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Wireless functionality is essential for the implementation of wearable systems, but its adaptation in stretchable electronic systems has had limited success. In this paper, the electromagnetic properties of stretchable serpentine mesh-based systems is studied, and this general strategy is used to produce high-performance stretchable microwave systems. Stretchable mechanics are enabled by converting solid metallic sections in conventional systems to subwavelength-scale serpentine meshes, followed by bonding to an elastomeric substrate. Compared to prior implementations of serpentine meshes in microwave systems, this conversion process is extended to arbitrary planar layouts, including those containing curvilinear shapes. A detailed theoretical analysis is also performed and a natural tradeoff is quantified between the stretching mechanics and microwave performance of these systems. To explore the translation of these concepts from theory to experiment, two types of stretchable microwave devices are fabricated and characterized: a stretchable far-field dipole antenna for communications and a stretchable midfield phased surface for the wireless powering of biomedical implanted devices. [ABSTRACT FROM AUTHOR]

In this paper, we consider the problem of obtaining a reduced-dimension parameterization of a propagation medium for the purpose of estimating the medium from transmission data. The application addressed is microwave remote sensing of tropospheric index-of-refraction profiles over the sea surface, using radar clutter returns. The proposed parameterization balances the desire to represent features prominent in the a priori statistics of the profiles versus the need to capture elements of the profile that significantly affect the observed clutter data. In linear estimation problems, basis vectors for the unknown parameter vector that optimizes this tradeoff have been derived as the reduced-rank Wiener filter or, equivalently, the generalized Karhunen-Loeve transform (GKLT). In this paper, we reinterpret the linear result, producing an extension to the nonlinear refractivity estimation problem. The resulting procedure produces basis vectors for tropospheric refractivity that are less dependent on features that have little effect on the clutter measurements. This results in a more efficient parameterization and reduces mean-square estimation error relative to an approach driven purely by the statistical prior. Application of the generalized KL technique to finding efficient basis vectors for refractivity profiles taken off the southern California coast is presented. [ABSTRACT FROM AUTHOR]

The congruential rule advanced by Graves for polarization basis transformation of the radar backscatter matrix is now often misinterpreted as an example of consimilarity transformation. However, consimilarity transformations imply a physically unrealistic antilinear time-reversal operation. This is just one of the approaches found in the literature to the description of transformations where the role of conjugation has been misunderstood. In this paper, the different approaches are examined, particularly in respect to the role of conjugation. In order to justify and correctly derive the congruential rule for polarization basis transformation and properly place the role of conjugation, the origin of the problem is traced back to the derivation of the antenna height from the transmitted field. In fact, careful consideration of the role played by Green's dyadic operator relating the antenna height to the transmitted field shows that, under general unitary basis transformation, it is not justified to assume a scalar relationship between them. Invariance of the voltage equation shows that antenna states and wave states must in fact lie in dual spaces, a distinction not captured in conventional Jones vector formalism. Introducing spinor formalism and with the use of an alternate spin frame for the transmitted field, a mathematically consistent implementation of the directional wave formalism is obtained. Examples are given comparing the wider generality of the congruential rule in both active and passive transformations with the consimilarity rule. [ABSTRACT FROM AUTHOR]

The development of protection circuits against a variety of electromagnetic disturbances is important to assure the immunity to interferences of an electronic system. In this paper protection elements which were investigated under UWB conditions are now to be tested with HPM signals to achieve a comprehensive protection. [ABSTRACT FROM AUTHOR]

This paper presents an examination of classical scattering models for radar cross sections of deciduous leaves, such as the generalised Rayleigh-Gans (GRG) model and the physical optics (PO) model. The PO model employs the resistive sheet approximation in this study. The validity regions of the analytical models for microwave scattering from deciduous leaves are investigated by comparison with the precise numerical results of the method of moment. It was found that the GRG and PO models extend their validity regions for estimating the scattering amplitudes as the thickness of a lossy dielectric disk decreases. The GRG and PO models can be used alternatively for computing the scattering matrices of natural deciduous leaves at microwave frequencies regardless of the size of the leaves, because of the very small thickness of the leaves (0.2–0.4 mm). [ABSTRACT FROM AUTHOR]

