Uwb antenna by debashish(IIT DELHI)
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UNDERSTANDING OF UWB TECHNOLOGY
AND UWB ANTENNA DESIGN FOR
UNDERWATER COMMUNICATIONS
Submitted byDEBASHISH PRADHANENTRY ID-2013EEE8271COURSE-EEL 760
Department of Electrical EngineeringIIT DELHI
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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 .
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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.
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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.
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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
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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)
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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
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Bow-tie antenna
If we consider the case of dipole antenna for 300 mHz frequencethen 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.
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VSWR of bow tie antenna
For L=76.5mm
D=1300
http://www.antenna-theory.com/antennas/wideband/bowtie.php
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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 .
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Study of permittivity of water
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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
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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.
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Parametric study
Angle and width
upcommons.upc.edu/.../UWB%20antenna%20design%20for%20underw
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Parametric study
Thickness and gap feeding
upcommons.upc.edu/.../UWB%20antenna%20design%20for%20underw
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Parametric study
radiusChoosing 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
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Radiation pattern(without internal isolation)
upcommons.upc.edu/.../UWB%20antenna%20design%20for%20underw
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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.
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Radiation pattern(with isolation)
upcommons.upc.edu/.../UWB%20antenna%20design%20for%20underw
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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.