Portable electronic device antenna structures, comprising: a common ground plane; first and second antennas (56, 60) that share the common ground plane, wherein the first and second antennas (56, 60) are each configured to operate at a common given communications frequency; and an antenna isolation element interposed between the first and second antennas (56, 60), wherein the antenna isolation element is formed from a resonating element arm connected to the common ground plane and serves to isolate the first antenna from the second antenna at the given communications frequency and wherein the resonating element arm of the antenna isolation element is configured to resonate at the given communications frequency, wherein the first and second antennas (56, 60) each comprise a resonating element arm (104, 108), wherein the resonating element arms (104, 108) resonate at the given communications frequency, characterized in that: the resonating element arms (104, 108) of the first and second antennas (56, 60) and the resonating element arm of the antenna isolation element are aligned in a collinear fashion with a common axis that is aligned with the longitudinal axis of each of the resonating element arms (104, 108, 100) of the first and second antennas (56, 60) and the antenna isolation element, said longitudinal axis being defined by the longest portion of the resonating element arms (104, 108, 100); and the resonating element arms (104, 108) of the first and second antennas (56, 60) and the resonating element of the antenna isolation element face in the same direction along the common axis. a common ground plane; first and second antennas (56, 60) that share the common ground plane, wherein the first and second antennas (56, 60) are each configured to operate at a common given communications frequency; and an antenna isolation element interposed between the first and second antennas (56, 60), wherein the antenna isolation element is formed from a resonating element arm connected to the common ground plane and serves to isolate the first antenna from the second antenna at the given communications frequency and wherein the resonating element arm of the antenna isolation element is configured to resonate at the given communications frequency, wherein the first and second antennas (56, 60) each comprise a resonating element arm (104, 108), wherein the resonating element arms (104, 108) resonate at the given communications frequency, characterized in that: the resonating element arms (104, 108) of the first and second antennas (56, 60) and the resonating element arm of the antenna isolation element are aligned in a collinear fashion with a common axis that is aligned with the longitudinal axis of each of the resonating element arms (104, 108, 100) of the first and second antennas (56, 60) and the antenna isolation element, said longitudinal axis being defined by the longest portion of the resonating element arms (104, 108, 100); and the resonating element arms (104, 108) of the first and second antennas (56, 60) and the resonating element of the antenna isolation element face in the same direction along the common axis. the resonating element arms (104, 108) of the first and second antennas (56, 60) and the resonating element arm of the antenna isolation element are aligned in a collinear fashion with a common axis that is aligned with the longitudinal axis of each of the resonating element arms (104, 108, 100) of the first and second antennas (56, 60) and the antenna isolation element, said longitudinal axis being defined by the longest portion of the resonating element arms (104, 108, 100); and the resonating element arms (104, 108) of the first and second antennas (56, 60) and the resonating element of the antenna isolation element face in the same direction along the common axis.