Ramin Sabry

Computer diagnosis and tuning of RF and microwave filters using model-based parameter estimation

This paper describes an efficient and robust approach for the computer diagnosis and tuning of RF and microwave filters relying upon model-based parameter estimation (MBPE) and multilevel optimization. The frequency sampled S-parameters are obtained from the measurement, and then an MBPE procedure based on adaptive sampling is employed to approximate the frequency-domain behavior of S-parameters in terms of rational functions. This approach uses a reduced-order system model. The effect of measurement noise is also considered. The approach is applied to coupled resonator filters that are modeled by a general equivalent circuit. The loss of each resonator is included in the model by a series resistor. A simple and efficient error function is used to reduce the computational effort of the optimization while improving the speed and robustness of diagnosis process for lossy filters. This approach can be applied to many classes of filters. The proposed approach is demonstrated through numerical examples and application to the manufactured filter.

On the determination of resonant modes of dielectric objects using surface Integral equations

Although surface integral equations have been extensively used for solving the scattering problem of arbitrarily shaped dielectric objects, when applied to the resonance problem, there are still some issues not fully addressed by the literature. In this paper, the method of moments with Rao-Wilton-Glisson basis functions is applied to the electric field integral equation (EFIE) for solving the resonance problem of dielectric objects. The resonant frequency is obtained by searching for the minimum of the reciprocal of the condition number of the impedance matrix in the complex frequency plane, and the modal field distribution is obtained through singular value decomposition (SVD). The determinant of the impedance matrix is not used since it is difficult to find its roots. For the exterior EFIE, the original basis functions are used as testing functions; for the interior EFIE, the basis functions rotated by 90/spl deg/ are used as testing functions. To obtain an accurate modal field solution, the impedance matrix needs to be reduced by half before SVD is applied to it. Numerical results are given and compared with those obtained by using the volume integral equation.

A Unified Framework for General Compact and Quad Polarimetric SAR Data and Imagery Analysis

Dual and compact polarimetric (CP) synthetic aperture radar (SAR) provide more target information than single-polarization SAR systems with less stringent data requirements than fully polarimetric SAR systems. Considering the incomplete nature of CP data to establish the quad or fully polarimetric scattering matrix, the applied CP mode determines the captured scattering properties. Present formalism enables investigation of various CP modes (e.g., general elliptical transmission) and products for general target backscattering characterization. This is done through decomposition of quad-pol covariance and CP modeling of respective basic scattering mechanisms. On this basis, derivation of optimal CP modes and design of suitable CP products are explored. In this approach, the need for a priori target assumptions is removed. The link established between general CP and quad polarimetric covariance matrices can be used to examine target property assumptions using various CP modes data. Accordingly, means is also provided to explore a priori target property assumptions and their suitability required for expansion of 2 × 2 CP covariance matrix to perform the pseudo-quad-polarimetric covariance analysis.

ADVANCED POLARIMETRIC SYNTHETIC APERTURE RADAR (SAR) AND ELECTRO-OPTICAL (EO) DATA FUSION THROUGH UNIFIED COHERENT FORMULATION OF THE SCATTERED EM FIELD

Exploitation of the backscattered field polarization over the wide electromagnetic spectrum, from visible to microwave frequencies, provides an approach to advanced target recognition in remote sensing applications. The framework for full coherent characterization of the scattered field that is established here, maximizes the extracted target information. It is also shown that such a methodology, which is theoretically similar to the concept of “partial or compact polarimetry”, yields comparable results to full or quadrature-polarized systems by incorporating judicious assumptions and assuming/implementing optimal transmitted or illumination field polarizations. On this basis, common characteristic features, interworking and fusion of different polarimetric sensor products in different regions of spectrum, e.g., radar/SAR and Electro-Optical, are investigated and formulated within a robust framework based on full coherent treatment of the scattered field.

