Integrable sleeve choke for radiation improvement of a printed monopole antenna for 2.4-GHz USB-dongle applications

By integrating a pair of short sleeves into the system ground plane of a wireless USB dongle, the improved radiation patterns of a printed monopole antenna in the E planes cut along the axial direction of the dongle can be attained. The monopole selected for studies has a symmetrical, short-circuited structure and is to operate in the 2.4 GHz (2400-2484 MHz) band for ZigBee or Wi-Fi dongle applications. When there were no sleeves in the system ground, the ground-plane length significantly affected the patterns and the peak-gain direction of the monopole- antenna radiation. With the incorporation of the sleeves set at proper location and in suitable size, the radiation became very similar to that of a conventional two-wire, dipole antenna. In this case, for a common USB dongle having system PCB longer than λ/4 (λ is the free-space wavelength at 2442 MHz), the maximum field strength is no more in the direction of the ground plane or even toward the main electronic device after plugging in the dongle.