Yaxun Liu

Application of DCIM to MPIE-MoM analysis of 3D PEC objects in multilayered media

The Formulation-C Greens functions for multilayered media are reformulated in this paper to extract z-dependent part when the source and observation points are in different layers. The discrete complex image method (DCIM), is applied to obtain complex images independent on z but dependent on z/spl acute/. For simulation of three-dimensional (3-D) perfectly electrical conduction (PEC) objects penetrating two or more layers, tables of complex images are built in a z/spl acute/-grid. During the matrix-filling stage of the mixed-potential integral equation, together with method of moments (MPIE-MoM), the spatial-domain Greens functions are interpolated from values in the z/spl acute/-grid, while these values are calculated from complex images in the z/spl acute/-grid. This interpolation scheme is more efficient than those directly storing the spatial-domain Greens functions. Numerical examples are given for analyzing a dipole in a two-layered media.

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.

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.

Printed plane-filling fractal antennas for UHF band

The printed Hilbert antenna has been used for UHF band since it is small, easy to fabricate and impedance-match to common types of planar transmission lines (X. Chen et al, IEEE Soc. Int. Conf. on Antennas and Propag., vol. 2, pp. 581-584, 2003). In this research we studied printed plane-filling antennas of different shapes, including Hilbert, Moore, Peano, Wunderlich 1, 2 and 3 curves. The input impedance and current distribution are calculated through method of moments (MoM) with mixed-potential integral equations (MPIE) formulation. The resonant frequencies are obtained by searching for the roots of the imaginary part of the input impedance. The dependence of the resonant frequency on the shape and size of the antennas are studied, and the current distributions along the antennas at resonant frequency are compared.

Comparison of SIE-MoM and VIE-MoM for determination of complex resonant frequency of dielectric resonators

The volume integral equation (VIE) and the surface integral equation (SIE) formulations of the resonant mode, frequency, and quality factor of arbitrarily shaped dielectric resonators (DR) in free space and in a semi-open multilayered medium are compared. Although both methods are very efficient tools for resonant field/frequency determination for microwave circuit design and analysis, we have found that SIE is not suitable for determining the quality factor of high quality DRs of interest in high performance microwave filters and oscillators. As the quality factor goes beyond several hundred, the quality factor obtained through SIE-MoM becomes erroneous. It may fluctuate randomly depending on the mesh. However, VIE-MoM has been found to be robust and reliable for DRs with very high quality factors.

Gain improvement of an array of sequentially rotated circularly polarized microstrip antennas using stacked parasitic patches

Sequentially rotated microstrip array antennas have been extensively used for circularly polarized radiation due to their wide VSWR bandwidth and polarization purity; however, in many cases, these arrays do not meet gain requirements. Stacked parasitic patches have been used to improve the gain of an array of sequentially rotated circularly polarized microstrip antennas. The gain can be improved within 2.5-3.2 dB by adding one parasitic patch to each array element, or 3-4 dB by adding two parasitic patches per element, with minor side effects on axial ratio. The dependence of the gain improvement on the height and size of the parasitic patches has been studied and verified by simulations. It is found that there are multiple local maxima in the curve of the gain versus the height of the parasitic patch. The maxima occur at heights near to multiples of a half of the wavelength in the spacer medium. Since the parasitic patches are fabricated on low dielectric constant substrates and are separated from the exciting patch by spacer or foam, this method of gain improvement is very simple and at the same time cost-effective.

Determination of resonant modes of dielectric resonators using MoM-SIE with combined entire-domain and subdomain basis functions

Method of moments (MoM) combined with surface integral equation (SIE) is a favorable approach for determining resonant modes of dielectric resonators. To decrease the number of unknowns, the subdomain basis functions are combined with an entire-domain basis function which is an approximate solution of the resonant mode. Since the main profile of the current distribution can be represented by the entire-domain basis function, only small refinements are needed for better depiction of the current distribution. As an example, the TE/sub 11/spl delta// mode of a rectangular dielectric resonator is simulated and compared with other methods.

Degenerated TE/sup x/y/ modes of rectangular DR in MIC environment and their application to dual-mode bandpass filter

Most previous research on rectangular DRs (dielectric resonators) has been focused on the TE/sup z//sub 11/spl delta// mode, where the z-axis is perpendicular to the substrate. However, for designing a dual-mode bandpass filter, two degenerated modes which have the same resonant frequency are needed. The degenerated TE/sup x/y/ modes of a rectangular DR with square cross-section in an MIC environment and their coupling to a microstrip line are studied. By cutting off a corner of the DR, the coupling between these two modes can be controlled. A dual-mode band-pass filter is designed and HFSS simulation results are presented.

The coupling between two TE/sup z//sub 11/spl delta//-mode rectangular DRs in MIC environment

For the design of microstrip line coupled dielectric resonator filters, the coupling coefficient between two dielectric resonators is required. Although research has been done on the coupling of circular DRs and rectangular DRs in free space, the coupling between two rectangular DRs in the MIC environment has not been fully studied. The method of moments, with combined entire-domain and subdomain basis functions, is applied to the volume integral equation for the simulation of two rectangular DRs in the MIC environment. The resonant frequency of the even-and odd-mode of the entire structure is obtained by searching for the minima of the reciprocal of the condition number of the impedance matrix. The coupling coefficient is then calculated based on the resonant frequencies. Numerical. examples are given to show the dependence of the coupling coefficient on the distance between two DRs.