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.

A parallel electromagnetic genetic-algorithm optimization (EGO) application for patch antenna design

Abstract: In this paper, we describe an electromagnetic genetic algorithm (GA) optimization (EGO) application developed for the cluster supercomputing platform. A representative patch antenna design example for commercial wireless applications is detailed, which illustrates the versatility and applicability of the method. We show that EGO allows us to combine the accuracy of full-wave EM analysis with the robustness of GA optimization and the speed of a parallel computing algorithm. A representative patch antenna design case study is presented. We illustrate the use of EGO to design a dual-band antenna element for wireless communication (1.9 and 2.4 GHz) applications. The resulting antenna exhibits acceptable dual-band operation (i.e., better than -10 dB return loss with 5.3 and 7% operating bandwidths at 1.9 and 2.4 GHz) while maintaining a cross-pol maximum field level at least 11 dB below the co-pol maximum.

Method and apparatus for tri-band feed with pseudo-monopulse tracking

Abstract: Methods and apparatus for a feed assembly for a reflector antenna including an aperture common to low, mid, and high frequency bands, a polyrod design to launch signals in the mid and high frequency bands, a horn to launch signals in the low frequency band, a co-located phase center for launching signals in the low, mid, and high frequency bands, and a low-band monopulse array located on a surface about the aperture to track a satellite.

THE ACS LCID PROJECT. III. THE STAR FORMATION HISTORY OF THE CETUS dSph GALAXY: A POST-REIONIZATION FOSSIL*

Abstract: We use deep HST/ACS observations to calculate the star formation history (SFH) of the Cetus dwarf spheroidal (dSph) galaxy. Our photometry reaches below the oldest main-sequence turnoffs, which allows us to estimate the age and duration of the main episode of star formation in Cetus. This is well approximated by a single episode that peaked roughly 12 ± 0.5 Gyr ago and lasted no longer than about 1.9 ± 0.5 Gyr (FWHM). Our solution also suggests that essentially no stars formed in Cetus during the past 8 Gyr. This makes Cetus' SFH comparable to that of the oldest Milky Way dSphs. Given the current isolation of Cetus in the outer fringes of the Local Group, the dominant old population implies that Cetus is a clear outlier in the morphology-Galactocentric distance relation that holds for the majority of the Milky Way dwarf satellites. Our results also show that Cetus continued forming stars until z 1, long after the universe was reionized, and that there is no clear signature of the epoch of reionization in Cetus' SFH. We briefly discuss the implications of these results for dwarf galaxy evolution models. Finally, we present a comprehensive account of the data reduction and analysis strategy adopted for all galaxies targeted by the LCID (Local Cosmology from Isolated Dwarfs) project. We employ two different photometry codes (DAOPHOT/ALLFRAME and DOLPHOT), three different SFH reconstruction codes (IAC-pop/MinnIAC, MATCH, and COLE), and two stellar evolution libraries (BaSTI and Padova/Girardi), allowing for a detailed assessment of the modeling and observational uncertainties.

The effects of noise on the autoregressive spectral estimator

Abstract: The autoregressive power spectral density estimator possesses excellent resolution properties. However, it has been shown that for the case of a sinusoidal autoregressive process the addition of noise to the time series results in a decrease in spectral resolution. It is proven that, in general, the effect of white noise on the autoregressive spectral estimate is to produce a smoothed spectrum. This smoothing is a result of the introduction of spectral zeros due to the noise. Finally, the use of a large-order autoregressive model to combat the effects of noise is discussed.

Dielectric Waveguide Phase Shifter

Abstract: Using ferrite waveguide toroids and dielectric ribs (epsilon/sub r/ = 50), we have demonstrated that a dielectric waveguide (no metal walls) phase shifter (Delta Phi = 600°) can propagate with reasonable insertion loss (/spl ap/3 dB) and modest cross coupling (/spl ap/ 15 dB). With brass inserts, the cross coupling can be further reduced (> 20 dB) with some sacrifice of insertion loss and phase shift. The use of dielectric waveguide phase shifters should allow simpler, lower-cost phased arrays in the conventional frequency range (3 to 20 GHz). At millimeter wave frequencies there is the possibility of making a column of phase shifters from slabs of ferrite and dielectric using flat-grinding and cutting techniques.