Date post: | 18-Jul-2015 |
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Two Types of Conformal Antennas
for Small Spacecrafts
Salahuddin Tariq
Electrical and Computer Engineering Department, Utah State
University,Logan,UT 84322
Auroral Spatial Structures Probe (ASSP ) Project
• A mission to measure small scale E-field
variations during breakup aurora and
geomagnetically active conditions of
upper atmosphere.
• Sounding rocket will have six identical
sub-payloads.
• Follows the work of a previous graduate student.
Sounding rocket sub-payload
Design Requirements for ASSP Project
Specification Description Comments
Diameter -Outside < 6.5 inch I.D.
Diameter-Inside 6.0 inch I.D. Surface mount onto a 6'' diameter cylinder
Height 4.0 inches tall Axial Length
Thickness < .25 inch
VSWR-S-band2.0 :1 Max ( 2210MHz to
2230MHz)Typical = 1.5 :1
VSWR-GPS< 1.5:1 @ 1575.42MHz Center
Frequency< 1.5 VSWR across 10MHz Bandwidth
S-band frequencyCentre at 2220 MHz ( 10MHz
BW)2210MHz to 2230MHz
GPS Frequency 1575.42MHz RHC Polarization
RF Connectors S-bandSMA Male "Flying Lead Coax
Cable"Cable Length TBD
RF Connectors GPSSSMA Male "Flying Lead Coax
Cable"Cable Length TBD
S-band Polarization Linear
GPS-Polarization RHC See Note #1
Material Non-magnetic Nickel Plating NOT allowed
Filter Notch Filter on GPS antennas 40dB rejection of S-band
Design Approach
• Multi-layer design approach for cylindrical
sub-payload antennas
• Developed a feedline to excite the antennas
• Studied the effects of metal boom on
performance of antenna array
• Simulated S-band as well as GPS-band
antennas on cylindrical sub-payload
• Optimized the whole design on HFSS for
best performance
Final Design of S-Band Antenna Array
Model of Final Design in HFSS
• Each boom has length = 333mm
• Structure has 32 air holes for
mounting different screws and
components
• Substrate material is Roger’s
RT/Duriod 6002 for both the
feedline design as well as
antennas
Return Loss of 4-GPS Band Antenna Array
Gain Plots of S-band Antenna Array
3-D Gain Plot of 4-S Band Antennas
2-D Gain Plot for theta = 90°
2-D Gain Pattern Cuts for all Phi (0° to 360° )3-D Gain Plot of 4-S Band Antennas ( Another View )
VSWR and Isolation between GPS and S-band
Antennas
VSWR of 4-S Band Antennas Isolation Between Feedlines of S-Band and GPS Antennas
Final Design of GPS-band Antenna Array
Return Loss of 4-GPS Band Antenna Array
3-D Gain Plot of 4 GPS-band Antennas
3-D Gain Plot of 4 GPS-band Antennas ( Another View)
2D Gain, Axial Ratio and VSWR Plots
2-D Gain Plot for theta = 90°
Axial Ratio at 1.575GHzVSWR Plot at 1.575GHz
2-D Gain cuts for all Phi ( 0 to 360)
Design Requirements
• To design the slot antennas for uplink and downlink frequencies of 485MHz
and 500MHz respectively on 3U CubeSat surface
• To obtain a method of circularly polarized radiation for both uplink and
downlink Frequencies
• To obtain impedance bandwidth of 10MHz for both uplink and downlink
frequencies
• To make the final design practically implementable for fabrication after
finishing the simulations on HFSS
Challenges
• A 3U CubeSat is form of a miniaturized satellite having a volume of 10cm X
10cm X 30cm;
• As per my recent study, there is NO antenna designed for CubeSat that
operates in UHF ( 400MHz- 500MHz) range;
• There is a competition between limited surface area and efficiency of
antenna, especially when solar panels have to be integrated on CubeSats;
• To get a good impedance bandwidth as well as circular polarization;
• The design needs to be shielded from inside so that we can place electronics
equipment but it conflicts with getting good impedance bandwidth.
Solution and Design Features
• A unique design which is totally conformal to the surface and does not have anymoving parts;
• Impedance bandwidth of 10MHz was achieved using cavity backed slot antennadesign;
• These type of slot antennas can be designed to operate as low as 300MHz by justchanging the length of slot;
• Integration of Solar panels is possible and slots take a minimum surface area;
• Circular polarization was achieved using T-junction feedline;
• This design is modular in approach and two or more 1.5U CubeSats can be stackedup to have multi-band functionality;
• The design is shielded from inside with a copper wall on all the four sides;
Solution and Design Features
• The design was extensively studied and simulated on HFSS beforefabrication;
• This design was fabricated in our facilities and results came out to bevery close to what we predicted on simulations;
• A paper detailing this project was accepted in APS/URSI 2015conference recently;
• Our Space Dynamics Lab (SDL) is also showing keen interest in thisdesign as it can replace conventional whip/wire type antennas that arecurrently employed in CubeSat missions.
Modelling in HFSS and Simulation Results
Reflection coefficient of lower slot (Center frequency = 485 MHz and 10dB impedance BW is
more than 10MHz)
3-D gain plot for lower slot
Final model in HFSS
Final Prototype and Measured Results
Final fabricated prototype of wraparound meandered slot Measured radiation pattern