## 2 Recommended Monopole Antenna Construction  
The recommended antenna structure is disclosed and presented in Figure 1--the proposed antenna design with the best characteristic, including small size, broadband bandwidth, and low-profile structure. The proposed antenna employed a clockwise spiral shape of two branches to achieve dual-band performance covering 2000 to 2742 MHz and 4062 to over 8000 MHz, as shown in Figure 1a,e. The proposed antenna is validated by a mini coaxial cable with the characteristic impedance of 50 ohms and connects to an SMA connector, as shown in Figure 1a. This design is suitable for eight novel wireless communication systems, including Beyond-5G for LEO Device to Device (D2D) application, 5G, 4G, V2X, DSRC, WiFi 6 band, WLAN, and WiMAX systems. The antenna material is simulated and fabricated using the most commonly used FR4 substrate in the industry, as shown in Figure 1b. The antenna area is placed on the edge side in a device design, and the related wireless and baseband function components for the vehicle applications will be designed in the ground plane to combine the antenna design. The design parameters of the FR4 substrate are with the dielectric constant (\(\varepsilon\)r) of 4.4, the dielectric loss tangent of 0.00245, and the height of 0.8 mm.  
Figure 1: Disclosure of recommended antenna structure: (**a**) view of the antenna structure and overall design of the measurement layout, (**b**) schematic diagram of the layout applied to IoT devices; (**c**) detailed dimensions and layout of the antenna; (**d**) antenna entity diagram; (**e**) the clockwise spiral shape of two branches (Strip 1 and Strip 2).  
The main antenna area with the dimension of 10 \(\times\) 7.5 mm, and the ground for system placement includes an integrated circuit with power, baseband, and wireless transceiver function, which is located the dimension of 10 \(\times\) 42.5 mm, as the detailed information displayed in Figure 1a-c. The actual antenna photo produced is shown in Figure 1d. The antenna design only needs the top surface to complete the design. Therefore, the tolerance sensitivity of this design is low, and it is easy to adjust the accurate operating frequency design. In addition, the clockwise spiral shape of two branches has defined Strip 1 and Strip 2 to explain the physical phenomena of surface current distribution analysis and resonance frequency, as shown in Figure 1e.  
The surface current distribution is analyzed in Figure 2. The lower band is displayed at 2350 and 2450 MHz in Figure 2a,b. The upper band at 5080, 5500, 5890, 6500, and 7150 MHz are in Figure 2c-g. There is a strong current on the branch of Strip 1 at the operation frequency of 2350 and 2450 MHz. Therefore, it can be clearly understood that the operating frequency in the low-frequency band is a quarter wavelength contributed by Strip 1. Strip 2 mainly excites resonance at operating frequencies of 5080 and 5500 MHz, as shown in Figure 2c,d of the current distribution diagram. Finally, the operation frequency over 5890 MHz is affected by the parallel coupling path of Strip 1, and Strip 2 produces a high-frequency broadband effect. The effect of the parallel coupling path of Strip 1 and Strip 2 is demonstrated in Figure 2e-g.  
Figure 2: _Cont._