Radar imaging

Radar systems combining coherent signals with frequency and angular diversity offer the possibility of synthesizing images of complex objects with spatial resolution of a few wavelengths. The availability of high-quality microwave sources and components, high-speed digital computers, and efficient signal-processing algorithms allows radar imaging to be implemented in laboratory environments using commercially-available equipment. The paper summarizes fundamental issues by addressing conceptual and practical limits of radar imaging and presents examples obtained from results of measurements in a laboratory environment. Implementation details of sophisticated operational imaging radars are not covered.©1993 John Wiley & Sons Inc     

A>400 GHz fmax transferred-substrate heterojunctionbipolar transistor IC technology

We report transferred-substrate AlInAs/GaInAs bipolar transistors. A device having a 0.6 μm×25 μm emitter and a 0.8 μm×29 μm collector exhibited f_τ=134 GHz and f _max>400 GHz. A device with a 0.6 μm×25 μm emitter and a 1.8 μm×29 μm collector exhibited 400 GHz f_max 164 GHz f_τ. The improvement in f_max over previous transferred-substrate HBT's is due to improved base Ohmic contacts, narrower emitter-base and collector-base junction areas, and slightly reduced transit times. The transferred-substrate fabrication process provides electroplated gold thermal vias for transistor heat-sinking and a microstrip wiring environment on a low dielectric constant polymer substrate     

An 18-GHz continuous-time Σ-Δ analog-digital converterimplemented in InP-transferred substrate HBT technology

We report an 18-GHz clock-rate second-order continuous-time Σ-Δ analog-digital converter (ADC) implemented using InP-transferred substrate HBTs. Under two-tone test conditions, the ADC achieved 43 dB and 33 dB SNR at signal frequencies of 500 MHz and 990 MHz, respectively. The IC occupied 1.95 mm² die area and dissipated ~1.5 W     

Severe community-acquired pneumonia. Assessment of severity criteria

Sixty-three of 209 (30.1%) samples of cattle feed that were collected from multiple commercial sources and from farms were found to contain Escherichia coli. However, none of the feed samples examined were culture-positive for E. coli O157. Replication of fecal E. coli, including E. coli O157, was demonstrated in a variety of feeds at temperatures that were similar to those found on farms in summer months. Fresh mixed rations containing corn silage were sampled from 16 dairies. Rations from 12 of these dairies were found to contain E. coli, and the rations from 5 dairies had concentrations of E. coli that were greater than 1000 cfu/g. The ability of experimental mixed rations to support the replication of E. coli was correlated with the concentration of organic acids in the corn silage that was used in the ration. Widespread contamination of cattle feeds with E. coli and the ability of E. coli to replicate in feeds suggest that feeds are a potentially important factor in the ecology of organisms that can be transmitted from feces to mouth, such as E. coli O157.     

43 Gb/s decision circuits in InP DHBT technology

Packaged master-slave D-flip-flops designed in InP DHBT technology with 150 GHz f/sub t/ and 180 GHz f/sub max/ are presented. Measurement results using a 43.2 Gb/s nonreturn to zero (NRZ), pseudo random binary sequence (PRBS) data (generated from 4 channels of 10.8 Gb/s, 2/sup 31/-1, PRBS data) and a 43.2 GHz clock, show a clock phase margin of 190/spl deg/. 2:1 Static frequency dividers designed using the D-flip-flops have been tested up to 50 GHz and show normal operation. These circuits are key building blocks in numerous front-end circuits used for 40 Gb/s optical communication systems.     

Submicron scaling of HBTs

The variation of heterojunction bipolar transistor (HBT) bandwidth with scaling is reviewed. High bandwidths are obtained by thinning the base and collector layers, increasing emitter current density, decreasing emitter contact resistivity, and reducing the emitter and collector junction widths. In mesa HBTs, minimum dimensions required for the base contact impose a minimum width for the collector junction, frustrating device scaling. Narrow collector junctions can be obtained by using substrate transfer or collector-undercut processes or, if contact resistivity is greatly reduced, by reducing the width of the base ohmic contacts in a mesa structure. HBTs with submicron collector junctions exhibit extremely high f_max and high gains in mm-wave ICs. Transferred-substrate HBTs have obtained 21 dB unilateral power gain at 100 GHz. If extrapolated at -20 dB/decade, the power gain cutoff frequency f_max is 1.1 THz. f_max will be less than 1 THz if unmodeled electron transport physics produce a >20 dB/decade variation in power gain at frequencies above 110 GHz. Transferred-substrate HBTs have obtained 295 GHz f_T. The substrate transfer process provides microstrip interconnects on a low-ϵ_r polymer dielectric with a electroplated gold ground plane. Important wiring parasitics, including wiring capacitance, and ground via inductance are substantially reduced. Demonstrated ICs include lumped and distributed amplifiers with bandwidths to 85 GHz and per-stage gain-bandwidth products over 400 GHz, and master-slave latches operating at 75 GHz     

