## 1 Introduction  
The wireless access for vehicular environment (WAVE) is a recently developed wireless communication technology that enables the instant update of traffic information to vehicles. Vehicular communication systems can be effectively used to enhance the traffic efficiency and to reduce traffic congestion [1, 2].  
The ubiquitous intelligent system is used to develop an intelligent vehicle communication technology on the basis of the advanced WAVE wireless vehicle communication technology for improving the functionality and reducing the risk of accidents [3].  
Systems with an efficient WAVE or multiple-input multiple-output (MIMO) antenna for a ubiquitous intelligent system are found to offer increased road efficiency in the case of high traffic conditions; these systems provide alternative routes to vehicles during high traffic conditions on the basis of the obtained traffic information, as well as providing improved communication services with Internet access [4,5].  
Further, WAVE communication systems with a high frequency range for vehicle-to-vehicle (V2V) communication and for vehicle-to-infrastructure (V2I) communication have attracted considerable attention owing to the fact that these systems are likely to achieve a high communication rate because of a wide bandwidth and low attenuation of radio propagation by the atmosphere [6,7].  
Typically, WAVE communication systems operate in the 5.850-5.925 GHz frequency band assigned by the Federal Communication Commission (FCC) [8]. Further, these systems adopt the advanced orthogonal frequency division multiplexing (OFDM) scheme to achieve high-speed data rates up to 6-27 Mbps. These characteristics make the WAVE communication system an attractive physical layer scheme with a high-efficiency antenna for a ubiquitous intelligent system.  
These systems consist of on-board units (OBUs) placed on vehicles and road-side units (RSUs) placed on infrastructures [9]. To maintain seamless communication among fast-moving vehicles, the antennas usually exhibit an elliptical beam pattern in the vertical cross-section of the azimuth. In cases where the antennas do not exhibit an elliptical beam pattern, the accessible distance for vehicular communication will be reduced owing to unnecessary radiations. Therefore, it is important for the OBU antennas to exhibit an elliptical beam pattern with a suitable bandwidth.  
Numerous studies have been conducted on antennas for WAVE communication systems. Most of these studies have only considered the frequency band and the omnidirectional beam pattern of OBU WAVE antennas. These OBU antennas exhibit an omnidirectional beam pattern suited to a WAVE communication system.  
Printed antennas were described with an omnidirectional beam pattern [10]. Further, other research showed the pattern characteristics of the printed antennas using a micro-strip patch and an etched-upon microwave substrate layer; from the results of their study, it was found that the printed antennas exhibit an appropriate omnidirectional beam pattern suited to global positioning system (GPS) satellite receiving systems [11]. However, it should be noted that printed antennas are not the most suitable antennas for our purpose, which require V2V/V2I (V2X) communication.  
We proposed the rectangle array patch antennas structure to increase the performance of the antenna by reducing the return loss and the side-lobs waves of unnecessary radiation.