Virtual prototype of innovative ka-band power amplifier based on waveguide polarizer

This paper outlines an innovative approach to design a spatial power-combining structure based on waveguide polarizers. It presents the 3D CAD model of the new structure with the transversal probes and considerations in positioning and optimization of them. Exploiting the transformation of the dominant input mode TE10 into an elliptically polarized wave, provided by the polarizer, it has been possible to achieve a division of power by eight, completely carried out in space. With the insertion of the transversal probes made by microstrips, the RF signal can be sent to the MMIC solid state power amplifiers, and then recombined in the output section. Thanks to the large number of power divisions made in the waveguide section, the insertion loss of the power divider/combiner is less than 0.5 dB across the 32-34 GHz band, achieving a great power density as well. At the authors’ best knowledge, this is the first work where a waveguide polarizer is used in Spatial Power Combining technology

An Innovative Lens Type FinLine to Microstrip Transition

Due to the disadvantages of vacuum tubes in terms of warm-up time, size, and highvoltage needs, solid-state power amplifiers (SSPAs) with gallium nitride (GaN) monolithic microwave integrated circuits (MMICs) are the key solution for power levels up to some kilowatts in continuous wave. An SSPA is the most convenient solution for these RF power levels due to its low weight, small size, negligible warm-up time, low-voltage operation, and high reliability. Spatial power amplifiers (SPAs) combining techniques are the best candidates for SSPAs due to the intrinsic low attenuation in dividing and combining functions. SPAs mainly use two types of probes: transverse and longitudinal, such as FinLines. This paper describes a broadband FinLine to microstrip (FLuS) transition based on dielectric lens theory. Comparative simulations with traditional FinLine transitions show a significant improvement in matching performances and a very significant increase in mechanical resistance of the transition. The proposed innovative FLuS uses a substrate shaping designed according to dielectric lens theory. Frequency simulations of a FLuS inside the WR22 waveguide are shown. These evidence the better performances of this transition than the classic FLuS transition using quarter-wave transformer (QWT) matching. A Q band spatial power combiner with dielectric lens FLuS was made and measured, showing the excellent performances of this innovative FLuS transition

Innovative Mode Enhancement for High Power Coaxial Vircators

The size and weight of a high power microwave (HPM) source can make a difference in strategic use. The compactness of the virtual cathode oscillator (vircator) is undoubtedly the most significant advantage of this device. Civil industry and agriculture can use it to treat objects, food, and soils for disinfestation and disinfection. Vircators could also generate electromagnetic pulses (EMPs) to force the arrest of vehicles and drones; EMPs could inhibit or activate improvised explosive devices (IEDs). The coaxial type vircator is a highly compact device. Due to its symmetric geometry, coaxial vircator is typically designed to work with a TM01 mode. Still, when radiated into space, this mode gives maximum RF energy away from the antenna axis, a situation not desired. Instead, the TE11 is convenient in applications involving precise antenna pointing since this mode gives a maximum RF energy precisely aligned to the antenna axis. By studying Mathieu functions applied to elliptical waveguides, we improve the performances of a TE11 mode coaxial vircator using an elliptic drift tube (EDT). This is a completely innovative solution to reduce the mode competition inside the coaxial vircator. The rms and peak output power efficiency of the EDT coaxial vircator were measured on the TE11 mode, obtaining the values of 6.1% and 10%, respectively, with a peak power of 450 MW in a highly compact device

A Probabilistic Approach for the Optimal Sizing of Storage Devices to Increase the Penetration of Plug-in Electric Vehicles in Direct Current Networks

The growing diffusion of electric vehicles connected to distribution networks for charging purposes is an ongoing problem that utilities must deal with. Direct current networks and storage devices have emerged as a feasible means of satisfying the expected increases in the numbers of vehicles while preserving the effective operation of the network. In this paper, an innovative probabilistic methodology is proposed for the optimal sizing of electrical storage devices with the aim of maximizing the penetration of plug-in electric vehicles while preserving efficient and effective operation of the network. The proposed methodology is based on an analytical solution of the problem concerning the power losses minimization in distribution networks equipped with storage devices. The closed-form expression that was obtained is included in a Monte Carlo simulation procedure aimed at handling the uncertainties in loads and renewable generation units. The results of several numerical applications are reported and discussed to demonstrate the validity of the proposed solution. Also, different penetration levels of generation units were analyzed in order to focus on the importance of renewable generation

A New Theoretical Approach of Studying Resonances in Single Finline Transitions

In this article an innovative method of studying and removing the resonances, inherently exhibit by some waveguide to microstrip transitions, is presented. By modeling an equivalent circuit, this new approach allows to obtain the constructive parameters of a finline to microstrip transition, only using the values of the resistance and capacitance components of the equivalent circuit. This procedure will allow small microwave design Companies to realize these transitions only implementing circuit analysis software, and not having to afford electromagnetic analysis software, which are very expensive and time-consuming. A full 3D electromagnetic analysis confirms that the simulation results are in excellent agreement with the results obtained by the new equations discussed in this work

