Determination of Complex Permittivity of Arbitrarily Dimensioned Dielectric Modules at Microwave Frequencies

A method of evaluating the microwave dielectric properties of any geometrically defined sample is described by general theory and through experimental verification. The typical mathematical relations that describe specimen loss tangent by cavity methods are uniquely modified through inclusion of the derivative of cavity resonant frequency with respect to dielectric constant of the material comprising the particular configuration studied. The dielectric modules under study need not meet the small volume requirements demanded by perturbation theory; they may even occupy a very large volume of the cavity. A particular advantage of the described evaluation technique is the continuity of use of a given dielectric specimen for tests at microwave frequencies, without geometric alteration, after its properties at lower frequencies have been determined.     

Modeling of Vegetation Permittivity at Microwave Frequencies

When materials are to be treated with microwaves for different purposes such as drying, online moisture measurements, disinfestation, and remote sensing, thorough knowledge of the material dielectric properties becomes extremely important. Unlike for other materials, measurement of vegetation dielectric properties is very complicated due to the nature of the materials themselves. Hence, vegetation dielectric models that require fewer accurately and easily measurable physical quantities are of great importance. Therefore, dielectric models that only require the measurement of moisture content (MC) have been investigated for alfalfa, a plant material that has high commercial value in national and international markets. The models were developed by measuring the dielectric properties by using an open-ended coaxial probe at frequencies ranging from over 300 MHz to 18 GHz at 22 degC and at an MC ranging from 12% to 73% in wet basis     

Complex Permittivity Instrumentation for High-Loss Liquids at Microwave Frequencies (Short Paper)

This note draws attention to the fact that the instrumentation system for the measurement of the complex permittivity of high-loss liquids proposed by Zanforlin can be improved so as to i) increase the sensitivity and stability of the demodulation process, ii) make the demodulation accurately linear rather than approximately square law, and iii) improve the degree of bridge balance and stability.     

低耗液体材料微波复介电常数的准确测试技术

本文提出了一种低耗液体材料微波复介电常数测试技术，利用一腔多模的ＴＥＯｍｎ高Ｑ圆柱测试腔，可对低耗液体材料的ε′γ和ｔａｎδ进行准确地测量．测试ε′γ的不确定度为±０．５％，ｔａｎδ的不确定度为±５．８％，且在一定频带范围内考察了ε′γ和ｔａｎδ３随频率变化特性。该技术测试简便、迅速、自动化程度高，可适用于多种低耗液体材料的测试。     

New Measuring Apparatus for Complex Permittivity at Millimeter-Wave Frequencies

A dielectric rod resonator excited by a nonradiative dielectric waveguide is used for measuring complex permittivity of low loss dielectric materials. The complex permittivties of single crystal sapphire, polycrystalline Ba (Mg_1/2 W_1/2) O₃ and Mg₂ Al₄ Si₅ O₁₈ (cordierite) have been obtained at 60 and 77 GHz by the new apparatus. The first time the measurement results of complex permittivity of brain grey and white matters from 15 to 50GHz utilizing a two-port microstrip test fixture is presented. S-parameters of Test fixture are simulated employing the finite-element method. 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 (68-118 GHz) frequency for specimens with a large range of absorption values, including highly absorbing specimens that otherwise would not be possible.     

An Approach to Permittivity Determination at Microwave Frequencies Through the Eigenvalue Problem

A simple method of solving the inverse medium problem in order to determine the complex dielectric constant of a lossy dielectric material at microwave frequencies is presented. The arbitrarily shaped dielectric sample placed in a rectangular waveguide is considered. Electromagnetic fields in the waveguide are expanded in series of harmonic functions. A set of linear equations is obtained using the finite–difference technique. An additional empirical condition, which is related to the measured reflection and/or transmission coefficients and results in an overdetermined system, is added and then the system is defined by the addition of a trivial extra parameter. The sample's dielectric properties are obtained by solving the resulting eigenvalue problem. An algorithm to extract proper results from the set of eigenvalues is defined by considering the properties of numerical solution. The system is tested by using an alternative method.     

