The combination of the unique properties of graphene with new device concepts and nanotechnology can overcome some of the main limitations of traditional electronics in terms of maximum frequency, linearity, and power dissipation. In this letter, we demonstrate the use of the ambipolar-transport properties of graphene for the fabrication of a new kind of RF mixer device. Due to the symmetrical ambipolar conduction in graphene, graphene-based mixers can effectively suppress odd-order intermodulations and lead to lower spurious emissions in the circuit. The mixer operation was demonstrated at a frequency of 10 MHz using graphene grown by chemical vapor deposition on a Ni film and then transferred to an insulating substrate. The maximum operating frequency was limited by the device geometry and the measurement setup, and a high-quality factor was observed with a third-order intercept point of +13.8 dBm.

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Graphene-Based Ambipolar RF Mixers

This paper presents a comprehensive study of intermodulation-distortion response asymmetries often observed in microwave nonlinear systems subject to a two-tone or multitone test. The reasons for the different amplitudes of the two adjacent tones are first investigated under small- and large-signal regimes, using a general circuit with frequency-dependent embedding impedances and resistive and reactive nonlinearities. It is shown that this intriguing phenomenon can be mainly attributed to the terminating impedances at the baseband or difference frequencies. Multitone behavior is also addressed and its main differences from the two-tone case explained. Those theoretical conclusions are then extrapolated for real circuits and validated by measured results obtained from microwave power amplifiers of two different technologies, i.e., a GaAs MESFET and an Si bipolar junction transistor.

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A comprehensive explanation of distortion sideband asymmetries

The currency of the research consists in the necessity if rethinking of the notion of culture in Russian contemporary thought in order to present more adequately the process of development of culture in a future. The paper aims to elucidate political origins of the movement of Proletarian culture that play the leading role in a creation of a new conception of culture. As a materials were used documents and archives, scientific paper of Russian and foreign researchers. As a maim method was used problematicanalytical reconstruction, explored in the framework of an enactive approach that allows to envelop the subject in its evolvement and to concentrate on concrete practical situations of its realization. Such reconstruction permits to accomplish the original interpretation of the problem. The authors focus in the pre-history of the movement. Analyzing the social-political context of the origin of the movement, the authors come to the conclusion about artificially created necessity of political enlightenment of the society by the revolutionaries. The paper demonstrates how agents of proletarian working circles manipulate by the public opinion of working class. As a result, the paper shows the process of formation the ideology of cultural movement revolutionary period and evaluates significance of ideological function in its realization. The authors produce critical evaluation of the history of the movement in original judgment about political grounding of culture.

Индикаторы качества светодиодных осветительных систем, применяемых в стоматологической практике для местного освещения операционного поля

Wireless power transmission (WPT) is an emerging technology that is gaining increased visibility in recent years. Efficient WPT circuits, systems and strategies can address a large group of applications spanning from batteryless systems, battery-free sensors, passive RF identification, near-field communications, and many others. WPT is a fundamental enabling technology of the Internet of Things concept, as well as machine-to-machine communications, since it minimizes the use of batteries and eliminates wired power connections. WPT technology brings together RF and dc circuit and system designers with different backgrounds on circuit design, novel materials and applications, and regulatory issues, forming a cross disciplinary team in order to achieve an efficient transmission of power over the air interface. This paper aims to present WPT technology in an integrated way, addressing state-of-the-art and challenges, and to discuss future R&D perspectives summarizing recent activities in Europe.

Wireless Power Transmission: R&D Activities Within Europe

In this paper, the intermodulation distortion (IMD) behavior of LDMOS transistors is treated. First, an analysis is performed to explain measured IMD characteristics in different classes of operation. It is shown that the turn-on region plays an important role in explaining measured IMD behavior, which may also give a clue to the excellent linearity of LDMOS transistors. Thereafter, with this knowledge, a new empirical large-signal model with improved capability of predicting IMD in LDMOS amplifiers is presented. The model is verified against various measurements at low as well as high frequency in a class-AB power amplifier circuit.

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Prediction of IMD in LDMOS transistor amplifiers using a new large-signal model

This communication deals with the implemented assemblies and characterisation test results of several Back End Modules at 44 GHz for the Planck Mission of the European Space Agency (ESA), which are low noise and broadband (20%) receivers having direct conversion to DC. They are parts of the 44 GHz radiometers. In order to perform integration tests, before the integration of Flight Model units, some representative demonstrators have been manufactured and tested. These demonstrators will be integrated in Jodrell Bank Observatory (Manchester, England) with the Front End Modules made there. Main magnitudes tested are effective bandwidth, RF to DC response, noise temperature, linearity, input matching, video bandwidth and knee frequency of low frequency 1/f noise at the output.

Demostradores de los módulos posteriores de 44 GHz para la misión Planck

In this paper, a simple and non expensive solution to be employed as constitutive element in receiving phased arrays is proposed. Properly adjusting a PHEMT gate biasing voltage, when used in an active mixing topology, the fundamental component of the time-varying transconductance may be controlled both in magnitude and sign. In this way, a downconverting I/Q architecture implemented over such mixers could allow introducing the desired level and phase shifting over the resulting intermediate frequency (IF) signal for beamsteering or beamforming purposes. A proof of concept lab model at the 900 MHz band has been designed and tested over the NE3210s01 device. A four quadrant phase control is demonstrated along a 10 dB level range, validating the suggested approach. The array unit performance in terms of the desired and intermodulation distortion components is also accurately predicted from the derivatives’ profile of device main nonlinearity.

