Piotr Kozakowski

Efficient implementation of the Cauchy method for automated CAD-model construction

An efficient and stable implementation of the multidimensional Cauchy method for creating high quality multivariate models of microwave circuits from electromagnetic (EM) simulation data is presented in this paper. The algorithm uses the total least squares method to solve the ill-conditioned interpolation problem and automatically determines the model order and distribution of support points in the parameter space in such a manner that instabilities are prevented. Numerical tests show that the method requires fewer support points to achieve similar accuracy as the rational function models published previously. The utility and accuracy of the technique is demonstrated on a filter design example involving three- and five-dimensional models.

Automated CAD of coupled resonator filters

A gradient-based optimization technique along with a new definition of cost function is applied to the CAD of coupled resonator filters. The topology of the structure is enforced at each step of optimization and its physical dimensions are used as optimization variables. The cost function is defined using location of zeros and poles of the filters transfer and reflection functions. Numerical tests show that with the new definition of the cost function, the optimization process converges from an arbitrarily selected starting point. This allows one to design filters even without a rough microwave synthesis which usually provides initial dimensions.

Quadratic Programming Approach to Coupled Resonator Filter CAD

A computer-aided design technique for coupled resonator filters is presented. The technique is formulated as a bound constrained quadratic programming (QP) problem and predicated upon coupling matrix identification. The identification relies on the derivation of a rational model of the filter response and is formulated as a bound constrained QP problem. The definition of the optimization procedure in the form of a QP problem with an assumption of linear dependence of the coupling coefficients on filter geometrical dimensions leads to a significant reduction of the number of the full-wave electromagnetic simulations required to satisfy specifications. The proposed procedure is verified by designing and fabricating three microstrip filters

Computer-aided design of in-line resonator filters with multiple elliptical apertures

A CAD procedure for a new type of in-line resonator filters with multiple elliptical-apertures irises is presented. The proposed design procedure, based on the concept of automated CAD of coupled resonator filters, considerably simplifies filter design since, with this approach, the choice of the initial geometrical dimensions is not critical. To increase the computational efficiency, at first optimization is carried out by using multivariate surrogate models derived from full wave analysis; final dimensions are then directly obtained by a rigorous full-wave optimization of the entire structure. Two examples of filters with two transmission zeros at lower and upper stop-band are presented in order to illustrate the approach.

Gradient-based optimization of filters using FDTD software

This letter discusses gradient optimization of band-pass filters using electromagnetic simulation software based on the finite difference-time domain algorithm. It is shown that even high-Q-factor circuits can be optimized in acceptable time if robust digital signal processing techniques that take into account signal dynamics are used to predict the frequency behavior of a structure from relatively short sample sequences.

Low-order models from FD-TD time samples

The authors introduce several techniques which allow one to create high-quality models of time domain signals produced by the finite-difference time-domain (FD-TD) method. Guidelines for automated selection of key model parameters, such as the length of training sequence for model building and the model order, are given. The application of the criteria for extraction of time signature features based on the initial time sequences proposed in the paper is illustrated on two microwave filters.

New Approach to Fast Full Wave Optimization of Microwave Filters

The gradient based optimization technique along with a new definition of a cost function is applied to the direct electromagnetic CAD of coupled resonators filters. The topology of the structure is enforced on each step of optimization and the cost function is defined using location of zeros and poles of the filters transfer function. With the new objective function the optimization process converges to the desired solution from an arbitrary selected initial point (provided the assumed topology permits it). Moreover, the new objective function is constructed form numerical processing of scattering matrix parameters computed at a very few frequency points. As a result the optimization is fast and very good filter designs can be obtained in short time without any need of microwave synthesis.

Multimode, multiparametric surrogate models for fast design of waveguide components

An efficient technique of the multiparametric model creation from EM data using multivariate Cauchy method is presented. The proposed solution comprises the adaptive sampling algorithm and automated technique of model order selection. The key feature of this approach is a small number of support points needed to create multiparametric model of requested scattering parameter with assigned accuracy. The method is applied to modeling of multimodal scattering matrix. The high quality of the multimode models is confirmed by the fast design of complex waveguide components, such as dual-mode filters.

Fast iterative procedure for wave scattering by cylindrical objects

This paper presents the analysis of electromagnetic wave scattering by multiple cylindrical objects located in free space and rectangular waveguide junctions. The novel nested iterative scattering procedure (NISP) was developed in order to increase the efficiency of the iterative scattering procedure (ISP). The proposed method was verified by a finite-difference time-domain software and very good agreement was observed. Several numerical examples for open and closed problems were presented.

Fast Analysis of Waveguide Junctions with Gyromagnetic Post Resonators

The nested iterative scattering procedure (NISP) is applied to obtain scattering matrix of the multi-port waveguide junction with ferrite cylinders. The technique is utilized to study the effects of the multi-posts geometry on the switching properties of the 4-port waveguide junction. Furthermore the aforementioned method is used to find the best possible switching configurations. The examples of 4-port waveguide junction with 2 and 4 ferrite posts are presented. The proposed technique has been verified by a finite-difference time-domain software with the excellent agreement