A wireless electronic device may include antennas formed at different locations on the device. The wireless electronic device may include transceivers that are used to wirelessly communicate in different frequency bands by transmitting and receiving radio-frequency signals in the frequency bands. The transceivers may include Wi-Fi® transceivers and cellular transceivers such as Long Term Evolution transceivers. The wireless electronic device may include antenna switching circuitry interposed between the transceivers and the antennas. The wireless electronic device may include control circuitry that controls the antenna switching circuitry to ensure that radio-frequency transmissions in adjacent frequency bands are routed to different antennas. By routing radio-frequency transmissions in adjacent frequency bands to different antennas, self-interference between communications in the adjacent frequency bands may be reduced. Self-interference may also be reduced by performing time division multiplexing to isolate radio-frequency signals that are transmitted in adjacent frequency bands.