Ata Zadehgol

Isotropic Spatial Filters for Suppression of Spurious Noise Waves in Sub-Gridded FDTD Simulation

A class of isotropic spatial filters is proposed to suppress spurious noise waves due to sub-gridding in finite difference time domain simulations. The proposed filters are suitable for both two-dimensional and three-dimensional applications. A simple procedure is introduced for the a-priori determination of the required filter order and the frequency with which the filter is applied based on the maximum temporal frequency bandwidth of the electromagnetic source. The proposed filters are easy to implement in the context of the standard Yee algorithm and are applicable for computational domains that involve quite arbitrary material and structural inhomogeneities.

Deterministic Reduced-Order Macromodels for Computing the Broadband Radiation-Field Pattern of Antenna Arrays in FDTD

The enhanced nodal-order reduction (ENOR) technique is used to perform model-order reduction (MOR) on a macromodel of a subgridded finite-difference time domain (FDTD) region which contains the deterministic fine structural features [1] of an aperture antenna array laying in a larger and relatively coarser FDTD grid, to solve the broadband time-varying electromagnetic fields emanating from the antenna array and to obtain the far-field radiation patterns. The far-field radiation pattern computed in FDTD is correlated against results computed through physical optics approximation. This work lays the foundation for a separate but related work to follow, in which we further develop the above deterministic macromodel into a stochastic macromodel that addresses the problem of uncertainty in fine features of structures with disparate spatial scales.

Stochastic Reduced-Order Electromagnetic Macromodels in FDTD

To enable an efficient stochastic-based design optimization methodology for multiscale structures of electrical devices, circuits, and systems, we propose the infusion of stochastic modeling with the electromagnetic macromodel in the method of finite-difference time domain (FDTD). We enhance the computational efficiency of the stochastic macromodel by applying the model order reduction techniques to produce the stochastic reduced-order macromodel. In addition, we provide a methodology and algorithms for the efficient generation and application of the stochastic reduced-order macromodel in the FDTD grid. The proposed methodology quantifies the impact of uncertainty in the electromagnetic system response that is manifested as random material and structural variations, through modeling and simulation. We demonstrate the proposed methodology by applying it to the computation of the stochastic transient electromagnetic fields in a 3-D bandgap structure comprising a rectangular waveguide, which contains an array of dielectric posts that exhibit uncertainty.

An Impedance Transfer Function Formulation for Reduced-Order Macromodels of Subgridded Regions in FDTD

Recently, model order reduction was applied to the macromodel of a subgridded region in the method of finite-difference time domain (FDTD), where an admittance transfer function formulation was used to model materials with electric conductivity. In this communication, we develop an impedance transfer function formulation for the reduced-order macromodel of a subgridded region; this formulation may be used to model materials exhibiting magnetic conductivity. The two macromodel types may be used together, in a complementary fashion, to model fine-featured subgridded regions in FDTD that contain materials exhibiting both electric and magnetic conductivity. Additionally, this communication greatly extends the range of both the deterministic and the stochastic macromodeling techniques recently developed in FDTD, thus enabling the solution of a much wider range of problems in computational electromagnetics.

A novel iterative method for approximating frequency response with equivalent pole/residues

Frequency domain modeling of interconnects has become the de facto standard for characterization in high-speed signal and power delivery systems. But time domain system level performance analysis calls for pole/residue representation followed by circuit level synthesis from the frequency domain sampled data model of interconnects. In this paper, a new iterative method that produces a set of equivalent poles and residues from discrete sampled frequency response data is proposed. Each iteration picks a few consecutive points from the given sampled response, identifies a local transfer function that matches their response and reduces error by subtracting the local transfer function. Two test cases, strip-line and package, are demonstrated. And results show that the proposed method has potential in fitting system frequency responses and has wide applications in signal and power integrity modeling and simulation of interconnect networks.

A novel algorithm for computing the zeros of transfer functions by local minima

We present a novel technique for computing the zeros of rational transfer functions in partial fraction form, by finding the local minima of the magnitude of the determinant of a block matrix comprised of state-space sub-matrices and the Laplace variable s. In this paper, the technique is developed for systems with real poles and residues, and successfully applied to a 10th order numerical example. In a separate paper, we further develop the technique to systems with complex-conjugate pairs of poles and residues.

Design and simulation of a four-arm hemispherical helix antenna realized through a stacked printed circuit board structure

Electrically small antennas have received much research attention and antenna designs have been developed that approach the Chu lower bound. One such antenna design is the spherical helix antenna which can achieve Q values that are 1.5 times the Chu limit. The spherical helix antenna presents a complex geometry that is a design challenge to implement, especially for use in printed circuit board assemblies. A novel hemispherical antenna design is developed and simulated that utilizes stacks of two-layer printed circuit boards to create the 3D hemispherical structure. The advantages of this approach are: the realization of complex antenna geometries using cost efficient printed circuit board technology and the ability to change substrate material to provide dielectric loading of the antenna, while achieving comparable performance with wire based designs.

Parallel, Optimized, Error Maxima-Agnostic, Pole Residue Equivalent System Solver

Fitting of sampled frequency response data to a rational function is often required for macromodeling of advanced microelectronic packages. The pole residue equivalent system solver (PRESS) method was recently proposed, as a novel fitting method that builds the global fit from local fits, computed from at most three data points at an error peak. To increase the fitting accuracy of PRESS, the error-maxima agnostic PRESS (EMPRESS) was proposed, but it is computationally intensive as the central processing unit needs to sequentially perform the local fits at all the frequency sample points before choosing the best among them. In this paper, we propose the parallel optimized EMPRESS (POEMPRESS) to reduce the computational complexity of EMPRESS while improving the fitting performance. POEMPRESS optimizes both the EMPRESS algorithm and its implementation through: 1) simplified local fit types, enabling the algorithm to rely on at most two data points only, and 2) an algorithm that can be implemented on graphics processing units for rapid parallel computation and evaluation of local fits at all the frequency points. The proposed algorithm is demonstrated on the interconnects of a microelectronic package. The results show that POEMPRESS is effective in fast macromodeling of complex interconnects for signal and power integrity simulations.

Electrically small PCB stack hemispherical helix antenna with air core

One benefit of electrically small antennas is the reduction in volume occupied by the antenna in a design. In order to further maximize the total volume afforded to the antenna, this paper investigates the impact of two different antenna core compositions that allow for circuit components to be placed within the antenna structure. An electrically small, hemispherical helix antenna realized through a stack of printed circuit boards has been evaluated with two different core configurations: an air core and a composite metal core. The composite metal core consists of both air and copper in order to achieve an integral Faraday cage, which is used to isolate the antenna from the components within the antenna structure.

A novel method for identifying complex zeros by searching the laplace-plane for local minima

In this paper, we develop a novel technique for computing the complex-conjugate zeros of rational transfer functions in partial fraction form, by searching the complex Laplace s-plane for the local minima of the determinant of a block matrix derived from the state-space equations. A higher resolution scan, in the vicinity of each local minima, may be used to increase precision of the zeros. This method can be applied to antennas to extract the zeros from the antenna response. One numerical example and one practical coax patch antenna example have been used to illustrate the efficiency and effectiveness of the proposed method.