UNDERSTANDING OF UWB TECHNOLOGY
AND UWB ANTENNA DESIGN FOR
Department of Electrical Engineering
What is ultra wide band(UWB)?
Ultra wide band is the band which occupies greater
than 500 MHz of band width or greater than 25% of
the operating center frequency.
FCC allocated the 3.1-10.6 GHz spectrum for
unlicensed use .
UWB technology transmit and receive pulse based
waveform compressed in time .
So in frequency domain band width of pulse is very
Because of compressed time pulse data rate is very
high and as the power of pulse is spread over the
large frequency band so noise interference is very
High data rates
Multiple-access capabilities, due to wide
band width of transmission
Propagation through solid material, due to
presence of energy at different frequencies.
Carrier less signal propagation
Simplicity in implementation, low cost of
High resolution radar-for example detection and
movement of objects near vehicle are more accurate
Wireless personal area network(WPAN)-Anyone can
Military communication- The probability to detect
UWB pulses is very low.
Imaging system-like ocean imaging medical
Emergency situation- As UWB spectrum can
penetrate obstacles .this property can be used to
detect and rescue survivors in disaster situation
Achieving Broader Bandwidth
There are several known antenna
topologies that are said to achieve broader
characteristics ,such as horn antenna
, Biconical antenna ,Helix antenna ,Bowtie
antenna ,spiral antenna.
biconical antenna bowtie antenna helix antenna
If we consider the case of dipole antenna for 300 mHz frequence
then length should be 0.5 m (to behave as a half wave dipole
If the frequency changes radiation pattern changes as the length
So the problem is that the above Half-Wavelength antenna design
depends solely on length.
What if instead, we could design an antenna that was completely
specified by Angles instead of Lengths? Angles do not depend on
distance - and hence don't depend on wavelength.
One of the popular UWB antenna is Bow-tie antenna.
VSWR of bow tie antenna
Signal propagation in water
Aquatic communication are limited by two factor
1)low speed of sound
2)time varying multi path propagation
So alternative approach is Electro-magnetic wave
Electromagnetic wave in water is only 9 times
slower than air.
As attenuation factor is directly proportional to
square root of freq and conductivity.
Propagation of high frequency component are not
possible in water .
Under water antenna analysis
If we put the bow-tie antenna inside water(without
any change in structure)
Folded Bow-tie antenna analysis
It is the combination of circular loop and bow-tie
The radiation pattern and return loss depends on
radius, angle , width, thickness, feeding and internal
isolation of antenna.
Angle and width
Thickness and gap feeding
Choosing best dimensions (width,thickness……)
As bw>500mhz so the designed antenna is a uwb antenna
Final shape with internal isolation
An antenna need battery and circuit to work but
cannot be touching water
Thus we have to isolate center of antenna with
The sphere can be air or air Teflon ball.