Transcript Vernon Davids

Implementation of a wideband phase
shifter for phased array antennas
MSc/M-Tech Electrical Engineering FSATIE/CPUT
Vernon Davids
Supervised by
Dr. R. R van Zyl
Overview
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Introduction
Objective
Phase shifting
Wideband phase shifter overview
• Switched-filter
• Reflection-type
• Switched-line
Methodology
Conclusion
Slide 2
29/11/2007
© CSIR 2006
www.csir.co.za
Wideband phase shifters for phased array antennas
Vernon Davids
Introduction
• Modern microwave systems require large operating bandwidths
• Phase shifters are utilised in phased array antennas to control
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Slide 3
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the phase in each element in the array in order to steer the
direction of the beam
Application areas include, phased array radars, satellite
communication systems and measurement instrumentations
© CSIR 2006
www.csir.co.za
Wideband phase shifters for phased array antennas
Vernon Davids
Objective
• Design and implement a wideband phase shifter for a phased
array antenna
Slide 4
© CSIR 2006
www.csir.co.za
Phase shifting
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Time harmonic signal e jt
where (t)  phase  
The time t  vl , v  l ,  2f and f  frequency
Solve phase phase    (t )  (2fl  )
Possible to alter the phase by changing
f  frequency
l  length
  permittivity
  permeabili ty
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© CSIR 2006
www.csir.co.za
Wideband phase shifters for phased array antennas
Vernon Davids
Phase shifting…
Phase shifting by changing frequency (Frequency scanning)
• Accomplished by series feeding the array and altering frequency
c
1
2
• c  
, f   and k   results in phase in electrical length
  t  2f
l
l
c l
 2 .  kl
v
 v
l
• From preceding equation f  
• Signal travels physically il and electrically ikl to the i
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© CSIR 2006
th
_ element
www.csir.co.za
Wideband phase shifters for phased array antennas
Vernon Davids
Phase shifting…
Phase shifting by changing length
• Utilised in series and corporate fed arrays
• Different matched transmission line lengths
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are switched in the signal path
Signal undergoes effective phase shift related
to the difference between selected line and
reference line
Switches used:PIN diodes, FETs
physical _ size  f
• Using substrate with high dielectric constant
give rise to smaller designs
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© CSIR 2006
www.csir.co.za
Wideband phase shifters for phased array antennas
Vernon Davids
Phase shifting…
Phase shifting by changing permittivity
• Changing the dielectric properties of a medium that a signal
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propagates through   
Using gaseous discharge or plasma I    
Ferroelectric materials  (E )
Dielectric constant, function of the applied electric field over
material
Slide 8
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© CSIR 2006
www.csir.co.za
Wideband phase shifters for phased array antennas
Vernon Davids
Phase shifting…
Phase shifting by changing permeability
• Changing the permeability of the material that a signal
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propagates through
Ferrimagnetic materials or ferrites
material is positioned in
Ferrite phase shifter
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 (H )
magnetic field that the
Drive wire through ferrimagnetic rod
Cascading different lengths of ferrimagnetic rods give rise to
different discrete phase shifts
© CSIR 2006
www.csir.co.za
Wideband phase shifters for phased array antennas
Vernon Davids
Wideband phase shifters
Switched filter
• Switch between two filter networks (High/Low-pass)
• Bandwidth ↔ Topology, bandwidth and isolation of switches
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used
Advantages
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Low cost
Small size
Low power
large Active Phased Array Radar (APAR)
Good broadband performance
• Disadvantages
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Parasitics degrade performance
PIN (P-type, Intrinsic, N-type) diodes, Field Effect Transistors (FETs)
and Metal-Semiconductor Field Effect Transistors (MESFETs) are
commonly used as switches
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© CSIR 2006
www.csir.co.za
Wideband phase shifters for phased array antennas
Vernon Davids
Wideband phase shifters
Reflection type
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Utilises a directional coupler
Two equal reflection terminations
Bandwith≈1octave
Advantages
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If size reduced can be designed for
applications requiring compact size
Can realize a phase shift of 0-360deg by cascading different loads
Good wideband performance
• Disadvantages
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Coupler take up most of the PCB area
Careful design and optimization necessary for matching the coupler
and reflection terminations.
© CSIR 2006
www.csir.co.za
Wideband phase shifters for phased array antennas
Vernon Davids
Wideband phase shifters
Switched line
• Switch between appropriate lengths of matched transmission
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lines
Signal undergoes an effective phase shift
PIN,FETs and MESFETs switches
Advantages
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Applicable phase shift characteristics
Simple structure, small number of
fabrication steps and negligible current
to drive RF switches when using FETs
Good linearity for loaded type switched-line phase shifter
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Susceptible to resonance and large phase deviation
• Disadvantages
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© CSIR 2006
www.csir.co.za
Wideband phase shifters for phased array antennas
Vernon Davids
Methodology
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Research
Simulation
Reflection and Switched-line phase shifters identified
RTPS:
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Good return loss and phase tuning range
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Design simplicity
• Switched-line:
• Topology with best bandwidth performance is pursued
• Phased array considered as end application and testing
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© CSIR 2006
www.csir.co.za
Wideband phase shifters for phased array antennas
Vernon Davids
Conclusion
• Phase shifters utilised in phased array antennas to control the
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phase in each element in the array
Possible to alter phase of the signal by changing:
• Frequency
• Electrical length
• Permitivity
• Permeability
Wideband phase shifters
• Switched-filter
• Reflection-type
• Switched-line
Bandwidth: Topology also isolation of switching device used
Slide 14
29/11/2007
© CSIR 2006
www.csir.co.za
Wideband phase shifters for phased array antennas
Vernon Davids
Thank you
Questions?
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29/11/2007
© CSIR 2006
www.csir.co.za
Wideband phase shifters for phased array antennas
Vernon Davids