A wireless device has receiver circuits and/or transmitter circuits supporting at least two simultaneous independent transmit paths in the same frequency band, and a multiport antenna with N ports, for the available receiver or transmitter circuits. The multiport antenna has a compact mechanical state and an extended mechanical state, and is connected to the N ports of the receiver and/or transmitter circuits by a 2N-port matching and decoupling network. This has multiple, selectable electrical states, each corresponding to at least one of the mechanical states. One combination of the mechanical state and the electrical state allows operation in a wireless channel of rank N. A second combination of the mechanical state and the electrical state allows operation in a wireless channel of rank less than N. Better MIMO performance with the extended antenna configuration can be obtained with the convenience of retaining limited performance when the user cannot use the extended antenna.