Spatial diversity is a popular multiple antenna system technique, due to simplicity in implementation. However, its application has thus far been limited to systems where the electrical separation between adjacent antennas typically exceeds half a wavelength. This is because a more compact design induces higher antenna correlation and impedance mismatch, which results in lower diversity gains. In this paper, the performance of a compact multiband diversity antenna is investigated in both simulations and measurements. The dual-antenna structure is designed for the future WCDMA bands of WCDMA850, WCDMA1800 and 3G EU (UMTS), where the antenna separation at the WCDMA850 band is 0.24*wavelength. The measured results indicate that an average effective diversity gain of 7.3 dB at the 1% probability level can be achieved for the three bands.