Transcript Microstrip Antenna Designs for Sensor and Communications Applications David Pozar Electrical and Computer Engineering University of Massachusetts at Amherst Amherst MA 01003 email: [email protected] slides: http://www.ecs.umass.edu/ece/pozar/AntResRev2005.ppt.

Microstrip Antenna Designs for Sensor and
Communications Applications
David Pozar
Electrical and Computer Engineering
University of Massachusetts at Amherst
Amherst MA 01003
email: [email protected]
slides: http://www.ecs.umass.edu/ece/pozar/AntResRev2005.ppt
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
Near Field Focused Microstrip Array
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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
Radiometric Temperature Sensor Antennas – Before and After
Original dielectric loaded horn antenna
Near field focused microstrip arrays
Calculated Near Field Contours of Microstrip Array
5
-24
-30
-36
-30
-36
4
-36 -30
3
-30
-36
2
Y axis (inches)
-30
0
-30
-30
-30
-24
-12
-36
-30
1
-36
-24
-24
-30
-18
-36
-36
-30
-36
-36
-18
-24
-6
-30 -18-12
-24
-30
-30
-24 -36
-12
-24
-18
-24
-30
-24
-1
-6
-30
-24
-30
-24
-6
-12
-36
-18
-30
-24
-30
-30
-36
-12
-2
-36
-36
-36
-24-18
-30
-30
-24
-30
-3
-36
-30
-4
-36
-30
-36
-36
-30
-36
-24
-24
-36
-30
-5
-5
-4
-3
-2
-1
0
1
X axis (inches)
2
3
4
5
Near Field Measurement of Microstrip Array at Hanscom AFB
Measured Near Field 3D Pattern of Microstrip Array
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
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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
Ku Band Array
176 patch elements, 2x4 and 2x6 subarrays
Improved Bandwidth Microstrip Reflectarray
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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
microstrip patches
ground plane
with apertures
variable length
tuning stubs
cross section
unit cell
Patches and apertures are identical for all elements;
stubs vary in length to control reflection phase.
400
360
350
270
f = 5.0 GHz
f = 5.2 GHz
f = 5.4 GHz
300
Reflection Phase (degrees)
Reflection Phase (degrees)
Reflection Phase vs. Patch / Stub Length
250
200
150
100
50
f = 5.0 GHz
f = 5.2 GHz
f = 5.4 GHz
180
90
0
-90
-180
-270
0
-360
1.2
1.4
1.6
1.8
2.0
Patch Length (cm)
variable-length
microstrip patches
2.2
2.4
0.0
0.5
1.0
1.5
2.0
Stub Length (cm)
stub-tuned aperture
coupled patches
2.5
3.0
Comparison of Gain Bandwidth
30
1 dB gain
bandwidth is
improved
from 3.5% to
9%
Gain (dB)
28
26
24
22
Variable Size Patches
Aperture Coupled Patches w/ Stubs
20
1.8
1.9
2.0
Frequency (GHz)
2.1
2.2