One of the goals of the Global Precipitation Measurement project, the successor to the Tropical Rainfall Measuring Mission (TRMM), is to produce a 3-hourly global rainfall map using several spaceborne microwave radiometers. It is important, although often difficult, to classify radiometer observations over land as either “rain” or “no rain” because background land surface conditions change significantly with time and location. In this study, a no-rain brightness temperature database was created to infer land surface conditions using simultaneous observations by TRMM Microwave Imager (TMI) and precipitation radar (PR) with a resolution of 1 month and 1° latitude × 1° longitude. This paper proposes new rain/no-rain classification (RNC) methods that use the database to determine the background brightness temperature. The proposed RNC methods and the RNC method developed for the Goddard profiling algorithm (GPROF; the standard rain-rate retrieval algorithm for TMI) are applied to all TMI observations for the entire year of 2000, and the results are evaluated against the RNC made by PR as the “truth.” The first method (M1) simply uses the average brightness temperature at 85-GHz vertical polarization [denoted as TB (85 V)] under no-rain conditions as the background brightness temperature at 85-GHz vertical polarization [denoted as TBe (85 V)]. The second method (M2) uses a regression equation between TB (85 V) and TB (22 V) under no-rain conditions from the database. Here, TBe (85 V) is calculated by substituting the observed TB (22 V) into the regression equation. The ratio of accurate rain detection by GPROF to all rain occurrences detected by PR was 59%. This ratio was 57% for M1 and 63% for M2. The ratio with the weight of the rain rate was 81% for M1 and 86% for M2; it was 80% for GPROF. These comparisons were made by setting a threshold using a constant coefficient k0 to make the ratio of false rain detection to all no-rain occurrences detected by PR almost the same (approximately 0.85%) for all three methods. Further comparisons among the methods are made, and the reasons for the differences are investigated herein. [ABSTRACT FROM AUTHOR]

Microwave imaging for breast cancer detection is based on the contrast in electrical properties of healthy fatty breast tissues and malignant tumors. This inherent contrast causes microwave reflections from tumors embedded in normal tissues. Radar-based breast imaging detects tumors by observing variations in microwave signals reflected from the tumors as the antenna location changes. The topics of this paper are the development of a compact antenna for the detection of cross-polarized reflections and the application of this antenna to radar-based breast cancer detection. The antenna is designed, simulated, constructed and measured. The capabilities and limitations of the antenna for detecting tumor models are investigated through simulation and experiments, demonstrating the potential of this method for the detection of tumors in the breast. [ABSTRACT FROM AUTHOR]

For safe driving in vehicles, an understanding of the surroundings by radar and information exchange with nearby vehicles by communication are considered to be necessary. We propose an intervehicle communication and ranging system that uses the spread spectrum system known as a boomerang transmission system to simultaneously communicate and range by carrying information on the radar waves. Pseudo-noise (PN) codes are used in a spread spectrum system, but since the number is limited, assigning a unique PN code to all of the vehicles is difficult, and codes must be reused. When multiple terminals temporarily use the same code at the same location because of the hidden terminal problem, severe interference occurs and the reliability of the communication and ranging is greatly damaged. Therefore, in this paper, a boomerang transmission system is proposed where code hopping eases the limitation on the number by switching multiple PN codes. Simulations verify the communication and ranging capabilities even when the desired wave and the interference wave use the same PN code sets for three systems: the slow-code-hopping boomerang transmission system (SCH), the fast-code-hopping boomerang transmission system (FCH), and the adaptive-code-hopping boomerang transmission system (ACH) with code collision avoidance. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 88(5): 50–60, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20078 [ABSTRACT FROM AUTHOR]

The major part of inconsistencies in the description of the mechanism of formation of nonhalide silver clusters under exposure to light is due to the lack of quantitative data on electronic-ionic processes in microdispersed silver halide systems. The use of the microwave photoconductivity technique partially fills the gap. The drift mobility of holes and electrons in powdered AgBr (0.8 and 60 cm2 V−1 s−1, respectively) and of electrons in powdered AgCl (40 cm2 V−1 s−1) and the rate constants of the recombination of localized electrons and free holes in powder AgBr (1.4 × 10−7 cm3 s−1) and of free electrons and holes in AgBr and AgCl (1.5 ± 0.5) × 10−11 and 2 × 10−12 cm3 s− 1, respectively) were determined. The range of the depth of traps formed by treatment with aqueous solutions of sodium thiosulfate in AgCl (0.45–0.63 eV) and by preliminary exposure of AgCl and AgBr grains (0.4 and 0.25–0.36 eV, respectively) was estimated. The rate constant of the hole capture by the centers formed by introducing AgI (7 × 10−9 cm3 s−1) was determined, and the lifetime of the Ag atom (10−4 s) was estimated. The paper summarizes the results obtained. [ABSTRACT FROM AUTHOR]

This paper considers new possibilities of turbulence intensity retrieval by using Doppler and Doppler-polarimetric radar sounding. Peculiarities of microwave scattering on moving droplets of different size and shape underlie new methods that are introduced, discussed, and checked by using radar data. [ABSTRACT FROM AUTHOR]

