microwave surface resistance and reactance of YBa₂Cu₃O₇ multilayers for MCMs have been studied as a function of thickness and relative permittivity of dielectric layers at 500 MHz and 10 GHz propagation frequency. Additionally, frequency properties of a YBCO/CeO₂/SrTiO₃/YBCO/LaAlO₃ multilayer have been analyzed and results compared with measurement results. Performed simulations have shown that a dielectric layer of high relative permittivity, necessary for good isolation between superconducting ground planes and power planes in the multichip modules, has negligible influence on the effective surface resistance and reactance up to 0.5 μm dielectric thickness.     

安捷伦4396B阻抗分析仪在测试吸波材料复相对介电常数上的应用

依据平行板电容器物理模型的基本原理、安捷伦4396B阻抗分析仪以及安捷伦16453A介质材料测试夹具,建立了1 MHz～1 GHz频率范围内复相对介电常数的测试系统.将测试结果与已知材料进行比对,结果表明,该系统的测试数据真实可靠.此测试系统可应用于新型吸波材料的仿真设计.     

Open Resonator System for Automatic and Precise Dielectric Measurement at Millimeter Wavelengths

As low loss dielectric materials, ZnS, MgF₂, MgAl₂O₄ and quartz ceramic have a very important application at millimeter frequencies. However, there is little information about their dielectric properties in the millimeter wavelength band. To obtain their dielectric properties, an automatic open resonator measurement system at Ka-band is designed and constructed. The importance on the precision determination of cavity length over a broad band and the checking of a measurement system are emphasized and their solutions are put forward in this paper for the first time so far as we know. The solutions of above problems ensure the credibility and high accuracy of our measurement system. The certified measurement system after a series of checking is used to measure the above materials. Lots of measurement results show that the standard deviation of measurement error is less than 0.154% in permittivity and 20.42% in loss tangent. Meanwhile, some experimental summaries on the open resonator technique are provided. Software that controls the measurement system is developed and it improves the testing efficiency greatly.     

Microstrip antenna on a high dielectric constant substrate: BaTiO3 (BTO)-CaCu3Ti4O12(CCTO) composite screen-printed thick films

The performance of microstrip antennas using composite thick films of (BTO-BaTiO₃) and CCTO (CaCu₃Ti₄O₁₂) as a substrate were studied. The dielectric permittivity and loss of (BTO)_x-(CCTO)_1−x thick films with x=0, 0.2, 0.5, 0.8, 0.9, and 1 were examined. These films were prepared in two-layer geometry using the screen-printing technique on Al₂O₃ substrates. Mechanical alloying followed by the solid-state procedure was successfully employed to produce powders of CCTO (CaCu₃Ti₄O₁₂) used in the films. We also studied the films dielectric permittivity (K) and loss (D) in the medium-frequency (MF) range (100 Hz to 1 MHz). The performance of a planar microstrip antenna that uses the (BTO)_x:(CCTO)_1−x thick films as a substrate of high K was also examined in the microwave range of frequencies. From the analysis of the antenna operation of the samples, one can conclude that the higher values of K in the range of 2.5–3.3 GHz antennas is presented by the BTO substrates. For the BTO film, the K value is ∼66 (2.6 GHz) and decreases to 34 for the CCTO film (3 GHz). For the BTO and CCTO films, the antenna bandwidths (BW) are ∼50% and ∼38%, respectively. The higher bandwidth presented by the BTO compared to the CCTO is certainly associated with the higher loss presented by the BTO phase, which is a ferroelectric phase. Therefore, these measurements confirm the potential use of such materials for small microwave planar antennas, where the miniaturization of the devices is crucial.     

Synthesis and Characterization of SrFe<Subscript>11.2</Subscript>Zn<Subscript>0.8</Subscript>O<Subscript>19</Subscript> Nanoparticles for Enhanced Microwave Absorption

SrFe₁₂O₁₉/ZnFe₂O₄ (SrFe_11.2Zn_0.8O₁₉) nanoparticles having superparamagnetic nature were synthesized by coprecipitation of chloride salts using 7.5 M sodium hydroxide solution. The resulting precursors were heat-treated at 900°C and 1200°C for 4 h in nitrogen atmosphere. During heat treatment (HT), transformation proceeds through instantaneous nucleation and three-dimensional diffusion-controlled growth with an activation energy of 175.9 kJ/mole. The hysteresis loops showed an increase in saturation magnetization from 1.044 emu/g to 61.227 emu/g with increasing HT temperature. As-synthesized particles had sizes in the range of 20 nm to 25 nm with spherical shape. Further, these spherically shaped nanoparticles tended to change their morphology to hexagonal plate and pyramidal shape with increasing HT temperature. The effects of this systematic morphological transformation of nanoparticles on dielectric (complex permittivity and permeability) and microwave absorption properties were estimated in the X-band (8.2 GHz to 12.2 GHz). The maximum reflection loss of the composite powder reached −29.81 dB at 10.37 GHz, making it suitable for application in radar-absorbing materials.     

