A Compact, Versatile Six-Port Radar Module for Industrial and Medical Applications

Hindawi Publishing Corporation Journal of Electrical and Computer Engineering Volume 2013, Article ID 382913, 10 pages http://dx.doi.org/10.1155/2013/382913 Research Article A Compact, Versatile Six-Port Radar Module for Industrial and Medical Applications Sarah Linz,1 Gabor Vinci,2 Sebastian Mann,1 Stefan Lindner,1 Francesco Barbon,1 R. Weigel,1 and Alexander Koelpin1 1 2 Institute for Electronics Engineering, University of Erlangen-Nuremberg, 91058 Erlangen, Germany InnoSenT GmbH, Am Roedentor 30, 97499 Donnersdorf, Germany Correspondence should be addressed to Sarah Linz; Received 4 October 2013; Accepted 21 November 2013 Academic Editor: Adriana Serban Copyright © 2013 Sarah Linz et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Six-port receiver has been intensively investigated in the last decade to be implemented as an alternative radar architecture. Plenty of current scientific publications demonstrate the effectiveness and versatility of the Six-port radar for special industrial, automotive, and medical applications, ranging from accurate contactless vibration analysis, through automotive radar calibration, to remote breath and heartbeat monitoring. Its highlights, such as excellent phase discrimination, trivial signal processing, low circuit complexity, and cost, have lately drawn the attention of companies working with radar technology. A joint project involving the University of Erlangen-Nuremberg and InnoSenT GmbH (Innovative Sensor Technology) led to the development of a highly accurate, compact, and versatile Six-port radar module aiming at a reliable high-integration of all subcomponents such as antenna, Six-port front-end, baseband circuitry, and digital signal processing in one single package. Innovative aspects in the RF front-end design as well as in the integration strategy are hereby presented, together with a system overview and measurement results. 1. Introduction Optical high-resolution, contactless distance measurement techniques such as laser interferometry and laser pulse timedifference measurements have been widely implemented for industrial and medical applications. The drawback of optical techniques is the difficulty to penetrate dust and fog with the laser in harsh environments as optical lenses and mirrors can get dirty. Furthermore, with increasing suspended particle density in the propagation environment dampening and scattering effects increase so that the laser cannot reach the surface of the object under investigation. These inconveniences of laser based systems are the cause of an increasing interest in alternative nonoptical measurement techniques that are robust against such industrial environment conditions. One of the main noncontact-based alternatives to laser is radar. Radar-based measurement techniques work also when a direct optical line of sight to the object under investigation is not guaranteed since radar waves can propagate much better through foggy or dusty air. Furthermore, even bulky and optically nontransparent dielectric slabs or nonmetallic shields can be penetrated by the radar signal [1, 2]. Within the last decade, radar technology has been rapidly expanding in industrial, automotive, and medical application areas [3]. Advanced positioning and sensor feedback tasks in automation processes rely on high precision radar-based distance detection, for example, to measure and track the movement of robots [4]. As an example for medical applications, high measurement accuracy is required to guarantee the safety of patients and the quality of therapies through vital sign monitoring systems. For instance, heartbeat and breath rate monitoring is of primary interest and can be achieved with particularly accurate radar-based displacement detection techniques [5]. The Six-port receiver recently raised the interest of the industry [6]. The excellent phase resolution offered by this alternative microwave receiver leads to high accuracy distance and angular measurement capabilities [7]. Historically, the Six-port receiver has been used as a reflectometer [8, 9]. 2 Journal of Electrical and Computer Engineering Figure 1: The developed Six-port radar module. Following the evolution of radar and microwave technology, the Six-port receiver has been also used as an alternative vector network analyzer for sensing applications. Mainly due to the progress in material and process technology, the Sixport technique has lately found several other implementation possibilities. As a result of a joint project involving the University of Erlangen-Nuremberg and InnoSenT GmbH (Innovative Sensor Technology), a radar sensor based on the Six-port technique has been developed (Figure 1). In this work, this compact and versatile Six-port radar system is presented along with design and simulation results of its passive components as well as hardware measurements and evaluations. The principles of Six-port receivers as well as the use of Six-port networks for radar applications have already been shown in many publications [9–11]. The developed monostatic Six-port radar front-end works in the ISM band at 24 GHz. It can be used in one-target scenarios for distance and vibration measurements [12]. After using a suitable calibration, the position and movement of a target can be calculated [11]. 2. System Overview The presented sensor is a monostatic Six-port radar with integrated patch antenna array, microwave front-end, and digital signal processing (DSP) board in one compact case measuring only (40 × 60 × 44) mm3 (width, length, height). The schematic view of the system concept is shown in Figure 2. The reference signal generated by a fractional-𝑁 frequency synthesizer is routed to the input port 1 of the Sixport. The transmit signal is sent to the target by a 16 elements patch array antenna with 14 dBi gain and 40∘ angular width (3 dB). The reflected signal from the target is coupled to the receive path and therefore fed into port 2 of the Six-port receiver. Its four output signals are downconverted to baseband by four Schottky diode power detectors and amplified with the help of two dual operational amplifiers. The analogto-digital conversion, error correction, and calculation of the target’s position or movement are done using a dedicated DSP board. Due to the use of a low-noise amplifier (LNA) with 18 dB gain in the receive path and two digitally adjustable attenuators in the reference as well as in the receive path, the system can be adapted to a variety of application scenarios. The attenuators can be programmed via SPI interfaces. The high flexibility of the system is needed because of the free space measurement environment. Depending on the distance between antenna and target as well as the target’s dimensions, the received power level may strongly vary. Like (...truncated)