understanding of uwb technology and design of uwb antenna for underwater application

1. UNDERSTANDING OF UWB TECHNOLOGY
AND UWB ANTENNA DESIGN FOR
UNDERWATER COMMUNICATIONS
Submitted by
DEBASHISH PRADHAN
ENTRY ID-2013EEE8271
COURSE-EEL 760
Department of Electrical Engineering
IIT DELHI

2. 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 .

3. WHY UWB?
 UWB technology transmit and receive pulse based
waveform compressed in time .
 So in frequency domain band width of pulse is very
high.
 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
less.

4. UWB ADVANTAGES
 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
devices.

5. UWB application
 High resolution radar-for example detection and
movement of objects near vehicle are more accurate
 Wireless personal area network(WPAN)-Anyone can
use
 Military communication- The probability to detect
UWB pulses is very low.
 Imaging system-like ocean imaging medical
diagnostic
 Emergency situation- As UWB spectrum can
penetrate obstacles .this property can be used to
detect and rescue survivors in disaster situation

6. UWB ANTENNA REQUIREMENTS
 Band width-3.1-10.6 GHz
 Radiation Efficiency-High(>70%)
 Phase-Nearly Linear(constant group
velocity)
 Radiation Pattern-Omnidirectional
 Directivity-low
 HPBW-wide(>60)
 Return loss-less(<-10db)

7. 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

8. Bow-tie 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
antenna)
 If the frequency changes radiation pattern changes as the length
is fixed.
 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.

9. VSWR of bow tie antenna
 For L=76.5mm
 D=1300
 http://www.antenna-theory.com/antennas/wideband/bowtie.php

10. 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
communication.
 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 .

11. Study of permittivity of water

12. Under water antenna analysis
 If we put the bow-tie antenna inside water(without
any change in structure)
 upcommons.upc.edu/.../UWB%20antenna%20design%20for%20underw

13. Folded Bow-tie antenna analysis
 It is the combination of circular loop and bow-tie
antenna.
 The radiation pattern and return loss depends on
radius, angle , width, thickness, feeding and internal
isolation of antenna.

14. Parametric study
Angle and width
upcommons.upc.edu/.../UWB%20antenna%20design%20for%20underw

15. Parametric study
Thickness and gap feeding
upcommons.upc.edu/.../UWB%20antenna%20design%20for%20underw

16. Parametric study
radius
Choosing best dimensions (width,thickness……)
Bw=1800 mhz-135mhz=1665mhz
As bw>500mhz so the designed antenna is a uwb antenna
upcommons.upc.edu/.../UWB%20antenna%20design%20for%20underw

17. Radiation pattern(without internal isolation)
upcommons.upc.edu/.../UWB%20antenna%20design%
20for%20underw

18. 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
sphere.
 The sphere can be air or air Teflon ball.

19. Radiation pattern(with isolation)
upcommons.upc.edu/.../UWB%20antenna%20design%20for
%20underw

20. Conclusion
 When the antenna has internal isolation ,the pattern
is more omnidirectional.
 Under water UWB communication is possible but
within short range because of conductivity of water.