Microstrip Antenna Designs for Sensor and Communications Applications

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Microstrip Antenna Designs for Sensor and
Communications Applications David
Pozar Electrical and Computer Engineering Universi
ty of Massachusetts at Amherst Amherst MA
01003 email pozar_at_ecs.umass.edu slides
http//www.ecs.umass.edu/ece/pozar/AntResRev2005.p
pt
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Outline
One of the main goals of the Center for Advanced
Sensor and Communications Antennas at the
University of Massachusetts is to identify and
develop antenna technologies with improved
performance and/or reduced cost for future
applications.

• Near field focused microstrip array
• Ku band fan beam microstrip array
• Improved bandwidth microstrip reflectarray

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Near Field Focused Microstrip Array

• Application to low-cost radiometric temperature
  sensor
• Food industry, chemical processing, materials
  manufacturing
• Radiometric technique works through smoke, dust,
  or steam
• Developed by ProSensing Inc (Amherst), and K.
  Stephan (Texas State U)
• 12.5 GHz, focus to a spot size of 2.6 at 12
  from aperture
• Two array versions were designed, fabricated, and
  tested
• Near field testing done at Hanscom AFB
• Resulting antenna is substantially smaller and
  cheaper than original horn

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Radiometric Temperature Sensor Antennas Before
and After
Original dielectric loaded horn antenna
Near field focused microstrip arrays
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Calculated Near Field Contours of Microstrip Array
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Near Field Measurement of Microstrip Array at
Hanscom AFB
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Measured Near Field 3D Pattern of Microstrip Array
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Measured Near Field E-plane Patterns of
Microstrip Arrays
f 12.45 GHz. Red curve for array using
non-symmetric feed network, green curve for array
with reversed patches in E-plane. Note main beam
peaks are off center due to mechanical
misalignment of test fixture.
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Ku Band Fan Beam Microstrip Array

• Application to short range ocean surface
  topography mapping
• Two arrays used for differential phase shift
  measurement of backscatter
• 45 long aperture at 16.15 GHz, 2 degree
  beamwidth
• 20 dB sidelobe level
• Short pulse duration requires time delay feeding
  across aperture
• Loss and space considerations require subarraying
  (2x4 and 2x6)
• Design completed, subarrays tested, final array
  being fabricated

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Ku Band Array
176 patch elements, 2x4 and 2x6 subarrays
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Improved Bandwidth Microstrip Reflectarray

• Microstrip reflectarray uses a flat aperture of
  microstrip patches with individual phase shifts
  to form a coherent beam
• Reflectarrays typically use variable-length
  patches, patches with tuning stubs, or CP patches
  with rotations to achieve required reflection
  phases
• Bandwidth (gain) is generally limited to 2-4
  with these methods
• A new technique using aperture coupled patches
  with stub tuners provides much better bandwidth
  properties,

see Microstrip Reflectarrays Myths and
Realities, JINA 2004, at http//www.ecs.umass.edu
/ece/pozar/jina.ppt for more discussion of
microstrip reflectarrays
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Microstrip Reflectarray
This reflectarray uses variable length microstrip
patches to provide a shaped beam pattern.
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Aperture Coupled Stub Tuned Microstrip
Reflectarray
unit cell
cross section
Patches and apertures are identical for all
elements stubs vary in length to control
reflection phase.
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Reflection Phase vs. Patch / Stub Length
variable-length microstrip patches
stub-tuned aperture coupled patches
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Comparison of Gain Bandwidth
1 dB gain bandwidth is improved from 3.5 to 9