Calibration of the standard ratio devices of integrated standards at rf and microwave frequencies

The results are given of developments and investigations of an automated apparatus for calibrating attenuators in the frequency range 10 MHz to 18 GHz for use as working attenuation standards. It is shown that automated apparatus for calibrating microwave wattmeters is suitable for calibrating coaxial fixed and stepped attenuators with an error of lower than ±0.02 dB per 10 dB. Translated from Izmeritel'naya Tekhnika, No. 5, pp. 45–48, May, 1997.     

Automatic material characterization at microwave frequencies

An instrument was assembled to measure complex permittivity at microwave frequencies in an efficient, inexpensive manner. It bridges the gap between traditional, tedious methods of characterization and expensive vector network analyzer techniques. A microcomputer is used to control the operation of a scalar network analyzer. Measurements of the magnitude of the reflection and transmission coefficients are automatically made as a function of frequency and temperature over a range of 2-18 GHz. A theory is developed covering the different regimes of operation: the thin sample, the multiple reflecting sample, and the high insertion loss sample. Sample thickness criteria for accurate measurements are reported. Results are presented for dielectric and semiconductor samples     

Electrical properties of films at microwave frequencies

A technique suitable for the measurement of electrical properties of films/sheets at microwave frequencies has been described. Groups of materials are identified for which the absence of any kind of electrodes in these microwave measurements can be utilised with advantage. Results are presented for a variety of materials such as metal films, superionic conductors, semiconductors and insulating polymers.     

Dielectric measurements on PWB materials at microwave frequencies

In quest of finding new substrate for printed wiring board (PWB) having low dielectric constant, we have made PSF/PMMA blends and evaluated the dielectric parameters at 8.92 GHz frequency and at 35°C temperature. Incorporating PMMA in PSF matrix results in reduced dielectric constant than that of pure PSF. The dielectric parameters of pure PMMA and PSF films of different thicknesses have also been obtained at microwave frequencies. We have used dielectric data at microwave frequencies as a tool to evaluate optical constants, absorption index ‘K’ and refractive index ‘n’. The blends of PSF/PMMA may be used as base materials for PWBs.     

Using a microwave multimeter as a microwave voltage standard

It is shown that because of its ability to measure with high accuracy the power and complex impedance in waveguide channels with a known characteristic impedance, a microwave voltmeter can be used as a precision standard of radio-frequency electrical voltage.Translated from Izmeritel'naya Tekhnika, No. 6, pp. 46–47, June, 1995.     

Metal slits and liquid crystals at microwave frequencies

While the use of liquid crystals (LCs) over the visible region is ubiquitous in flat-screen displays, there has been little by the way of applications at other wavelengths. Specifically, notwithstanding the continuing permittivity anisotropy to be found at longer wavelengths, there has been virtually no development in the microwave domain. This is largely due to the fact that scaling up the micrometer-thick LC layers used for visible radiation to millimetre dimensions is seen as impractical. In this study, it is shown how, using thin slits in metal structures, a completely new generation of LC devices for use at microwaves may be realized. Such structures include slatted metal Fabry-Perot resonators, beam-steering devices, thin flexible voltage tunable filters and even cascade structures with strongly enhanced and reshaped microwave fields.     

Quantum amplifiers at microwave frequencies using Josephson junctions

Abstract

Josephson junctions are quantum mechanical devices with sinusoidal nonlinearity and their use as amplifiers of non-classical microwaves in cavities at low temperatures, is discussed. Self-pumped amplifiers as well as externally pumped three- and four-photon amplifiers are considered, and a quantum theory that describes their operation is developed. It is shown that the sinusoidal nonlinearity can be expanded into a series of terms, the first few of which are familiar from quantum optical amplifiers that use nonlinear optical materials, while the others are higher order corrections.     

Magnetodielectric composite with ferrite inclusions as substrates for microstrip patch antennas at microwave frequencies

A study has been conducted to estimate the complex permittivity and permeability along with magnetic characterization of different volume fractions of magnetodielectric composites with cobalt ferrite nano inclusions. Using an in touch superstrate technique dielectric properties are estimated. Cavity perturbation technique is used to study the complex permeability of the samples. 4πM_s value and coercivity is measured using vibrating sample magnetometry. Structural and surface morphologies on the composite samples are conducted to determine the size and homogeneous distribution of nano inclusions. The average grain size of cobalt ferrite nanoparticles is found to be ～10 nm. The real part of permittivity and permeability of the samples varies from ～1–2.905 to ～1.01–1.05 with increase in inclusion content from 1% VF to 5% VF, respectively. The tan δ of permittivity and imaginary part of permeability is found to be of the order of ～10^?3 and ～10^?1 respectively. Verification of these composites as potential substrates for microstrip patch antenna is carried out by fabricating simple rectangular patch at 9.5 GHz using transmission line model. Rectangular patch is designed on 5% VF composite system. The return loss for the composite system was found to be ～?19.451 dB which is comparable with that designed on standard glass epoxy substrate (?_r = 4.5).     

