Biomedical Engineering Reference
In-Depth Information
Fig. 1
Two-branch
ultra-wideband (UWB)
tapered slot antenna (TSA)
used in the experimental
investigation of spatial
diversity for on/off-body
radio propagation channels
Measurement Setup for Ultra-Wideband On/Off-Body Diversity
For UWB on/off-body antenna diversity measurements, a two-branch tapered slot
antenna (TSA) was used as shown in Fig.
1
. The spacing between the two ele-
ments shown in Fig.
1
is 0.34
λ
0
to keep the mutual coupling well below
−
15 dB.
Diversity antennas with different spacings are fabricated and are used during mea-
surements. A detailed discussion on mutual coupling is presented later in this chapter.
For UWB on/off-body diversity channel measurements, an Agilent four-port PNA-
X (programmable vector network analyzer), model number N5244A, was used to
capture the frequency response of the two diversity branches, as shown in Fig.
2
.A
single TSA was used as the transmitter (Tx) antenna (connected to port 2 of PNA),
while a two-branch diversity TSA antenna, with various spacings, was used for the
receiver (Rx) antenna connected to port 1 and port 3 of PNA (as shown in Fig.
2
). The
PNA was remotely controlled by computer software written in Labview
TM
version
8.5. The data measured by the PNA was stored in the computer hard disk by the
Labview
TM
software in the form of a.s4p files containing the magnitude (in dB) and
phase (in degrees) of all transmission responses. During the measurements, the PNA
was always calibrated to exclude the losses that incurred in the cables and thus, the
measured data reflects the signal measured at the ports of the antenna. The calibration
also ensured that a total power of 0 dBm is transmitted by the transmitting antenna.
The PNA was set to capture 3,201 data samples, with a sampling time of 6.6 ms.
The sampling time was carefully chosen to capture all variations made by any fast
movements of the human subject and to keep the sampling frequency higher (at least
double) than the resulting Doppler shift. The Doppler shift is discussed later, in this
chapter. The sampling time of 6.6 ms (sampling frequency of 150 Hz) was selected
to ensure that all the variations caused by the movement of the body were captured,
by making the sampling frequency more than twice the maximum body Doppler
shift. The maximum Doppler shift was calculated assuming relative speed of motion
Search WWH ::
Custom Search