I have designed and manufactured an antenna that works around 900 MHz. The design includes a ground plane and metallic enclosure that are not strictly necessary, but do affect the performance of the antenna. At the moment I don’t have the ground plane ready, but I would like to test my antenna already. Would a typical, very thin, household aluminium foil be conductive enough to simulate a ground plane at around 900 MHz or should I wait for the actual PCB with copper?
At 900 MHz aluminium foil is good, the skin effect https://en.wikipedia.org/wiki/Skin_effect prevents a thicker plate to give any advantage. The skin depth is about 0,003 millimeters, a 0,01 millimeters thick foil would be in practice as good as much thicker solid aluminium. Tightly layered two 0,005 mm foils would perform as well as one 0,01 mm foil assuming there's no lossy material between them.
One millimeter uneveness of the surface means nothing at 900MHz. You can put it on something stiffer(=wood, iron, plastic, cardboard) to prevent it losing its form due to gravity, wind or a slightest thump. Making a good contact to the feeding line needs some experimenting. There are plenty of aluminium soldering tutorials but I have never tried one.