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Each of the stages has four fins, which won't do much on the accent, since we are hopefully starting very high from a balloon, but after they are jettisoned, and the stage starts falling back, a drogue chute is deployed out of the top of the rocket as is usual, but the system that ignites the ejection
charge also unlocks the fins from their vertical position. Inside each of the fins is an embedded 2.5Ghz (802.11B wifi freq) yagi antenna. Basically several electrically isolated strands of wire that guide RF frequencies towards a single antenna to create a directional antenna. Old TV antennas on roof tops are yagis, but since these are antennas for a much higher frequency, the elements are much smaller. The elements are approximately half a wavelength of the frequency or in this case about 1.5 inches (3.74cm). Each of these four directional antennas are hooked up to a crystal tuner where the incoming beacon signal from the ground transmitter is compared and then used to slightly turn the fins perpendicular to the best signal to steer the rocket towards the signal. When a predefined power level is received, meaning that the returning stage is very close to the transmitter, the second chute is deployed to provide a soft landing.
All that you need on the ground is a powerful transmitter that you can use to guide the returning stages back to your retrieval point. All you need on the stage is a watch battery, four crystal tuners, twin comparator circuits and piezo deflectors for the fins.
I’d rather not use this frequency because of all the background noise, so it could be redesigned for 23cm ham bands by using tiny coils of wire instead of straight strands, but I think if you are pointing a Cantenna or parabolic dish type antenna powered by a legal limit transmitter, you should down out all the background noise. Also you could go up to 10GHz ham bands and make really small antennas, but that might have problems with clouds.
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