1,721,041 research outputs found
Microwave and millimetre wave active devices for radioastronomy applications: characterization and circuit design
No full textLASEK V/S PRK vantaggi e limiti delle due metodiche refrattive rispetto alla sintomatologia
No full textGli A.A. mettono a confronto le due metodiche di chirurgia fotorefrattiva. Valutano i vantaggi di una tecnica rispetto all’altra. Prendono in considerazione le complicanze. Analizzano i risultati alla luce di un foll-up di circa due anni.Materiali e metodi : 20 pazienti con miopia di grado compreso tra –3 e -10 sono stati sottoposti a PRK in OD e LASEK in OS . Hanno quindi risposto a domande circa il confort post operatorio , all’immediatezza del recupero visivo, etc.
Risultati : I risultati a breve ed a lungo termine non hanno evidenziato differenze sostanziali tra le due metodiche.Conclusioni: Pur non presentando differenze sostanziali ai fini refrattivi si possono valutare dei vantaggi della LASEK rispetto alla PRK se vengono osservati degli accorgimenti tecnici opportun
A Dual-Band MMIC Low frequency 180 ° Hybrid
Full text linkIn this paper design formulas,for the development of an unusual 180 ° hybrid working in two distinct frequency bands,are provided.In particular the design formulas of a lumped-element rat race,starting from a conventional transmission-line rat-race,are found out.In order to generalize the matching problem the input and output port impedances are considered to be different
A Fast AM/AM and AM/PM Characterization Technique
Full text linkIn this paper a novel AM/AM and AM/PM power amplifier characterization technique is presented, exploiting signals interference properties. Key features of the proposed measurement technique are the simplicity, requiring basic scalar power measurements only, and the low cost of the utilized set-up; moreover, it allows a power amplifier distortion characterisation in a very short time if compared with a more conventional method utilizing a Vector Network Analyzer. A description of the measurement set-up used to perform AM/AM and AM/PM characterisation is given. Lastly,in order to validate the measurement technique, comparisons with vector network analyzer measurements, for a 2W,2GHz power amplifier, are reported
Novel 4-points input pattern for large band noise measurements
Full text linkFour parameters are necessary for a complete characterization of the noise behavior of a linear device.The parameters can be experimentally determined by a minimum set of four equations,which can be obtained by an equal number of synthesized reflection coefficients at the input of the DUT,forming a pattern on the Smith chart.To increase the accuracy in the determination of the noise parameters,it is a common procedure to implement an heavily redundant pattern,with a random selection of more than the strictly necessary four points,so forcing the adoption of an expensive tuner.This paper introduces a novel ad hoc selected 4-points pattern,and demonstrates how it can simplify the measurement system without appreciably affecting the measurement accuracy.The proposed pattern is synthesized by easily realizable transmission lines,and a study has been performed to determine lines characteristics for use in wideband noise measurements
A novel noise model extraction technique for microwave and millimeter wave HEMT
Full text linkIn this paper a novel method to extract the noise parameters of active devices up to millimeter wave frequencies is presented.The method is based on parameters and 50 ΩΩΩΩ noise figure measurements only;the extraction of the small-signal equivalent circuit model of the device is not required.The method may be applied to FET with low parasitic elements,e.g.devices having a coplanar layout.A brief description of the measurement set-up used to perform noise figure measurements is given.Lastly,the validity of the proposed technique is demonstrated applying it to a low noise HEMT device from NEC,and comparing the results with those of a more conventional method based on the full knowledge of the device small-signal equivalent circuit
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