Frequency Selective Surfaces for Extended Bandwidth Backing Reflector Functions

with the use of frequency selective surfaces (FSS) to increase the efficiency bandwidth product in wideband antenna arrays, whose efficiency is limited by the front-to-back ratio. If the backing reflector for the antenna is realized through a single metal plane solution, its location will be suitable only on a relatively limited frequency range especially if wide angle scanning is required. In order to extend the frequency range of usability, an FSS can be sandwiched between the antenna and the ground plane, providing an additional reflecting plane for an higher frequency band. The possibility to integrate in the antenna different functionalities, otherwise performed by several antennas, is also discussed in the paper. The proposed backing structure composed by the FSS and the ground plane has been designed to be used in conjunction with a wideband antenna consisting of an array of connected dipoles. A hardware demonstrator of the backing structure has also been manufactured and tested. CURRENT trends in the design of military ship masts foresee the integration of several functionalities on the same antenna aperture in order to satisfy the demand of an increasing number of services to be installed on board, while still responding to the requirement of reducing the radar cross-section (RCS) of the ship itself. In view of this, multiband/broadband planar or quasi-planar antennas with large scanning capabilities are required. Existing solutions, such as the Vivaldi antenna show good performances at the cost of low cross polarization purity, which limits the range of possible applications. Other antennas, such as the connected array without a backing reflector, as described in , show excellent performances in terms of operating bandwidth, but an efficiency that can be as low as 50 %, because of the poor front-to-back ratio. To overcome this problem, the most common approach consists in introducing a backing reflector. This backing reflector should be located at a distance of a small fraction of wavelength from the antenna if maximum gain is required, as outlined in . However, a widely adopted choice is to place the reflector at a quarter wavelength distance from the antenna, as for example in . Although this choice still allows obtaining a good antenna matching, with only a modest degradation of the achievable gain, the functioning of the backing reflector is optimal only in a relatively small frequency band . Therefore, the improvement of the front-to-back ratio comes at the expense of the antenna bandwidth

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