Dielectric properties of conducting polymer composites at microwave frequencies

The dielectric properties of conducting polymer composites containing polypyrrole (PPy) crushed films, PPy powder, polyaniline (PAn) base and acid powders as the dispersants and silicone rubber and vinyl ester as matrix materials have been investigated in the frequency range 2-18 GHz. The dielectric parameters such as the real part, , and imaginary part, , of the permittivity and loss tangent, tan, increase with increasing conductivity and concentration of the dispersant. The geometrical shape of the dispersant governs the ability of conductive network formation which is indicated by a large drop in the resistivity of the composite. Also, dispersant/matrix interactions and physical properties of the matrix influence the agglomeration of the dispersant phase which, in turn, affects the dielectric properties of the composites. Flakes of PPy obtained by crushing highly conductive films and large PAn powder aggregates were unable to form a conducting network. The composites without a network of dispersant exhibit low dielectric parameters. On the other hand, high values of tan ranging from 0.7–1.1 were achieved for the PPy powder (15 parts)/silicone rubber composites where a conducting network was observed.     

Some properties of nickel-coated carbon fibre-polypropylene composite at microwave frequencies

Some properties of nickel-coated carbon fibre-polypropylene composite are considered at microwave frequencies in the range 8 to 12 GHz. The paper presents the measured values of the insertion and return losses and the equivalent input impedance in the above frequency band. Measurements were performed on composite material for different nickel-coated fibre concentrations of 0, 5, 10, 16 and 28 wt%. The filler effects shows a transition region and identifies the dependency of the electrical properties on these concentrations. Furthermore, shielding effectiveness is calculated for the given concentrations and it is found that its value could reach more than 30 dB over the whole frequency band for a specimen of 2.6 mm thickness and with 28 wt% concentration.     

Measurement of dielectric properties of high-absorption materials at microwave frequencies

A method is proposed for measuring the dielectric constant ε′ and dielectric loss ε″ of high-absorption dielectric materials by measuring the reflection of electromagnetic radiation with the aid of an adjustable quarter-wave matching plate of nonabsorbing material close to the dielectric surface. Translated from Izmeritel'naya Tekhnika, No. 5, pp. 45–47, May, 1999.     

Low temperature microwave characterisation of lithium fluoride at different frequencies

Precise knowledge of dielectric properties of materials is required to implement the material in high frequency devices and circuits. At microwave frequencies complex permittivity (dielectric constant and loss tangent) are the two mandatory parameters prior to any design. We have identified Lithium Fluoride as a potential candidate, which can be used in conjunction with superconducting and non-superconducting parts of several microwave communication devices. Even though dielectric constant of LiF is known at room temperature there only limited data presented at cryogenic temperatures. We have used a dielectric post resonator for the microwave characterisation of the rod shaped LiF crystal. In this paper, we have reported the dielectric constant (perpendicular component of the real part of complex permittivity) and loss tangent of two LiF crystals as a function of temperature (15–290 K) at frequencies of 8 and 16.5 GHz. We have also studied and reported the temperature coefficient of frequency and permittivity. The concept of using temperature coefficient of frequency as a standard is proved to be wrong in this paper. Microwave properties of other Fluorides are also compared with the LiF crystal.     

低频矢量声场建模及其应用研究

浅海近距离矢量声场携带了丰富的信息可以用来识别目标。采用射线理论对浅海低频矢量声场进行建模,并且分析了该模型在浅海或深海低频时的适用性。经过与波动理论的比较,说明该模型仅是矢量声场传播损失的简单近似。通过分析浅海声压场的特性,提出了一种目标运动参数估计的方法,海试数据分析说明了其有效性。近距离目标辐射的低频宽带噪声通过浅海声场后,在LOFAR图上形成双曲线干涉条纹。运用图像处理中边缘提取的常用方法——Hough变换,提取双曲线参数,可以得到运动目标的航速、航深及距离的信息。     

Measurement of electromagnetic parameters of materials at radio and microwave frequencies

Translated from Izmeritel'naya Tekhnika, No. 9, p. 11, September, 1994.     

Broadband magneto-dielectric response of particulate ferrite polymer composite at microwave frequencies

Complex permittivity and permeability of a magneto-dielectric composite material is studied using shielded, conductor-backed coplanar waveguide technique over X-band. The propagation constant over the test frequency range is evaluated using element-to-element correspondence of the ABCD matrix computed from scalar scattering parameters without modifying the coplanar structure. The mathematical formulation is verified by performing permittivity and permeability measurements for air over the range 9.5–12.045 GHz. Nano-sized nickel ferrite particles was synthesized using co-precipitation technique at different sintering temperatures. Average crystallite diameter is found to be 6.63–17.55 nm. The composite with 2% and 4% volume fractions is fabricated by reinforcing 6.63 nm ferrite particles in low density polyethylene matrix. The complex permittivity and permeability of the composite obtained from this method are also verified with cavity perturbation technique. The composite shows low saturation magnetization of 1.8745 emu/g and reduced hysteresis loss at room temperature.