Is there a basic passive GPS reference antenna design that would be considered fair-use or "free to use" that can be placed on a PCB as a strip antenna or patch antenna? I'm looking not to violate copyrights of an antenna design on a project I eventually might want to sell. Thanks
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If you want to be on the safe side and have enough board real state, I highly recommend you simply use a 1"x1" ceramic patch antenna soldered to your PCB.
The patch antenna is circularly polarized while most of the PCB trace antennas are linearly polarized. This gives the patch antenna at least 3dB of performance advantage since GPS satellites transmit using circular polarization. If you have assisted GPS, then you may have room for a not-so-efficient antenna.
If you really want to go down the path of using a trace antenna (for cost or space restrictions, for instance), my recommendation is to use the inverted-F (IFA) topology. You should be able to find reference designs on the web. Keep in mind that the ground plane is an integral part of the antenna, so you may have to tweak the trace dimensions depending on the specific ground plane geometry of your board. Most likely you'll need to fine-tune the radiating element length after you build the first prototype. A network analyzer will be extremely helpful for that.
I would not worry about patent infringement when using an IFA antenna. This is a public domain solution. As far as copyright, it's probably a very, very week case for an antenna made of 2 traces. You will have to tweak its geometry to tune it for your particular board anyways.
Having said all that, GPS receivers are tricky to make work and the antenna design will be just the first of your problems. Mitigating the presence of interference from other parts of your circuit that reduce the sensitivity of your receiver (desense) is a major source of headaches.
Good luck!
