A spaced antenna drifts experiment was implemented for the Jicamarca mesosphere-stratosphere-troposphere radar. The whole radar antenna was used to transmit a radio signal vertically, and three separate quarters of the antenna were used to receive the scattered radio signal. Drifts data from the mesosphere were analyzed by the method of similar fades. This technique appears not to be as well adapted to measure horizontal velocities as the Doppler beam swinging technique usually used at Jicamarca. It was shown that for large antennas the error in the estimated horizontal velocity increases with increasing antenna dimensions. It follows directly from this finding that an increase in aspect sensitivity of the scattered power will also cause an increase in the error in the measured horizontal velocity. It was shown that short-period (<15 min) oscillations in the calculated drift of the irregularity pattern over the ground are most likely to be caused by horizontal variations in the vertical velocity within the scattering volume in the mesosphere.