Tunable Reflectarray Cell for Wide Angle Beam-Steering Radar Applications

An electronically tunable reflectarray element is proposed in this work to design beam-steering antennas useful for radar applications. A reduced size reflectarray unit cell is properly synthesized in order to extend the antenna beam scanning capabilities within a wider angular region. The radiating structure is accurately optimized to provide a full phase tuning range by adopting a single varactor load as phase shifter element. A 0.46λ-reflectarray cell is designed at the frequency of 11.5？GHz, obtaining a phase agility of about 330°. The cell is successfully adopted for the design of a reconfigurable reflectarray. The antenna is numerically tested for different configurations of the varactors capacitance values, and good beam-steering performances are demonstrated within a wide angular range. 1. Introduction Modern radar systems usually adopt phased array antennas as transmission/reception modules. Phased arrays integrate the actual radiating structures, consisting of an array of elementary antennas, with phase shifter components, tunable power amplifiers, and switches [1]. These additional devices allow to control the input signal of each radiating element, thus offering the capabilities to electronically steer the radiated main beam. Phased arrays offer many advantages with respect to mechanically scanned antennas, such as low profile, agile beams, and scalability. Furthermore, electronically scanned antennas offer increased data rates, instantaneous positioning of the radar beam, avoiding also mechanical vibrations, and errors associated with mechanically scanned systems. An attractive alternative to traditional phased array antennas is offered by the reflectarray antenna concept [2]. As a matter of fact, reflectarrays may be specifically designed also for applications requiring pattern reconfigurability or beam-scanning capabilities. Reconfigurable reflectarrays may offer many advantages over conventional phased arrays, such as reduced costs and volume, a simpler architecture due to the absence of complicated beam-forming networks, and increased efficiencies due to the adoption of spatial feeding. They consist of an array of microstrip elements illuminated by a feed antenna (Figure 1(a)). Each radiator is properly designed to compensate for the phase delay in the path coming from the feed and to introduce a phase contribution able to create a total reradiated field with some desired features, such as prescribed beam directions and/or shapes. Figure 1: (a) Reflectarray antenna and (b) aperture-coupled reconfigurable reflectarray cell. Many