Mohammed Serhir

Transient UWB Antenna Near-Field and Far-Field Assessment From Time Domain Planar Near-Field Characterization: Simulation and Measurement Investigations

In this paper, we present the experimental validation of time domain (TD) near-field to near-field (NFNF) and near-field to far-field (NFFF) transformations for ultrawideband (UWB) antenna transient characterization. The used computation schemes for near-field to near- or far-field transformations are based on the Greens function representation of the radiated field where NF and FF are directly calculated in the TD. The first step of the validation process comprises the electromagnetic simulation results dedicated to evaluate the accuracy of NFFF and NFNF transformations. The second step uses near-field measurement data of a Vivaldi antenna to validate the developed computation schemes, whereas the measurement and calibration procedures are fully described. The measured NF data using Supelec planar and cylindrical near-field facilities are also compared with the electromagnetic simulation transient results of the Vivaldi antenna.

Antenna Far-Field Assessment From Near-Field Measured Over Arbitrary Surfaces

A matrix method is developed to calculate the antennas radiation pattern from near-field data measured over arbitrary surfaces. The principle of the matrix method is to determine the modal expansion coefficients by solving a system of linear equations. The number of required measured samples is deduced from the number of modes considering the cylindrical or the spherical wave expansion of antenna radiated fields. Once the modal coefficients are known, the far field of the antenna under test (AUT) is obtained. The matrix method has been implemented, and its potentialities are evaluated using two specific arbitrary surfaces (square section cylinder surrounding the AUT and a closed cylinder). Numerical (dipoles array) and experimental (base station antenna) results are provided to illustrate the efficiency and the stability of the proposed method.

A Compact Dual-Polarized 3:1 Bandwidth Omnidirectional Array of Spiral Antennas

A circularly polarized wideband omnidirectional array of spiral antennas is presented. It covers the frequency band from 1.2 up to 3.6 GHz while keeping a good S11 and an omnidirectional coverage. This array achieved a dual polarization using left- and right-hand Archimedean spiral antennas. The gain of the array is enhanced using a unique cavity for the entire array, and the realized gain is above the maximum theoretical gain of a single spiral antenna.

A wideband omnidirectional conformal array for passive radar

A wideband antenna array, conformed to a cylinder, is presented. It covers 360° from 1.2 GHz up to 3.6 GHz. It is made of 10 spiral antennas and backed by a ten face ground plane. Its diameter is 28cm, so almost one lambda at 1.2 GHz. It is designed for passive radar.

On the radiation of antennas within a subwavelength-separated wire distribution, super-localization and time-reversal

Electromagnetic time-reversal enabling potential super-resolution in telecommunication systems when operated within complex media - imaging is left aside from now - has been much studied, in particular since [1]. Yet it remains a controversial issue [2]. Here, one illustrates what could be the behavior of a radiating broad-frequency device when operated in a properly-structured, finitely-extended medium. One attempts to see whether the field observed in that medium (deterministic, no randomness here as sometimes ad-hoc explanation) and outside it, in the far-field or at least far enough (so as evanescent fields in principle do not matter) can be such that super-resolution, or better said super-localization, can be achieved via time-reversal.

Super-resolution characteristics based on time-reversed single-frequency electromagnetic wave

ABSTRACT A sub-wavelength three-antenna array that is able to perform super-resolution focusing with single-frequency signal excitations is investigated using time-reversal. The antenna array is loaded with a set of uniformly distributed thin metal wires, which when combined with single-frequency electromagnetic waves from a time-reversal mirror yields a 1/35 wavelength super-resolution focusing at the targeted antenna. The length of the metal wires in particular determines the frequency band enabling super-resolution performance. The results have significance for the super-resolution investigation of multi-band compact antenna arrays involving micro-structures, with potential linkage with recent studies on super-resolution mechanisms in deterministic complex media.