Miniature Tunable Antennas for Power Efficient Wireless Communications

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Miniature Tunable Antennas for Power Efficient
Wireless Communications
Darrin J. Young Electrical Engineering and
Computer Science Case Western Reserve
University Cleveland, Ohio 44106
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Acknowledgement
NASA under Grant NAG3_2578 Collaborator
Professor Wen Ko Graduate Student Brian Quach
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Outline

• Motivation
• Proposed Power Efficient System
• MEMS Tunable Capacitors
• MEMS Fabrication Technology
• Conclusion

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Motivation
Low Power Transceiver Critical for Wireless
Communication
3 dB Loss
2 W PA output ? 1 W _at_ antenna Shortened battery
life Degraded receiver sensitivity
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Proposed Power Efficient Architecture
Eliminating Duplexer ? Power Saving! Narrow-Band
Antennas ? Frequency Tuning
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Patch Antenna
1.6 GHz Patch Antenna
S11 Measurement
Patch Antenna Tuning
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Tuning Capacitor

• Nominal Capacitance 1 2 pF
• Tuning Ratio 100 with 5 to 10 V ? (100MHz)
• High Quality Factor (Q) 100 at RF (GHz)
• High Voltage Handling 1 W ? 20 V peak to peak
• Insensitive to RF Signals

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MEMS Tunable Capacitor
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MEMS Capacitor Design
Diaphragm Radius
Diaphragm Thickness
Gap
Insulator Thickness
Electrode Radius

• Critical Design Parameters
• Touch point pressure (TPP) 12 psi
• Large TPP ? small initial touched area ? large
  tuning ratio
• (2) Diaphragm thickness 2 mm (small initial
  capacitance accurate process control)
• (3) Gap 1 mm (accurate process control)
• (4) Diaphragm Radius 120 mm (for TPP of 12 psi)
• (5) Insulator (Oxide) Thickness 300 Å (Thin
  Layer ? Large tuning, limited by BD)
• (6) Bottom Electrode Radius 80 mm

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MEMS Capacitor Simulation
MEMS Capacitor Under 0V
MEMS Capacitor Under 10V

• Nominal Capacitance 2 pF
• Tuning Ratio 55 _at_ 5V and 120 _at_ 10V
• Estimated Q _at_ 1GHz 340

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Fabrication Technology
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Current Status Future Plan

• Current Status
• Devices in fabrication
• Future Plan
• Device characterization
• Tunable antenna perform evaluation

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Conclusions

• Tunable patch antennas for low power wireless
  applications
• MEMS tunable capacitor provides
• High-Q
• Large tunable range
• Large voltage handling
• Insensitive to RF signals
• MEMS capacitors for tuning patch antennas
• transmitter output matching networks
• high spectral purity RF oscillators