Dielectric Properties in the Microwave Range of K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>NbO<Subscript>3</Subscript> Ceramics

Dielectric properties of a potassium sodium niobate (KNN) system in the microwave range up to GHz have rarely been studied. Since K_0.5Na_0.5NbO₃ is the most common and typical type of KNN materials, non-doped K_0.5Na_0.5 NbO₃ ceramics were synthesized at different temperatures (1080°C, 1090°C, 1100°C, and 1110°C) by a traditional solid reaction method for further characterization and analysis. The ceramics were in perovskite phase with orthorhombic symmetry. A small quantity of second phase was found in the 1110°C sintered specimen, which resulted from the volatilization of alkali oxides as the temperature increased. The complex permittivity was measured for the first time in the microwave range (8.2–12.4 GHz) and in the temperature range from 100°C to 220°C, and the effects of annealing on the dielectric properties were studied. The results indicate that the complex permittivity of KNN ceramics over the microwave range increases mainly due to high bulk density and the additional dielectric contributions of oxygen vacancies at high temperature.     

太赫兹频段基于NR迭代法的复介电常数提取

伴随着6G通信的发展,雷达遥感、检测成像等多个领域向太赫兹频段拓展,获取材料在该频段的介电常数显得愈发重要。本文基于NR迭代法提取了太赫兹频率下样品的复介电常数,分析了迭代法的初值选取对提取结果的影响。在325～500 GHz频段(Y频段)搭建了一套由矢量网络分析仪(VNA)、扩频模块和四抛物面镜组成的8f准光系统,实现散射参数S₂₁的自由空间测量。由电磁波传输模型推导出复介电常数与S₂₁之间的关系式,利用迭代法提取出了特氟龙(Teflon)、丙烯腈-丁二烯-苯乙烯共聚物(ABS)和聚甲基丙烯酸甲酯(PMMA)样品的复介电常数谱,与其他文献报道的结果一致,验证了系统和方法的有效性。     

Characterization of the complex permittivity of brain tissues up to 50 GHz utilizing a two-port microstrip test fixture

Broad-band complex-permittivity values of biological tissues above 20 GHz obtained from direct measurements have not been reported in the literature. This paper presents for the first time the measurement results of complex permittivity of brain grey and white matters from 15 to 50 GHz utilizing a two-port microstrip test fixture. Test fixture S-parameters are simulated employing the finite-element method. To apply the data obtained from the simulation in complex-permittivity extraction, an efficient procedure, using the linear least square technique, is introduced to fit the modeling results to a rational function of complex permittivity, which is similar to the transfer function for a linear system. This fitting procedure is computationally more efficient than the previously developed fitting methods. Measurements are performed on slices of brain sample using a calibrated network analyzer utilizing custom designed through-reflect-line (TRL) calibration standards. The measurements are corrected for the residual errors observed in the measurement results due to the lack of performance repeatability of coaxial-to-microstrip launchers utilized in the TRL calibration standards. Finally, the measured results for brain matters are fitted to a single term Cole-Cole relation representing the dispersion characteristics of white and grey matters up to 50 GHz.     

Effect of oxygen plasma on the properties of tantalum oxide films

The effect of oxygen plasma on the leakage current, permittivity, and the dielectric loss tangent of Ta₂O₅ thin layers (300–400 nm) is studied. It is suggested to treat tantalum oxide films in oxygen plasma to control their electrical and dielectric characteristics.     

A comparison of microstrip models to low temperature co-fired ceramic–silver microstrip measurements

A number of analytical and numerical models for microstrip lines are used for analyzing the propagation loss of CaO–B₂O₃–SiO₂-based low temperature co-fired ceramics (LTCC) subjected to different processing conditions. An optimal microstrip model is identified for the frequency range between 0.5 and 15 GHz and used for the extraction of dielectric loss for this material system. The measurements show that the dominant loss contribution changes from the conductor to dielectric loss as the processing temperature for the LTCC dielectrics is lowered. Comparison with microstructural analysis shows that the increase in dielectric loss is strongly correlated to an increase in the amorphous SiO₂ content in the ceramic matrix.     

Electromagnetic characterization of ceramic material produced with natural zeolite

The aim of this study is to investigate the electromagnetic characterization of ceramic panel produced with natural zeolite via considering the frequency-dependent transmission (T), reflection (R) and absorption (A) coefficients. For this purpose, first of all, frequency-dependent complex dielectric values(dielectric permittivity and tangent loss) of material are measured via LCR meter and complex dielectric values used in three dimensional(3D) electromagnetic simulation tool. Then, Debye parameters such as static permittivity(ε_s), optic permittivity(ε_∞) and relaxation time(τ) are derived by using genetic algorithms. Finally, to validate the simulation results, T, R and A coefficients obtained from simulations are compared with frequency-dependent T, R and A values calculated by using the transmission-line equation.     

