13,418 research outputs found
Large signal 2nd harmonic on wafer MESFET characterization
An automatic test set which performs a real time harmonic load-pull characterization is proposed. An active load technique is used in order to set the load at the test frequency and its harmonics and a complete set of device parameters useful for power amplifier design purposes can be measured versus the harmonic loads. The calibration procedure, based on substrate and coaxial standards, has been mainly developed for on wafer measurement in order to set the reference planes directly on the DU
Save the "THRU" in the A.N.A. calibration
The conventional network analyzer (NWA) two-port calibration procedures require a standard thru line to be connected between the ports. Unfortunately in many applications, for example when measuring MMIC or on-wafer devices with not aligned ports, a custom thru line must be used. The procedure here applied overcomes the difficulty due to the poor knowledge of this thru element since it is based on a generic reciprocal unknown two port structure, provided that its S21 phase shift is roughly known. Some experimental comparisons with other well sound calibration techniques will be here presented where different reciprocal two-port structures were used as unknown thr
Structural instability of nonlinear plates modelling suspension bridges: mathematical answers to some long-standing questions
We model the roadway of a suspension bridge as a thin rectangular plate and
we study in detail its oscillating modes. The plate is assumed to be hinged on
its short edges and free on its long edges. Two different kinds of oscillating
modes are found: longitudinal modes and torsional modes. Then we analyze a
fourth order hyperbolic equation describing the dynamics of the bridge. In
order to emphasize the structural behavior we consider an isolated equation
with no forcing and damping. Due to the nonlinear behavior of the cables and
hangers, a structural instability appears. With a finite dimensional
approximation we prove that the system remains stable at low energies while
numerical results show that for larger energies the system becomes unstable. We
analyze the energy thresholds of instability and we show that the model allows
to give answers to several questions left open by the Tacoma collapse in 1940.Comment: 33 page
Saddle Points Stability in the Replica Approach Off Equilibrium
We study the replica free energy surface for a spin glass model near the
glassy temperature. In this model the simplicity of the equilibrium solution
hides non trivial metastable saddle points. By means of the stability analysis
performed for one and two real replicas constrained, an interpretation for some
of them is achieved.Comment: 10 pages and 3 figures upon request, Univerista` di Roma I preprint
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Partial symmetry and existence of least energy solutions to some nonlinear elliptic equations on Riemannian models
We consider least energy solutions to the nonlinear equation posed on a class of Riemannian models of dimension
which include the classical hyperbolic space as well as manifolds
with unbounded sectional geometry. Partial symmetry and existence of least
energy solutions is proved for quite general nonlinearities , where
denotes the geodesic distance from the pole of
Accurate on-wafer power and harmonic measurements of mm-wave amplifiers and devices
A novel integrated test system that accurately measures on-wafer S-parameters, power levels, load-pull contours and harmonics over 1 to 50 GHz is presented. The system measures power and S-parameters with single contact measurements and integrated hardware. There are two keys to this system: first, the network analyzer samplers are used as frequency-selective power meters with large dynamic ranges; second, all measurements are vector-corrected to the device under test reference planes. The capabilities and accuracy were demonstrated by measuring the power at the fundamental frequency and four harmonic frequencies of a 50-GHz traveling wave amplifier and the load-pull contours of a MODFET at 30 GH
Uniqueness of the thermodynamic limit for driven disordered elastic interfaces
We study the finite size fluctuations at the depinning transition for a
one-dimensional elastic interface of size displacing in a disordered medium
of transverse size with periodic boundary conditions, where
is the depinning roughness exponent and is a finite aspect ratio
parameter. We focus on the crossover from the infinitely narrow () to
the infinitely wide () medium. We find that at the thermodynamic
limit both the value of the critical force and the precise behavior of the
velocity-force characteristics are {\it unique} and -independent. We also
show that the finite size fluctuations of the critical force (bias and
variance) as well as the global width of the interface cross over from a
power-law to a logarithm as a function of . Our results are relevant for
understanding anisotropic size-effects in force-driven and velocity-driven
interfaces.Comment: 10 pages, 12 figure
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