  We report on the design, first observing season, and analysis of data from a
new prototype millimeter-wave interferometer, MINT. MINT consists of four 145
GHz SIS mixers operating in double-sideband mode in a compact heterogeneous
configuration. The signal band is subdivided by a monolithic channelizer, after
which the correlations between antennas are performed digitally. The typical
receiver sensitivity in a 2 GHz band is 1.4 mK sqrt(s). MINT observed the
cosmic microwave background (CMB) from the Chilean Altiplano. The site has a
median nighttime atmospheric temperature of 9 K at zenith (exclusive of the
CMB). Observations of Mars, Jupiter, and a telescope-mounted calibration source
establish the system's phase and magnitude stability. MINT is the first
CMB-dedicated interferometer to operate above 50 GHz. The same type of system
can be used to probe the Sunyaev-Zel'dovich effect in galaxy clusters near the
SZ null at 217 GHz. We present an analysis of sideband-separated, digitally
sampled data recorded by the array. Based on 215 hours of data taken in late
2001, we set an upper limit on the CMB anisotropy in a band of width Delta
ell=700 around ell=1540 of delta T < 105 microK (95% conf). Increased
sensitivity can be achieved with more integration time, greater bandwidth, and
more elements.
