Mohamed A. Moharram

GENERAL DECOUPLING NETWORK DESIGN BETWEEN TWO COUPLED ANTENNAS FOR MIMO APPLICATIONS

A general design procedure of decoupling networks, between two coupled antennas, is proposed using a single transmission line connected between the input ports of the antennas at a specifled distance. A rigorous analysis for the decoupling circuit is introduced considering the return loss of the antennas into calculations. Furthermore, using numerical optimization, enhancement of decoupling between the antenna ports achieved. Full-wave analysis and measurements are provided to verify the proposed technique.

Modified Wheeler cap method for measurement of antenna efficiency

A new non-circuit model method to predict the antenna efficiency via means of Wheeler cap measurements is proposed. The method uses an interpolated prediction of the quality factor of the antenna in the radiating and non-radiating modes with the help of Wheeler caps. The method works for narrow, multiple, and wide band antennas with a complete immunity to the effect of the cavity modes. Also, the semi-analytical approach in dealing with the reflection coefficient embraces an insightful view to individual resonators in the measurements. The proposed procedure provides a simpler, more accurate, and straight forward method to measure the antenna efficiency than other Wheeler cap based alternatives. The results of the proposed methods are verified with a commercial full wave solver and measurements.

Electromagnetic Scattering From Two-Dimensional Arbitrary Objects Using Random Auxiliary Sources

A simple, fast, and efficient numerical solution for the electromagnetic scattering from 2-D arbitrary objects is proposed. Based on the surface equivalence principle and the use of novel equivalent problems with random auxiliary sources, more degrees of freedom are added, resulting in significantly fast solutions. Furthermore, the simplicity of the implementation is ensured by placing equivalent sources away from the surfaces to avoid any singularity treatment. Nevertheless, an iterative solution is invoked to ensure an acceptable error in satisfying the boundary conditions through any randomly generated equivalent sources. The presented technique promises a significant reduction in the execution time and memory requirements compared with the surface-equivalent-based method of moments (MoM) as the inherent properties of this procedure are used. Moreover, different boundary conditions are considered. Furthermore, comprehensive studies are performed to ensure the best performance, and the advantages of the technique are highlighted. The results of the presented technique are compared with series solutions for circular cylinders and the MoM for arbitrarily shaped objects and combinations of different materials.

Contactless Wheeler cap concept for antenna radiation efficiency measurements

A new design for Wheeler cap is introduced that does not require contacts for the cavity cap to the ground plane. The concept is based on adding a flange of magnetic conductor that is parallel to the ground plane to suppress the waves from leaking out. The magnetic conductor is artificially realized using the electromagnetic bandgap (EBG) concept, which usually has a limited bandwidth. However, a cascaded design concept is used to widen the bandwidth beyond what is normally achievable. Since the cascading concept requires large flange size, a new compact EBG unit cell is designed and the bandwidth is limited to about 4:1. As such, the Wheeler cap becomes able to make measurements for wideband antennas and make it possible to use the same cap for varieties of antennas without the need for the cavity contact with the ground plane. Exact and simplified full wave models verify the proposed approach.

MIMO Antennas Efficiency Measurement Using Wheeler Caps

A simple and reliable measurement-based procedure is proposed to predict the radiation efficiency of multiple-input-multiple-output (MIMO) antennas using Wheeler caps. Based on only measuring the S-parameters of the MIMO antenna system in free-space and inside a shielded Wheeler cap, the method approximately predicts the radiation efficiency of each uncoupled MIMO antenna port. The method makes use of the recently developed contactless Wheeler cap concept and the improved quality factor method to facilitate the processing of the results. The procedure is verified by comparing full-wave results with prediction through measurements.

The use of Random Auxiliary Sources for reflectarray feed analysis

Accurate modeling for reflectarray antenna feeds is performed via using equivalent Random Auxiliary Sources (RAS) problems for both radiating and scattering modes. The developed models are proposed to accurately predict aperture efficiency components for reflectarray analysis. They are also used in an iterative process using the multiple reflection algorithm (P. Kildal et al, IEEE Trans. on Antennas and Propagations, 45, 7, 1130–1139, 1997) to accurately predict the gain and radiation pattern of the reflectarray antenna in the presence of the feed.

Design of optically transparent reflectarray antenna unit cell integrated with solar cells

An optically transparent reflectarray antenna unit cell design is proposed for integration with solar cells using staked perforated sheets of Acrylic. The design accommodates accurately the effect of solar cells on adjacent electromagnetic waves. The choice of the best possible transparent material for the design is presented based on the availability and ease of machining to the desired structure. Moreover, a study is presented to determine the optimum placement of solar cells with respect to the feed antenna to provide minimum losses in the antenna.

Optimum reflectarray feed pattern synthesis

An investigation is performed to find the optimum radiation patterns for a reflectarray feed for maximum aperture efficiency. The radiation pattern is synthesized to uniformly illuminate a reflectarray aperture within a specified subtended angle through an inverse problem. Theoretical efficiency analysis for the proposed radiation pattern and its realizable approximation is invoked in comparison to conventional cosine tapered radiation patterns showing potential increase in aperture efficiency.

Efficient frequency domain technique for electromagnetic scattering from arbitrary objects using the Random Auxiliary Sources

Summary form only given. Electromagnetic scattering from 3D objects of arbitrary boundary condition is presented implying the use of Random Auxiliary Sources (RAS) method. This technique provides a fast electromagnetic solver for arbitrarily shaped objects in the frequency domain. The technique is based on enforcing the boundary conditions by replacing the object by equivalent random electric and/or magnetic sources that are arbitrarily distributed within a controlled pre-specified domain. The proposed equivalent problems involve the use of few randomly distributed current filament for two dimensional problem (2D) and infinitesimal dipole sources of arbitrary orientations and moments for three dimensional problems, apart from the boundary of the object, which values are determined via least square method. Consequently, no need for singularity extraction is required. An acceptable tolerance bound of the boundary condition satisfaction error is insured using iterative procedure. Nevertheless, an optimum choice of procedure parameters is made via statistical analysis to provide the fastest and yet accurate solution. The present solutions provided by the proposed technique promise significant reductions in the execution time and memory requirements better than method of moment solutions based on surface integral equations. The technique is verified by comparing current distribution on spheres with Mies series solution. Also, significant simulation time reduction is achieved over the commercial integral equation solver of CST-MWS (CST Microwave Studio, Ver. 2012, Framingham, MA, 2012) package using the method of moments (MoM) with direct or iterative solvers. The potential of the proposed technique can be explored by comparing the execution time and the required number of unknowns with CST-MWS package using only single core processing with double precision. These results are shown as an example. The technique will be presented with more examples to further illustrate the simplicity and efficiency of the proposed technique.

Electromagnetic domain decomposition for 2D multi-scatterer problem using randomly distributed sources

An efficient procedure of electromagnetic scattering from a multi two dimensional objects is presented based on the use of Random Auxiliary Sources (RAS) method. Due to the use of the auxiliary sources, the numerical solution is simple and very fast as compared with the same procedure based on the Method of Moments (MoM). The results of the proposed technique are presented in comparison with the MoM.