Tuesday May 10 2002 Avionics Conference Call
Participants: Glenn, Tim and Andrew, on the phone with Spencer Webb.
Spencer Webb, located in New Hampshire (see http://www.antennasys.com) designs antennas for a living. He's got an impressive array of antennas on his web site, take a look if you have some free time.
We originally approached Spencer for help about 6 months ago. He suggested getting the book Antenna Engineering Handbook which we then bought and indeed, it had a cylindrical patch antenna design just like we wanted. Glenn read the article, did a bunch of research on microwave matching networks, and came up with a first rev of a design.
Andrew wrote a MATLAB routine to calculate some parameters given everything else, and by Thursday evening the design was done. We faxed it over to Spencer, and called him the next day.
Spencer verified that our design looked sane. We threw a ton of questions at him, and the interesting points were:
- Our antenna is horizontally polarized, not circularly polarized like we thought.
- Polystyrene - coffee cups - have an er (dielectric constant) of 1 which is excellent for microwaves. We could make our own patch antennas using copper tape and coffee cups - something we should try just to say we did it ;)
- Our best bet for ground antennas are monofilar helical antennas(??). They're apparently easy to build, work almost all the time, have about a 35 degree (??) 3dB point, and have a gain of (??). They're also apparently very easy to tune.
We talked after the conference calls and decided on a few key points:
- We need to locate the telemetry ground station some distance from the launch tower - like 1 - 4 miles. We'll need to do a real calculation with a link budget to determine where exactly it should be.
- We should do manual, single axis tracking with the helical antennas. At a distance away, it should be fairly easy to do, and we can set a start and stop point given the apogee of the rocket.
- The rocket can act as a relay between the telemetry station and the LCM if we need the communication between the computers.