改进矩形腔微扰法测试微波电介质复介电常数

本文讨论了测试电介质微波复介电常数的矩形腔微扰法。对介质样品加载后的ＴＥ１０ｎ模矩形腔腔内场进行了理论分析。通过对腔内场的数值求解，得出了与微扰公式相似的、已修正的准确计算公式。     

Measurements of Permittivity, Dielectric Loss Tangent, and Resistivity of Float-Zone Silicon at Microwave Frequencies

The complex permittivity and resistivity of float-zone high-resistivity silicon were measured at microwave frequencies for temperatures from 10 up to 400 K employing dielectric-resonator and composite dielectric-resonator techniques. At temperatures below 25 K, where all free carriers are frozen out, loss-tangent values of the order of 2times10^-4 were measured, suggesting the existence of hopping conductivity or surface charge carrier conductivity in this temperature range. Use of a composite dielectric-resonator technique enabled the measurement of materials having higher dielectric losses (or lower resistivities) with respect to the dielectric-resonator technique. The real part of permittivity of silicon proved to be frequency independent. Dielectric losses of high-resistivity silicon at microwave frequencies are mainly associated with conductivity and their behavior versus temperature can be satisfactory described by dc conductivity models, except at very low temperatures     

Permittivity Measurements of Lossy Liquids at Millimeter-Wave Frequencies

A measurement system is described which allows the determination of the complex permittivity of high-loss liquids at millimeter waves. Basically, the setup consists of a waveguide interferometer whose unknown arm embodies a liquid holder irradiated by an open-ended rectangular waveguide. The sample thickness is varied by means of a piston driven by a micrometer screw. The bridge output then is read as a function of the liquid thickness. Best fitting between experimental and computed data through a suitable model of the system enables the permittivity to be determined. The system can operate, with high sensitivity, over the whole frequency range of the dominant mode propagating in the waveguide setup employed. System performance is described through a set of experimental results obtained on ethanol, methanol, and pure water at 20° C and 70 GHz.     

Television Broadcasting at Microwave Frequencies

Over 125 Multipoint Distribution Service (MDS) transmitting stations have been constructed over the past seven years. Each of these stations is equivalent to a low power television broadcast station operating on a microwave frequency at approximately 2,150 MHz. The problems encountered in the design and construction of an MDS station differ markedly from a VHF or UHF television station. The propagation characteristics, likewise, are significantly different than for either UHF or VHF frequencies. The solution to the problem of effective coverage and reception throughout a service area requires innovative designs and techniques, and these are described.     

Duplexing Systems at Microwave Frequencies

The paper reviews the various methods of duplexing at microwave frequencies. General principles, including the use of passive and solid-state devices, are first discussed. The characteristics of gaseous-discharge duplexing tubes of both self- and externally-excited types are examined and data for typical examples given. The various arrangements of discharge tube duplexers and methods of measuring their performance are described. The survey concludes with a bibliography.     

聚合物薄片的复介电常数微波测量方法

提出了一种在微波频域测量聚合物样品薄片复介电常数的方法,它利用自动测量线测试系统测量出电压驻波比和相角,然后采用级数各阶次展开方法,由反射系数推导出复介电常数.级数低阶次方法求解厚度较大的被测样品复介电常数时,为确保结果具有较高的精确度,要求测量频率不超过1.5GHz.为了克服这种测量频域的局限性,可采用级数高阶次展开方法来求解复介电常数.用级数展开方法测量聚苯乙烯、多乙酸乙烯酯和聚亚胺酯的复介电常数值,结果与真实值相近,可以和传输/反射法相媲美.     

