The direction finding performances of a novel passive, wideband and radiation pattern reconfigurable vector antenna are reported. Accurate estimation of the direction of arrival of incoming electromagnetic fields across the 3-D half-space is obtained over a 1.69:1 impedance bandwidth from the radiation pattern reconfigurability of a 4-port vector antenna. This antenna consists of only two orthogonal and co-located semi-circular arrays of Vivaldi antennas. Due to its reconfigurability, more radiation patterns can be used in addition to those commonly employed in standard vector antennas to estimate the direction of arrival of incoming electromagnetic fields. A new method based on the Cramer-Rao lower bound is proposed in order to select the radiation pattern diversity that improves the estimation accuracy across the overall bandwidth. Measured and simulated results are found in good agreement. The present study brings a further step towards developing new concepts of reconfigurable vector antennas.
The implementation of wind farms establishment in France is increasing. When wind farms are located close to radionavigation systems, it becomes important to evaluate their electromagnetic effects on existing radionavigation instalations. In this study, the radionavigation system is a VOR (VHF omnidirectional radio) operating at about 110 MHz. Because rotor blades are made of a balsa and dielectric multilayers composition, their electromagnetic behavior differs from that of metal blades at VHF frequences. In this study, we first obtain an electromagnetic CAD model from a real structural design; then we calculate the far field scattering matrix from an integral method (CESC code [1] method of moment) for a (30 m) dielectric blade and compare it with a metal one using RCS (radar cross section) calculation. The impact of (40 m long) dielectric blades is compared with the (65 m high) metal mast effect in terms of scattered field, and then the VOR error (bearing error) is evaluated. These results are analyzed for several geometrical configurations of a three-bladed rotor and compared with the mast. The study is extended on wind farms to discuss geometrical configuration effects with regard to a VOR location.
Abstract-In this letter, a reconfigurable grounded wideband antenna is proposed in view of vector sensor applications. This antenna combines two orthogonal and colocated semi-circular arrays of Vivaldi antennas mounted over a metallic support. The radiation patterns of two wideband magnetic dipoles and one wideband electric dipole can be synthesized thanks to an appropriate antenna excitation. Measurement results are in good agreement with the simulated results obtained from fullwave electromagnetic simulations. The proposed antenna exhibits stable radiation patterns over a wide impedance bandwidth of 1.69:1, a high radiation efficiency and a good isolation between the antenna input ports. This antenna is a good candidate for wideband 3D direction finding using a vector sensor.Index Terms-wideband magnetic and electric dipoles, Vivaldi antennas, vector sensor, direction-ofarrival antenna, reconfigurable antenna.
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