!5.8G 天线——ieee

TABLE I SOME CONCERNED PARAMETERS ON READER'S ANTENNA OF PHYSICAL LAYER IN THE ETC-DSRC NATIONAL SPECIFICATIONS OF CHINA TypeB Parameter Type A Downlink 5.83GHz Carrier 5.83GHz Cl Frequency 5.84GHz C2 5.84GHz <5MHz <5MHz Occupied bandwidth 8<38° 8<38° Antenna's Horizon half-power lobe width Vertical \0<45° Right-hand CP RSUt>15dB RSUt>IOdB 5.79GHz 5.80GHz <5MHz \0<45° Right-hand CP RSUt>15dB RSUt>IOdB 5.79GHz 5.80GHz <5MHz
Gain
�
41253
(kpx45
=
(1)
From Eq.l and Table I, the design indices of the antenna are drawn out and listed in detail as Table II.
84
B.
Single Element
of
I I
According to the Table, (), the transmlttmg-recelvmg antenna's half-power lobe width in the horizon plane is less than 38° and rp that in the vertical plane less than 45° , and so the minimum gain of the antenna could be estimated by the following forrnula[4].
Another important parameter, the input impedance at the feed point location could be obtained by Cavity Model Method[3][6], or using simulation software such as Agilent ADS software.
XPD
Polarization I Peak gain direction I -3dB domain Uplink Carrier Cl Frequency C2 Occupied bandwidth
TABLE II DESIGN INDICES OF THE READER'S ANTENNA Requirement Parameter Type Microstrip Array Antenna Center Frequency 5.82GHz Cover the range Bandwidth 5.785GHz-5.845GHz >14dBi Gain <38° Antenna's horizon half-power <45° vertical lobe width Polarization Right-hand CP RSUt>15dB I Peak gain direction XPD I -3dB domain RSUCIOdB
To improve the performance of the antenna such as gain and AR bandwidth, sequential feeding network technology[7] is applied for the application with the four same CP patch antennas arranged as shown in Fig.2(a), where all patched are placed at same spacing at vertical or horizon direction, FJ, Fz, F3 and F4 are feed point where each of the elements is excited in the same amplitude and 900 phase delay in an anti-clockwise sequence. There are several concrete implementations such as parallel feeding network, series feeding network and hybrid ring parallel feeding network[8]. Among these, the parallel feeding network is applied in this paper for the simplicity and ease of implementation shown as Fig 2(b), where Zp is the input impedance of the element and Zin the impedance of the feeder. Meanwhile AgO is the waveguide wavelength of the microstrip transmission line and h,lz are the adjustable lengths to fit the position of the feed points.
Index Terms-ETC, RHCP, Microstrip Antenna, ADS Software
1.
INTRODUCTION
Electronic Toll Collection(ETC) system is a kind of modem traffic toll collection means based on RFID technology[1]. By using the microwave dedicated short range communication (DSRC) operating at 5.8GHz between the tag or so-called on board unit(OBU), which are installed on the front window of vehicles and the reader or road side unit(RSU) on the ETC road of toll collection station, the passing vehicles' toll could be collected automatically without stopping. The time spent on each vehicle is less than two second and the ability for vehicles' passing of ETC passage is five to ten times of manual toll collection passage. For these reasons, ETC system has been developed and spread rapidly in recent years at home and abroad. On March 2007, the national specifications of China on ETC&DSRC, GB/T20851-2007[2], had been published. Some needs on the reader's antenna have been defined in it. According to the specifications, the microstrip antenna array is the leading choice for the RSU because of its low cost, low profile and ease of fabrication[3] as well as the gain of the array is easy to meet the demands. In this paper, the design indices about the reader's antenna are listed and discussed, then a microstrip array antenna resonating at 5.8GHz and providing a peak gain of about 15dBi at center frequency is developed. It radiates a right­ hand circular polarization beam with half-power lobe-width 18° in the horizon plane and 34° in the vertical plane. And the lOdB return 10ss(RL) impedance bandwidth and 3dB axial ratio bandwidth of the antenna is greater than 200MHz. II. D ESIGN INDICES AND M ETHOD A. Design Indices In accordance to the national specifications, the same right­ hand circular polarization(RHCP) antenna is used in the RSU for either transmitting or receiving signal. Some concerned parameters of the antenna are listed in Table 1.