UWB Radar Technology
What is Ultra-Wideband (UWB)?
In radio engineering the signals are called Ultra-Wideband (UWB) if they occupy ultra wide frequency spectrum range. UWB systems are radio communication or radio location systems which operate with UWB signals.
Main requirement to the frequency spectrum range of UWB signals was put forward by DARPA in 1990, which says that for such signals relative frequency band h has to be no less than 0.25:
h = (fHIGH - fLOW)/(fHIGH + fLOW)
Video impulse radio location and radio communication systems satisfy to this requirement. Such systems use signals having their duration from parts of nanoseconds to several nanoseconds formed by impact excitation of the UWB antenna with a short unipolar video impulse or bipolar mono-impulse. This type of signals is also called carrier-free signals. Especially often such signals are used in georadars.
Commercialization of the UWB technology brought correction in the signals classification. At first FCC in 2000 and then ETSI issued documents which standardize using UWB signals in radio communications and radio location. In accordance with these documents signals having spectum bandwidth greater than 500 MHz measured at -10 dB level from spectrum maximum are also classified as UWB signals. Thus short radio impulses with high frequency filling have become UWB signals.
Also, there were defined standards on licensed frequency bands and permitted impulse and average power levels for license-free operation of UWB systems.
Separately to be said about complex signals which utilize various modulation schemes (e. g. LFM) for extending frequency spectrum band. Using such signals in RF systems brings some advantages and some disadvantages. However, if frequency spectrum band complies with the aforementioned requirements, these complex signals are also considered as UWB signals.
Advantages of UWB Signals
Using UWB signals gives several advantages among conventional narrowband systems:
- Energy of UWB signal is distributed over wide frequency band while frequency components of the signal do not have high intensity. This enables UWB and narrowband systems coexistence. Moreover using ortogonal UWB signals enables several UWB systems coexistence.
- In radio communication systems data transfer rate gets significantly increased.
- In radio location systems range resolution gets significantly improved. Consequently in multiposition systems angle resolution gets significantly improved as well. Dead area lessens emphatically which makes visibility area starting at antenna edge.
- In radio location systems capability to measure targets portrait emerges.
- In radio location systems capability to form narrow range sensitivity zone and thus eliminate side effects arises.
- Signal depression gets lower because of re-reflections interference.
- Low spectral density of signal power enable UWB systems to operate secretly and be hidden from detection.
UWB Technology at Present and in the Future
Technologies which utilize UWB signals are used in radio location for a long time. As it is written above they are used mainly in georadars.
In late 1990s and early 2000s it was great interest towards using UWB technology in radio communication. Leaders in semiconductor industry started their work on SoC development which would be implementing physical and logical layers of UWB protocol stack enabling data transmittion up to 10 meters at about 500 Mbps speed. There were several announcements about such SoCs.
In 2007 the first commercial UWB devices implementing Wireless USB protocol between PC and peripherals were presented.
However, by some unknown reasons, radio communication systems based on UWB technology have not obtained mass distribution. In 2008 Intel, which was one of the leaders in UWB radio communications, closed development in this direction. Apparently permanently growing data transfer rate in narrowband systems, such as IEEE 802.11n, took away main advantage of UWB systems - enhanced data rate. Analytical articles in mass media more and more often claim that there is no future for UWB communication systems in 3.1 - 10 GHz frequency band.
Lately short range high speed UWB communication systems development has been moved to frequencies around 60 GHz.
As for using UWB signals in short range radio location, we think that here we have good opportunities for solving certain challenges where today's narrowband solutions are not able to reach effect. There are some IC vendors working on SoC UWB radar implementation. As soon as such SoCs are available in the market it will be possible to create tiny radiolocation systems with high technical parameters.
There are several areas where using UWB signals is very reasonable. They are actively being developed by several companies including NanoPulse, Inc.: various motion sensors, impulse range finders, bio-radiolocation, positioning systems, nondestructive testing etc.