Two Types of Conformal Antennas

for Small Spacecrafts

Salahuddin Tariq

Electrical and Computer Engineering Department, Utah State

University,Logan,UT 84322

Study # 1: Auroral Spatial Structures Probe (ASSP )

Project

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)

Study # 2: Dual Band Circularly Polarized UHF

Slot Antenna Design for a 3U CubeSat

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

Fabrication Process

Final Prototype and Measured Results

Final fabricated prototype of wraparound meandered slot Measured radiation pattern

Reflection Coefficient and VSWR Results

Reflection coefficient ( -23dB at 486MHz) VSWR ( 1.1 at 486 MHz)