Piezoelectric MEMS Variable Capacitor for a UHF Band Tunable Built-in Antenna

Abstract

A UHF band tunable built-in antenna is realized using piezoelectric MEMS variable capacitors. The variable capacitor, which is driven by a piezoelectric actuator, has a tuning ratio of 11 with control voltage ranging from 0 to 8 V and quality factor of more than 37 at 650 MHz. The built-in antenna, which is an inverted-F antenna, is mounted at the top of an upper PCB board of a clamshell mobile phone, and the antenna element has a meander shape for a built-in structure. In the tunable built-in antenna, the variable capacitor is connected to one point of the meander structure of the built-in antenna. The antenna covers a frequency from 510 to 800 MHz with an efficiency of more than -3.5 dB, or the relative bandwidth of 44% by changing the value of the variable capacitor.