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Ultra-wideband Radar

conventional
narrow-band system
Ultra
Wideband
System
thermic
noise

Figure 1: The UWB-radar transmits in a wide spectrum with very low power

conventional
narrow-band system
Ultra
Wideband
System
thermic
noise

Figure 1: The UWB-radar transmits in a wide spectrum with very low power

What is an UWB radar?

Ultra-wideband Radar

Ultra-wideband radar (UWB- radar) transmits exploratory signals with a much larger spectrum than conventional radars. They require much less pulse power, which makes the radar transmitter non-detectable. The transmitted signal is even smaller than the allowed interference power level of various electrical devices (e.g., a hairdryer). Usually, pulse generators with extremely short pulse widths are used, shorter than 1 ns.

The spectrum of these extremely narrow pulses becomes more and more similar to white noise as the pulses become narrower. However, these extremely narrow pulses also require a much larger receiver bandwidth than conventional radars.

The amount of spectrum occupied by the ultra-wideband Radar transmit signal (i.e., the bandwidth of the ultra-wideband signal) is at least 25% of the amount of the center frequency of the transmitter. So a center frequency of 2 GHz has a bandwidth of 500 MHz, and the minimum bandwidth from an ultra-wideband signal with the center frequency of 4 GHz is then 1 GHz. Bandwidths of more than 1 GHz are often used.

This large bandwidth requires special assemblies for the ultra-wideband radar. The antenna must have an extremely wideband characteristic that often several antennas for different frequency bands are used in parallel. Therefore, horn radiators or Vivaldi antennas are used commonly. This also doesn't allow the receiver to have a resonant frequency. Any resonance in the frequency is narrowband, and this narrowband should be avoided here.

An example of a typical ultra-wideband radar is the pulsed noise radar used for training purposes. This radar transmits single pulses on the center frequency of 24 GHz with a length in the range of a few nanoseconds and a pulse power of 4 mW. Its bandwidth is thus 8 GHz. Whether this radar is transmitting or not cannot be determined by external measurement, since its transmission pulses do not differ from the ambient noise.