科研之友
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摘要
Three patch antennas suitable for integration and operation in a compact 24ˋGHz wireless sensor node with radar and communication functions are designed, characterized, and compared. The antennas are manufactured on a low loss glass wafer using thin film (BCB/Cu) wafer level processing (WLP) technologies. This process is well suited for 3D stacking. The antennas are fed through a microstrip line underneath a ground plane coupling into the patch resonator through a slot aperture. Linear polarization (LP), dual mode (DM) operation, and circular polarization (CP) are achieved through the layout of the slot aperture and rectangular patch dimensions. Antenna gain values of ~5.5ˋdBi are obtained in addition to the 10 dB impedance bandwidths of 900ˋMHz and 1.3ˋGHz as well as 500ˋMHz CP bandwidth with a 3ˋdB axial ratio for the LP, DM, and CP patch antennas, respectively. 1. Introduction Autarkic wireless sensor networks are becoming widespread in industrial applications and have been in the focus of many research activities [1]. The development and application of tiny radio sensor nodes that are equipped with radar and communication functions are of interest for gathering spatial information in addition to sensor information [2]. The 24ˋGHz unlicensed ISM (industrial, scientific, and medical) frequency band, with a free space wavelength of 12.5ˋmm, allows the realization of radar with a spatial resolution in the cm-range. There is also more bandwidth (250ˋMHz) available for frequency modulated communication and radar signals compared to the popular ISM band at 2.4 GHz. Another advantage of the short wavelength is that efficient antennas can be realized for integration in the sensor node platform increasing the miniaturization potential. The integrated antenna plays a crucial role in the overall system performance of such sensor node applications. To date, much research has focused on planar antenna designs for quasi millimeter-wave applications using PCB or LTCC technologies [3每5]. However, highly integrated sensor node platforms comprise compact 3D stacks, where the antenna is integrated in one of the stack modules [6每8]. For this purpose, antenna designs suitable for 3D stacks and thin film processing have been reported. These include patch antennas processed directly on silicon substrates [9]. Since silicon substrates are lossy, micromachining techniques [10], used to create cavities, and high resistivity silicon (HRS) substrates [11] have been employed to increase the antenna efficiency. These approaches, however, lead to high costs. Therefore, in order to
