An extensive international campaign to observe Polar Mesospheric Summer Echoes was conducted with the European Incoherent Scatter radars in July and August 1988. During this period, two short experiments used the flexibility of the VHF system to transmit two simultaneous beams which could be used to determine the horizontal variation of the scattering irregularities. On the first occasion the echoes appear to originate from noncoplanar points near 84 km altitude. On the second occasion, only the temporal behaviour could be studied for a short interval.