Raytheon

About: Raytheon is a company organization based out in Waltham, Massachusetts, United States. It is known for research contribution in the topics: Signal & Antenna (radio). The organization has 15290 authors who have published 18973 publications receiving 300052 citations.

Radiative and Multiphonon Relaxation of Rare-Earth Ions in Y 2 O 3

Abstract: Spontaneous-emission probabilities for electric- and magnetic-dipole transitions from excited electronic states of ${\mathrm{Pr}}^{3+}$, ${\mathrm{Nd}}^{3+}$, ${\mathrm{Eu}}^{3+}$, ${\mathrm{Er}}^{3+}$, and ${\mathrm{Tm}}^{3+}$ impurities in ${\mathrm{Y}}_{2}$${\mathrm{O}}_{3}$ are calculated using eigenstates in intermediate coupling and experimental intensity parameters. The predicted radiative lifetimes are in good agreement with experimental lifetimes measured using pulsed-selective-excitation techniques for those levels where unit quantum efficiency is expected. Discrepancies do exist, however, which indicate the importance of $J$-state mixing and possible breakdown of the closure approximation used in Judd and Ofelt's treatment. Nonradiative decay rates were determined by subtracting the radiative contribution from the observed lifetime. The rates of multiphonon emission in ${\mathrm{Y}}_{2}$${\mathrm{O}}_{3}$ exhibit a systematic variation with proximity of the next-lowest level, and contribute significantly to the decay for levels having energy gaps to the next-lowest level of less than 3000 ${\mathrm{cm}}^{\ensuremath{-}1}$. Selection-rule restrictions are evident from the reduced relaxation rates for the $^{5}D_{J}$ levels of ${\mathrm{Eu}}^{3+}$. The concentration dependence of the excitation spectra and excited-state lifetimes of ${\mathrm{Tm}}^{3+}$ were investigated to establish the importance of ion-pair relaxation; however, these processes were generally avoided.

Performance of low-loss RF MEMS capacitive switches

Abstract: 'This letter details the construction and performance of metal membrane radio frequency MEMS switches at microwave and millimeter-wave frequencies. These shunt switches possess a movable metal membrane which pulls down onto a metal/dielectric sandwich to form a capacitive switch. These switches exhibit low loss (<0.25 dB at 35 GHz) with good isolation (35 dB at 35 GHz). These devices possess on-off capacitance ratios in the range of 80-110 with a cutoff frequency (figure of merit) in excess of 9000 GHz, significantly better than that achievable with electronic switching devices.

A Method of Analysis of Symmetrical Four-Port Networks

Abstract: An analysis of four-arm symmetrical networks such as a branched directional double stub coupler or the hybrid ring (rat race) is presented. The input wave is broken into an even and an odd mode and the vector amplitude out the various arms is computed from the sums or differences of the reflection or transmission coefficients for the two modes. A zero decibel directional coupler is described and its possible use as a duplexer is proposed. The design of multiple stub directional couplers for any degree of coupling is discussed. A method of computing the bandwidth of all these couplers is outlined, and the bandwidth curves, the power out the various arms with respect to frequency of the zero decibel coupler, are computed. A tabulation is made for six different 3 db couplers (even-power split) and their standing wave ratio, evenness of power split and isolation of the fourth arm as a function of frequency assuming perfect performance at the band center.

Trapping effects in GaN and SiC microwave FETs

Abstract: It is well known that trapping effects can limit the output power performance of microwave field-effect transistors (FETs). This is particularly true for the wide bandgap devices. In this paper we review the various trapping phenomena observed in SiC- and GaN-based FETs that contribute to compromised power performance. For both of these material systems, trapping effects associated with both the surface and with the layers underlying the active channel have been identified. The measurement techniques utilized to identify these traps and some of the steps taken to minimize their effects, such as modified buffer layer designs and surface passivation, are described. Since similar defect-related phenomena were addressed during the development of the GaAs technology, relevant GaAs work is briefly summarized.

Work characteristics and employee health and well-being: Test of a model of healthy work organization.

Abstract: This paper presents an initial test and validation of a model of healthy work organization. A questionnaire based on the proposed model was completed by 1,130 employees of a national retailer. The instrument measured 29 first-order constructs underlying the six higher-order domains of the model. The overall model fit and relationships among the second-order factors were examined using AMOS structural equation-modelling procedures. The structural analyses presented here support the proposed model. An acceptable overall fit was demonstrated, and all second-order, and second- to first-order, relationships were significant. Employees' perceptions of their organization affect their perception of the climate, which impacts the way people relate to their job and see their future in the organization, ultimately impacting their work adjustment, health and well-being. This model has implications for both research and practice.