Design and optimization of RF ICs with embedded linear macromodels of multiport MEMS devices

In this paper, we demonstrate efficient modeling approach for simulation, analysis, design, and optimization of multiport radio frequency microelectromechanical systems (RF MEMS) resonating structures embedded in RF circuits. An in‐house finite element method (FEM) solver is utilized to develop accurate and efficient macromodels that capture all the essential characteristics of the device. Using the datasets generated from the FEM simulations, the artificial neural network models are trained for two‐way mapping between the physical input and electrical output parameters. Realized model is implemented in a circuit simulator, enabling a simple yet accurate circuit simulator compatible modeling and optimization procedure instead of memory and time demanding FEM analysis. The derivation of dynamic macromodels with preserved electromechanical behavior of the multiport resonating structures is also presented. Capabilities of the proposed approach are demonstrated with several examples featuring capacitively actuated MEMS resonating structures: a clamped–clamped beam, a free–free beam, and a coupled clamped–clamped beam. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007.     

Double-slot antennas on extended hemispherical and ellipticalsilicon dielectric lenses

Far-field patterns and Gaussian-beam coupling efficiencies are investigated for a double-slot antenna placed on hemispherical lenses with varying extension lengths. The radiation patterns of a double-slot antenna on a silicon dielectric lens are computed using ray-tracing inside the dielectric lens and electric and magnetic field integration on the spherical dielectric surface. The measured radiation patterns at 246 GHz and Gaussian-beam coupling efficiencies show good agreement with theory. The theoretical results are presented in terms of extension-length/radius and radius/λ, and therefore result in universal design curves for silicon lenses of different diameters and at different frequencies. The theoretical and experimental results indicate that for single units, there exists a wide range of extension lengths which result in high Gaussian-coupling efficiencies (50-60%) to moderately high f 's. These Gaussian-coupling efficiencies can be increased to 80-90°% with the use of a λ_m/4 matching-cap layer. For imaging array applications with high packing densities, an extension-length/radius of 0.38 to 0.39 (depending on frequency) will result in peak directivity and a corresponding Gaussian-coupling efficiency 15-20% lower than for single units     

Ultra-Wideband Bandpass Filters Using Quarter-Wave Short-Circuited Shunt Stubs and Quarter-Wave Series Transformers

This letter introduces a topology of a very wideband filter intended for the use in ultra-wideband 3.1-10.6 GHz applications. Basic filter configuration consists of quarter-wave short-circuited stubs and quarter-wave series transformers. To improve the out-of-band rejection, a low-pass filter is added across the symmetry plane. The proposed component is fabricated in a planar microstrip configuration; however, the topology can be easily adopted for other technologies including those based on surface micromachining. The measurements have shown an insertion loss below 0.86 dB, return loss above 14 dB, group-delay variation under 0.15 ns, and the third harmonic rejection better than 16 dB.     

Kinetics of internal oxidation in Ag-6Sn-2In-1Te-0.2Ni and Ag-6Sn-0.6Cu-1Bi-0.2Ni type alloys

Internal oxidation process was followed in Ag-6Sn-2In-1Te-0.2Ni and Ag-6Sn-0.6Cu-1Bi-0.2Ni alloy types in free air and oxygen at 650 °C and 680 °C. It was found that the Cu and Bi bearing alloy had a higher rates of internal oxidation in all of the tested conditions, whish was due to Bi effect accelerating the internal oxidation. In the early stage of internal oxidation of the Ag-6Sn-2In-1Te-0.2Ni alloy, an inhomogeneous structure revealed, which changed to a homogenous pattern after longer oxidation times. Such a structure was suppressed in the Bi bearing alloy. The applied 6 bar oxygen atmosphere brought on a 5–6 times higher rate of internal oxidation, with a homogenous structure compared to the free air oxidation. In free air after long time oxidation (200 h–250 h), the rate of internal oxidation was found to have almost doubled in both alloys.     

Millimeter-wave double-dipole antennas for high-gain integratedreflector illumination

A double-dipole antenna backed by a ground plane has been fabricated for submillimeter wavelengths. The double-dipole antenna is integrated on a thin dielectric membrane with a planar detector at its center. Measured feed patterns at 246 GHz agree well with theory and demonstrate a rotationally symmetric pattern with high coupling efficiency to Gaussian beams. The input impedance is around 50 Ω and will match well to a Schottky diode or SIS detector. The double-dipole antenna served as the feed for a small machined parabolic reflector. The integrated reflector had a measured gain of 37 dB at 119 μm. This makes the double-dipole antenna ideally suited as a feed for high-resolution tracking or for long-focal-length Cassegrain antenna systems     

Calmodulin antagonists suppress cholesterol synthesis by inhibiting sterol Δ24 reductasereductase

Preincubation of hepatoma cells and human skin fibroblasts in the presence of the calmodulin antagonists trifluoperazine and N-(6-aminohexyl)-5-chloro-1-naphthalene sulfonamide resulted in a dose-dependent suppression of [¹⁴C] mevalonolactone incorporation into cholesterol. At a calmodulin antagonist concentration of 25 μmol, the incorporation of [¹⁴C] mevalonolactone into cellular cholesterol was suppressed to about 30% (hepatoma cells) and 10% (human skin fibroblasts) of control values. When the total nonsaponifiable [¹⁴C] lipids were separated and analyzed by two-dimensional thin layer chromatography, an accumulation of [¹⁴C] desmosterol was observed along with reduced formation of [¹⁴C] cholesterol. However, when cells were preincubated in the presence of [¹⁴C] dihydrolanosterol, [¹⁴C] cholesterol formation was not inhibited by the calmodulin antagonists. About 25% of the cell-associated dihydrolanosterol radioactivity was converted to cholesterol in both control and calmodulin antagonist-pretreated cells. The data suggest that calmodulin antagonists prevent the conversion of desmosterol into cholesterol by inhibiting sterol Δ²⁴ reductase and that the enzymes catalyzing sterol ring modifications are not affected by the inhibitors.     

Off-axis properties of silicon and quartz dielectric lens antennas

The theoretical far-field patterns and Gaussian-beam coupling efficiencies are investigated for a double-slot antenna placed off aids on extended hemispherical silicon and quartz lenses. Measured off-axis radiation patterns at 250 GHz agree well with the theory. Results are presented that show important parameters versus off-axis displacement: scan angle, directivity, Gaussicity, and reflection loss. Directivity contour plots are also presented and show that near-diffraction limited performance can be achieved at off-axis positions at nonelliptical extension lengths. Some design rules are discussed for imaging arrays on dielectric lens antennas