Current mobile communication systems in W-CDMA systems are assigned three frequency bands in Japan. We present and investigate a multi-resonant printed monopole antenna (80×120×1.6 mm3) for a small wireless packet communication module (called a ubiquitous communication module). The proposed monopole antenna uses a small ground plane (0.2 λ of the lowest frequency) to achieve miniaturization. This paper proposes employing impedance matching (V.S.W.R. (voltage standing-wave ratio) < 1.8) to avoid the influence on incurred from a coaxial feed cable by using a microstrip feed line with a balun, impedance converter, and step- impedance. Furthermore, calculation and measurement results confirm that the radiation patterns are roughly omnidirectional in the φ plane in W-CDMA systems. (6 pages)