Radiation Improvement of Printed, Shorted Monopole Antenna for USB Dongle by Integrating Choke Sleeves on the System Ground

By integrating a pair of short sleeves into the system ground plane of a 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 chosen 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 are no sleeves in the system ground, the ground-plane length significantly affects the patterns and the peak-gain direction of the antenna radiation. With the incorporation of the sleeves set at proper location and in suitable size, the radiation becomes very similar to that of a conventional two-wire, dipole antenna. In this case, for a common USB dongle having system printed circuit board (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.