2-DIMENSIONAL DIRECT IMAGES WITH A SPATIAL FFT INTERFEROMETER

Two-dimensional direct radio imaging was achieved at the Nyquist rate by a sixty-four-element digital interferometer. We have observed the C rab Nebula passing across the window of an image plane of 8x8 pixels a s the earth rotated. The observed frequency was 10.65 GHz. Direct imag es were obtained by a digital lens (a 2D spatial FFT processor), which transforms complex amplitudes in 2D space (the electric-fields over t he array antennas) to those in momentum space (k space). Using a newly developed phase-measuring technique, the instrumental phase errors we re corrected before the observation. As a result, the first direct 2D images were obtained with the radio interferometer. ''Direct'' means t he capability to image non-ergodic (time average not-equal ensemble av erage) sources, such as pulsars or communciation signals, of which Fou rier-synthesis telescopes could not make images.