Khaldoun Alkhalifeh

Efficient MoM Simulation of 3-D Antennas in the Vicinity of the Ground

A novel fast technique is presented to account for the effect of an arbitrary soil permittivity in the analysis of ground penetrating radar antennas in the presence of a flat layered ground. We named the method fast ground coupling matrix because it is expressed as an additional method-of-moment (MoM) impedance matrix obtained from the radiation patterns of the basis/testing functions and the ground reflection coefficient. The advantage of this method is the independence of radiation patterns from the grounds physical and electromagnetic parameters (layer thickness, complex permittivity, permeability, and so on). The new matrix formulation efficiently calculates the impedance matrix due to the grounds contribution, with a loop over the ground parameters (permittivity, conductivity, and/or permeability), and changing the distance between antenna and ground. The number of samples in (complex) spectral domain is dramatically reduced by explicitly compensating truncation with aliasing errors in the spectral integration. To demonstrate the accuracy and efficiency of the proposed method, numerical results for 3-D metallic Vivaldi and typical dipole antennas are presented. Good agreement among the exact MoM solutions, the simulation results, and measured data is observed over an ultrawide bandwidth.

Wheel-of-time array devoted to near-field imaging applications

The design and fabrication of an ultrawideband (UWB) imaging radar system for near-field applications is presented. First, the geometric parameters related to the elliptical curve of Vivaldi antenna, i.e. major and minor radii and center, are introduced as additional design parameters. Second, the complete circular UWB radar imaging system is fabricated. Finally, time-domain responses of a target under test are processed. An initial near-field image of the target under test in the area of radiation exposure is depicted, and the target is localized.

Design of a 3D UWB linear array of Vivaldi antennas devoted to water leaks detection

The design of a linear Vivaldi antenna array for water leaks detection is presented. We show the 3D antenna design with the bandwidth of interest between 250-2000 MHz, which is necessary for sufficient depth penetration and high resolution imaging and characterization. New modifications on features with respect to the traditional Vivaldi antenna design are discussed. The radiation patterns show that the directivity increases with frequency. Near-fields in E and H planes in the front of the antenna are depicted and display smooth spreading over a sufficiently narrow area of radiation exposure. The impact of the ground on the antenna is analyzed. The complete design of a linear array of 4 elements is presented, and the mutual coupling between elements is illustrated.

Open-circuit to embedded pattern approach with harmonic optimization in ESPAR

The radiation characteristics of Electronically Steerable Parasitic Array Radiators (ESPAR) can be modified by changing the loads attached to the parasitic radiators. The open-circuit pattern to embedded pattern approach is employed to compute the radiation pattern, when dynamic loads are attached to the parasitic radiators. It provides results exactly matching to those of full-wave simulations without any approximation and it is computationally highly efficient in the optimization phase. The weighted mean squared error is used as a cost function for optimization to obtain the objective radiation pattern. The optimization is carried out using a harmonic decomposition of load values versus the position index of parasitic elements and it provides results within a minute with an average error below 1dB between objective radiation pattern and obtained radiation pattern within the main lobe.

Compact mathematical description of sectorially symmetrical arrays

The proposed approach is being developed in the framework of compact direction-finding systems that include polarization estimation. This work concentrates on sectorially symmetrical arrays, and combines the classical Array Scanning Method (ASM) with a Spherical Waves Decomposition (SWD) in order to directly compute the SWD coefficients based on the ASM current distributions. This approach offers the advantages of a fast computation based on the current distribution on only one antenna, as well as a reduced set of parameters needed to evaluate the embedded element patterns.