How can I improve the performance of my GSM/LTE mobile phone antenna?

There are several ways to improve the performance of your GSM/LTE mobile phone antenna. One way is to use an external antenna that provides higher gain and range than your phone's internal antenna. Another option is to use the phone near a window or outdoors to get a better connection. You can also try changing the location of your phone or downloading an app that helps you optimise the signal strength.