Pattern diversity antenna for on-body and off-body WBAN links

Authors: SEMA DUMANLI

Abstract: Maintaining the quality and the reliability of a wireless body area network (WBAN) has a variety of challenges, one of which is the design of the on-body antenna. The on-body antenna often forms both on-body and off-body links and needs to have an application-specific pattern to secure the connection. The antenna should direct its energy in parallel to the human skin while establishing an on-body link, ideally omnidirectionally, while an on-body link would benefit from a directional radiation pattern perpendicular to human skin. Moreover, the lossy body tissue is within the reactive region of the antenna affecting the antenna performance; hence, the antenna design flow should include this effect. Here a novel antenna is presented that creates the aforementioned radiation patterns using two switches. For the on-body and the off-body links, the TM$_{00}$ and the TM$_{01}$ modes are excited, respectively. The TM$_{00}$ mode generates a quasi-omnidirectional pattern with a simulated directivity of 2 dB in the horizontal plane while the TM$_{01}$ mode generates a directional pattern with a directivity of 4.5 dB. Both modes are matched at the 2.45 GHz ISM band. Finally, using numerical and physical phantoms and male subjects, the antenna has been shown to perform well near human bodies: insignificant detuning was observed and the degradation in the radiation efficiency was measured to be 17 % in the worst-case scenario of locating the antenna on the body with 0 mm separation. Note that the size of the antenna is no bigger than a conventional half-wavelength patch antenna.

Keywords: Radiation patterns, patch antennas, body area networks

Full Text: PDF