Phase compensation experiments with the paired antennas method

Several kinds of techniques are under development for effective correction of a tropospheric phase fluctuation in millimeter- and submillimeter-wave radio interferometry, including very long baseline interferometry (VLBI). We report here the results of phase correction experiments using a method called “paired antennas method.” In the method, pairs of closely located antennas are used for obtaining the fringe phases of both an observing source and an adjacent reference calibrator simultaneously, and the temporal variation of the obtained fringe phase of the target source is corrected by using the calibrator phase. In cases where the separation angle between the target source and the calibrator is sufficiently small, the correction will be almost perfectly made. The experiments were carried out with the Nobeyama millimeter array (NMA) with a special emphasis on examining the separation angle dependence of the degree of the phase compensation. We simultaneously observed the Japanese Communication Satellite (CS) and a quasar 3C279 passing near the satellite at 19 GHz using four antennas of the NMA in order to measure the fluctuation of the difference in their fringe phases in dependence on the angular separation. The standard deviation of the differential fringe phase estimated for 500-s time interval is reduced from 50°–70° to 10° as the angular separation decreases from 20° or greater to a few degrees. The results indicate that the method is very useful for the correction of the tropospheric phase fluctuation in millimeter- and submillimeter-wave interferometry.