The built-in antenna is an antenna device integrated inside electronic equipment for receiving FM radio signals within the 76–108 MHz frequency band. It can replace traditional earphone wire antennas or external antennas, and is applied to electronic products such as mobile phones and portable radios.It captures radio waves via PCB traces, tiny metal sheets or special antenna structures. Restricted by electrical size effects, it suffers from drawbacks including low gain, narrow bandwidth and insufficient radiation efficiency. Besides, its signal reception is vulnerable to human body interference and signal shielding.