Ultrawideband PIFA With a Capacitive Feed for Penta-Band Folder-Type Mobile Phone Antenna

An ultrawideband planar inverted-F antenna (PIFA) with a capacitive feed in the folder-type or clamshell mobile phone for penta-band operation is presented. The antenna is placed at the hinge position between the main and upper ground planes of the folder-type mobile phone. With the use of the capacitive feed, a very wide operating bandwidth (3:1 VSWR or 6-dB return loss) of about 1.5 GHz (from 820 to 2345 MHz) is obtained, although the antenna is with a small radiating plate of size $8times 40 {rm mm}^{2}$ and a low profile of 7.8 mm above the top edge of the main ground plane. The very wide bandwidth covers GSM850/900/1800/1900/UMTS penta-band operation for the mobile phone in the open (talk) state. In addition, when in the closed (standby) state, although the groundplane condition greatly differs from that in the open state, the impedance matching over the operating bands can still be better than 6:1 VSWR (3-dB return loss), acceptable for standby operation in the practical applications.