Wideband frequency and in situ characterization of ultra thin ZrO2 and HfO2 films for integrated MIM capacitors

High-κ dielectrics are promising candidates to increase capacitor integration densities but their properties depend on manufacturing process and frequency because relaxation and resonance mechanisms occur. Complementary characterization protocols are needed to analyze high-κ insulator behaviour from DC to microwave frequencies. The extraction of Plasma Enhanced Atomic Layer Deposition HfO₂ and ZrO₂ complex permittivity was performed up to 5 GHz using dedicated test vehicles allowing an in situ characterization as a function of dielectric thickness. The measurement procedure was thus validated, highlighting the potentiality of these two dielectrics to cover a wide range of frequencies.     

Structural and optical properties on thulium-doped LHPG-grown Ta2O5 fibres

Structural, spectroscopic and dielectric properties of thulium-doped laser-heated pedestal Ta₂O₅ as-grown fibres were studied. Undoped samples grow preferentially with a single crystalline monoclinic structure. The fibre with the lowest thulium content (0.1 at%) also shows predominantly a monoclinic phase and no intra-4f¹² Tm³⁺ recombination was observed. For sample with the highest thulium amount (1.0 at%), the appearance of a dominant triclinic phase as well as intraionic optical activation was observed. The dependence of photoluminescence on excitation energy allows identification of different site locations of Tm³⁺ ions in the lattice. The absence of recombination between the first and the ground-state multiplets as well as the temperature dependence of the observed transitions was justified by an efficient energy transfer between the Tm³⁺ ions. Microwave dielectric properties were investigated using the small perturbation theory. At a frequency of 5 GHz, the undoped material exhibits a dielectric permittivity of 21 and for thulium-doped Ta₂O₅ samples it decreases to 18 for the highest doping concentration. Nevertheless, the dielectric losses maintain a very low value.     

Theoretical and Experimental Investigation of a Ka-band Gyro-TWT with Lossy Interaction Structure

The stability analysis of a Ka-band gyrotron traveling-wave tube amplifier (gyro-TWT) operating in the circular TE₀₁ mode at the fundamental cyclotron harmonic is presented. The small signal linear theory is used to analyze the amplification of operation mode and oscillation of parasitic modes. The optimum dielectric parameters including loss layer thickness and permittivity are given. Propagation loss of operation mode is 3 dB/cm with the thickness of loss layer d = 0.7 mm and relative permittivity ξ″ = 11−6j, and propagation loss per unit length of parasitic modes TE₁₁, TE₂₁, TE₀₂ at each oscillation frequency (24.85 GHz, 27.85 GHz, 61.2 GHz) is 2.5 dB/cm, 6 dB/cm, 7.5 dB/cm, respectively, sufficient to suppress oscillations of operation and parasitic modes. Taking advantage of the optimized parameters of loaded dielectric, a high gain scheme has been demonstrated in a 34-GHz, TE₀₁-mode gyro-TWT, producing 160 kW saturated output power at 40 dB stable gain and 22.8% efficiency with a 3-dB bandwidth of 5%.     

New dielectric material system of Nd(Mg1/2Ti1/2)O3–CaTiO3 at microwave frequency

The microwave dielectric properties of (1 − x)CaTiO₃–xNd(Mg_1/2Ti_1/2)O₃ (0.1  x  1.0) ceramics prepared by the conventional solid state method have been investigated. The system forms a solid solution throughout the entire compositional range. The dielectric constant decreases from 152 to 27 as x varies from 0.1 to 1.0. In the (1 − x)CaTiO₃–xNd(Mg_1/2Ti_1/2)O₃ system, the microwave dielectric properties can be effectively controlled by varying the x value. At 1400 °C, 0.1CaTiO₃–0.9Nd(Mg_1/2Ti_1/2)O₃ has a dielectric constant (ε_r) of 42, a Q × f value of 35 000 GHz and a temperature coefficient of resonant frequency (τ_f) of −10 ppm/°C. As the content of Nd(Mg_1/2Ti_1/2)O₃ increases, the highest Q × f value of 43 000 GHz for x = 0.9 is achieved at the sintering temperature 1500 °C.     

Millimeter-wave measurements of the complex dielectric constant of an advanced thick film UV photoresist

The first measurement of the relative permittivity (ε_r) and loss tangent (tan δ) of EPON™ SU-8 advanced thick film ultraviolet photoresist is reported at frequencies between 75–110 GHz (W-band). The problems associated with such a measurement are discussed, an error analysis given, and values of ε_r=1.725±0.08 and tanδ =0.02±0.001 are determined.