An electronic device may have wireless circuitry with antennas. The electronic device may have a dielectric housing. A printed circuit board with electrical components may be mounted in the dielectric housing. Heat spreader structures may be used to dissipate heat from the electrical components. The heat spreader structures be configured to form antenna cavities. The antennas in the electronic device may be formed from the antenna cavities and may have antenna resonating elements formed on the printed circuit. An electrical component such as a light-emitting diode may be mounted in one of the antenna cavities. Each antenna element may be an inverted-F antenna resonating element with short and long arms. The short arm of each antenna resonating element may be formed from edge plated metal traces on an edge of the printed circuit.