BMR Characterization of Antennas through the Combined TD/FD Approach - Broadband Reflectometry for Enhanced Diagnostics and Monitoring Applications - page 135

(a) (b)

Fig. 6.1 a RFId-reader antenna. b biconical antenna [3]

is the Clampco Sistemi AP3000 biconical antenna: a wideband biconical antenna
(Fig. 6.1(b)).
These antennas have very different characteristics in terms of operating frequency
band; in fact, the former is a narrow-band antenna and operates in the 865 MHz-
940 MHz frequency range, whereas the latter is a wide-band antenna designed to
work in a larger frequency range (80 MHz-3 GHz). The different performance of
these two antennas allow assessing the proposed approach for different possible
practical conditions.
The TDR measurements were performed through the TDR80E04 module.

6.3 Acquisition in Time Domain

To obtain the corresponding FD information, TDR waveforms are suitably win-
dowed and processed through the FFT-based algorithm described in subsections
3.4.1 and 3.6.2. It is worth noting that for the TD-acquisition, a rectangular window-
ing is a wise choice, since it provides good balance between amplitude accuracy and
frequency resolution for the subsequent FD-transformation.
Averaged TDR measurements were performed setting the maximum number of
acquisition points (4000 points), thus forcing the time domain resolution (or sam-
pling period, T c ) to the minimum allowed by the instrument for each considered
time window.
When acquiring a TD waveform for a fixed maximum number of measurement
points, the only parameter that can be modified is the time window duration. As will
be clarified, the choice of this parameter has direct consequences in terms of mea-
surement performance. In order to understand how the time windowing affects the
final results, let us briefly recall how the TDR instrument performs measurements.