1,721,105 research outputs found
HEMT-HBT matrix amplifier
No full textA novel matrix amplifier using simultaneously high electron-mobility transistors (HEMT's) and heterojunction bipolar transistors (HBT's) is proposed in this paper. The amplifier includes HEMT's in the first tier and HBT's in the second tier. The HEMT-HBT matrix amplifier in comparison to the HEMT matrix amplifier presents a notable lower de power consumption without remarkable gain and bandwidth Seduction, maintaining the advantage of using HEMT's in the first tier, A theory to demonstrate that the amplifier performance can be optimize if the HBT's in the second tier are properly chosen is also proposed. A comparison among the HEMT-HBT matrix amplifier, HEMT matrix amplifier, and HBT matrix amplifier is also presented
A simplified procedure to calculate the power gain definitions of FET's
No full textA graphical method to easily derive the power gain definitions of field-effect transistors (FET's) is proposed in this paper. This method is applicable to MESFET's and high electron-mobility transistors described by the typical pi-model. A new set of simple expressions of the S-parameters, functions of the circuit elements of the FET complete model, is derived. These expressions are presented in graphic form to quickly compute the modules of the FET S-parameters and then the power gains, The accuracy of this approach has been proven by comparison with simulations of the FET complete model
On the Analysis and Improvement of Yield for TWT Small-Signal Gain
No full textTraveling-wave tube (TWT) performance is sensibly affected by fabrication tolerances. An accurate yield evaluation and comprehension of the factors that contribute to yield degradation is fundamental to avoid excess costs in the fabrication process. In this paper, a procedure to evaluate and improve the yield of multisection helix TWTs in the design phase will be proposed, assuming a small-signal gain performance goal as the design target. An extended set of fabrication parameters is considered to provide a reliable estimate of the manufacturing tolerance effect on the final result. The introduction of yield sensitivity histograms together with cathode voltage adjustment demonstrates a relevant TWT yield improvement, together with indications on which fabrication step requires higher accuracy
Analysis of dielectric rods with arbitrary shape for low-dispersion slow-wave structures in helix TWTs
No full textThe introduction of rods with optimized cross-sectional shape in slow-wave structures (SWSs) for wideband helix traveling-wave tubes can sensibly improve the dispersion maintaining an adequate interaction-impedance level. In this brief, a procedure for analyzing helix SWSs loaded with rods of arbitrary shape, by using an analysis method adopting the inhomogeneous dielectric loading approach, is proposed. The advantages, in terms of SWS-dispersion improvement, of adopting optimized rod shapes in comparison to the typical rod shapes (i.e., rectangular, circular, and T-shaped) utilized up to now, are also demonstrated
On the influence of electron-beam parameters on TWT small-signal gain
No full textThe electron beam is one of the main components in traveling-wave tubes (TWTs). A study on the influence of the parameters related to the electron beam on small-signal gain of TWTs is proposed. In particular, the effect of the variations of electron-beam voltage, the perveance of the electron gun, and electron beam radius are investigated. A five-section TWT was considered in the study. (C) 2002 Wiley Periodicals, Inc
Improved rod shapes for helix slow wave structures
No full textNovel rod shapes, to improve dispersion and interaction impedance of helix slow-wave structures for wide band traveling wave tube, are proposed. Cold parameters are validated by 3-D electromagnetic code demonstrating the accuracy of the adopted analytical method
An HBT unilateral model to design distributed amplifiers
No full textA novel heterojunction bipolar transistor (HBT) unilateral model oriented to a fast prediction of the performance of HBT monolithic-microwave integrated-circuit distributed amplifiers is proposed. The HBT unilateral model includes, by simple expressions, the effects caused by the HBT parasitics. A graphical design procedure for HBT distributed amplifiers is also proposed. This method is based on a set of generalized charts and represents a simple and fast design tool for designers. Comparisons between the performance of specially designed HBT distributed amplifiers and the results obtained using the HBT unilateral model demonstrate the validity of the proposed approach
Narrow corrugation rectangular waveguide for terahertz TWTs
No full textTerahertz (THz) vacuum travelling wave tubes require slow-wave structures (SWSs) realisable by microfabrication processes, which assure an effective interaction with the electron beam. A corrugated rectangular waveguide with the corrugation narrower than the width of the waveguide is proposed as a slow-wave structure for THz travelling wave tubes (TWTs). A complete cold parameter analysis by a 3D electromagnetic simulator is presented, and the validity of the structure is demonstrated
Cathode voltage adjustment to compensate helix pitch tolerance in TWTs
No full textThe correct definition of helix pitch profile in multisection helix travelling-wave tubes is fundamental to obtain the required performance. The impact of tolerances on helix pitch manufacturing is a relevant reason for significant degradation of the small-signal gain. A detailed study analysing the effectiveness of compensating the effect of helix pitch error by a cathode voltage adjustment is proposed
Accurate analysis of helix slow-wave structures
No full textIn this paper, the helix slow wave structure (SWS) of traveling wave tubes (TWT's) has been analyzed, Dielectric supporting rods of arbitrary cross section have been considered in this analysis. The inhomogeneous dielectric loading factor has been accounted for by modeling the discrete support with a number of continuous dielectric tubes of appropriate effective dielectric permittivity, The helix tape model has been used for the field analysis. Furthermore the thickness of the helix tape has been considered. A rigorous solution of the field equations, including the contribution of the space harmonics, was performed to evaluate the phase velocity and the interaction impedance up to millimeter-wave frequencies. The nonuniformity of radial propagation constant over the structure cross section has been also included. With respect to other approaches, a closed-form expression of the field constants has been obtained. A study to choose the optimum number of space harmonics and dielectric tubes to be used in the analysis, has shown how the results are more sensitive to the number of space harmonics than to the number of dielectric tubes, beyond a certain number of the latter. The validity of this theory has been proved by comparison between measurements and simulations for helix SWS with different dimensions, rod shapes and operating frequency band
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