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Conversor de frecuencia con control vectorial para aplicaciones de conformado de haz en agrupaciones de antenas en recepción

In this paper, a comparative study of two types of antennas typically used in portable telephones is presented and discussed. These include a half-wavelength dipole and a quarter -wavelength monopole mounted on top of a metal box designed for operating in GSM900, DCS1800 and PCS1900 frequency bands. In this research work, the specific absorption rate (SAR) levels of the dipole antenna is evaluated and compared with that of the monopole antenna. Four different human head models have been implemented: homogenous spherical head, spherical seven layer model, Specific Anthropomorphic Mannequin (SAM) phantom and HUGO human head model. All the simulations are done for three different distances between the antenna and the head model (5 mm, 10 mm and 20 mm). The SAR levels for the head tissues are calculated for and in accordance to the two currently accepted standards: Federal Communications Commission (FCC) and International Commission on Non-Ionizing Radiation Protection (ICNIRP). All numerical simulations are performed using the Ansoft HFSS Software and CST Microwave Studio.

Comparison and Evaluation of SAR Induced in Four Human Head models for Two Types of Antennas Used in Mobile Telephones

In this article an exhaustive study of the nonlinear behavior of a vector control active patch is presented. The potenciality for controlling the radiation pattern at the intermodulation distortion (IMD) components is shwon when this control unit is employed in linear arrays. Adequately selecting the phase value for the radiated field from each element, an improvement in the carrier to IMD ratio could be obtained in the main lobe direction. At last, a selective biasing technique is considered to increase the array linearity/efficiency trade off , with independence of the individual phase excitation. I. INTRODUCCION Entre los cada vez mas exigentes requisitos que se imponen a las estructuras radiantes de los actuales sistemas de comunicacion destacan la capacidad de controlar electronicamente el apuntamiento y de variar el conformado del haz [1]. Ambos requisitos demandan un control preciso de la amplitud y la fase de la senal de excitacion de cada antena. La manera de conseguir esta variacion puede ser polar, mediante la conexion en cascada de un desfasador y un amplificador/atenuador de ganancia/atenuacion variable, o rectangular a traves de una unidad de suma vectorial [2]. La necesidad de encontrar soluciones comerciales de bajo coste y poco tamano empleando estas complejas tecnicas tradicionales ha generado un tremendo interes en el desarrollo de aplicaciones con antenas activas Sin embargo, el hecho de emplear elementos activos no lineales obliga a considerar las fuertes restricciones en cuanto a distorsion de la senal impuestas por los actuales sistemas. En estos medios se emplean modulaciones digitales complejas que exigen un bajo crecimiento espectral de las bandas de frecuencias adyacentes, por lo que hay que tener especial cuidado en el control de la intermodulacion. En [3] se ha propuesto un parche activo con control vectorial de senal para aplicaciones de control de haz. Basado en amplificadores sobre tecnologia PHEMT con control de ganancia, ofrece la posibilidad de utilizar la estrategia de alta linealidad propuesta en [4]. En este articulo se presenta un estudio exhaustivo del comportamiento no lineal de esta estructura. Analizando los niveles de distorsion a su salida en funcion de la ganancia de cada uno de sus amplificadores, se puede intentar controlar su patron de distorsion. Se contempla el uso de dicho parche en agrupaciones lineales (arrays) con capacidad de controlar el haz, por lo que se realizara un analisis detallado de los patrones de radiacion a la frecuencia fundamental y de intermodulacion, senalando las diferencias entre la topologia propuesta y la de una conexion en cascada. II. UNIDAD DE CONTROL DE AMPLITUD Y FASE En [4] se ha presentado un parche activo con control de amplitud y fase en un cuadrante. En la siguiente figura se presenta un esquema de la unidad propuesta. Fig. 1.Esquema de la antena activa propuesta con control de amplitud y fase basada en un metodo de suma vectorial. Como se puede observar, la senal de entrada alimenta a un hibrido de 90o, dividiendose en dos ramas en cuadratura de fase que alimentan dos amplificadores de ganancia variable (VGA). Las senales de salida de ambos excitan los puertos de una antena consiguiendo combinar espacialmente ambas senales. De esta manera se elimina el combinador de senal necesario en un esquema de suma vectorial, reduciendo las perdidas inherentes a cualquier elemento impreso. Siguiendo un esquema vectorial, cada rama representaria un vector base cuya amplitud se variaria cambiando la ganancia de cada amplificador, consiguiendo asi controlar la amplitud y la fase del vector resultante. Teniendo en cuenta la naturaleza no lineal de los VGAs de la unidad de suma vectorial, es necesario estudiar su distorsion final para diferentes ganancias y fases. El principal elemento no lineal en los transistores FET, la corriente drenador-fuente, Ids, se puede caracterizar por un desarrollo en serie de Taylor de dos dimensiones [5] (1): ... 3 2 2 3 2 2 1 ) , ( ) , (

Análisis del comportamiento no lineal de un parche activo con control vectorial de señal

A novel mode converter that transforms circular waveguide transverse magnetic ( ) 01 TM to transverse electric ( ) 11 TE circular waveguide is investigated, providing over 48% bandwidth of extraneous-mode-free operation at a conversion loss of less than 0.05dB. The design philosophy is based upon the unique use of two intermediate modes: coaxial TEM and a rectangular waveguide 10 TE , which provide input to output isolation of converter modes.

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Ángel Mediavilla Sánchez

Papers

Demostradores de los módulos posteriores de 44 GHz para la misión Planck

Conversor de frecuencia con control vectorial para aplicaciones de conformado de haz en agrupaciones de antenas en recepción

Comparison and Evaluation of SAR Induced in Four Human Head models for Two Types of Antennas Used in Mobile Telephones

Análisis del comportamiento no lineal de un parche activo con control vectorial de señal

Nueva estructura convertidor de modos ancha banda TM01-a-TE11