Implementation of Ultra-Wideband (UWB) Sensor Nodes for WBAN Applications - Ultra-Wideband and 60 GHz Communications for Biomedical Applications - page 116

Fig. 11 Waveforms taken at
various points of the sensor
nodes (the points are marked
with reference to the positions
marked in Fig. 8 )

Amplifier-Based RF Module

Figure 12 depicts the amplifier-based sensor node design. In the amplifier-based
implementation, the narrow baseband pulses are filtered using a BPF in the band
of 3.5-4.5 GHz. The UWB pulses are then amplified using a wideband low noise
amplifier (LNA) to meet the

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41.3 dBm transmission power level. This amplifier
has been included to guarantee that the amplitudes of the UWB pulses are sufficient
enough for the distance targeted by a WBAN application.
The power spectrum of the UWB pulses generated using the UWB pulse generator
and the RF module that has a pulse width of 0.5 ns and 20 MHz PRF is shown in
Fig. 13 . This power spectrum consists of several frequency lobes spread throughout
the UWB bandwidth. The amplitudes of these frequency lobes decrease toward the
upper part of the UWB spectrum. The UWB sensor node is designed to transmit
UWB signals in the band of 3.5 to 4.5 GHz. As shown in Fig. 13 a the amplitude
of the frequency lobe within the 3.5-4.5-GHz band is well below the maximum
allowable power level by the FCC ( 41.3 dBm/MHz). The amplifier-based ver-

sion of the UWB sensor node employs two amplifier stages in order to boost the power

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