# Simulation and Design of Three 5G Antennas
## 1 Introduction
[12] integrated antennas into the metal frame of mobile devices, where the metal frame acted as both a structural component and a radiation element. This innovative design effectively mitigated the impact of the metal frame on antenna performance. In [13], L-shaped monopole slot antennas and C-shaped coupled feed antennas were mutually orthogonally designed to create an 8-element MIMO array antenna with an isolation of over 12.5 dB, without the need for external decoupling structures. Despite the enhanced isolation achieved in these studies, the MIMO array antennas designed were relatively large. Therefore, there is a pressing need to minimize the MIMO array size while improving isolation. The structure of this paper is organized as follows:  
Research and development of a 4 \(\times\) 4 microstrip array antenna operating in the LTE band 42 (3.4-3.6 GHz). A novel approach to antenna array feeding is introduced, combining embedded feeding and coaxial feeding, utilizing rectangular microstrip line patches with embedded structures for feeding. By adjusting the depth and width of the embedded microstrip lines, a relatively wide bandwidth is obtained, while the entire array utilizes coaxial feeding to suppress coupling between antenna elements, achieving effective decoupling. Simulation and measurement results demonstrate that the array provides coverage in the 5G LTE band 42 (3.4-3.6 GHz). In comparison with traditional patch antennas, this chapter's array antenna achieves a bandwidth of 373 MHz (3.321-3.694 GHz), corresponding with a relative bandwidth of 10.7%. The antenna exhibits a gain of 12.7 dBi and maintains excellent directivity without distortion. A study of a two-element \"ring-slot\" MIMO antenna for 5G metal frame mobile terminals. The impact of integrating a metal frame on mobile terminal signal strength is analyzed. Subsequently, a ring antenna unit and a slot antenna unit are designed as the basis for the two-element \"ring-slot\" MIMO antenna structure. After simulating and optimizing the ring and slot antennas, their overlapping arrangement is determined. Without external decoupling structures, the antenna units still achieve high isolation. The paper delves into the theoretical principles underlying this design's decoupling effectiveness, affirming its reliable performance. Investigation of an eight-element MIMO array antenna for 5G metal frame mobile terminals, realizing coverage in LTE band 42 (3.4-3.6 GHz) [14]. Building upon the innovative \"ring-slot\" structure introduced in Chapter 4, the study analyzes the impact of three different placement methods on antenna performance. The optimal \"ring-slot\" module layout and inter-element spacing are determined, achieving a compact and miniaturized antenna structure. Furthermore, a T-shaped decoupling structure is etched on the ground plane between adjacent \"ring-slot\" structures along the longer edges of the antenna, effectively enhancing antenna performance. Simulation and measurement results highlight an isolation of over 17 dB, radiation efficiency ranging from 65.8% to 73.7%, and a low envelope correlation coefficient. The paper also analyzes the antenna-specific absorption rate (SAR) concerning human exposure, demonstrating favorable MIMO performance. A concluding summary of the three innovations presented in the paper is followed by an analysis of design limitations and future directions.