A Multilayered Broadband Reflect-Array

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A Multilayered Broadband Reflect-Array

• Manuel Romero

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Outline

• Introduction and Project Goals
• Ideal Reflect-Array Cell
• Proposed Cell
• Experimental Results
• Conclusions

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Introduction Reflect-Arrays

• Reflect-arrays alter the scattered EM field to
  form a radiation maximum in a desired direction
• The reflection phase of the individual array
  elements is modified to form the desired
  scattered beam pattern

• A phase agility of 360 degrees per array element
  allows for a beam maximum at any angle
• Many applications in radar and communication
  systems.

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Introduction Microstrip Reflect-Arrays

• Microstrip reflect-arrays are low cost, low loss
  and low profile
• Potential substitutes for parabolic reflector
  antennas used in terrestrial and satellite
  communication systems.
• Previous work has focused on the patch antenna as
  the main array element
• Vary patch size, stub length and tilt angle to
  modify the reflection phase.
• The resonant nature results in poor phase agility
  and bandwidth

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Project Goals

• To design a reflect-array at a center frequency
  of 10GHz
• Non-resonant structure unit cell
• Linear reflection phase as function of frequency

• Fully printable structure
• low cost
• low profile
• low loss

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Ideal Reflect-Array Cell
cell at (N-1)?x

• Sample phase characteristic of each cell at fo
• These samples create the phase gradient across
  the surface
• Large bandwidth if ?F constant over frequency
• Linear phase profile desired
• Matching helps achieve linear reflection phase

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Final Surface Unit Cell and Equivalent Circuit

• Center frequency of 10GHz
• Vary radii (r1 and r2) to obtain required phase
• Achieve high phase agility by increasing mismatch
  with free space

• Three layers provide sufficient phase agility gt
  360
• Use minimum mismatch for required phase agility

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Measurements

• Measurements agree with theory
• High side lobes of -5dB due to phase errors in
  fabrication
• Achieved small error of 4 in maximum beam
  direction within 20 bandwidth around 10GHz

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Conclusions

• Radiation beam direction controlled by reflection
  phase
• Linear phase gradient equivalent to slanted metal
  sheet
• Not limited to linear phase gradient
• Designed unit cell at 10GHz cell with phase
  agility gt 360
• Phase agility - by increasing impedance mismatch
  with free space
• Smaller unit cell possible at the expense of
  phase agility
• Thicker dielectric can offset the loss in phase
  agility for smaller cells
• Designed, built and tested a reflect-array at
  10GHz with proposed cell
• Works for both TE and TM polarizations at various
  incidence angles
• Achieved small beam direction error over 20
  bandwidth