RESEARCH POSTER PRESENTATION DESIGN © 2012
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Hypersonic vehicles oftentimes experience diminished electromagnetic communication and
sensing capabilities due to dense plasma that forms around the vehicle during re-entry.
They can block or attenuate the radio signals, moreover, depending on the electron
density, it will severely affect the performance of the communication antennas including
the Global Position System (GPS) antenna. When operating in a plasma environment, these
antennas’ performance is affected by (i) signal loss / attenuation through the plasma
layer, (ii) polarization mismatch and (iii) impedance mismatch; (ii) and (iii) further reduce
the antenna’s operational bandwidth. While little can be done to reduce signal loss,
proper design of the antenna may mitigate (ii) and (iii). This paper proposes a novel
double-feed dual band GPS antenna with AR bandwidth exceeding 150 MHz in both the L1
and L2 bands, thereby rendering making the antenna polarization highly insensitive to
plasma loading. Besides, to achieve acceptable impedance bandwidth with various plasma
environment, a feedback system including a sensing antenna, controller and tunable
matching network is designed.
Abstract
During the hypersonic re-entry procedure of a vehicle, a continuously
changing plasma layer is formed around the vehicle and block the
electromagnetic communication.
• Continuous plasma layer could be discretized as several lossy dielectric
layers, the relative permittivity for the dielectric is given by the
classical equation
Introduction
Result for the antenna in plasma environment without matching network
Simulation result
In order to mitigate the polarization and impedance mismatch, the
following antenna system is proposed.
• Broadband branch-line coupler
• Dual band antenna with two capacitive feeds
• Tunable matching circuit based on varactor diode
• Single band sensing antenna
Models
Conclusion
• An ultra-wide axial ratio bandwidth dual band GPS antenna is proposed
to compensate the polarization mismatch caused by the dynamic plasma
environment, and a self-matching mechanism is implemented by a
feedback system including tunable matching network and a sensing
antenna.
• Future work will be further optimized the antenna, study the response
time for the self-adjusting process, and apply some alternatives, like
the MEMS varactors to the tunable matching network.
References
[1] Z.H. Qian, R.S. Chen, K.W. Leung, et al. Progress Electromagn Res 52(2005).
[2] L. Zhao, B. W. Bai, W. M. Bao, and X. P. Li, Int. J. of Antennas Propag. (2013) 823626
[3] Li, J-T., and L-X. Guo. J. of Electromagn. Waves and Appl. 26.13 (2012): 1767-1778
[4] K. L. Wong, Compact and Broadband Microstrip Antennas, New York, 2002: Wiley
Dept. of Electrical Engineering and Computer Science, University of Michigan
Xiuzhang Cai a, Eric Michielssen a, Xiaoying Gu a and Amir Mortazawi a
Adaptively matched GPS antenna for plasma environments
ε = (1 −ωp2
ω2 + ν2+ j
ωp2 νω
ω2 + ν2)ε0
(a) 휀𝑟′ for different plasma layers (b) tan 𝛿 for different plasma
Fig. 1: One case of plasma modeling in discretized lossy dielectric at 1.227GHz
1.10 1.13 1.15 1.18 1.20 1.23 1.25 1.28 1.30Freq [GHz]
-50.00
-40.00
-30.00
-20.00
-10.00
0.00
dB
(St(
Cylin
de
r2_
T1
,Cylin
de
r2_
T1
))
HFSSDesign1Return loss ANSOFT
m1
m2
m3
m4
