A Parallel-Plate Luneburg Lens Sensor Concept for Automatic Cruise Control Applications Marwan Younis, Alexander Herschlein, Young Jin Park and Werner Wiesbeck Institut fur Hochstfrequenztechnik und Elektronik, Universitat Karlsruhe, Kaiserstr. 12, 76128 Karlsruhe, Germany Tel. +49-(0)721-608 6267 E-Mail: m.younisieee.org ABSTRACT A new system concept for Automatic Cruise Control (ACC) is introduced which is able of covering a wide field-of-view and offers the ability of high azimuth resolution for the detection of several object within one range cell. The system makes use of digital beamforming on-receive-only to simplify the hardware requirements and to facilitate the use of high efficiency processing techniques. INTRODUCTION Future automotive Automatic Cruise Control (ACC) systems require sensors that cover a wide field-of-view (FOV). In forward direction a high resolution is required to provide data on the location and speed of other vehicles and objects relative to the host vehicle. For Stop-and-Go operation only low angular resolution is need for tilted look direction [1]. For state of the art systems, the system requirement of a wide FOV, a high angular accuracy and simple hardware are contradicting. A high angular accuracy requires narrow beams. To cover a wide FOV a large number of these narrow beams are necessary, which result in higher costs for the complex RF-hardware. This paper describes a novel system configuration for an ACC sensor, which overcomes the misery of contradiction between wide FOV and high angular resolution, while keeping the hardware simple. The transmit and receive path are separated using separate antennas to overcome the losses involved in using a common antenna for transmission and reception. The presented system utilise a rotational symmetric Parallel-Plate Luneburg Lens (PPLL) to generate scan angle independent beams. The PPLL is designed to operate at 76.5GHz, the polarisation is vertical. Each antenna beam covers the complete FOV, thus reducing the size of the PPLLs. Different half power beam widths (HPBW) are generated for the forward (centred at 00) and tilted (centred at ±200) beams by using appropriate feeding techniques. THE PARALLEL-PLATE LUNEBURG LENS (PPLL) In Fig. la, a cross-sectional view of a parallel-plate waveguide Luneburg lens is illustrated. The lens transforms a cylin- drical wave from a primary feed into a plane wave as shown in Fig. lb. This lens is considered as a promising device for use in wide angle scanning applications which require a thin lens [2]. The variation of refraction index within the PPLL is satisfied with a homogeneous isotropic dielectric whose thickness is varied in radial direction or a photonic bandgap structure (PBG) [3]. The PPLL shows excellent characteristics such as low sidelobe levels, multiple beams capability, ray tube 1 metal plate feed ai r= 0 isotropic homogeneous )dielectric -1 real aperture a) dilcrcb) Fig. 1. TEM flat-plate Luneburg lens a) Cross-sectional view and b) Top view and ray tube in the lens negligible losses and relatively simple fabrication. The electric field is given by an integral expression, which can be eval- uated numerically for different lens radii and feeding configurations [4]. Very good agreement between measurements and simulation is obtained, allowing a fast adaption of the PPLL to the ACC requirements.