Rémi Sarkis

Circular array of wideband 3D Vivaldi antennas

This communication presents a novel 3D Vivaldi antenna array with 4∶1 bandwidth without the need for balun feeding. A circular array of 8 elements of this 3D Vivaldi antenna is simulated using the Array Scanning Method applied to Method of Moments. It is found that connecting the antennas provides a smoother frequency response. The array is well suited for wideband direction finding with good polarimetric sensitivity. Its calibration made easy by the circular symmetry of the structure.

Compact representation of the effects of mutual coupling in non-regular arrays devoted to the SKA telescope

This paper shows how an accurate, compact and fast representation of the embedded element patterns can be provided by the combination of spherical waves. Examples will be given for wideband non-regular arrays of bow-tie antennas containing up to 1000 elements, at the level of embedded-element and array patterns. It is expected that the provided representations will facilitate research on methods for array calibration for the SKA project.

Gridded Vivaldi Antenna Feed System for the Northern Cross Radio Telescope

The design of a broadband antenna feed system for the cylindrical offset parabolic reflector of the Italian Northern Cross radio telescope is described. Its operative frequency band spans from the Low Frequency Array (LOFAR) upper band, i.e. 120-240 MHz, to the present telescope operative band centered at 408 MHz. The proposed configuration consists of a linear array of gridded Vivaldi (tapered slot) radiators inside a wired subreflector. Numerical simulations have been carried out using both commercial software and a specialized Method-of-Moments approach. They show that the designed feed system provides both a good impedance matching and an efficient illumination of the main reflector in the overall frequency band.

An Open-Source Code for the Calculation of the Effects of Mutual Coupling in Arrays of Wires and for the ASM-MBF Method

A general description of mutual coupling in finite and infinite antenna arrays is provided and an open-source code is described for the analysis of mutual coupling in linear arrays of parallel dipoles. The ASM-MBF method is illustrated with the help of that code and it is shown that the method also can handle situations where eigenmodes are supported by the array: single machine precision is achieved with four Macro Basis Functions only.

Modeling of an Ultra-Wideband antenna array devoted to near-field imaging

This paper presents the mutual coupling analysis in Ultra-Wideband (UWB) antenna arrays devoted to near-field imaging from 1 to 4 GHz. Vivaldi antennas have been designed to build the antenna array. The Method of Moments (MoM) in iterative form is used to find the array impedance matrix and the different near-field patterns. Very strong agreement between the simulated and the measured coupling coefficients, testifies the validity of the modelling of the antenna array. The localization of isolated targets with an accuracy of the order of 2 mm is also demonstrated.

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.

Fast numerical method for Focal Plane Array simulation of 3D Vivaldi antennas

This paper presents the design and analysis of large Focal Plane Arrays (FPA) of thick Taper Slot Antennas (TSA). This communication extends the application of fast numerical method based on Macro Basis Functions (MBF) produced by Array Scanning Method (ASM) to the simulation of planar array of 3D Vivaldi antennas. This simulation technique is validated through the comparison with the brute force solution of a planar array containing 31 thick bowtie antennas. We also studied an array of 71 thick Vivaldi antennas in which we investigated the truncation effects at the array borders. Finally, the manufacturing feasibility of this type of thick Vivaldi antennas is verified by the development and measurement of an array of 4 thick metal only Taper Slot Antennas.

Amplitude and phase correction of the radiation pattern in compact planar antenna array for direction finding applications

In the design of compact antenna arrays, high coupling causes identical antennas to present different radiation patterns depending on their position in the array. In direction finding algorithms similar radiators are assumed to have the same radiation pattern, that is why it is important to present a simple procedure to compensate this difference. The purpose of this communication is to present a very compact array design devoted to direction finding applications in emergency situations, together with a correction procedure for the amplitude and phase of the radiation pattern, based on a minimal set of measurements.

Fast full-wave analysis of wideband circular antenna arrays devoted to accurate direction-finding and polarimetry

Calibration at the array level as well as the development of specific algorithms for direction finding and accurate polarimetric estimation are presented for a circular array of eight connected wideband 3D Taper Slot Antennas (TSA). A straight relation is established between the number of spherical modes used to describe the embedded element patterns and the precision on the angle of arrival and polarization estimation.

Thick Vivaldi antenna for focal plane applications

This communication deals with the design of metal only thick Vivaldi antenna, hollow inside to host a Low Noise Amplifier adjacent to the antenna, that is suitable to focal plane array devoted to radio astronomy. The impedance frequency band of the array goes from 0.75 GHz to 1.5 GHz and has a half-power beam width of 60 degrees over the same frequency band. Numerical simulations have been carried out to study the radiation patterns using the Method-of-Moments approach for infinite array simulations, followed by the implementation of fast numerical methods combining the Array Scanning Method with Macro basis Functions for the simulation of an array consisting of 5x5 elements.