We need

• A low profile antenna that doesn't get in the airflow
• A radiation pattern that ideally has telem going to the ground and GPS to the horizon and up
• Resonant on about 868MHz for telem and 1.6GHz for GPS

Problems include

• Rocket bodies all conductive so can't easily put an antenna inside
• Nosecones an option on boosters only, and even then they separate so not ideal

Some easily discarded designs/ideas

• Dipole on the outside. Wouldn't really work over a ground plane/metal
• Dipole or bazooka dipole inside. Doesn't work inside conductive tube

Possible options

• Slot (maybe with cavity)
• Folded F
• Patch array
• Cylindrical patch antennas

Probably the cylindrical patch is the best option. Some details…

• Dielectric permittivity sets the size of the patch, so higher would be better
• But higher dielectrics give lower bandwidths and efficiencies
• Also the dielectric gap has a small effect on the size, and a big effect on the bandwidth and efficiency
• We'd like a very small gap but that would give a very small bandwidth
• Radiation pattern is broadside from the rocket which is not ideal
• Various options for feeding - inset feed with a probe might match to 50R but is hard to do with multiple feedpoints. End feeding gives 200R impedance but we can use a microstrip feed network to match and distribute. This seems the most common approach