1. Introduction
In recent years, the demand for antennas for use in automotive communication systems has continued to increase, which has caused research on the Internet of vehicles (IOV) [
1], such as vehicle-to-everything (V2X), vehicle-to-vehicle (V2V), vehicle-to-network (V2N) and In-vehicle Infotainment (IVI) communication, to flourish [
2,
3]. In the future, the Intelligent Transportation System (ITS) will be able to obtain real-time traffic information, such as road conditions, road information, and pedestrian information through the connection of the Internet of vehicles and the base station, which can also improve driving safety, avoid traffic congestion, and improve transportation efficiency [
4]. Furthermore, currently, people are using cars more and more often to move to their destinations, and cars are fully integrated into our lives. Based on the above reasons, improving road traffic safety is an important topic, hence the emergence of intelligent vehicle technology research and development [
5]. The rapid development of the Internet of vehicles (IOV) and the promotion of new technologies bring great convenience to our lives and transportation. It has also helped governments in various countries and regions effectively control the use of roads and highways and improve road safety. In addition, with the development of vehicle communication technology, V2X and satellite communication antennas in the ITS have also attracted great attention [
6].
In addition to V2V connections with roadside units (RSUs) and nearby vehicles, each vehicle is also connected to satellites [
7]. For vehicle-to-vehicle connection, the key technologies of the current vehicle communication system also bring development to the research of LEO satellite antennas [
8,
9]. In the V2X communication system, in addition to maintaining higher safety during vehicle driving, such as through vehicle distance and remote driving, V2X also includes V2V and vehicle-to-infrastructure (V2I) connections. It offers many advanced features, such as blind spot detection, forward distance warning, emergency vehicle approach warning, and road condition data, for predicting the shortest route to a destination and the safest driving conditions, all of which require a high-performance antenna to maintain a stable connection [
10,
11].
Low-earth-orbiting (LEO) satellite communication is also an essential technology for IOV communication. LEO satellites are currently deployed in the Ku band, Ka band, and Q/V band [
12]. Therefore, many connected vehicle devices are also developing toward these frequency bands. The rapid development of these infrastructures will affect the connection between the IOV and autonomous vehicles [
13]. IOV devices require antennas to achieve stable connections. Therefore, the antennas require a wideband and multi-band design to achieve high-data-volume signal transmission. Broadband also makes accommodating various wireless communication design standards in one device easier. In addition, the communication system also grasps certain variables, such as pressure, humidity, or temperature, when connecting devices. These environmental variables are also considerations when designing antennas [
14]. IOV devices are small, compact, and easy to install in the desired environment. Therefore, the design of the antenna must meet the small size specifications without affecting the performance of the antenna.
Furthermore, designing antennas on particular substrates, such as car windows or windshields, is also challenging because of the limited area that the antenna can use. Therefore, only very thin conductive strips can be used, which also makes designing and installing the antenna more complex [
15]. Antenna design should be considered a top priority regardless of the wireless communication product. Therefore, antenna engineers must have a comprehensive vision when making design decisions, including cost, area, and future achievability, that should be paid attention to when designing. The mass transportation of wireless data will be in great demand in the future. With the coexistence of many wireless network transmissions, antennas still occupy a larger area for communication between vehicles and low-orbit satellites than integrated circuits for data processing and analysis. Therefore, the designed antenna must be compact, multi-functional, and multi-band to be more economical and convenient for today’s multi-band wireless communication systems [
16].
