In mobile data devices, the antenna is the only component that "touches" the network, so optimizing the performance of 4G antennas is becoming more and more important. 

However, the challenges of designing 4G antennas in smartphones and tablets are daunting. 

While there are a variety of possible solutions to these challenges, each has potential performance tradeoffs. 

There are many factors that affect the antenna performance of handheld mobile communication devices. 

Although these factors are related, they can usually be divided into three categories: antenna size, mutual coupling between multiple antennas and equipment usage model. 

Antenna size depends on three elements: working bandwidth, operating frequency and radiation efficiency. 

Today's bandwidth requirements are getting higher and higher, driven by FCC frequency allocation in the United States and operator roaming protocols around the world; different regions use different bands. 

"bandwidth and antenna size are directly related" and "efficiency and antenna size are directly related"-which usually means that larger antennas can provide greater bandwidth and higher efficiency. 

In addition to bandwidth, the size of the 4G antenna also depends on the operating frequency. 

In North America, operators Verizon Wireless and AT&T Mobility choose to promote LTE products that work in the 700MHz band, which was part of the FCC UHF-TV reallocation band a few years ago. 

These new bands (17704-746MHz and 13746-786MHz) are lower than the traditional cellular bands used in North America (5824-894MHz). 

This change is huge, because the lower the frequency, the longer the wavelength, so longer antennas are needed to keep the radiation efficiency constant. 

In order to ensure the radiation efficiency, the size of the antenna must be larger. 

However, equipment system designers also need to add larger displays and more functions, so the length and overall size of the available 4G antennas are greatly limited, thus reducing the antenna bandwidth and efficiency. 

The high-speed wireless protocol for updating mutual coupling between 4G antennas requires the use of MIMO (multiple input multiple output) antennas. 

MIMO requires multiple antennas (usually two) to operate at the same frequency at the same time. 

Therefore, multiple antennas need to be placed on the telephone equipment, and these antennas should work at the same time and can not affect each other. 

When two or more antennas are close to each other, a phenomenon called mutual coupling occurs.