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This paper deals with the development of a microwave noise-adding radiometer, which is purposely designed for the fire detection in forest environments. The sensor operates at 12.65 GHz and exploits commercial Satellite Television (SAT-TV) components such as a parabolic dish and a low-noise block. First, a simple system model is presented to estimate the radiometric contrast due to the presence of fire (increase in the antenna noise temperature with respect to the background) at a certain distance from the receiving antenna. Then, the design of the sensor is addressed, underlining the key technologies that allow the required performance to be attained at low industrial costs. An experimental characterization of the developed radiometer is reported focusing on both accuracy and sensitivity issues. Due to a continuous gain calibration based on the noise-adding procedure, the antenna noise temperature can be retrieved with an absolute error of 4 K without any thermal stabilization of the instrument electronics. Last, real fire detection experiments have been carried out both in laboratory and open-space environments. A radiometric contrast of 8.8 K has been recorded for a wooden fire of 0.2 [m.sup.2] placed at a distance of about 30 m from the antenna. Index Terms--Calibration, fire detection, microwave radiometry, microwave receivers, remote sensing.

The inclusion of lumped elements, both linear and nonlinear, into the finite-difference time-domain (FDTD) algorithm has been recently made possible by the introduction of the lumped-element FDTD method. Such a method, however, cannot efficiently and accurately account for two-terminal networks made of several lumped elements, arbitrarily connected together. This limitation can be removed as proposed in this paper by describing the network in terms of its impedance in the Laplace domain and by using appropriate digital signal-processing methodologies to fit the resulting description to Yee's algorithm. The resulting difference equations allow an arbitrary two-terminal network to be inserted into one FDTD cell, preserving the full explicit nature of the conventional FDTD scheme and requiring a minimum number of additional storage variables. The new approach has been validated by comparison with the exact solution of a parallel-plate waveguide loaded with lumped networks in the transverse plane. Index Terms - FDTD method, lumped networks, global modeling.

The lumped-element finite-difference time-domain method is used to analyze quasi-optical multipliers based on diode loaded slot antennas. The method is validated firstly for a passive microstrip-fed structure then for the diode loaded case in both small- and large-signal regimes. The diode model is separately validated using a series diode mounted on a microstrip line. Input return loss and radiation patterns show good agreement with measurements and the concept of effective conversion loss is introduced and results show reasonable agreement between measurement and simulation. A new diode arrangement is introduced where dual offset diodes are placed in the slot instead of the conventional central diode. The diode position can then act as an extra design parameter. The performance of the two structures has been compared; currently best performance is still obtained for the central-diode structure. Finally, a fully quasi-optical structure is simulated with plane-wave excitation. Central and dual-diode structures are again compared and the diode position and input plane-wave field strengths are optimized. Slot voltage distributions, radiation patterns, and effective quasi-optical conversion losses are presented. Index Terms--CAD, FDTD, multipliers, quasi-optics, slot antennas.

In this paper, the bonding-wire interconnection has been studied from the points of view of its modeling and electrical characterization. Both single- and double-wire structures have been considered, the latter under the assumption of parallel wires. Two electrical models of the bonding wire are discussed. First, the finite-difference time-domain (FDTD) method is proposed for the rigorous analysis of such structures. This method uses a suitable discretization technique, which accounts for the wire curvature by means of a polygonal approximation. A quasi-static model of the bonding wire, suitable for commercial microwave computer-aided-design tools is then proposed. This model is based on the representation of the structure with four sections of a uniform transmission line and the model parameters are evaluated analytically from the dimensions of the interconnection. Accuracy and applicability of the quasi-static model have been assessed by analyzing several test structures, the reference results being obtained with the FDTD method. Finally, the quasi-static model has been used to provide an extensive electrical characterization of the bonding wire versus its main geometrical parameters. This characterization is given in terms of an equivalent series inductance and two equivalent shunt capacitances forming a [Pi] low-pass network. This representation is particularly useful in the matching of the bonding-wire discontinuity. Index Terms--Bonding wire, CAD, FDTD, interconnections, packaging.

Recently, a novel method has been proposed that allows general linear lumped networks to be incorporated within finite-difference time-domain (FDTD) simulators. In this paper, this method is extended in such a way as to represent two-terminal nonlinear lumped networks in a single FDTD grid cell. In particular, the extended method is applied to the rigorous modeling of packaged Schottky diodes. The implementation is first validated in the case of a diode connected to a voltage source. The SPICE simulator has been used to provide reference results. The same structure has also been used to establish the accuracy of the method. It has been demonstrated that such accuracy is significantly increased with respect to that of the conventional lumped-element-FDTD approach. Finally, the technique has been validated against measured results, showing a good agreement. Index Terms--FDTD method, packaging, Schottky diodes.

A revised formulation of modal absorbing and matched modal source boundary condition is proposed for the efficient analysis of a waveguide circuit with the finite-difference time-domain (FDTD) method. The formulation is based on a suitable translation operator modeling, in time domain, the propagation in a uniform hollow waveguide. By applying this operator, a multimodal absorbing boundary condition is obtained. Moreover, a source algorithm is developed that generates a given incident wave, while absorbing each modal component reflected from a discontinuity. The source is capable to separate incident and reflected waves without requiring any presimulation of long uniform waveguides. The validity and effectiveness of the formulation is verified by means of three numerical experiments. The first two refer to waveguide discontinuities. In these cases, the FDTD results are compared versus mode-matching results. The third example is a transition from waveguide to printed circuit transmission line. The numerical simulation is compared with published experimental results. The presented examples show that the generalized scattering matrix of a waveguide circuit can be evaluated accurately in the smallest computational space allowed by the structure. Index Terms--FDTD method, generalized scattering matrix, matched modal source, modal absorbing boundary conditions, waveguide circuits, waveguide impulse response, waveguide transitions.