Electronic devices with passive radio-frequency power distribution circuitry

An electronic device may include a transceiver, first and second antennas, and a passive radio-frequency power distribution circuit. The distribution circuit may have a first port coupled to the transceiver, a second port coupled to the first antenna, and a third port coupled to the third antenna. The distribution circuit may include a transformer coupled between the ports. The transformer may have at least two intertwined inductors formed from conductive traces on a dielectric substrate. The intertwined inductors may be concentric about a common point. The intertwined inductors may extend from the common point to the second and third ports. The intertwined inductors may have a coil or spiral shape and may wind around the common point at least once. Intertwining the inductors may serve to minimize the lateral footprint of the distribution circuit in the device.