Carrier Pulses at Microwave and Millimeter-Wave Frequencies

This paper discusses some recent experimental results obtained using special gallium arsenide point-contact diodes for the generation of phase-locked carrier pulses in the microwave and millimeter-wave bands. Several methods of generating such pulses are described. 11.2-Gc microwave phase-locked carrier pulses of about 1.0-nanosecond base duration have been generated at a 160-megabit/second rate. These microwave pulses, which are generated directly from a baseband signal, normally have peak power levels in excess of 0.5 mw. Millimeter-wave phase-locked carrier pulses have also been generated at 56 Gc. These very high frequency pulses have a base duration as short as 0.25 nanosecond and occur at a 160-megabit/second rate. Furthermore, phase-locked carrier pulses have been generated at frequencies as high as 89.6 Gc. A simple method of generating nonphase-locked 0.3-nanosecond millimeter-wave carrier pulses directly from 1.92 gigabit/second rate baseband pulses has also been investigated. The experimental arrangement used to demonstrate the "turn on" and "turn off" principle of transient carrier pulse generation is described.     

Biological Tissues Characterization at Microwave Frequencies

The present work is concerned with the measurement of dielectric permittivity and conductivity of various high loss tissues from freshly sacrificed animals. The measurement makes use of the 'infinite sample' technique which involves mounting of the sample in a rectangular waveguide system excited in the TE/sub10/ mode at 9.4 GHz. A more complex system consisting of skin-fat-muscle combination is also studied. An evacuation of relaxation times is made in all the cases. It is hoped that these data will be relevant in further quantifying the available results in this frequency range.     

Power and Area-Efficient Adaptive Equalization at Microwave Frequencies

We present a low power analog adaptive equalization technique suitable for combating inter-symbol-interference at very high data rates. The proposed technique, which we term the lumped parameter equalizer, addresses several of the problems associated with conventional microwave equalizers based on the tapped delay line structure. The theory is given, and simulation results comparing it with the performance of ideal tapped delay line filters are shown. Circuit implementations are discussed, along with the effect of nonidealities on equalizer performance.      

A Sensitive Method for Measuring Complex Permittivity with a Microwave Resonator

The proposed method was carried out to make easier dielectric studies em powders under controlled pressure when the frequency varies. A TE/sub 01n/-mode resonator is needed. The substance under test is contained in a tube of quartz, placed along the axis of a cylindrical cavity. The mathematical formulation for the complex permittivity is given in rigorously accounting for the presence of the tube. Typical ditticulties are discussed, and experimental results given. The absolute precision of the measurement can be compared with that of the classicrd method (/spl plusmn/2 percent for /spl epsi/' and /spl plusmn/ 10 percent for /spl epsi/'). The greatest error arises from an insufficiently precise determination of the geometrical and electrical characteristics of the quartz tube. This error is systematic, and thus it is possible to demonstrate the very small permittivity variations (/spl plusmn/ 0.3 percent for /spl epsi/' and /spl plusmn/ 5 percent for /spl epsi/').     

Ferrites with Planar Anisotropy at Microwave Frequencies

Materials with an easy plane of magnetization (planar anisotropy) have recently been discovered. The large anisotropy field that tends to keep the magnetization in the easy plane reduces the field required to cause ferromagnetic resonance, which makes the material promising for microwave applications. Equations are derived for the susceptibility, taking into account losses and a finite medium. Propagation in a longitudinal and transverse static field is considered. The location of a slab in a rectangular waveguide for minimum loss in the forward direction, and the use of the material as a phase shifter, are discussed. Experimental microwave data on some materials are given, and also data on an isolator and phase shifter incorporating these materials.     

Nonlinearities in Metal Contacts at Microwave Frequencies

Generation of intermodulation products arising from nonlinearities at metal-to-metal contacts for microwave frequencies has been investigated. Detailed studies concentrated on the intermodulation products generated at contacting faces between both similar and dissimilar metals, and included contact materials of copper, beryllium-copper, brass, oxygen-free nickel, mild steel, stainless steel, aluminium, and twelve home-made steels with various compositions. The surface properties of the materials were found to be of prime importance. Measurements were carried out at frequencies around 1.5 GHz. The variations of the 3rd- and 5th-order intermodulation product levels with power levels of the fundamental signals and with the axial force applied to the contact were studied.