An Innovative Odd-Power Divider by means of a Triple FinLine Waveguide to Microstrip Transition

This paper outlines a novel approach to design a waveguide to microstrip finline transition that allows a division by three, of the RF power traveling inside a rectangular waveguide. The possibility of obtaining an odd power division of microwave and millimeter-wave signals with such finline transition is completely unexplored yet a harbinger of great opportunities. Starting from a 3D CAD model of the structure and continuing with electromagnetic simulations, the obtained results completely describe a transition able to achieve an almost perfect power splitting by three. Multyphisics simulations show an intrinsic resistance to vibrations of such transition, allowing it to be installed on aircraft or satellites modules. Thanks to this achievement, a totally new kind of power devices will come next, exploiting this odd power division. In fact, it will be possible to realize different types of microwave amplifiers, increasing the efficiency and decreasing the occupied size. To the author’s best knowledge, it is the first time a divider by three finline transition is reported in the literature

Multiphysics Design of High-Power Microwave Vacuum Window

This paper presents the Multiphysics Analysis of a High- Power Microwave Window for a Ka-Band Klystron providing 16MW of peak power. After the optimization of the electromagnetic performances, we analyze the effect of RF heating effect and the stress of the pressure on the window. We also analyze the multipactor effect, that is a common cause of window failure. Using such approach, it is possible to realize a virtual prototype capable to represent in a complete way the real prototype to be manufactured

Studies of a Ka-band high power klystron amplifier at INFN-LNF

In the framework of the Compact Light XLS project [1], a Ka-band linearizer with electric field ranging from 100 to 150 MV/m is requested [2, 3, 4]. In order to feed this structure, a proper Ka-band high power klystron amplifier with a high efficiency is needed. This paper reports a possible solution for a klystron amplifier operating on the TM010 mode at 36 GHz, the third harmonic of the 12 GHz linac frequency, with an efficiency of 44% and 10.6MW radiofrequency output power. We discuss also here the high-power DC gun with the related magnetic focusing system, the RF beam dynamics and finally the multiphysics analysis of a high- power microwave window for a Ka-band klystron providing 16 MW of peak power

Local and systemic vascular hemodynamic response to passive static stretching in young healthy humans

The aim of the present study was to determine the acute effects of passive static stretching (PSS) on femoral blood flow (FBF) in a stretched and non-stretched limb. Our hypothesis was that PSS would increase FBF in the stretched limb mainly through local vasodilator mechanisms. PSS effects may be expected also in the non-stretched limb possibly through an imbalance between the systemic hemodynamic control and the local vasodilator response. To this purpose, eight young healthy individuals (age: 22\ub13 yrs) underwent PSS (5 cycles of 45 s stretch/15 s rest) of the knee extensors of the dominant limb. Femoral artery blood velocity and diameter were taken from both limbs by ultrasound. FBF was then calculated. PSS increased FBF by 3c78% in the stretched limb (from 495\ub1110 to 882\ub1121 ml/min; P<0.05). FBF returned to baseline within the end of the 45 s stretch. Conversely, FBF decreased transitory by 3c71% (from 334\ub1155 to 138\ub117 ml/min; P<0.05) in the non-stretched limb during PSS maneuver. In conclusion, PSS increased FBF in the stretched limb, and induced a FBF decrease in the contralateral limb. These findings may suggest the predominance of a local vasodilator mechanism in the stretched limb during PSS maneuver, probably induced by nitric oxide release. On the contrary, a possible systemic vasoconstriction, likely mediated by an elevation of sympathetic nerve activity, may prevail in the contralateral limb

From field analysis to nanostructural investigation: A multidisciplinary approach to describe natural occurrence of asbestos in view of hazard assessment

The environmental impact of natural occurrences of asbestos (NOA) and asbestos-like minerals is a growing concern for environmental protection agencies. The lack of shared sampling and analytical procedures hinders effectively addressing this issue. To investigate the hazard posed by NOA, a multidisciplinary approach that encompasses geology, mineralogy, chemistry, and toxicology is proposed and demonstrated here, on a natural occurrence of antigorite from a site in Varenna Valley, Italy. Antigorite is, together with chrysotile asbestos, one of the serpentine polymorphs and its toxicological profile is still under debate. We described field and petrographic analyses required to sample a vein and to evaluate the NOA-hazard. A combination of standardized mechanical stress and automated morphometrical analyses on milled samples allowed to quantify the asbestoslike morphology. The low congruent solubility in acidic simulated body fluid, together with the toxicity-relevant surface reactivity due to iron speciation, signalled a bio-activity similar or even greater to that of chrysotile. Structural information on the genetic mechanism of antigorite asbestos-like fibres in nature were provided. Overall, the NOA site was reported to contain veins of asbestos-like antigorite and should be regarded as source of potentially toxic fibres during hazard assessment procedure