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.

The recent star formation histories of m81 group dwarf irregular galaxies

Abstract: We present observations and analysis of nine dwarf irregular galaxies (dIs) in the M81 Group taken with the Advanced Camera for Surveys aboard the Hubble Space Telescope. The nine galaxies (the Garland, M81 Dwarf A, DDO 53, Ho IX, Ho I, DDO 165, NGC 2366, Ho II, and IC 2574) span 6 mag in luminosity, a factor of 1000 in current star formation rate, and 0.5 dex in metallicity. We use color-magnitude diagrams of resolved stellar populations to study the star formation histories (SFHs) of these galaxies. Dividing the sample at MB = − 15, we analyze the similarities and differences in the SFHs, birthrate parameters (b), fraction of stars formed per time interval (f), and spatial distribution of stellar components. As function of luminosity, we find only minor differences in SF characteristics among the M81 Group dIs despite a wide range of physical properties. We extend our comparison to select dIs in the Local Group (LG) and, again, find little variation in SF parameters. Our average f parameters are consistent with a constant SFH; however, individual galaxies can show significant departures from this. We find this result underlines the importance of stochastic SF in dIs. We also compare possible formation scenarios of the fainter and candidate tidal dwarfs (TDGs) in the M81 Group. The SFHs and the spatial distribution of associated red stars suggest that the Garland and Ho IX are not dIs and are potentially TDGs. A noteworthy difference between the LG and the M81 Group is the lack of TDGs in the LG.

Phased array system

Abstract: A phased array antenna utilizing a parasitic reflector in which the area of the array of radiating elements is smaller than the area of the reflector. The reflector has a concave surface which, in one embodiment of the invention, is a hyperbola of revolution for collimating the rays of radiation incident thereupon from the array of radiating elements. The surface of the reflector is particularly adapted to permit the generation of a set of phase shift command signals by means of a novel ray tracing program to provide a collimated beam which may be scanned in response to the phase shift imparted through radiation radiated by the radiating elements. A narrow beam of radiation is obtained by virtue of the relatively large sized reflector even though the dimensions of the array of radiating elements are relatively small.

RF MEMS‐based tunable filters

Abstract: This paper overviews the application of RF MEMS switches in tunable filters as well as circuit developments for bandpass filters covering 110 MHz to 2.8 GHz. RF MEMS have several desirable features, including small size, low power requirements, and low loss. The basic operation of Raytheon's RF MEMS capacitive membrane switch is described. An overview of the technique used to integrate the switch into a variable capacitor structure with sixteen capacitance states is provided. Variable capacitor structures are used to construct multipole lumped bandpass filter designs, each with sixteen states. Finally, measured data from two representative five- and six-pole bandpass filters are presented. Characterization data demonstrates that the insertion loss for the five-pole filter using on-chip inductors was between 6.6 and 7.3 dB, and between 3.7 and 4.2 dB for the six-pole filter using off-chip inductors. © 2001 John Wiley & Sons, Inc. Int J RF and Microwave CAE11: 276-284, 2001.

Effects of Range-Doppler Coupling on Chirp Radar Tracking Accuracy

Abstract: Attention is called to the phenomenon of ?range-Doppler coupling,? characteristic of linear FM (chirp) waveforms, and the strong effect this coupling may have on tracking accuracy. Numerical results are presented for simple three-state filters and for a realistic reentry vehicle tracking problem.

Monolithic microwave integrated circuits (mmics) having conductor-backed coplanar waveguides and method of designing such mmics

Abstract: A MMIC having: a substrate; a plurality of active and passive electrical elements disposed on a top surface of the substrate; a plurality of coplanar waveguide transmission line sections disposed on the top surface of the substrate for electrically interconnecting the active and passive electrical elements; an electrical conductor disposed on a bottom surface of the substrate under the coplanar waveguide section. Edges of ground plane conductors of the coplanar waveguide (CPW) sections have slots therein in regions thereof connected to the active and passive devices. The design of such circuit includes mathematical models of the CPW with the pair of local ground planes and the strip conductor thereof have relatively narrow connectable ports.