A Multiple Beam Antenna System using Discrete Lens Arrays

Conventional radar systems are usually based on complex structures employing not only high performance antennas but also baseband or RF processors. The antennas shall scan the space in the search for potential targets. Scanning can be usually made either mechanically or electronically. Mechanical scanning, although trivial in its conception, is usually expensive and not agile enough for some applications. Electronic scanning, a very elegant approach, usually demands the use of phase shifters or complex beam forming architectures, which can also lead to very expensive systems. As an example, Butler Matrixes, which allows the generation of multiple beams, make use of complex structures with vertical transitions, rather cumbersome when dealing with planar circuits. In addition, phase shifters at high frequencies introduce undesirable losses that degrade the radar noise figure. In this paper, a simple solution using lenses is presented, using a planar construction. A discrete lens array (DLA) operating at 8.2GHz, built entirely with conventional planar circuit techniques is designed and measured. The prototype was able to scan the far field region within -40deg and +40deg, both in azimuth and elevation as for a circular lens. RF-MEMS switches can be employed for confiring agility to the system. The optical system proposed here allows a first-order real time determination of the direction of arrival (DOA) for a target, using a DLA as the main element. The DOA accuracy is a function of the array size, as shown in this work.