Curve Info
dB(St(Cylinder2_T1,Cylinder2_T1))Setup1 : Sw eep1
Name X Y
m1 1.2200 -9.7155
m2 1.2600 -46.0949
m3 1.2260 -11.4569
m4 1.3000 -24.0920
1.10 1.13 1.15 1.18 1.20 1.23 1.25 1.28 1.30Freq [GHz]
0.00
10.00
20.00
30.00
dB
(Axia
lRa
tio
Va
lue
)
HFSSDesign1Axial Ratio ANSOFT
m2m1
m3
m4
Curve Info
dB(AxialRatioValue)Setup1 : Sw eep1Phi='0deg' Theta='0deg'
Name X Y
m1 1.2760 1.2019
m2 1.2900 3.1073
m3 1.2620 2.9841
m4 1.2260 10.1892
1.10 1.13 1.15 1.18 1.20 1.23 1.25 1.28 1.30Freq [GHz]
-37.50
-25.00
-12.50
0.00
dB
(St(
Cyl
ind
er2
_T
1,C
ylin
de
r2_
T1
))
HFSSDesign1Return loss ANSOFT
m1
m3 m4
Curve Info
dB(St(Cylinder2_T1,Cylinder2_T1))Setup1 : Sw eep1
Name X Y
m1 1.2260 -22.6350
m3 1.1800 -10.2265
m4 1.2900 -10.1453
1.10 1.13 1.15 1.18 1.20 1.23 1.25 1.28 1.30Freq [GHz]
0.00
10.00
20.00
30.00
dB
(Axia
lRa
tio
Va
lue
)
HFSSDesign1Axial ratio ANSOFT
m1m3m2
Curve Info
dB(AxialRatioValue)Setup1 : Sw eep1Phi='0deg' Theta='0deg'
Name X Y
m1 1.2280 0.8512
m2 1.2160 2.9369
m3 1.2420 2.9255
Fig. 2: Comparison of the antenna performance in free space and plasma environment for one wide impedance band GPS antenna
• The performance for the communication antenna will be severely
influenced in the presence of plasma
• Polarization mismatch
• Impedance mismatch
Fig. 3: Block diagram for the antenna system with matching network and feedback circuit
Fig. 4: Top view for the broadband branch-line coupler
Fig. 5: Side view and top view for the dual band GPS antenna
Fig. 6: Tunable LC matching network
(a) Side view with the plasma model (b) Top view
(a) Symbolic representation (b) Schematic
Result of the antenna after applying the matching network
Impedance shifting for the GPS antenna at 1.227GHz and sensing antenna
at 1.3GHz in Smith chart
(a) Total return loss at L2 band (b) Total return at L1 band
(c) Axial ratio at L2 band (d) Axial ratio at L1 band
(e) RHCP realized gain at L2 band (f) RHCP realized gain at L1 band
Fig. 7: Simulation result for the antenna system in different plasma environment without matching network
Plasma # RL not matched(dB) RL matched(dB) Bandwidth(MHz)
1 -11.9 -19.7 35
2 -6.6 -21.5 35
3 -5.6 -21.1 42
4 -5.8 -20.3 55
5 -5.9 -20.7 49
6 -6.3 -20.6 46
7 -8.6 -20.8 43
8 -13.0 -19.7 40
Table 1: The return loss and bandwidth comparison at L2 band for the
matched and not matched GPS antenna with variable plasma environments
From the figure, the shifted impedance for the GPS antenna at 1.227GHz
and that of the sensing antenna at 1.3GHz has a linear relationship, by
linear regression method, their relation could be revealed as:
𝑍𝐺𝑃𝑆 = aZt + b
With a=1.1318+j*0.6696, b=-0.0506-j*0.628, and with mean squared
error(MSE) of 1.134 × 10−5 + j ∗ 5.13 × 10−4 for normalized impedance.
Thereby, the impedance for the GPS antenna could be obtained from the
return loss of the sensing antenna. Then, the required capacitance value
for the tunable matching network and the corresponding bias voltage can
be determined.
Fig. 9: Matching range for the designed tunable matching network
Fig. 8: Impedance shifting for both GPS antenna and the sensing antenna
Fig. 10: Capacitance of the varactordiode with different bias voltage
Fig. 11: Total return loss for the model with and without matching
(a) model With plasma 4 (a) model With plasma 7
(a) In free space (b) In plasma environment
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