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Compact Coupled Circularly Polarized Patch Antenna for Medical Applications

Supervised by:Professor Dr. Md. Mostafizur Rahman

Presented By: Sharmila Taluckder Roll no:1109041 Course no:4000

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OUTLINES Introduction General structure of patch Feeding methods Coupling & circular polarization Antenna design & description Simulation & parameter calculation Results Future work Conclusions

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INTRODUCTION

A single-fed coupled circularly polarized patch antenna is designed & experimentally demonstrated.

Proposed antenna has good circular polarization property & biocompatibility issue is addressed in proposed design.

Main goal to design compact antenna for medical application

Patch antenna used because they are versatile in terms of impedance, polarization & pattern.

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GENERAL STRUCTURE OF PATCH ANTENNA

Consists of radiating patch, dielectric substrate, feed & ground plane Radiating patch is metallic sheet may be of many geometric shape Ground plane is metal where radiating patch is mounted. Dielectric substrate is low loss insulating material where antenna

shapes are printed

Fig. 1: General structure of patch

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FEEDING METHODS

Two types of feeding methods in patch antenna- Contacting methods: RF power fed directly to radiating patch using connecting element. 1. Micro-strip line feed 2. Coaxial probe feed

Non-contacting methods: Power transferred between micro-strip line & radiating patch through electromagnetic coupling.

1. Aperture coupling feed 2. Proximity coupling feed

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MICROSTRIP LINE FEED

Conducting strip connected directly to the edge of patch Smaller in width as compared to patch

Advantage: Can be etched on same substrate Easy feeding scheme & simplicity un modeling

Disadvantage: As thickness of dielectric substrate increases, it

hampers the bandwidth of antenna

Fig.2: Micro-strip line feed

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COAXIAL PROBE FEED

Inner conductor of coaxial connector extends through dielectric & soldered to radiating patch.

Outer conductor connected to ground plane.

Advantages: Can be placed any desired location inside patch Easy to fabricate & low spurious radiation

Disadvantages: Narrow bandwidth & difficult to model Input impedance become more inductive for thicker substrates

Fig.3:Coaxial probe feed

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COUPLING & CIRCULAR POLARIZATION

When elements are placed collinearly along E-plane, called E-plane arrangement .

When elements are placed collinearly along H-plane ,called H-plane arrangement

Coupling: coupling between two patch is a function of position of one element

relative to the other. successful attempts have been made using transmission-line model &

cavity model but difficult to do.

Fig.4: E-plane & H-plane arrangement

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CONTINUE………Circular polarization: Electric field varies in two orthogonal planes with same magnitude & 90 degree phase difference.

When phases are 0 & -90 degree ,called Right hand circular polarization.

When phases are 0 & 90 degree ,called Left hand circular polarization.

Single feed arrangement can be obtained- introducing slight perturbation by truncating patch corners, adding tails and cutting cross slots , adopting aperture-coupled feeding configurations cutting gap to a loop antenna Fig. 5: Single feed CP

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ANTENNA DESIGN

40mm

40mm

10mm

10mm 5mm

8mm

Fig.6:Top views of proposed antenna

Single feed

10mm

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ANTENNA DESCRIPTIONIn the proposed antenna- design concept is something like sandwich. have a top FR-4 substrate then Ground plane at the middle and

then Teflon at the bottom. Teflon isolates ground plane from human body, to avoid direct

electrical contact.. Four small patches connected to small square loop with coupling. Antenna is fed at quadrant IV. Single Feed circular polarization is obtained from coaxial probe

feed.

Feeding arrangement: Outer cover is metal called Cover pin & used for ground. At middle is called Teflon pin & used for isolating ground and

main feed At centre is Metal pin and used for main signal.

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SIMULATION & PARAMETER CALCULATION

S-parameter: represents how much power is reflected from the antenna.

If S11=0 dB, all the power is reflected from antenna and nothing is radiated. If S11=-10 dB, implies that if 3 dB of power is delivered to antenna, -7 dB is

reflected power For ideal antenna ,S11 is less than -10 dB.

Fig.7: S-parameter curve

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CONTINUE………….

Voltage standing wave ratio (VSWR): Describes how well antenna is impedance matched to transmission line. Minimum value of VSWR is 1, hence no power is reflected from

the antenna. In proposed antenna, value of VSWR is 1.57

Fig.8: VSWR of proposed antenna

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CONTINUE………Reflection coefficient:. Describes amount of power reflected from antenna Reflection coefficient,(┌) = Reflected power in dB = 20 log (┌)

Mismatch loss: Amount of power is lost due to impedance mismatch Mismatch loss in dB = 10log(1- )

Antenna efficiency: Relates power delivered to antenna & radiated or

dissipated within antenna. If most power is radiated ,antenna is high efficient If most power is absorbed as losses, antenna is low

efficient. Total efficiency Radiation efficiency.

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CONTINUE……

Antenna Gain: Describes how much power is transmitted in direction of

peak radiation of isotropic source. When no direction specified, ‘gain’ is understood to the

peak value radiation. Gain of proposed antenna is -0.397 dB.

Fig.9: Far-field gain plot polar

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CONTINUE………

Directivity: Measures power density of antenna radiates in direction

of its strongest emission, versus power density radiated by ideal isotropic radiator.

Directivity of proposed antenna is 7.67 dBi.

Fig.10: Far-field directivity polar

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CONTINUE…….

Axial ratio: It is the ratio of orthogonal components of an E-field. From this figure, axial ratio is 2.67 dB Axial ratio 3dB means circular polarization

Fig.11:Axial ratio plot

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RESULTS Resonant frequency= (5 - 5.1 )GHz S11= -13.97dB VSWR= 1.57dB Reflection coefficient= 0.2 Reflected power = -13.97dB Mismatch loss= -0.1773 dB Gain= -0.397dB Directivity= 7.67dBi Radiation efficiency= -8 dB Total efficiency= -12.4 dB Axial ratio= 2.67 dB

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FUTURE WORK

Modify antenna configuration

Shift resonant frequency to medical band

Implement proposed antenna in human body

Comparison of simulated & measured results

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CONCLUSION An single feed circular polarized patch antenna is

proposed with coupling for medical application.

The biocompatibility issue is addressed in antenna by using TEFLON as substrate below ground plane.

Return loss, Voltage standing wave ratio, Reflection coefficient, Gain, Efficiency have been studied and simulated.

Also mentioned the future work to improve proposed antenna for medical application.

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REFERENCES www.antenna-theory.com “Antenna theory analysis and design” by CONSTANTINE A. BALANIS www.wikipedia.com W. Greatbatch and C. F. Homlmes, “History of implantable devices,” IEEE Eng. Med. Biol. Mag., vol. 10, no. 3, pp. 38–41, Sep. 1991. G. J. S. and N. H. Lovell, “CMOS neurostimulation ASIC with 100 channels, scaleable output, and bidirectional radio- frequency telemetry”. Z. M. Chen, K. W. Cheng, Y. J. Zheng, and M. Je, “A 3.4 mW 54.24 Mbps burst-mode injection-locked CMOS FSK transmitter,” in Proc. IEEE Asian Solid State Circuits Conf., Nov. 14–16, 2011, pp. 289–292. F. Merli, B. Fuchs, J. R. Rosig, and A. K. Skrivervik, “The effect of insulating layers on the performance of implanted antennas,” IEEE Trans. Antennas Propag., vol. 59, no. 1, pp. 21–31, Jan. 2011.

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THANK YOU ALL