I added a flexible passive GPS antenna to one of my PinePhones. These antennas are meant to be adhered directly to the inside of a plastic enclosure, far from any metal or ground planes. The datasheets I have read for similar antenna recommend at least 12mm distance to the ground plane. This particular antenna I got off of eBay from China, and has no datasheet. It does work quite well though. I taped the antenna to a piece of plastic from a SIM card to make it more rigid. It is paper thin, except for the area where the cable is soldered. Like on the Franken-Phone I removed the U.FL connector from the end of the cable and soldered it in place. This time I removed the spring contacts so that it would not make contact with the existing antenna in the mid-frame. I left the spring contact for the WiFi antenna intact. I shaved some of the plastic from the mid-frame so that the cable would fit between it and the metal shield of the modem. I also cut a slot in the back case with a Dremel cut