Very short range radars can be usefully adopted for many applications: GPR, monitoring of physiological activity both for safety and security contexts, electronic travel aids, automotive. In the first stage, the goal of the work is the design and the optimization of an array of patch antennas, considering the array radiating in free space, and working in the 77 GHz frequency band, in order to achieve a miniaturized, cheap, and conformable device. This study is developed using CST MICROWAVE STUDIO® (CST MWS), which allows us to carry out a parametric analysis and its result is the antenna shown in figure 1, having more 4 GHz of bandwidth centered at the desired frequency, as shown in figure 2. The most critical part of the work is the analysis of the interaction between the antenna array and objects in the surrounding environment, located at a distance in the range of tens to hundreds of wavelengths. This distance is usually too large to consider the object to be in the near field region and to include the object in the same work space of the antenna. Moreover, in this part of the work, we use the Time Domain Solver because signal processing will include transit time calculation and auto-correlation in order to have an estimation of the position, the material and maybe also the shape of possible obstacles. To overcome the problem related to the numerical analysis of large volumes containing objects with small geometrical details (the antennas), we tried to analyze using far field plane wave decomposition, but this method gives some inconsistencies even when we scaled the frequency down to 10 GHz. Finally we tried to separate the whole problem into two simpler sub-problems, possibly having different meshes, using the field source utility which is an implementation of Equivalence Theorem and is available into CST MWS. Preliminary result were shown at the CST User Group Meeting, 2010.
Alfredo De Leo, Università Politecnica delle Marche