Electronic device with foam antenna carrier

Electronic devices may include radio-frequency transceiver circuitry and antenna structures. The antenna structures may include a dielectric carrier such as a foam carrier. The foam carrier may be formed from a material that can withstand elevated temperatures. Metal traces for antennas can be formed on the foam carrier by selectively activating areas on a powder coating with a laser and plating the laser-activated areas. Metal for the antennas may also be formed by attaching layers such as flexible printed circuit layers and metal foil layers to the foam carrier. Solder may be used to attach a coaxial cable or other transmission line, electrical components, and other electrical structures to the metal antenna structures on the foam carrier. The foam carrier may be formed from open cell or closed cell foam. The surface of the foam may be smoothed to facilitate formation of metal antenna structures.