Compact ETSI compliant DSRC Transponder for Vehicular Communications at 5.8 GHz Stefano Maddio, Alessandro Cidronali, Stefano Maurri, Gianfranco Manes Dept. of Electronics and Telecomm., University of Florence, I-50139 Florence, ITALY (e-mail: first.last@unifi.it) Abstract—This paper details the implementation and perfor- mance of a new compact 5.8GHz Transponder for Dedicated Short-Range Communication (DSRC). The core of the system is a low power RFIC composed of an amplifier and supeheterodyne converter, while the radiative system consists of an original low profile planar antennas operating in Left Hand Circularly Polarization (LHCP) for both Tx/Rx channel. The planar antenna technology offer the benefits of low-cost, ease of manufacture and low-profile, but it requires accurate and time-consuming tunings to reach optimal radiation and matching condition. The performance of the proposed DSRC transponder are boosted by efficient design for both Tx and Rx antennas which is based on a evolution of the original solution proposed by the authors. Measured results of a fabricated prototype show a wide and regular angular response and a net gain exceeding 15 dB in the linear range of function. Index Terms—DSRC, 5.8 GHz, Circular Polarization Anten- nas. I. I NTRODUCTION There is a great momentum in the direction of advanced ac- tive safety in the vehicular industry and Intelligent Transporta- tion Systems (ITS). Dedicated Short-Range Communications (DSRC) are a set of short/mid range protocols specifically designed for vehicular communication-based applications such as Electronic Toll Collection (ETC) system. In August 2008 European Telecommunications Standards Institute (ETSI) has allocated spectrum bands in the 5 GHz to 6 GHz band for ITS applications [1]. ETSI standards recommends a 5.8 GHz carrier frequency within a 10 MHz bandwidth. The RF spectrum in the 6 GHz range shows specific environmental and propagative characteristics suitable for vehicular environments such as long distance high data rates and reduced weather dependence. On the other side, this choice is disadvantaged by narrow bandwidth and low power capacity. The paper presents a smart DSRC device based on a custom RFIC coupled with Tx/RX antennas operating in circular polarization at 5.8 GHz. The novelty of the system lies in the innovative antenna design which grant very compact dimen- sions, low coupling, high Gain and high cross-polarization discrimination. The fabricated prototype is compliant to the CEN TC278 specifications. II. DESIGN OF THE SYSTEM An On-Board Units (OBU) is a dedicated device allowing wireless identification or communication with roadside units in ITS applications. OBU’s can be classified into two types: the active (transceiver) system and the passive (transponder) system. The passive choice is typically preferred since it is simpler and cheaper. A passive OBU is basically a RF Rx Tx x A PM ~ RFIC Ztx Zrx Fig. 1. Schematic structure of a DSRC Transponder. transponder composed by a Receiving antenna, an amplifier, a mixer, a sub-modulator unit and, a transmitting antenna. Also, a small primary battery must be inserted in the unit. The schematic of a card-type OBU transponder is depicted in 1. In the downlink mode (Rx) the beacon sends data with a rate of 500 kbit/s to the OBU via amplitude modulation (AM) at a carrier frequency of 5.8 GHz. In the uplink mode (Tx) the OBU is woken by an interrogating signal - an unmodulated 5.8 GHz carrier - and transmits back a coded response modu- lating the incoming carrier with a Phase Modulated (2-PSK) sub-carrier at 1.5 or 2 MHz, with a data rate of 250 kbit/s. Such systems are low consumption power since do not need a local oscillator. The active part of the proposed system is a custom RFIC containing all the signal processing modules, i.e. the amplifier, the mixer and the PM subsystem. This RFIC is custom chip in the form of a standard QFN 28 package of 4.5 mm × 4.5 mm. The active gain of the module is around 3 dB, an adequate trade-off with the low consumption specs, which in turn guarantees high performance in term of lifetime [2]. It is mandatory to provide a highly efficient antenna system, !" #