Dedicated short-range communications (DSRCs) is a novel short-to medium-range wireless protocol designed for automotive use. The DSRC signals are circularly polarised and allocated in the 5.8 GHz band. Described is the development of a monolithic and compact patch antenna with left-hand circular polarisation intended for the on-board unit equipment of a DSRC system. The 40×60×2.455 mm fabricated prototype exhibits a circularly-polarised gain of about 5.52 dBc with a cross-polar discrimination of about 20 dB.Introduction: Circularly-polarised waves have many advantages for short-range communication, as they can be used to reduce the interference due to reflections and allow a polarisation match independent of the antennas' angular orientation. In fact, the wireless communication standard known as Dedicated Short-Range Communications (DSRC) [1], used for automotive applications like electronic toll collection, employs circularly-polarised antennas. The EN12253 standard [1] specifies the antenna requirements for the on-board unit (OBU) of a DSRC system. For the OBU a cross-polarisation discrimination (XPD) greater than 10 dB in boresight direction and greater than 6 dB within the −3 dB area are required, moreover a reduced size and a low cost are mandatory.In the literature there are several examples of circularly-polarised antennas in the 5.8 GHz range that satisfy the conditions stated in the standard, but these antennas are often not monolithic structures [2] and therefore they are not suitable for series production. On the other hand, simpler configurations (for Road Side Units where compactness is not mandatory) make use of antenna arrays and sequential rotation to meet the characteristics required by the standard [3]. In several applications, miniaturisation is a great advantage and there are several examples of small-size patch antennas at frequencies other than 5.8 GHz that are both monolithic [4] and suspended [5]. A 5.8 GHz DSRC-compliant antenna has been reported in [6], wherein, however, the proposed suspended-patch non-monolithic solution requires an ad-hoc feeding network with power divider and branch coupling lines resulting in the use of extra board area. To the best of our knowledge, a circularly-polarised, miniaturised and monolithic antenna compliant with the DSRC system has not been proposed so far: in [7] a monolithic linear polarisation antenna, with 3dB polarisation loss, is proposed and in [8] a DSRC patch antenna is designed (on a substrate with height h=3.2 mm and permittivity ε r =2.2), for a total height of 4.7 mm.In this Letter, we report on the development of a microstrip patch antenna suitable for integration on a circuit board. The antenna is realised in a monolithic configuration with a reduced total height and area.
In this work a 2-D electronic beam steering array is presented. The 8×8 antenna operates in the frequency range 4.4 ÷ 5 GHz. Each radiating element is connected to an independently controlled analog phase shifter, thus allowing a continuous steering of the main beam both in elevation and in azimuth. The whole antenna is realized in printed technology, and all the RF and biasing circuitry is realized on a single layer, while the radiating part is realized by an array of cavitybacked slot-fed patches, thus resulting in an extremely compact and modular solution. Preliminary measurements show the good performance achievable and confirm the beam-shaping and interference-nulling capabilities of the presented antenna system.
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