J. Zapata

Analysis of passive microwave circuits by using a hybrid 2-D and 3-D finite-element mode-matching method

A method of analysis of passive microwave circuits based on the segmentation concept is introduced. Complex three-dimensional (3-D) structures are divided into regions delimited by arbitrarily shaped waveguide ports, in which a modal expansion of the field is made. Waveguides can also be filled with inhomogeneous and/or anisotropic media. The regions are analyzed by the mode-matching method (MM) combined with either a two-dimensional (2-D) finite-element method (2-D FEM/MM) or a 3-D FEM (3-D FEM/MM). Open regions are dealt with using the perfectly matched layer. The result of the 3-D FEM analysis is a multimode multiport generalized admittance matrix, from which a generalized scattering matrix is computed. Finally, the method is applied to the analysis of a coax-to-waveguide transition and of a pair of unshielded microstrip lines coupled through an aperture in the common ground plane.

Analysis of cavity-backed microstrip antennas by a 3-D finite element/segmentation method and a matrix Lanczos-Pade algorithm (SFELP)

A methodology that combines the domain segmentation technique, the three-dimensional finite-element method (3-D FEM), and a symmetric matrix Lanczos-Pade algorithm, is used for the fast frequency-sweep analysis of cavity-backed microstrip antennas by using a spherical mode expansion on the radiation boundary. Results for a circular patch antenna validate the proposed method.

SFELP-an efficient methodology for microwave circuit analysis

A hybrid method based on the segmentation technique, the finite-element method, and a matrix Lanczos-Pade algorithm (SFELP) for the analysis of microwave circuits is introduced in this paper. This method computes symmetric matrix-Pade approximations of a matrix transfer function for any number of inputs and outputs via a Lanczos-type process (SyMPVL) for obtaining the generalized admittance matrix of a microwave circuit on a wide band of frequencies. The formulation that provides the three-dimensional finite-element/segmentation method is suitable for applying the symmetric Pade via Lanczos algorithm, except for the frequency dependence of the matrix of excitation vectors. In this paper, this problem is analytically overcome for the case in which excitation vectors correspond to modes of homogeneous waveguides or transmission lines. The accuracy and efficiency of the proposed method are shown by means of different examples.

Broad-band cavity-backed and capacitively probe-fed microstrip patch arrays

The full wave analysis method developed Gonzalez, Encinar, Zapata and Lambea, (see IEEE Trans. Antennas Propagat., vol.46, no.2, 1998) is applied to investigate cavity-backed microstrip patch arrays with thick substrates and coaxially fed through a capacitive coupling. The objective is to obtain a broad bandwidth without a decrease in the scan coverage and efficiency and without the drawback of a high cross-polarisation owing to the surface-wave generation.

Full-wave analysis of cavity-backed and probe-fed microstrip patch arrays by a hybrid mode-matching generalized scattering matrix and finite-element method

A full-wave method to analyze probe-fed infinite phased arrays of arbitrarily shaped microstrip patches residing in a cavity is proposed. The method is based on a combination of the mode matching and finite-element methods (MM-FEM) and provides a rigorous characterization of the coaxial feed. The radiated field to the half space is expressed as a Floquets harmonic expansion reducing the analysis to a single elementary cell of the periodic antenna. The unit cell is analyzed as an open-ended succession of homogeneous waveguides of diverse cross sections. Each transition between waveguides is solved by a hybrid MM-FEM procedure to obtain its generalized scattering matrix (GSM). Finally, the GSM of the structure, which characterizes the array, is obtained from the individual GSMs by a cascading process. The method is also extended to the analysis of conventional probe-fed microstrip arrays by using the waveguide simulator model. Several prototypes, implemented and measured in a waveguide simulator, have been analyzed to prove the validity and efficiency of the proposed method.

Radiation pattern computation of cavity-backed and probe-fed stacked microstrip patch arrays

In this paper, two different methods based on Floquets harmonic expansion of the electromagnetic field in half-space are proposed to determine the active element pattern of infinite planar arrays. They allow us to obtain the radiating characteristics without the limitations of the conventional method from the active reflection coefficient. Both are applied to analyze the scan performance in the case of probe-fed and cavity-backed microstrip arrays from its generalized scattering matrix (GSM), computed previously with a full wave numerical procedure. Numerical results are presented and compared with other techniques.

An efficient finite element formulation to analyze waveguides with lossy inhomogeneous bi-anisotropic materials

In this paper a finite element formulation in terms of the magnetic field is presented for the analysis of waveguides with bianisotropic media. Such a formulation can deal with lossy inhomogeneous materials characterized by simultaneous permittivity, permeability, and cross-coupling (as in optical activity) arbitrary full tensors. The analysis takes into account arbitrary cross sections, and results in spurious-mode suppression, complex-mode computation, and the possibility of alternatively specifying the frequency or the complex propagation constant as an input parameter. In this way, many novel classes of waveguides with promising applications, such as chirowaveguides and chiroferrite-waveguides, can be analyzed. The formulation leads to a quadratic sparse eigenvalue problem which is transformed into a sparse generalized eigenvalue problem. This eigensystem is solved by the subspace method, the sparsity of the matrices being fully utilized. The proposed method has been validated by analyzing waveguides with biisotropic and bianisotropic materials. The agreement with previously published data is found to be excellent.

Microwave Circuit Design by Means of Direct Decomposition in the Finite-Element Method

In this paper, a domain decomposition approach for design purposes is proposed. The analysis domain is divided into subdomains according to the arbitrarily shaped parts that should be modified in the synthesis process. A full-wave matrix-valued transfer function describes each decomposition subdomain, namely, an admittance-type matrix. Field continuity between subdomains is directly enforced by an admittance matrix connection. This methodology makes it possible to analyze only those parts of the analysis domain that are supposed to evolve in order to satisfy the design specifications. Furthermore, several modifications in the shape of the components are allowed as a consequence of the easy matrix connection process, where the consideration of different admittance-type matrices or absence of them gives rise to distinct geometric structures. A model order reduction technique is also considered for fast frequency sweeping. Finally, several numerical examples illustrate the capabilities of the proposed procedure, as well as its accuracy.

Efficient full-wave analysis of mutual coupling between cavity-backed microstrip patch antennas

A full-wave methodology for a broadband analysis of isolated cavity-backed and probe-fed arbitrarily shaped microstrip patch antennas is combined with an analytical method based on the properties of rotation and translation of spherical modes for obtaining an efficient scattering matrix description of the mutual coupling in a two-element array. The proposed procedure is validated and results are given for identical circular cavity-backed patch antennas.

MAM—A Multipurpose Admittance Matrix for Antenna Design Via the Finite Element Method

Further exploitation of matrix-valued transfer functions describing electromagnetic phenomena is proposed. In addition to traditional modal port inclusion in finite element analysis, new computational domain ports are allowed as field expansion in terms of piecewise basis functions is considered. An admittance-type matrix arises and, as a result, a multiport network manages all electromagnetic complexity. Circuit handling of this network efficiently outperforms full-wave analyses for different modifications of the actual structure, thus, making it possible to use this methodology for design purposes. A model order reduction process is also used for fast frequency sweeping and special emphasis is placed on its accuracy. Finally, numerical examples demonstrate the robustness, capability and versatility of the proposed technique.