48-GHz digital ICs and 85-GHz baseband amplifiers usingtransferred-substrate HBT's

Using substrate transfer processes, we have fabricated heterojunction bipolar transistors with submicrometer emitter-base and collector-base junctions, minimizing RC parasitics and increasing f_max to 500 GHz. The process also provides a microstrip wiring environment on a low-ϵ_r dielectric substrate. First design iterations of emitter-coupled-logic master-slave flip-flops exhibit 48 GHz maximum clock frequency when connected as static frequency dividers. Baseband amplifiers have been demonstrated with bandwidths up to 85 GHz     

Incidence of enteropathogens in patients with human immunodeficiency virus infection

BACKGROUND: To establish the incidence of diarrhea and its evolution over time, the causal microorganisms, recurrence and associated mortality in patients with AIDS or severe immunologic alterations (CD4 lymphocytes lower than 0.5 x 10(9)/l). METHODS: A prospective longitudinal study was carried out from 1984 to 1992. The following patients were included in the study: 1) all those patients with diarrhea in whom a pathogenic microorganism was identified in the stools, and 2) patients with fever and positive blood cultures for enteropathogenic bacteria. The patients belonged to a series of 1,456 patients with infection by HIV. RESULTS: Of the 1,456 controlled patients, 253 (17%) had infection by enteropathogenic microorganisms. The incidence was greater in homosexual patients (26%) than in drug addicts (12%). The most frequent germs were Cryptosporidium, in 104 episodes and Salmonella sp. in 78 episodes (31 as isolated bacteria). The mortality in the 15 days following isolation was 2%, the referred microorganisms being the most frequent responsible for the deaths. The mean of CD4 lymphocytes in the patients with enteropathogens was 0.17 x 10(9)/l). SD 0.14 x 10(9)/l). In patients with infection by Cryptosporidium the CD4 lymphocyte count was lower than that observed in the cases of infection by Isospora belli. Prior to 1988, 21% of the patients had infection by enteropathogenic bacteria and 23% by parasites, those percentages being 3% and 6%, respectively in 1991. CONCLUSIONS: Infections by enteropathogenic microorganisms in patients with infection by the human immunodeficiency virus in an advanced stage are frequent, particularly, in homosexuals. The patients with enteritis by Cryptosporidium have a greater grade of immunosuppression (CD4 lymphocytes lower than 0.1 x 10(9)/l) than patients with infection by other enteropathogenic microorganisms. In the last few years, the incidence of enteropathogenic bacteria, especially Salmonella sp. and protozoa has decreased [corrected].     

Aperture Synthesis by Object Rotation in Coherent Imaging

Doppler processing is an established method for obtaining spatial resolution of objects which exhibit radial motion relative to an observing sensor. When applied to rotating objects, Doppler processing yields resolution in cross-range along an axis normal to both object rotation and line-of-sight axes. In this case, the cross-range resolution performance is dictated by the angular interval over which the data are observed and processed. This paper treats a tomographic extension of Doppler processing in the case of a rotating object (or a rotating planar array of point scatterers). It uses a stationary, continuous-wave (CW) irradiating source and sensor, co-located in the plane being imaged. The processing of data from a rotating object is shown to be equivalent to synthesizing an aperture which is a segment of a circle, however, processing over large angular rotations requires a focusing correction. Angular rotations up to and including 2? radians are considered. For this latter condition the system simulates an annular aperture which encloses the object. With this technique, high resolution may be obtained in all directions in the object plane without the use of a wideband signal, and equal point-objects separated by a quarter wavelength may be resolved. The imaging process provides high resolution for sparse arrays of objects of similar strength which are small in comparison to a wavelength. The imaging capability in the case of dense object arrays or large objects is limited and has a restricted dynamic range.