An electronic device such as a wireless earbud may have antenna structures that are configured to form one or more antenna portions or antennas for transmitting and receiving wireless signals. The device may include control circuitry that is configured to selectively activate one or more antennas or antenna portions to transmit and receive wireless signals for the device. The device may include sensor circuitry that provide sensor data to the control circuitry. The control circuitry may use the sensor data to select and activate an optimal antenna based on the orientation of the earbud or the environment of the device. The antennas may be formed on opposing sides of a housing for the device. By providing configurable antenna structures, the device may be configured to adapt to the current environment and efficiently perform communications operations.