Antenna - spacecraft-design-lab-2019/documentation GitHub Wiki

Assumption:

The antenna will be a tape-measure dipole, secured by burn wire until deployment. Mechanical retention via killswitch is not acceptable. Dipole antennas are mildly directional but perform best in a direction perpendicular to the antenna. Placing the antennas on the camera side plate of the satellite seems the best case for ground-seeing access and minimizing shadows.

Current plans: 433mhz frequency: ~2x170mm antennas 2.4ghz frequency: ~~2x30mm antennas ~~ Patch antenna on camera side of satellite.

• TODO: Patch antenna size/position on board -> board design question
• TODO: Antenna tape selection
• TODO: Antenna folding method
• TODO: Test Antenna burn wire
• TODO: make mockup (using 3d printed prototype or scratch build)
• TODO: Start testing (in bell jar? Need to figure out gravity concerns)

Patch antenna requirement - current plan for s-band.

Simple, standard option: https://static1.squarespace.com/static/5b3bd5a9266c077a5bdfcafd/t/5b649b406d2a73ddb1ddff1f/1533320001896/TUNA-CAN-ANTENNA-DESIGN-FOR-CUBESAT-MISSIONS.pdf

Super complicated, but mechanically elegant set up: https://www.nrl.navy.mil/news/sites/edit-www.nrl.navy.mil.news/files/archive/pressreleases/2014/AMS-Paper-A-Nichrome-Burn-Wire-Release-Mechanism-for-CubeSats-Final-Adam-Thurn.pdf

DESIGN THOUGHTS: (10/21/2019 Meeting)

• We're currently holding them down with screws.
• Bentness is with holes and washers.
• Size - 1/4" wide tapes.
• Length - divisions of 340mils.
• Longer one is the exact same as PyCubed.
• There's a single component under the board that's a connector - it's not SMA.
• Top board needs 2.5 mil of clearance under it.
• UFL connector.
• Long Antenna Length: 17cm
• Shorter Antenna Length: 3cm. Put the shorter ones at the edges
• Mounting holes: 2.2mm diameter, subject to change.

Possible Option: Put S-band on bottom.

Nitinol Ideas:

• Use nitinol superelastic strip/wire as antenna or antenna support
  • Long term storage under tight packaging constraints might permanently deform steel tape - test both materials
• Might be worthwhile to use copper as actual conductor?
  • Electrical Resistivity
    • Nitinol 82μOhm-cm
    • Copper 110 (ASTM B3) 1.72μOhm-cm
  • Use nitinol to pull high-gauge copper wire taut
• Nitinol.com (supplier)
  • Round Superelastic Wire min. order 50ft at $2.3/ft -> $115
  • Flat Strip 0.12"x.0195" (3x0.5mm) min. order 30ft at $9.86/ft -> $296

Size of coiled antenna

• http://mathworld.wolfram.com/ArchimedesSpiral.html
  • r = aθ
• http://tutorial.math.lamar.edu/Classes/CalcII/PolarArcLength.aspx
  • ds = sqrt(r^2 + (dr/dth)^2) dth = sqrt(r^2 + a^2) dr/a

Matlab code for antenna length in given coil i/o radii:

syms r a r0 rf real
ds = sqrt(r^2/a^2 + 1)
L = int(ds, r, r0, rf)
rf = vpasolve(subs(L, [a, r0], [0.5/(2*pi), 1]) == 170, rf)

• For 170mm antenna length, 0.5mm antenna thickness (nitinol strip), 2mm coil ID, coil OD is 10.6mm