A new low-profile broadband dual-frequency planar antenna is developed for wireless handsets. The dual-frequency antenna consists of a two-strip monopole for the 2-GHz band and a planar monopole for the 5-GHz band. The developed antenna features a low profile due to the introduction of an S-strip and a T-strip which are separately printed on the two sides of a thin substrate (no via process is involved in the fabrication), forming the two-strip monopole. The bandwidth of the dual-frequency planar antenna is enhanced by taking advantage of the two-strip configuration and the mutual coupling between the planar monopole and the two-strip monopole. The dual-frequency planar antenna achieves a bandwidth of ~35% at the 2-GHz band (1.6-2.3 GHz) and ~15% at the 5-GHz band (5.0-5.9 GHz) with an antenna height of 7-8 mm, which may find applications in mobile/wireless communication devices. A theoretical analysis and verifying experimental results are presented.