The transmitter architecture uses a filter bank of as many as 24 adjacent filters. At the input of this filter bank, a UWB pulse (covering the whole 3.1–10.6 GHz bandwidth) is generated with a repetition period of Tr. On each line, the relatively narrowband (from 250 to 500 MHz) pulses are modulated by an OOK modulation at the rate of 1/Tr.
Conversely, a second solution uses a bank of local oscillators, ensuring the frequency transposition toward each sub-band. Notice that oscillators are only used to provide transposition. Coherence is not required. And the OOK modulation controls the activation of each oscillator. In this solution, the constraint on the pulse width generated is relaxed (2 ns for 500 MHz bandwidth). In both sketches, each narrowband pulse is added to produce a UWB signal that is transmitted through the antenna. An interesting feature to notice here is that the architecture permits a simple power control in each
sub-band. This kind of flexibility can be useful to fulfill a regional power spectral density mask.
Energy splitters and combiners used in the bands of 3.1–10.6 GHz are readily available on the shelves. With regard to the switches that provide the OOK modulation, the concern is not the switching times, which are lenient, but the
insertion loss. These are also easily available in the market.
As for the antenna, the issue is its bandwidth that must cover the entire 3.1–10.6 GHz bandwidthbut this is not restricting. Thanks to the energetic nature of the processing, which makes signals sensitive to phase and distortion. Nevertheless, to implement the functional scheme described above with minimized physical constraints, we could consider M antennas each of them followed by a filter bank of N filters, with N x M typically equal to 24.
For example, in a realistic implementation, six antennas working in a range of 1 GHz could each be followed by four filters of 250 MHz. This kind of antenna’s form factor is compatible with the overall system integration.
Moreover, to ease constraints on both pulsers and energy splitters, a solution based on multiple pulsers is envisioned. In the previous example, each of the six pulsers feeds a splitter that distributes the energy over the four filters as illustrated in Figure 3.