Juan F. Izquierdo

Mutual Coupling Compensation Matrices for Transmitting and Receiving Arrays

A general method to obtain a matrix which allows the compensation of mutual coupling effects in transmitting arrays for the total field in all directions is introduced. This method is independent of the numerical method used in the analysis and it can include the effect of the antenna platform. The starting point can be the active element patterns or the spherical mode expansion from spherical near-field antenna measurements. Additionally, the spherical mode expansion is also used to find a matrix which allows the compensation of mutual coupling effects in receiving arrays. Through this theory, a simple relation between the compensation matrices of the transmitting and the receiving arrays is found. As a consequence, the scattering matrix of a circuit that allows the simultaneous compensation of mutual coupling effects for the transmission and the reception problem can be easily defined. Finally, it will be shown how the capabilities of the compensation in all directions depend strongly on the array element.

Antenna Modeling by Elementary Sources Based on Spherical Waves Translation and Evolutionary Computation

A method based on spherical waves translation and evolutionary computation is used to model antennas efficiently. A set of infinitesimal dipoles is taken into account instead of the antenna, optimizing the number and positions of the dipoles by using a binary genetic algorithm (GA) for modeling the near field with a desired accuracy. It is shown how this approach can model volumetric antennas by a set of equivalent sources placed on a ground plane accurately. Moreover, large finite arrays can be quickly simulated since GA is only applied to analyze an isolated element, avoiding the need of distributing equivalent sources regularly over an equivalent surface.

Antenna-Generalized Scattering Matrix in Terms of Equivalent Infinitesimal Dipoles: Application to Finite Array Problems

A full-wave antenna modeling method by means of elementary sources described in terms of colocalized infinitesimal dipoles is presented in this paper. The procedure provides a generalized scattering matrix (GSM) in terms of equivalent infinitesimal dipoles from the GSM of the antenna by using rotation and translation of spherical modes. The number of equivalent infinitesimal dipoles and their positions are optimized by using a genetic algorithm. The application to the full-wave analysis of arrays is also presented, providing very accurate results even when the minimum spheres of the antennas in the array environment overlap considerably, which cannot be solved by the direct coupling of generalized scattering matrices in terms of spherical waves. Some examples of antenna modeling and their application to the analysis of arrays of antennas on a metallic plane will be shown.

Relation Between the Array Pattern Approach in Terms of Coupling Coefficients and Minimum Scattering Antennas

The well-known approach for the calculation of the radiation pattern of a finite array from the scattering parameters between the array feeding ports (coupling coefficients) is connected to the theory of minimum-scattering antennas (MS antennas) by making use of spherical mode expansions. It is shown how this approach for array radiation patterns involves an MS Antenna approximation in the first order of reflections (mutual coupling) between the elements in the array. For this purpose the generalized scattering matrix (GSM) formalism for a finite array in terms of spherical modes is used. Finally, the MS antenna theory is applied to estimate the radiation pattern of an array of waveguide-fed apertures.

Spherical-Waves-Based Analysis of Arrays of Volumetric Antennas With Overlapping Minimum Spheres

Arrays of volumetric antennas whose minimum spheres overlap are efficiently analyzed by means of translational addition theorems for spherical modes in this letter. For this purpose, an improved model of the isolated antenna in terms of elementary sources of infinitesimal dipoles is used. The model provides a generalized scattering matrix (GSM) in terms of infinitesimal dipoles that allows synthesizing the whole behavior of the isolated antenna and enables its precise application to array environments by using translational addition theorems. The search region for the optimization procedure that finds the positions of the elementary sources to model the isolated antenna has been extended to the volume occupied by the antenna, so that the model becomes very precise. As a consequence, even when the minimum spheres of the array elements are strongly overlapped, it provides accurate results since the equivalent models will never overlap. Additionally, the optimization procedure is carried out only once for a wide band. The proposed approach has been validated by means of two different radiating elements such as monopoles and dielectric resonator antennas (DRAs), with good agreements obtained in comparison to the full-wave results simulated by commercial software.

Full modeling of wideband volumetric antennas by elementary sources placed on the ground plane

A very accurate modeling technique of volumetric antennas is presented in this work. Specifically, an equivalent model based on a set of elementary sources of infinitesimal colocalized dipoles is obtained by using a genetic algorithm jointly with the application of the translational addition theorems of spherical waves. The equivalent sources that model the whole behavior of the volumetric antenna (not only the transmitting characteristics, but also its reflection, reception, and scattering properties) are located on the metallic ground plane, i.e. a planar set of sources is achieved to model nonplanar radiating devices, which increases its efficiency significantly, since the number of infinitesimal dipoles can be reduced considerably allowing the process to be much faster. Efficient wideband modeling is achieved by means of the construction of different models at very few frequency samples. The obtained full models are valid outside of the antenna minimum sphere. This way, it can be employed to the study of near–field interactions, such as arrays of antennas whose minimum spheres do not overlap.

Efficient Radiation Antenna Modeling via Orthogonal Matching Pursuit in Terms of Infinitesimal Dipoles

In this letter, the Orthogonal Matching Pursuit algorithm is introduced to model the radiation of antennas in terms of elementary sources. This algorithm, combined with the application of the Translational Addition Theorems of spherical waves, provides an accurate sparse approximation of the transmitting coefficients of spherical waves by placing a reduced set of infinitesimal dipoles in the antenna location. The efficiency of the proposed method is demonstrated by showing its capability to deal with electrically large antennas, the ease of implementation, and the computational efficiency. Numerical results are also presented for an array of cavity-backed patch antennas and a pyramidal horn antenna .

Array Thinning of Coupled Antennas Based on the Orthogonal Matching Pursuit Method and a Spherical-Wave Expansion for Far-Field Synthesis

This work is focused on the array thinning problem in shaped beam far-field synthesis. The orthogonal matching pursuit algorithm, which allows finding sparse solutions in linear systems, is combined with a fast full-wave analysis method for antenna arrays based on a spherical wave expansion, thereby taking mutual coupling between real antennas into account in the thinning process. To this aim, the original iterative algorithm is modified so that the current residual is obtained for the selected real coupled antennas in each step of the algorithm. In this way, the remaining nonselected elements are effectively removed instead of turned off. Results for arrays made up of microstrip patch antennas and dielectric resonator antennas arranged in triangular and rectangular lattices are presented.

A Fast Technique to Estimate the Mutual Coupling Coefficients From the Transmitting Characteristics of an Isolated Element

This letter presents a fast technique to estimate the mutual coupling between the elements in an antenna array from the transmitting characteristics of an isolated element. This approximation is obtained from the transmitting coefficients in terms of spherical waves in reciprocal antennas by using the translational addition theorems. The external coupling is interpreted as a contribution of all different orders of reflection between the array elements where the first order of coupling interactions does not depend on the scattering characteristics of the elements. This method is validated through the estimation of the mutual coupling between different elements compared to the full-wave response.

A novel hybrid technique for mutual coupling modeling of antennas with strongly overlapped minimum-spheres

A novel technique to calculate the mutual coupling between antennas whose minimum spheres are strongly overlapped is presented in this paper. For this purpose, we obtain a Generalized Scattering Matrix (GSM) in terms of equivalent infinitesimal dipoles from a 3-D Finite Element /Modal Analysis method by making use of Singular Value Decomposition (SVD) and rotation and translation of spherical modes. Since infinitesimal dipoles correspond with the lower order of spherical modes whose minimum spheres have a vanishing radius, the overlapping of higher-order spherical modes is avoided. Several examples will be given, showing that the efficiency of the method to analyze arrays is improved, and the results will be compared with those provided by purely numerical full-wave methods.