Wideband and ultrawideband (UWB) technologies have achieved: notable progress in recent years, aided immeasurably by improvements in solid-state manufacturing, computers, and digitizers. As a result, wideband systems that were difficult or impossible to implement ten years ago are now being built for an increasingly wide variety of applications including transient radar, concealed object detection, mine clearing, pipeline inspections, archeology, geology, electronic effects testing, and communication. In this paper, we discuss current wideband source technology around the world as well as laboratory and test facilities. We also will briefly touch on frequency limitations of anechoic chambers, design of transmission line simulators, frequency regulation requirements for outdoor ranges, and personnel exposure limits. [ABSTRACT FROM AUTHOR]

Current amplifier research at the Naval Research Laboratory Vacuum Electronics Branch emphasizes techniques to extend the bandwidth and average power capability of gyro devices for millimeter wave radar applications. This paper will discuss the implementation of a wideband high-gain gyro-traveling wave tube amplifier design, with a measured peak output power of 78 kW, gain ∼60 dB, and a 3-dB bandwidth of 4.2 GHz (12%) at 52 kW in Ka -band. The 3-dB saturated bandwidth at 70 kW is 6 GHz (17%), which is also the instantaneous bandwidth with appropriately tailored input power (e.g., gain equalizer). The amplifier operates in the TE11 mode and for stabilization employs a high -average power compatible diffractive loading technique. [ABSTRACT FROM AUTHOR]

In this paper, the phenomenology of wave propagation through foliage and forest ground reflectivity is investigated for assessing the feasibility of foliage-Covered target detection at millimeter-wave frequencies. An experimental procedure for simultaneous measurements of foliage attenuation and ground reflectivity is outlined. This measurement procedure is implemented for two different tree stands, one mostly coniferous and the other deciduous, using a nadir-looking, high-resolution, 35-GHz radar positioned above the tree canopy. Statistics of the two-way attenuation and ground reflectivity for these two well-characterized stands are derived. Strong spatial and angular fluctuations in the two-way foliage attenuation coefficient are observed. The mean, standard deviation, and median of the measured two-way attenuation factor at Stand 1 (mostly coniferous trees with 0.140 trees/m² stocking density and 45.45 Kg/m² green biomass) are -25.4, -18.3, and -48.2 dB, respectively, while the mean, standard deviation, and median of the measured two-way attenuation factor at Stand 2 (deciduous trees with 0.1055 trees/m² stocking density and 30.90 Kg/m² greenbiomass) are -15.4, -12.7, and -33.6 dB,respectively. The mean attenuation rates of Stand 1 and Stand 2, derived from the measured two-way attenuation factor, are 0.40 and 0.24 Np/m, respectively. Only a small percentage of the data had two-way foliage attenuation values exceeding 70 dB. The mean, standard deviation, and median of the power reflectivity of the forest floor at Stand 1 are -14.2, -11.0, and -21.1 dB, respectively, while for Stand 2, the same statistical measures are -16.0, -14.3, and -22.2 dB, respectively. The results demonstrate the potential for using MMW nadir-looking radars for the detection of targets underneath foliage-cover. [ABSTRACT FROM AUTHOR]

This paper describes the design, implementation, and characterization of a high-efficiency 10-GHz amplifier with dynamic drain bias control that maintains high efficiency over a range of output power levels. The power amplifier (PA) operates in class-E switched mode with 67% drain efficiency at an output power of 20.3 dBm, 0.7 dB less than the specified maximum power for the device. A coupler and detector at the output of the PA provide a feedback signal to the drain-bias controller based on a 96% efficient Buck dc-dc converter. When compared with a PA with constant drain bias (4 V), the average efficiency of the PA with dynamic biasing is improved by a factor of 1.4. Over an output power between 15-20 dBm, the drain bias varies from 2 to 4 V, and the efficiency improves from 22% to 65% at the lower power level. The efficiency includes the losses in the dc-dc converter. [ABSTRACT FROM AUTHOR]

For the image reconstruction of the snow search radar based on the principle of multifrequency holography method, the values of the relative permittivity of snow to be interrogated are needed. Since the relative permittivity of snow changes by various factors, it was necessary to measure it by some means at the same time as the search. The relative permittivity of the snow with low water content which is the medium of the snow search radar has a strong correlation with the density of the snow. Hence, the relative permittivity was estimated by measurement of the density in the past. To eliminate such a procedure, it is necessary to estimate the relative permittivity of the snow from the multifrequency hologram which comprises the data obtained by the snow search radar. In the multifrequency hologram, the information along the frequency axis and that on the azimuth axis are recorded independently. In addition, the distance information in each axis varies in the direction opposite to that of the change of relative permittivity. This property was used for automatically estimating the relative permittivity of snow by discriminating the focusing of the reconstructed image. In this paper, a method is presented for estimating the relative permittivity of snow from the data of the snow search radar. The results are given for processing of actual data. [ABSTRACT FROM AUTHOR]