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Microstrip Antenna Designs for Sensor and Communications Applications
David Pozar
Electrical and Computer Engineering
University of Massachusetts at Amherst
Amherst MA 01003
email: pozar@ecs.umass.edu
slides: http://www.ecs.umass.edu/ece/pozar/AntResRev2005.ppt
Outline
Near field focused microstrip arrayKu band fan beam microstrip arrayImproved bandwidth microstrip reflectarray
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
• 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
Original dielectric loaded horn antenna
Radiometric Temperature Sensor Antennas – Before and After
Near field focused microstrip arrays
Calculated Near Field Contours of Microstrip Array
-36
-24-30
-36-36
-36
-36
-36
-30
-30-30
-24
-24
-30
-30
-36
-36
-24
-24
-24
-18 -18
-18
-18
-18
-36
-36
-12
-12
-12
-12
-30
-30
-30
-30
-30 -30
-30
-30
-6
-6-6
-24
-24
-24
-24
-24
-30
-30
-24
-24
-24
-30
-30
-30
-30
-30
-36
-36
-36
-30
-30
-12
-36
-36
-36
-36
-36
-18-30
-36
-36
-24
-24
-30
-36
-36-30
-30
-24
X axis (inches)
-5 -4 -3 -2 -1 0 1 2 3 4 5
Y a
xis
(inch
es)
-5
-4
-3
-2
-1
0
1
2
3
4
5
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.
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
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
Microstrip Reflectarray
This reflectarray uses variable length microstrip patches to provide a shaped beam pattern.
Aperture Coupled Stub Tuned Microstrip Reflectarray
ground plane with apertures
microstrip patches
variable length tuning stubs
unit cellcross section
Patches and apertures are identical for all elements; stubs vary in length to control reflection phase.
Reflection Phase vs. Patch / Stub Length
Stub Length (cm)
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Ref
lect
ion
Pha
se (d
egre
es)
-360
-270
-180
-90
0
90
180
270
360
f = 5.0 GHzf = 5.2 GHzf = 5.4 GHz
Patch Length (cm)
1.2 1.4 1.6 1.8 2.0 2.2 2.4
Ref
lect
ion
Pha
se (d
egre
es)
0
50
100
150
200
250
300
350
400
f = 5.0 GHzf = 5.2 GHzf = 5.4 GHz
variable-length microstrip patches
stub-tuned aperture coupled patches
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