Christian Brousseau

Characterization of an OAM Flat-Plate Antenna in the Millimeter Frequency Band

Electromagnetic waves bearing orbital angular momentum in the radio frequency range is a growing subject of study. The design of systems able to produce and/or to receive such waves is then of crucial importance. The aim of this letter is to characterize, in an anechoic chamber, a new type of antenna in the millimeter frequency band. The index-varying flat plate generates an electromagnetic wave carrying orbital angular momentum. We then extract the various modes from the radiated field.

Performance analysis of a hierarchical shipboard Wireless Sensor Network

Wireless Sensor Networks (WSN) have recently gained a great attention in several applications such as environmental monitoring and target tracking. Applying this technology to shipboard monitoring systems may be a cost-effective solution to reduce the cost of wires installation and maintenance. However, wireless communications on board ships may be severely obstructed by the metallic structure of bulkheads. In this paper, we analyze the efficiency of a shipboard WSN by measurement and simulation. A measurement campaign is conducted to study the radio wave propagation and to verify the feasibility of a WSN on board a ship. Based on the measurement results, a hierarchical group-based topology for a large-scale shipboard WSN is proposed. A realistic simulation model of the ship, taking into account the environment particularities, is then performed using OPNET network simulator. Performance of the WSN architecture is evaluated using the ZigBee model. Measurement results show the feasibility of WSN technology on board ships, while simulation results show significant performance of proposed architecture in terms of end-to-end delay and packet delivery ratio.

Wireless Sensor Network on board vessels

Wireless Sensor Networks (WSNs) have been used recently in different applications such as environmental monitoring and target tracking. Few papers have investigated the viability of this technology on board ships. We study in this paper the possibility of replacing the wired shipboard monitoring system by a WSN. This environment has a specific metallic structure which makes the wireless communication more difficult than in other classical indoor and outdoor environments. Two types of experiments have been carried out on board a ferry-type boat during sailings and stopovers. The first experiment consists of point-to-point measurements using ZigBee-based equipments and the second one consists of deploying and testing a WSN on board the ferry. These tests have been conducted during realistic conditions on board the ferry, which give a high level of reliability to results with respect to the earlier experiments on board ships moored to the harbor. In spite of the harsh metallic structure and the dynamic environments on board the ferry, the obtained results have shown that the wireless solution may be a cost-effective alternative to the huge amount of cables used currently to connect sensors to central control units.

Development of a tree structured hierarchical wavelet representation of synthetic database to NCTR

In this paper, problem of efficient representation of large database of target radar cross section is investigated in order to minimize memory requirements and recognition search time, using a tree structured hierarchical wavelet representation. Synthetic RCS of large aircrafts, in the HF-VHF bands, are used as experimental data. Hierarchical trees are built using wavelet multiresolution representation and K-means clustering algorithm. Criteria used to define these hierarchical trees are described and the obtained performances are presented.

Determination of the topological charge of a twisted beam with a Fresnel bi-prism

The self-interference pattern of a Laguerre Gaussian beam using a Fresnel bi-prism is shown to be very different from what could be expected from a usual laser beam. It resembles the interference pattern that could be obtained using a double slit experiment. The interferences are shifted and the topological charge and its sign can be readily determined considering the shift order of the pattern only. However, since there is no diffraction nor absorption losses unlike in a double slit interference, such a set up could be used even for low power twisted beams or beams with high topological charge. Even fractional topological charges could be determined with an absolute precision of 0.05.

Application of Wireless Sensor Network for the Monitoring Systems of Vessels

This chapter studies the feasibility of WSN on board ships. Several measurement campaigns are conducted on board a ferry-boat to verify the possibility of wireless communications between ship parts and to analyse the performance of WSN on board. These measurements aim at determining path loss models for typical shipboard environments and testing the possibility of wireless communication between adjacent rooms or adjacent decks. Using the results of these experiments, a WSN is tested on board the ferry. The results obtained from the measurement campaigns are then used to propose an architecture for a large-scale shipboard WSN. As the network test uses a limited number of nodes, the full monitoring system based on the proposed architecture is simulated using a network simulator.

New improvements in HF Ionospheric Communication and Direction Finding Systems

This chapter presents new HF (3–30 MHz) systems dedicated to ground to ground radio links with applications to ionospheric characterisation, channel modelling, radio communications, direction finding and single site localisation. The received signals result from the vectorial addition of the multipaths generated by the ionosphere. Considering the acquisitions at the outputs of an array of identical antennas (homogeneous array), a high level of spatial and temporal correlation can be observed. Therefore, it appears relevant to additionally discriminate the incoming modes by considering their polarisations. The purposes of the different systems which are described in the following sections are the use of a heterogeneous array. This polarisation-sensitive solution for array processing is principally characterized by the spatial distribution of non identical antennas. Consequently, the applications to digital communication involve a multi channel processing in the receiver as a SIMO (single input multiple output) structures. The correlation factors depend on the polarisation characteristics of the incident wave. Moreover, the heterogeneous array is still efficient with a reduced space diversity (set up in a limited place), the differences in the polarisation parameters balancing the weak values of the differential geometrical phases. In the following developments, the suggested techniques aim to take some better advantage of the ionospheric medium in several applications.

Possible use of the LOCAPI ionospheric prediction software to digital communications

Abstract The LOCAPI ionospheric propagation software, developed by the University of Rennes 1, uses the multiquasi-parabolic expression for the electron density profile. Its inputs are : date, frequency, transmitting and receiving locations. An original fast and accurate algorithm determines the output parameters : MUF, occultation LUF, elevation angles, group delays, pathlosses for an important range of possible O and X propagation modes. The accuracy of the simulated results permits the use of LOCAPI software to determine the slope of the group time delay as a function of frequency of HF radio links, for each propagation mode, and to evaluate the coherent bandwidth for a digital communication channel. In addition, improved results can be obtained if the polarization and antennas effects are taken into account.

Study of OAM waves reflection on different types of surfaces or objects at 2.45 GHz

Application of OAM waves in radiofrequency bands presents very interesting perspectives in communication and radar domains [1] [2]. These applications are based on the orthogonality property between the different topological charges of the received wave. In free space, this property can be conserved along the propagation path, but in a real environment, multipath effects can degrade the orthogonality between OAM modes, in particular due to the reflection on surfaces (ground, buildings ...) or objects, and the interference between waves.

Horn antenna for generating Orbital Angular Momentum (OAM) waves

We present a novel horn antenna to generate radio waves bearing Orbital Angular Momentum (OAM) by using a circular waveguide. The OAM mode ℓ = 1 is generated by using a spiral phase plate (SPP) inside a circular waveguide. We present here two methods to transform the classical guided modes to OAM wave. The resulting electrical field distribution and the radiation patterns evidence the properties of waves carrying OAM.