An electronic device may have wireless circuitry with antennas. An antenna resonating element arm for an antenna may be formed from peripheral conductive structures running along the edges of a device housing that are separated from a round by an elongated opening. The electronic device may have a central longitudinal axis that divides the antenna resonating element arm and other antenna structures into symmetrical halves that exhibit mirror symmetry with respect to the central longitudinal axis. The antenna structures may include symmetrical slot antenna resonating elements on opposing sides of the central longitudinal axis. Electrical components such as switches and antenna tuning inductors may be coupled to the antenna structures in a configuration that is symmetrical with respect to the central longitudinal axis. The electrical components may be used to place the antenna structures in an unflipped configuration or in a symmetrical flipped configuration.