Js. Colburn et Y. Rahmatsamii, HUMAN PROXIMITY EFFECTS ON CIRCULAR POLARIZED HANDSET ANTENNAS IN PERSONAL SATELLITE-COMMUNICATIONS, IEEE transactions on antennas and propagation, 46(6), 1998, pp. 813-820
Satellite-based systems are the next step in mobile communications. Re
cently, several low and medium earth orbit mobile communication satell
ite systems have been proposed and are currently being deployed. For a
ll these systems, high-performance circularly polarized antennas for t
he mobile terminals are of importance. Although considerable material
is available on circularly polarized antennas, there is an absence of
information on how the human's close proximity to the antenna affects
the circular polarization purity of the radiated field. This paper pre
sents an analysis of representative circularly polarized helical hands
et antennas. Although other physically less obtrusive circular polariz
ed antennas are available for the handset, the helix is used because o
f its wide bandwidth properties and capability to provide both circula
r and linear polarization, Thus, this element could be used for handse
ts that are planned to work with both the terrestrial-based communicat
ions systems of today and the satellite-based communication systems of
tomorrow, The intent is to characterize the effects the close proximi
ty of a human head model has on the computed performance of the circul
ar polarized antenna, The method of moments (MoM) and finite-differenc
e time-domain (FDTD) numerical techniques are used to study various he
lix structures on top of a small box representing a handset. In order
to be able to effectively apply FDTD, a novel square helix structure i
s introduced. Results computed with these two techniques are compared
to illustrate the accuracy of each implementation, The results indicat
e significant polarization purity degradation caused by the presence o
f a human head. For the particular geometry simulated, the presence of
a head model degraded the average axial ratio within a verticle 50 de
grees cone from 2.9 to 9.1 dB, This significant increase in axial rati
o can have profound effects on link budgets.