uwb antenna by debashish(iit delhi)

UNDERSTANDING OF UWB TECHNOLOGY

AND UWB ANTENNA DESIGN FOR

UNDERWATER COMMUNICATIONS

Submitted byDEBASHISH PRADHANENTRY ID-2013EEE8271COURSE-EEL 760

Department of Electrical EngineeringIIT DELHI

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 .

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.

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.

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

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)

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

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.

VSWR of bow tie antenna

For L=76.5mm

D=1300

http://www.antenna-theory.com/antennas/wideband/bowtie.php

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 .

Study of permittivity of water

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

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.

Parametric study

Angle and width


Parametric study

Thickness and gap feeding


Parametric study

radiusChoosing best dimensions (width,thickness……)

Bw=1800 mhz-135mhz=1665mhz

As bw>500mhz so the designed antenna is a uwb antenna


Radiation pattern(without internal isolation)


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.

Radiation pattern(with isolation)


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.