MEA RF Front End

1
MEA RF Front End
a0
PA
a1
PA
x(t)
a2
PA
a0
LNA
a1
y(t)
LNA
a2
LNA
2
60GHz System Must Have Better Antenna

• Friis Formula
• Assuming dipole antennas,
• 10m separation

Even 1 big antenna is an array with fixed
weighting. Take control of the weighting and
there can be a big win.
3
Beamforming

• Antenna arrays are spatial (angular) filters.
• The array factor, AF(z) has a certain form
• AF(z) (a0zN-1a1zN-2 aN-1) / zN-1
• Where the ais are the antenna weighting factors.
• Synthesis and Analysis can be done in MATLAB

Analysis roots() Synthesis poly()
4
Pattern Multiplication
Total array pattern is product of AF in each
dimension and element factor.
5
Mixer for Array

• Only need 1, or 1 pair for IQ, for up-convert,
  and also for down-convert
• Versus N of them for a fully adaptive system.
• Full system has N xcvrs, and can do all
  weighting/combining at baseband (SVD).
• This system is limited to beamforming, cant do
  multiple data streams.
• At 60GHz the problem is range, not bandwidth or
  data rate.

6
Phase Shifters

• Vector modulator

x(t)
?
90
7
Power Amplifiers

• Output power of the N power amplifiers is added
  spatially, forms the antenna pattern.
• Therefore, only need 1/N as much power in each
  individual PA.
• Operation frequency is very close to fT/fmax of
  the technology, so use Class A or AB.
• These have higher RF output power, and lower
  input voltage drive requirements, so overall
  system efficiency could be higher.

N Times Power
PA
PA
PA
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Low Noise Amplifiers

• For parallel system signal sees gainGN, noise
  sees gainGN1/2, so we get an SNR gain of N1/2.
• We get N copies of the input signal for free,
  each with uncorrelated noise.
• We design the RFE from antenna through LNA, so we
  dont need 50O, can use different impedances to
  alleviate problems.

LNA
LNA
The opposite of spatial power combining.
LNA
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Antenna Elements

• An efficient antenna needs to be ?/2 long.
• ?(60GHz, e0) 5mm
• Need ?/2 lateral spacing between elements
• maximum directivity without grating lobes.
• Vertical spacing is slightly greater than ?/2,
  but ?eff is slightly less than ?0, so spacing is
  2.5mm.
• Antenna unit cell is approx. 2.5mm x 2.5mm

2.5mm
2.5mm