Isolation between internal UMTS and WLAN antennas for a dual-mode wireless device

Isolation performances of the internal (universal mobile telecom- munications system (UMTS) and wireless local area networks (WLAN) antennas (one patch planar inverted-F antenna (PIFA) and one strip PIFA) embedded in a wireless device (such as a mobile phone or PDA phone) for cellular/WLAN dual-mode operations are studied. Results indicate that the isolation S21 between the two antennas is strongly controlled by their relative position in the system ground plane of the wireless device and varies in a wide range of larger than 20 dB (from about −10 dB to less than −30 dB). In addition, the isolation is found to be strongly related to the excited surface current distributions in the system ground plane. Measured and simulated results are presented, and the isolation performances are analyzed.