Anisotropy of the diffuse background at millimeter wavelengths

The anisotropy of the diffuse background radiation has been measured with a 10-deg FWHM beam in a broad spectral band from 0.6 to 4.0 mm. A dipole anisotropy is detected with magnitude consistent with previous measurements; the present data may, however, be contaminated by atmospheric emission. Upper limits are set to fluctuations at higher-order multipoles. The most stringent limit is at l = 4, where a 95-percent confidence-level limit of less than 0.00025 is set. The observed level of isotropy sharply constrains the possibility of local astronomical origin for the submillimeter excess.