Designing a Small Planar Antenna Designing a Small Planar Antenna for Agricultural Sensor Network for Agricultural Sensor Network Wonbin Hong Wonbin Hong Purdue University Purdue University 1
Overview Overview � Agricultural Sensor Network Agricultural Sensor Network � � Usage of Smart Sensor Network � Usage of Smart Sensor Network � Antenna/ Packaging � Antenna/ Packaging � System Design Requirements � System Design Requirements � Antenna Design Antenna Design � � Design Approach � Design Approach � Methods � Methods � Results � Results 2
Smart Sensor Network? Smart Sensor Network? � Where do we use Where do we use it? it? � How does it work? How does it work? � How big is it? How big is it? 3
Microstrip vs. Dipole Antenna Microstrip vs. Dipole Antenna � Why use a microstrip Why use a microstrip antenna? antenna? � Size and operating Size and operating frequency frequency c = wavelength/ frequency c = wavelength/ frequency � Packaging Packaging 4
Planar Antenna Planar Antenna � Design Approach Design Approach � Inverted L antenna � Inverted L antenna � Inverted F antenna � Inverted F antenna (PIFA) (PIFA) 5
Designing the PIFA Designing the PIFA � Coupling Coupling – – Magnetic vs. Electric Magnetic vs. Electric Ω port Matching with the 50 Ω � Matching with the 50 port 6
Designing the PIFA Designing the PIFA � Results with capacitive Results with capacitive coupling coupling � Bandwidth � Bandwidth � Radiation Efficiency � Radiation Efficiency 7
Efficiency and Bandwidth Efficiency and Bandwidth � Efficiency and Radiation Efficiency and Radiation resistance resistance L C R = R Efficiency + R R R Loss � Bandwidth and Q Bandwidth and Q � Bandwidth ~ 1/ Q � Bandwidth ~ 1/ Q High-Q Lower-Q 8
PIFA with Capacitive Load PIFA with Capacitive Load � greater Smaller l � � Smaller l greater impedance (Z = cot(Bl)) impedance (Z = cot(Bl)) β � smaller capacitance � β smaller capacitance � Counter the reduction � Counter the reduction � Length can be reduced Length can be reduced dramatically dramatically 9
Coupling Two Resonators Coupling Two Resonators � Electrically couple two Electrically couple two resonators to increase the resonators to increase the bandwidth bandwidth � Creates two resonant � Creates two resonant frequencies frequencies � Parameters determining Parameters determining the coupling the coupling � Gap between the two � Gap between the two plates plates � Distance between the � Distance between the shorted walls shorted walls � Capacitive feed � Capacitive feed 10 10
Results Results � Not enough coupling Not enough coupling � Radiation Efficiency is Radiation Efficiency is sufficient – – 84 percent 84 percent sufficient � Possible Solutions? Possible Solutions? � Usage of patch antennas � Usage of patch antennas with slots with slots � Lumped element � Lumped element – – chip chip resistor? resistor? 11 11
Acknowledgment Acknowledgment � Prof. William J. Chappell Prof. William J. Chappell � Bosui Lui Bosui Lui � Xun Gong Xun Gong � James Brad Dodson James Brad Dodson � Mike R. Arens Mike R. Arens � Chin Chin- - Lung Yang Lung Yang � “ “ D D” ” Sivaprakasapillai Sivaprakasapillai 12 12
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