To make the working frequency of the antenna more diverse, many antennas used in LEO communication applications are designed with multi-band and broadband as the design goal. These technologies include the use of patch antennas and a power divider with a tapered angle. Although the overall gain is reduced by 2 dBi, the bandwidth can be increased by 109%, achieving a dual-band effect [
10]. Multi-band use has been obtained by bending the monopole antenna and adding branches. Using a gradual impedance change, the dual-band bandwidth increases by 31.22% and 65.29%, and multi-band use has been achieved [
13]. A loop patch antenna design with rectangular slots and partially slotted ground planes can be used to achieve broadband. The main goal of using parasitic loop elements is to improve antenna performance [
17]. Through the elliptical patch, the grounding branch, and the T-shaped branch, the surface current at the operating frequency between the patch antenna elements is effectively blocked or absorbed in this design, thereby reducing the mutual influence and achieving a broadband effect [
18]. The multi-frequency effect is secured by combining two bow-tie-like curves so that the antenna can achieve resonance in different frequencies, and the extended twists and turns make the antenna operate at a lower frequency [
19]. An X-band patch antenna with a coplanar waveguide (CPW) structure which can be directly connected to the antenna and transmit receiver modules without additional wiring is proposed. Therefore, when external factors are affected, unnecessary movement can be controlled and the deterioration of antenna performance can be reduced to a minimum [
20]. Rectangular slot patches can also achieve impedance bandwidth by stacking cylinders with perforations and etching a rectangular slot on the ground side. The operating frequencies are combined to create a broadband hybrid dielectric resonator antenna. Alternatively, using shared aperture technology with an array design, the same aperture can be reused on dual frequency bands [
21,
22]. In patch antennas, slots are carved into the surface to generate resonance and shorting pins and slots are used to generate the required radiation [
23]. Broadband characteristics are achieved by truncating the rectangular microstrip patch, and notch characteristics are obtained using the electromagnetic bandgap structure [
24]. The coplanar waveguide structure can reduce loss. Optimizing the ground plane and the radiation patch can achieve a wide impedance bandwidth, and a patch antenna can achieve broadband [
25]. A rectangular microstrip antenna and a defective ground structure (DGS) can make the antenna achieve broadband. The overall size of the antenna is 60 × 60 mm
2 [
26]. They use patch antennas and change the structure so that the patch is different from the traditional rectangle and the elliptical radiator design achieves the broadband effect. Dual-frequency bands for satellite communication applications can use reconfigurable circular polarization to achieve 10.8–11.8 GHz and 14–15.4 GHz, with bandwidths of 7.6% and 4.3%, respectively [
27]. The whole antenna is constructed only through the substrate-integrated waveguide (SIW) and produces a mixed-mode resonance at 9.85 GHz. When the short slot is cut into the top of the cavity, dual resonances at 14 GHz are caused. The antenna measured peak gains of 6.62 dBi and 6.44 dBi at 9.85 GHz and 14 GHz, respectively [
28]. These technologies can give the antenna a good connection in satellite communication.
Currently, the LEO antenna uses a phased array structure to allow satellites and point-to-point communications to have better transmission quality. The antenna in this paper uses a simple structure, which makes the antenna easy to install on the vehicle and gives it a good connection with the base station, the vehicle, and LEO. Therefore, the antenna designed in this paper has the advantages of miniaturization and simple use of gradual impedance change and slotting to achieve dual-band performance to achieve Internet of vehicles applications. Therefore, to meet the requirements of multiple transmissions, the antenna in this paper uses a non-phased array structure to achieve multiple transmissions and proposes a dual-frequency antenna applied to the Internet of vehicles (IOV) system. The association diagram in the communication scene of the Internet of vehicles is shown in
Figure 1.
Furthermore, dual-band use is provided through the U-shaped slot in the middle of the cut triangular patch and the antenna. Moreover, the antenna performance is analyzed in the electromagnetic simulation software. The excellent performance characteristics of bandwidth, gain, and efficiency are analyzed in detail. To verify feasibility, the proposed antenna was fabricated and measured using and in the SATIMO StarLab Chamber to obtain data such as reflection coefficient, gain, radiation pattern, and efficiency. The results confirm that the proposed antenna is suitable for vehicular LEO satellite systems. The antenna designed in this paper can be installed on the roof, as shown in
Figure 2.
Moreover, it provided exemplary performance in the Ku band. The proposed antenna has dual-frequency bands and can cover the X band (11.13~12.45 GHz) and Ku band (14.96~16.28 GHz). The antenna efficiency is 50–80.8% and 50–74% in the X band and Ku band. In addition, the antenna gain is about 3.34–6.08 dBi and 3.50–4.65 dBi in the X band and Ku band, respectively, and the highest gain value is 6.08 dBi. This frequency band can be used for vehicle-to-satellite, IOV communication applications, and vehicle data transmission.