ESP2110WIFI ANTENNA DESIGN PROJECT

Picture from [1], p. 353

ContentsIntroduction1. Fabrication, design and parts

2. Reason for choice

Theory3. Loop

4. Archery-target antenna

5. Impedance matching

6. VSWR

User design and future considerations

Performance analysis

Field testing

Conclusion

Credits

Introduction

FabricationArchery target antenna

Parasitic elements Main back reflector Front annular reflector Center small reflector Wooden back base for physical support

Driven element Z-shape 1λ circular loop

Design overview

Basic design and dimensions from existing literature

Optimum dimensions derived mainly from experimentation and occasionally FD-TD method

Modifications not tested before include

1. the addition of secondary rim

2. use with specified driven element

Picture modified [2], p. 227

Back Reflector

Front + center reflector

1λ circular loop

Introduction

Reason for choice Good match with project

requirement

Relatively small size for its Performance

Flexibility with modifications : type of driven element used configuration of reflectors

Characteristics required

Archery-target

Antenna

High gain √

High directivity √

Fixed, narrow band

√

WIFI frequency band

√

Loop theory

1λ circular loop

Radiation pattern

Pictures modified from [3]

4:1 delay line type coax Balun 1λ loop feedpoint impedance (Ω) ≈ 80-150 L = 1/2λ

Causes 180° phase shiftas desired

Provides balanced input

Balun theory

Pictures from [5] and [6]

Endoresonance antenna: open cavity Can be considered similar to

waveguide operation (resonant modes)

Archery-target antenna theory

Pictures from [1], p. 19

Archery-target antenna theory

Influence of sub-reflector size

Small

Large

Pictures modified from [7], p. 4

Archery-target antenna theory

Evolution of front reflectors

Maintaining backfire effect while enlarging aperture size

Increasing directivity with secondary rim on reflectors

Archery-target antenna theory Estimated radiation plot and

directivity

Graphs from [2], p. 226

Impedance matching

Determine lengths x1 and x2 using software Smith v3.10

Smith chart and VSRW of antenna with original 1λ line segment

Impedance matching

Practical approach to impedance matching

Since Smith chart of antenna line segment is favourable

And accuracy loss due to connectors and small physical length of λ

Take x1 ≈ 0

Impedance matching

Impedance matching

New Smith’s Chart and VSWR with stub

User design & future considerations

User design Handle/ portable Rigid back wooden support Weather resistant due to lacquered wood

Future considerations Selective frequency using translucent aperture Increase aperture efficiency by using better dielectric Wider bandwidth using main conical

reflector and a smaller centre reflector

Pictures from [8], p. 115

Performance analysis

-80

-60

-40

-20

0

20

40

60

80

100

120

RSSI

signalQuality

2m

• RSSI -10 to 15• Signal Quality 100

25m

• RSSI -50• Signal Quality 80

2m

• RSSI -10 to 15• Signal Quality 100

Loop A (Directed)

Loop A

Loop B

Loop B (Opposite)

2m

• RSSI -35• Signal Quality 100

25m

• RSSI -58• Signal Quality 80

2m

• RSSI -37• Signal Quality 97

Field hunting

Field hunting – Objective A

Field hunting – Objective A

Field hunting – Objective B

Field hunting – Objective B

Field hunting – Objective C

Field hunting – Objective C

Field hunting - Summary

Conclusion

Fabrication Our antenna is durable and portable Well suited for the Objective

Overall Performance Up to standard for field testing Good Signal Quality

References and Credits [1] A. Kumar, H.D. Hristov, Microwave cavity antennas , Norwood, MA :

Artech House , 1989 [2] M. Vidmar, “An Archery-Target Antenna”, Microwave Journal, Vol.

48, No. 5, pp.222-230, May 2005. [3] J. Bernhard, E.Michielssen and L. C.Godara, Eds., “Antenna

Parameters, Various Generic Antennas and Feed Systems, and Available Software”, in Handbook of antennas in wireless communications , Boca Raton, FL : CRC Press, 2002, ch. 5, sec. 3.2

[5] T. Tribuzio. (2011, Mar. 2). About Balun [Online]. Available: http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=3767

[6] A. Vernucci. (2011, Mar. 2). A Simple 50-ohm Single-Band Balun [Online PDF]. Available: www.qsl.net/i0jx/balun.pdf

[7] M. Rayner, A.D. Olver, A.D. Monk, “FD-TD design of short backfire antennas”, IEE Proc.-Microw. Antennas Propag., Vol. 144, No. 1, pp. 1-6, Feb 1997

[8] G. S. Kirov, “Design of Short Backfire Antennas”, IEEE Antennas Propagat. Mag., Vol. 51, No. 6, pp. 110-120, Dec 2009