Efficient simulation of rectangular dielectric resonators using volume MPIE-MoM formulation with combined entire-domain and subdomain basis functions

An efficient method-of-moments (MoM) formulation using combined entire-domain and subdomain basis functions is proposed for simulating the resonant modes of a rectangular dielectric resonator in free space. An approximate analytical solution for the resonant mode of the DR is used as the entire-domain basis function, while a set of tetrahedral basis functions are used as subdomain basis functions. Since the main profile of the resonant mode can be well represented by the entire-domain basis function, only small number of subdomain basis functions are needed for further refinement of the representation. Compared with the MoM formulations using only subdomain or entire-domain basis functions, this method is much faster for the same accuracy. Numerical results are given and compared with other methods.

Simulation of resonant modes of rectangular DR in MIC environment using MPIE-MoM with combined entire-domain and sub-domain basis functions

An efficient method-of-moments volume integral formulation using combined entire-domain and subdomain basis functions is proposed for simulating the resonant modes of a rectangular DR in an MIC environment. The formulation is based on the mixed-potential integral equation using Michalskis formulation-C Greens functions. The spatial-domain Greens functions are calculated by using the complex image method. Different from the simple sinusoidal entire-domain basis functions used by previous methods, an approximate solution for the resonant modes of rectangular DR in MIC environment based on Marcatilis method is used as the entire-domain basis function, while a set of tetrahedral basis functions are used as sub-domain basis functions. Since the main profile of the resonant mode can be represented well by the entire-domain basis function, only a small number of sub-domain basis functions are needed for further refinement of the representation. Compared with the method-of-moments formulations using only sub-domain or entire-domain basis functions, this method is much faster for the same accuracy. Numerical results are given and compared with other methods.

FORMULATION OF EMISSION FROM RELATIVISTIC FREE ELECTRONS IN A RING STRUCTURE FOR ELECTRO-OPTICAL APPLICATIONS

A new scheme for high-speed electro-optical conversions with potential application to data communication is investigated. As the core of investigation, a ring model utilizing relativistic electrons is introduced and the operating characteristics such as coupled wavelengths, gain and power are derived for a circular type of interaction. Advantages are addressed and practical challenges associated with the realization of this conceptual scheme are discussed in light of advances in fundamentally similar relativistic free electron lasing schemes.

Generalized reaction and unrestricted variational formulation of cavity resonators. I. basic theory

Based on the reciprocity theorem, the reaction concept in electromagnetic theory is generalized to the cases where both surface electric and magnetic currents overlap across boundaries, i.e., neither the E-field, nor H-field meets the continuity conditions. An improved systematic method is then developed to obtain unrestricted variational expressions in a cavity resonator for which the tangential components of the trial fields can be discontinuous across its interior boundaries.

Prediction of Polarimetric-SAR Field-Orientation Rotation Due to Topographical Slope Variation for Squint Operations

Local surface slope variations can impact synthetic aperture radar (SAR) imagery by changing the perceived polarization state of the imaged region. Correction of the topography-induced effects results in more accurate evaluation of polarimetric parameters. In this letter, the polarization-orientation angle (POA) correction is analytically estimated for a general polarimetric-SAR scenario operating at a known squint angle based upon a digital elevation model, permitting correction of the topography-induced effects. It can also aid to identify a squint angle that can counteract the effect of a specific POA rotation. Model parameters are demonstrated through a software implementation.

Generalized reaction and unrestricted variational formulation of cavity resonators. II. Nonorthogonal and free-boundary mode-matching method

For pt. I see ibid., vol. 50, no. 11, p. 2480-90 (2002). This paper addresses a systematic method whereby the conventional mode-matching method is generalized to the cases where the set of modes used for the field expansion within a cavity resonator are relaxed to be orthogonal or satisfy any specific boundary conditions. It is shown that this approach is based on the unrestricted variational formulation of a cavity resonator. Reciprocity theorem and generalized reaction are the mathematical foundations of this new formulation. We have shown that the conventional mode-matching method is a special case of this generalized formulation and indeed is variational in nature. More precisely, we have proven that, if the field distribution obtained based on the conventional mode-matching method is used as a trial one in some variational formulas, the resonant frequency will be the same as the one obtained by the mode-matching method.