# Simulation and Design of Three 5G Antennas
## 4 Metal Frame Mobile Terminal Dual-Element \"Loop-Groove\" MIMO Antenna Design  
### The Impact of Metal Frame on Mobile Terminals  
Metal frame smartphones have gained popularity due to their durability and aesthetic appeal. Led by Apple's iPhone, earlier iPhone models like the iPhone 4, 4s, 5, and 6, among others, featured metal frames or bodies. Some brands like Meizu MX3 and Xiaomi 4 utilized austenitic 304 stainless steel. Later, many smartphones began using materials like aluminum and magnesium alloys, which provide better protection against wear and impact. Furthermore, metal frames facilitate heat dissipation by quickly transferring heat generated during operation to the surrounding air, resulting in improved cooling efficiency. These reasons contribute to the preference for metal-framed smartphones by many users.  
However, as 5G communication systems have developed, the number of 5G smartphones with metal bodies in the market has decreased. This change is primarily due to the nature of wireless signals, as metal frames can affect the signal quality. A metal body can attenuate signals, thus influencing connection speed and strength, especially when the user's hand covers the antenna areas during calls. For instance, signal strength often weakens when entering elevators because elevators are enclosed metal spaces, effectively creating a metallic shield that significantly interferes with wireless signal reception. In simple terms, metal has a shielding effect on electromagnetic waves. As 5G operates at higher frequencies and uses pulse waves, it is even more sensitive to the presence of metal.  
To simulate the impact of using a metal body on signal quality with 5G, a Huawei P40 Pro (5G) smartphone was selected for experimentation. Although the phone's rear cover is made of precision ceramic material, the screen frame is still constructed of stainless steel. Given the innovative design of the phone's curved screen, the metal frame makes up only one-third of the phone's width. Figure 26 depicts the initial signal strength tests with the phone in a bare state.  
Subsequently, a metal phone case was installed to simulate a widened metal frame, and its impact on signal quality was tested in the same environment, as shown in Figure 27.  
As evident in Figure 26, when the smartphone is tested in its bare state, the 5G signal strength is within the range of (\(-67\) dBm, 73 asu). However, after installing the metal phone case, as depicted in Figure 27, the 5G signal strength decreases to (\(-94\) dBm, \(46\) asu).  
Figure 26: Signal strength of the bare smartphone.  
To meet the demand for metal frame smartphones, higher standards are required when designing antennas for 5G terminal products. Nevertheless, due to the presence of metal frames, integrating multiple antennas together with high isolation becomes increasingly challenging. Previous research on metal frame smartphones has shown that some suffer from low isolation across the entire operating frequency band, failing to meet the required isolation standards. Additionally, some solutions have relatively larger dimensions, compromising the aesthetics of smartphones. Therefore, this section aims to design a new dual-element MIMO antenna with high isolation, specifically suitable for 5G metal frame smartphones.