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Interface Between Antenna and Transceiver

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									Wireless Communication for Wildlife Research
ECE 445 Final Presentation Spring 2005 Prof. Scott Carney Christos Bais Mike Cristiano Tim Eggerding TA: Shenghui Zhang

Introduction
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Project in conjunction with Illinois Natural History Survey Wildlife radio tracking using remote Yagi antenna arrays Remote stations log data, transmit to central station Current communications via wired LAN

Design Criteria
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Economize power Operate in rain, cold 3-5 km data transmission above audio rate (256 Kbps) Allow ‘ad-hoc’ mode to increase range Low maintenance, high reliability Comply with FCC regulations

Protocol Design
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OSI protocol stack Design layers 1-4 Allow for ‘ad-hoc’ mode Data rate above quality audio (256 Kbps)

Design Approaches
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Construct transceiver hardware, write protocol Use stock radio modem Bluetooth for hardware and protocol standard Use existing protocols for layers 2-4
• TCP/IP, UDP

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Solutions
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Transceiver design, protocol writing too involved, not robust Bluetooth chips difficult to program, build Radio modems not fast enough (<200 Kbps)

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Need to integrate existing protocol with stock transceivers

Lantronix Wiport
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Fully integrated 802.11b transceiver, TCP/IP stack Ad-hoc network rates up to 11 Mbps Requires 250mA @ 3.3V Operates at -40 – 70 C Serial RS-232, RS-485 interface Serial, telnet, or Web configurable $119

Integration
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Lantronix supplies evaluation board Cheaper, more flexible design needed for production Power, status LED’s, serial interface Serial communication driven by MAX3223, male and female 9-pin DSUB for each serial port Optional Ethernet interface

PCB Design

Antenna Design
Overview: Basic Antenna Yagi-Uda Principles Friis Equation Simulations Yagi-Construction Testing/Comparison

Basic Antenna

Yagi-Uda Principles

Friis Equations
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PL = (2 qr Gr |pr*pt|2 Gt qt Ps)/(4r)2 PL = Receive Sensitivity  = c / 2.448 GHz = 12.2464 cm qr,t = mis-match, r =receive, t=transmit Gr,t = Antenna Gain Ps = power available from source r = distance in meters |pr*pt|2 = Polarization match

Friis Equation…cont.
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Wi-Port Sensitivity:
Sensitivity Theoretical Range
6dB buffer

• -82dBm • -87dBm • -89dBm • -92dBm

for for for for

11Mbps 5.5Mbps 2 Mbps 1 Mbps

Simulations Using Nec

Final Design

Yagi Construction

Testing/Comparison

Antenna Wi-Port Interface
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Balun
• Connects a balanced device to an unbalanced device

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Matching Network
• Allows for maximum transfer of power from transceiver to antenna • Transmit power of Wi-Port 14dBm (25mW)

Balun Construction
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Link from antenna (balanced) to coaxial cable (unbalanced) Implemented folded balun Balances current with quarter wave length coaxial cable

Impedance Matching Network
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Match impedances between load (antenna and source output (PCB) 50 ohms Designed using transmission lines
• Frequency 2.4 GHz • Rated lumped elements are difficult to find

Measuring Antenna Impedance
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Performed measurements of the Network Analyzer Recorded impedances at start, stop and center frequencies Checked the return loss of the antenna

Definitions
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Smith Chart – Shows how close impedance match is to 50 ohms
Return Loss - Amount of Power reflected
• -3dB • -6dB • -10dB • -15dB 50% power transfer 75% 90% 97%

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Antenna Results

Return Loss

Smith Chart

Design and Simulation
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Created several matching networks and simulated in Puff Simulations showed design requirements fulfilled

Different Designs

Broadband Match Results

Return Loss

Smith Chart

Problems and Conclusions
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Matched at center frequency but return loss at band edges poor Placed 150 ohm load at end to verify design Conclusion
• Q of antenna too high • System limited to highest Q • Power transfer sufficient for 5km range

Testing Procedures
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Wiport set up via serial interface Each Wiport assigned an IP address Terminal Emulation software used to communicate to the Wiport via serial Wiport connects to remote host, transmits serial data via IP

Testing Results
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18 April - Communication between Everitt, Grainger 24 April – ½ mile test, South 1st St. 25 April – 2 km test between Market Place Mall, Prospect & Olympian Tests conducted at night in rainy conditions 26 April – 650 m demonstration between Everitt, Beckman Parking Structure Distances verified via GPS

Conclusions
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Benefits
• Inexpensive • Low Power

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Design Considerations
• Robust • Reliable • Repeatable

Acknowledgements
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Professor Scott Carney Dr. Ron Larkin Ben Kamen Shenghui Zhang Professor Steven Franke Professor Jennifer Bernhard Professor Eric Michielssen


								
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