International Journal of Microwave and Wireless Technologies cambridge.org/mrf Research Paper Cite this article: Khan O, Meyer J, Baur K, Arafat S, Waldschmidt C (2019). Aperture coupled stacked patch thin film antenna for automotive radar at 77 GHz. International Journal of Microwave and Wireless Technologies 11, 1061–1068. https://doi.org/10.1017/ S1759078719000795 Received: 30 November 2018 Revised: 1 May 2019 Accepted: 5 May 2019 First published online: 10 June 2019 Keywords: Millimeter-wave antennas; thin film; aperture- coupled antenna; bi-phase power divider Author for correspondence: Osama Khan, E-mail: osama.khan@de.bosch. com © Cambridge University Press and the European Microwave Association 2019 Aperture coupled stacked patch thin film antenna for automotive radar at 77 GHz Osama Khan 1 , Johannes Meyer 1 , Klaus Baur 1 , Saeed Arafat 1 and Christian Waldschmidt 2 1 Engineering Components Radar, Robert Bosch GmbH, 71229 Leonberg, Germany and 2 Institute of Microwave Engineering, University of Ulm, 89081 Ulm, Germany Abstract A hybrid thin film multilayer antenna for automotive radar is presented in this work. A 2 × 8 aperture coupled stacked patch antenna array is realized on a single layer printed circuit board (PCB) using a novel thin film-based approach. Using a compact 180 ° phase difference power divider, inter-element spacing in a 2×2 sub-array is reduced. Measurement results show a 19% (67.9–82.5 GHz) impedance bandwidth and a wideband broadside radiation pattern, with a maximum gain of 15.4 dBi realized gain at 72 GHz. The presented antenna compares favorably with other multilayer PCB antennas in terms of performance, with the advantage of simpler manufacturing and robust design. The antenna can be employed in mid-range automotive radar applications. Introduction Millimeter waves are being used extensively for commercial applications. Recent frequency allocation of the 76–81 GHz band for automotive radar sensor applications [1] has allowed development for such sensors for driver assistance systems. An important component of radar sensors is the antenna. It determines the most important range and field of view prop- erties of the radar sensor. The antenna design is hence a very crucial part of the sensor development. For many commercially available sensors, single layer printed circuit board (PCB) antennas such as the microstrip (MS) patch antenna or the substrate integrated waveguide antenna are used in antenna arrays. For small substrate thicknesses, these antennas suffer from narrow impedance bandwidth [2]. Due to single sided feeds and linear arrays, such antennas also have relatively narrow radiation pattern bandwidths. Recent multilayer antenna designs employing wideband antenna elements such as the grid array antenna [3–5], when used as linear arrays fed in the center, have larger impedance bandwidths as well as larger radiation pattern bandwidths. Such designs rely on multilayer PCB and hence are more expensive and complex to manufacture than single layer PCB designs. Recently, a hybrid approach to designing multilayer antennas was demonstrated by the authors [6]. Instead of employing a multilayer PCB, this approach uses a single layer PCB and multilayer thin films that house the complete antenna element. These thin films are attached at the radiating positions on the PCB. In addition to being simpler to manufacture, this approach is also more flexible in terms of combination of antenna elements and feed net- work, as was shown in [6] where the same antenna element was integrated with three different feed networks. This work presents a novel multilayer grounded coplanar waveguide (GCPW) fed aperture coupled stacked patch (ACSP) antenna using the explained hybrid approach. The GCPW feed network is realized on the single layer PCB, whereas the stacked aperture coupled patch is realized on a multilayer thin film. This paper is organized as follows: the section “Antenna design” describes the design and attachment process for the antenna. The section “Array design” describes the array design where a compact power divider is described. Measurement results are provided in the section “Measurement results”. In the section “Comparison of multilayer antenna concepts”, a comparison in terms of antenna performance and manufacturing aspects is performed between multilayer PCB antennas and those based on the presented hybrid approach. The paper concludes with the section “Conclusion”. Antenna design The layer construction of the antenna is shown in Fig. 1 A multilayer low loss RF qualified thin film houses the complete antenna element. It is attached to the single layer PCB using a non- conducting epoxy-based adhesive [7]. The thin film consists of two substrate layers, Rogers Ultralam liquid crystal polymer (LCP) with ϵ r,TF1 = 3.00 and h = 100 μm, and Dupont https://doi.org/10.1017/S1759078719000795 Downloaded from https://www.cambridge.org/core. 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