A Dual-Band Dual-Sleeve Monopole Antenna

This letter proposes a dual-band monopole antenna with two sleeves. The lower sleeve is short-circuited to the monopole at its bottom end, while its top end is an open circuit since the length of the coaxial line formed by the sleeve and the monopole is one quarter-wavelength at the higher operating frequency. Meanwhile, the upper sleeve is so designed that a short circuit is produced across the gap between these two sleeves at the lower operating frequency, and therefore, these sleeves are virtually connected. As a result, this antenna is able to operate like a quarter-wavelength monopole at both frequency bands. A prototype of this dual-sleeve monopole is fabricated, and its measured results are in good agreement with simulated ones. It is found that this dual-sleeve monopole not only has good impedance matching, but also can radiate like a quarter-wavelength monopole at both bands.