30m Reflector Antenna Geometry

1
30-m Reflector Antenna Geometry
VHF-band region
11 m

30 m
3.3 m
2.8 m
UHF VHF array feed
13.5 m
X
X
UHF-band region
Y
Z
Parabolic Antenna F/D0.45
Array Feed
YRS-2-2003
2
Dual-Band Low-Frequency Soil Moisture Radar
3.3m
1.1m
3
Dual-Band Low-Frequency Soil Moisture Radar
Array Feed
3-element patch array patterns at 137.5 MHz
H-port principal-plane patterns for probes 1,3
and 5
V-port principal-plane patterns for probes 2,4
and 6
4
30 meter Parabolic AntennaFreq137.5 MHz
H-Plane pattern
E-Plane pattern
Current on the reflector
YRS-2-2003
5
30 meter Parabolic AntennaFreq435 MHz
H-Plane pattern
E-Plane pattern
Current on the reflector
YRS-2-2003
6
3.65m Parabolic AntennaScaled Reflector Geometry
(Scale 30/3.65)
40.174 cm
Array Feed
X
X
Y
Z
Parabolic Antenna F/D0.33
Array Feed
YRS-2-2003
7
Existing 3.65m parabolic reflector antenna at JPL
to be used for scaled frequency measurements
YRS-2-2003
8
3.65 meter Parabolic AntennaFreq3.57 GHz
E-Plane
45o-Plane
H-Plane
Current on the reflector
YRS-2-2003
9
3.65 meter Parabolic AntennaFreq1.13 GHz
45o-Plane
E-Plane
H-Plane
Current on the reflector
YRS-2-2003
10
3.65 meter Parabolic Antenna
Freq3.57 GHz
Freq1.13 GHz
YRS-2-2003
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DualFrequency Dual-Polarization Stacked Patch
Feed Design
U2
U1
L
GP
Top-view of Stacked Patch
Stacked patch built at Antenna Lab (UCLA) 1 and
2 are the feed points for lower patch 3,4,5 and
6 are the feed points for the upper patch
Side-view of Stacked Patch
Grid used in FDTD Simulation of Stacked Patch
YRS-2-2003
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VHF / P-Band Stacked Patch Array
39.1 square
39.1 square
12.46 square
12.46 square
9.01
21.47
5 square hole
2.585
2.585
(0.791?o _at_ 435 MHz)
Dimensions for the scaled feed element
Lower patch frequency 1.13GHz Upper patch
frequency 3.57GHz Dimensions L 13.3 cm L1
12.0cm L2 3.9cm L3 2.7cm L4 0.8 cm L5
7.4cm Substrate thickness for lower patch
6mm Substrate thickness for upper patch 3mm
YRS-2-2003
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Simulated Return-Loss for Stacked Patch
Grid used in FDTD Simulation
Bandwidth 20MHz
Bandwidth 80MHz
S11 result ( feed at lower patch)
S11 result ( feed at upper patch)
YRS-2-2003
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S11 Measurement Results for Stacked Patch Array
Lower Patch
Upper Patch
Bandwidth 8MHz
Bandwidth 35MHz
S11 , S22 are the reflection coefficient values
measured at ports 1 and 2
S33 , S44 , S55 , S66 are the reflection
coefficient values measured at ports 3,4,5 and 6
YRS-2-2003
15
Simulated Radiation Pattern for Stacked Patch
Grid used in FDTD Simulation
Radiation pattern (feed at upper patch)
Radiation pattern (feed at lower patch)
YRS-2-2003
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Measured Radiation Patterns for Stacked Patch
(Upper Patches)
Port 4
Port 3
Port 6
Port 5
YRS-2-2003
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Comparison of Simulated and Measured Results at
Port 6
Performance of port 6 is not satisfactory.
YRS-2-2003
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Accomplishments and Observations

• Dual-stacked patch configuration design has been
  completed
• Completed patch design for the scaled frequencies
  of 1.13GHz and 3.57GHz
• Evaluated and performed parametric studies
  (return-loss, bandwidth and radiation pattern)
  for the stacked patch array configuration using
  the Finite-Difference Time Domain Method
  (UCLA-FDTD code)
• Completed building and measurement of the scaled
  frequency feed element
• Observations
• The simulated radiation pattern for the lower
  patch shows a high back-radiation due to a small
  ground plane (twice the substrate thickness is
  required to account for fringing fields)
• Measurements could not be performed due to the
  limitations of the anechoic chamber at such low
  frequency.
• The S11 measurement results for the lower patch
  have a narrower bandwidth than expected. We
  believe it is because of the small diameter of
  the flexible coaxial cable used for feeding the
  patch
• The far-field pattern at port 6 (refer to
  picture) shows a very high cross-polarization
  both in measurement and simulation. We need to
  relocate port 6 similar to port 4 to make the
  configuration symmetric and feed it out of phase
  in an array configuration.

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Future Goals for Array/Reflector Design

• Replace the small diameter flexible coaxial
  cable with a thicker diameter rigid
• cable for the lower patch
• Relocate port 6 to make the patch configuration
  symmetric
• Perform measurements for the rebuilt stacked
  patch array at the new
• anechoic chamber at UCLA or at JPL
• Perform elaborate study on the power-divider
  network for feeding the array
• Perform evaluation models for studying the array
  with the feed network
• Build the three element array with the feed
  network and evaluate its
• performance
• Integrate the measured array patterns with
  reflector antenna analysis

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UCLA Team Prof. Y. Rahmat-Samii K. Kona
(PhD student) M. Manteghi (PhD student) F. Yan
(Post Doc) J. Robinson (Undergrad student)
Publications 1 Keerti S. Kona and Yahya
Rahmat-Samii, Design and Analysis of a Novel
Probe-feeding method for Stacked Microstrip Patch
Antennas, IEEE AP-S Int. Symp.,Columbus, Ohio,
June 2003. 2 Keerti S. Kona and Yahya
Rahmat-Samii, Novel Probe-feeding Architectures
for Stacked Microstrip Patch Antennas, Annual
Research Review Symposium, 2002, UCLA