A simple and efficient procedure for modeling of scattering and noise parameters for a class of microwave transistors manufactured in the same technology is presented in this article. It is based on multilayer perceptron artificial neural networks (ANN), whose inputs are device gate width, biases, and frequency that produce scattering and noise parameters at their outputs. After the ANN training, the scattering and noise parameters' prediction under different operating conditions for any device from the class requires only calculation of the ANN response, without changes in the ANN structure. Numerical examples for S-and noise parameters modeling for one specific series of pHEMT devices are presented to show the validity and effectiveness of this approach. Figure 5 Scattering parameters for bias points not used for the training process: (a) S11 black symbols, ATF35143 (2 V, 15 mA); white symbols, TF34143 (3 V, 20 mA); solid lines, neural model output; (b) S12 black symbols, ATF35143 (2 V, 15 mA); white symbols, ATF34143 (3 V, 20 mA); solid lines, neural model output; (c) S21 black symbols, ATF35143 (2 V, 15 mA); white symbols, ATF34143 (3 V, 20 mA); solid lines, neural model output; (d) S22 black symbols, ATF35143 (2 V, 15 mA); white symbols, ATF34143 (3 V, 20 mA); solid lines, neural model output ABSTRACT: An on-chip implementation of a low loss 1:9 transmission line transformer (TLT) is presented. The TLT was fabricated with broadside coupled microstrip lines in a GaAs HBT process. The wide metal transmission lines allow the high-quality factor and the high-current capability. The measured insertion loss is 0.88 dB at 880 MHz. The

that is, over-wavelength focusing is achieved if the time interval during which the source is switched on is larger than the travel time of the light between the source and the focus, along the corresponding ray of light. This is a rather intuitive and obvious condition from the standpoint of geometrical optics. CONCLUSIONThe focusing properties of physical LHM slabs have been found to be mainly limited by the slab thickness, the material losses, and the dispersive behavior of the LHM, rather than by the free-space wavelength of the incident field. The limitations for sub-and over-wavelength focusing, imposed by material losses and dispersion, have been quantitatively expressed, and numerical examples which illustrate these expressions have been provided. A very strong (logarithmic) dependence of the sub-wavelength focusing properties on both the loss tangent and the dispersive characteristics of the LHM has been found. This strong dependence may constitute a severe limitation from a practical standpoint, but does not constitute a fundamental limit for sub-wavelength focusing. In addition, it has been shown that the condition for over-wavelength focusing of realistic quasimonochromatic sources has a simple and rather intuitive interpretation in terms of geometrical optics. ACKNOWLEDGMENTSThis work has been supported by the Spanish Ministry of Science and Technology and FEDER funds (project no. TIC2001-3163).

A simple procedure for extraction the intrinsic noise wave temperatures in the wave representations of microwave transistors is presented in this paper. A set of equation describing the noise parameters as the function of three equivalent noise temperatures is implemented within the circuit simulator Libra. After that, the wave noise model is defined as new user-defined element of program Libra library. Good agreement between modeled and measured noise parameters is observed.

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