Loss characteristics of high-/spl epsiv//sub r/ microstrip lines fabricated by an etchable thick-film on ceramic MCM technology

Etchable thick-film multi-chip-module (MCM) technology has led to the possibility of fabricating microwave integrated circuits (MICs) with performance similar to MICs produced using more expensive conventional thin-film MCM-D techniques. However, little data is available on the loss characteristics of the technology at microwave frequencies. This paper describes an experimental investigation into the loss properties of high-definition etchable thick-film MCM microstrip lines formed on a variety of high dielectric constant (high-/spl epsiv//sub r/) ceramic substrates. Substrates investigated comprise 96% alumina (/spl epsiv//sub r/=9.5), (Zr,Sn)TiO/sub 4/(/spl epsiv//sub r/=36.6) and BaO-PbO-Nd/sub 2/O/sub 3/-TiO/sub 2/ (/spl epsiv//sub r/=90.9). Microstrip loss properties are determined by fabricating a series of loosely coupled half-wave resonators on each substrate, with a range of characteristic impedance values. Measurements to 6 GHz are compared to those for similar lines fabricated using conventional thin-film MCM-D technology. The results demonstrate that etchable thick-film MCM technology provides many of the advantages of thin-film MCM-D technology, such as low-loss and high-definition conductors, and is suitable for the cost-effective fabrication of miniaturised high-performance microstrip MICs in high volume.     

Functional domains of the alpha1 catalytic subunit of the AMP-activated protein kinase

The AMP-activated protein kinase is a heterotrimeric enzyme, important in cellular adaptation to the stress of nutrient starvation, hypoxia, increased ATP utilization, or heat shock. This mammalian enzyme is composed of a catalytic alpha subunit and noncatalytic beta and gamma subunits and is a member of a larger protein kinase family that includes the SNF1 kinase of Saccharomyces cerevisiae. In the present study, we have identified by truncation and site-directed mutagenesis several functional domains of the alpha1 catalytic subunit, which modulate its activity, subunit association, and protein turnover. C-terminal truncation of the 548-amino acid (aa) wild-type alpha1 protein to aa 312 or 392 abolishes the binding of the beta/gamma subunits and dramatically increases protein expression. The full-length wild-type alpha1 subunit is only minimally active in the absence of co-expressed beta/gamma, and alpha1(1-392) likewise has little activity. Further truncation to aa 312, however, is associated with a large increase in enzyme specific activity, thus revealing an autoinhibitory sequence between aa 313 and 392. alpha-1(1-312) still requires the phosphorylation of the activation loop Thr-172 for enzyme activity, yet is now independent of the allosteric activator, AMP. The increased levels of protein expression on transient transfection of either truncated alpha subunit cDNA are because of a decrease in enzyme turnover by pulse-chase analysis. Taken together, these data indicate that the alpha1 subunit of AMP-activated protein kinase contains several features that determine enzyme activity and stability. A constitutively active form of the kinase that does not require participation by the noncatalytic subunits provides a unique reagent for exploring the functions of AMP-activated protein kinase.     

CAD of high‐εr microstrip bandpass filters

A simple design procedure is described for miniaturized microstrip bandpass filters on high‐ε_r substrates. Costs and design times are reduced by replacing experimental measurements with EM simulations. The procedure is confirmed through the design of a miniaturized microstrip hairpin‐coupled bandpass filter at 1.8 GHz on BaO? PbO? Nd₂O₃? TiO₂ (ε_r=90.9) ceramic substrate. © 2002 Wiley Periodicals, Inc. Int J RF and Microwave CAE 12: 229–235, 2002.