Design and simulations of a nulling interferometer using a single Martin-Puplett interferometer for double-sideband operation

We propose a new quasi-optical setup for a nulling interferometer at short millimeter and submillimeter wavelengths employing a single Martin-Puplett interferometer (MPI) for side-band separation. The new design allows the simultaneous use of both sidebands, thus avoiding the loss of sensitivity from conventional sideband filters. Although intended for solar flare observations, the quasi-optical setup can be applied to cancel any extended circular source, while at the same time preserving the full sensitivity toward a point-like source on or near the extended one. Numerical simulations show that the sinusoidal transmission characteristic of the MPI limits the usable relative bandwidth to one-third of the IF. Compared to an instrument employing lossless sideband filters, an increase of the response to a point-like continuum source by a factor of ~ 1.6-2 is expected, depending on the source position and relative bandwidth. Index Terms--Interferometry, radio astronomy, solar radiation, submillimeter-wave receivers, submillimeter-wave technology.