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This paper ties together several different aspects of linear stability analysis as it applies to microwave circuits. In particular, it reviews how the Rollett proviso enters into the well-known stability parameter tests and how the proviso can be evaluated using standard computer-aided-design software. Index Terms--Microwave amplifier stability, network determinant, normalized determinant function (NDF), Nyquist test, oscillator stability, Rollett proviso, unconditional stability.

We analyze the wind direction signal for vertically (v) and horizontally (h) polarized microwave radiation at 37 GHz, 19 GHz, and 11 GHz and an Earth incidence angle of 53[degrees]. We use brightness temperatures from SSM/I and TMI and wind vectors from buoys and the QUIKSCAT scatterometer. The wind vectors are space and time collocated with the radiometer measurements. Water vapor, cloud water and sea surface temperature are obtained from independent measurements and are uncorrelated with the wind direction. We find a wind direction signal that is noticeably smaller at low and moderate wind speeds than a previous analysis had indicated. We attribute the discrepancy to errors in the atmospheric parameters that were present in data set of the earlier study. We show that the polarization combination 2v - h is almost insensitive to atmospheric changes and agrees with the earlier results. The strength of our new signals agrees well with recent JPL aircraft radiometer measurements. It is significantly smaller than the prediction of the two-scale sea surface emission model for low and intermediate wind speeds. Index Terms--Microwave radiometers, ocean wind vector retrieval.

This paper presents a full-wave analysis method for printed apertures in anisotropic stripline structures. Both electric and magnetic anisotropy of the most general form are assumed. Working in the Fourier domain, closed-form expressions for the transformed electromagnetic fields are derived. Special attention is dedicated to the particular case of dielectrics with uniaxial anisotropy. In this case, spectral Green's functions in compact and closed form are obtained. Effects of the anisotropic ratio on the input impedance of a printed slot are presented. Index Terms--General anisotropy, input impedance, method of moments, printed apertures, spectral domain, stripline structures.

We present a Green's function for a circular loop in a toroidal cavity in a high-permeability material. We show that under certain conditions, Green's function may be expressed in terms of Jacobi's theta functions. We demonstrate an application of such a Green's function in analyzing the performance of pot core transformers. Results compare well with the values obtained by other analytical methods and by the measurement. Index Terms--Coupled circuits method, elliptic functions, Green's function, pot core transformers.

For the first time, we present modeling of microwave circuits using artificial neural networks (ANN's) based on space-mapping (SM) technology. SM-based neuromodels decrease the cost of training, improve generalization ability, and reduce the complexity of the ANN topology with respect to the classical neuromodeling approach. Five creative techniques are proposed to generate SM-based neuromodels. A frequency-sensitive neuromapping is applied to overcome the limitations of empirical models developed under quasi-static conditions. Huber optimization is used to train the ANN's. We contrast SM-based neuromodeling with the classical neuromodeling approach as well as with other state-of-the-art neuromodeling techniques. The SM-based neuromodeling techniques are illustrated by a microstrip bend and a high-temperature superconducting filter. Index Terms--CAD, design automation, microstrip filters, microwave circuits, neural network applications, neuromodeling, neural space mapping, optimization methods, space mapping.

Printed-circuit lines exhibit interesting behavior due to leakage of power. We have attempted to work toward a more profound understanding of uniplanar circuit properties when it comprehends planar transmission lines. Our work has focused on the slotline. We realized that the solution of its dispersion equation is multivalued. This enabled us to identify and report a new leaky wave on the slotline. The leaky wave brings down the upper cutoff frequency of the bound wave propagating over the slotline due to overlapping of the bound- and leaky-mode regions. For this case, we present some simple closed-form formulas providing this frequency limit when there is a frequency gap or when simultaneous propagation of the bound and the first or second leaky wave occurs. Propagation of the bound and leaky wave at the same time is a straightforward consequence of the multivalued nature of the solution of the dispersion equation. Evolution of the real and complex improper solutions of the equation in dependence on slotline dimensions demonstrates this clearly. We believe that conclusions drawn for the slotline also hold generally for other printed-circuit lines. Index Terms--Cutoff frequencies, electromagnetic surface waves, leaky waves, operation modes on slotlines, printed-circuit lines, slotlines.