A new radar interferometer technique has been developed and used successfully at the Jicamarca Radio Observatory in Peru to study the strong nighttime plasma turbulence in the equatorial electrojet. The technique represents a major step forward in radar probing of turbulent irregularities such as (but not limited to) those in the electrojet. In many situations it provides far more information than previous Doppler measurements. We form the cross spectrum of the backscattered signals received from approximately overhead on two antennas, separated in this case along an east-west baseline, as well as the individual power spectra. From the phase of the cross spectrum at different Doppler frequencies we can determine the individual positions of plasma wave packets propagating vertically with different velocities, and we find, for example, that oppositely propagating waves always come from distinctly separated regions. The data allow us to study the eddy structure within the electrojet in far more detail than hitherto possible, and by using the irregularity patches as tracers and following their east-west motion, we can obtain a vertical profile of drift velocity. Our first observations of this sort have shown that at night the vertical Doppler velocity at times may substantially exceed the mean horizontal velocity of the patch and the small horizontal velocity near the top and bottom of the layer may actually be westward when the main motion is eastward.