Miniaturisation of Antennas for Specknet

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Miniaturisation of Antennas for Specknet

• Griogair Whyte
• Ultrafast Systems Group
• Glasgow University
• G.Whyte_at_elec.gla.ac.uk
• Supervisor Iain Thayne

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Outline

• How do you miniaturise?
• Miniaturisation trade offs.
• Current Work.
• Comparison of shift up in freq v. propagation
  loss.
• Some commercially available antennas.
• Future Work/conclusions.

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How do you Miniaturise
Dipole in free space.
L 61.2mm

• Frequency 2.45 GHz
• Permittivity (?r 1
• Effective wavelength free space / sqrt
  effective permittivity

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Miniaturisation trade offs

• Reduced efficiency (or Gain).

• Shorter range.

• Smaller useful bandwidth.

• Increased sensitivity to external factors.

• Hence more critical tuning.

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Circularly Polarised (CP) Patch Antenna _at_2.45 GHz

• Orientation doesnt matter.
• Bandwidth Limited.

BW 50 MHz
Gain 6 dB
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Compact Patch Antennas

• Increase frequency.
• Higher permittivity substrate.
• Shorting to reduce length.

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Increase Permittivity

• Just under 50 reduction in size going from
  permittivity of 3.48 to 12.9.

• But gain and BW decrease.

32mm x 32mm x 1 mm
18mm x 18mm x 1 mm
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Gain and RL patterns for permittivity shift
Perm 3.48
Perm 12.9
Gain 6.1 dB
Gain 5.2 dB
BW
BW
Bandwidth(BW) 40 Mhz
Bandwidth(BW) 12.5 MHz
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Shorting

• Insert either plates or posts to reduce size.
• But efficiency decreases (5)
• Shorting plate is used hard to match.
• Gain also decreases (Gain eff x Directivity).

32mm x 32mm
16mm x 32mm
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Gain patterns and RL for MSA shorted and MSA
Gain 2.9 dB
Gain 6.1 dB
BW
Efficency 77 Radiated Power 0.76 Accepted
Power 0.96
Efficency 72 Radiated Power 0.53 Accepted
Power 0.73
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Increase Frequency

• Going from 2.45 GHz to 5.8 GHz results in a
  approx size reduction of a third.
• But propagation losses increase by 7 dB.
• Show gain is approx same.

32 mm x 32mm x 1 mm
13.2 mm x 13.2mm x 1mm
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Gain Patterns and RL at 2.45 and 5.8 GHz
Gain 6.1 dB
Gain 6.4 dB
BW
BW
Bandwidth(BW) 40 Mhz
Bandwidth(BW) 110 Mhz
Free space propagation loss(radius 10 cm) _at_
2.4 GHz 20 dB _at_5.8 GHz 27 dB
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GaAs patch at 5mm x 5 mm x 800 micron
BW 120 MHz

• Resonant Frequency 8.95 GHz
• Return Loss -15 dB
• Radiated / accepted power 0.92 / 0.97
• Efficiency 95
• Gain 6.6 dB
• Free space propagation loss _at_ 8.95 31 dB

• Therefore if you have a compact antennas with no
  gain at 2.45 GHz, loss 20dB.

• Hence at 8.95 GHz with antennas having gain of
  6.6 dB, free space loss 17.8dB.

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Dielectric Resonator Antenna _at_ 2.45 GHz

• Excellent efficiency (99).
• Good Gain and radiation pattern.
• 20mm x 20mm x

17mm
BW
Gain 6.3 dB

• Size reduces as a factor of 1/sqrt(permittivity).

• fo 7.4 GHz for 5mm x 5mm x 2.5mm (Perm 90).

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Picoradio Antenna

• This antenna is from Tyco Electronics (Rangestar)
• Smallest Bluetooth Antenna is 2.5mm x 1.6mm x 1.6
  mm

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Conclusions

• Can you reduce size so as to fit onto a Speck?
• Moving up in frequency (5.8 GHz).
• Higher permittivity.
• What will the layout and configuration of the
  Speck be?

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Miniaturisation of Antennas for Specknet

• Griogair Whyte
• Ultrafast Systems Group
• Glasgow University
• G.Whyte_at_elec.gla.ac.uk
• Supervisor Iain Thayne