  Radio interferometric observations are less susceptible to radio frequency
interference (RFI) than single dish observations. This is primarily due to :
(1)fringe-frequency averaging at the correlator output and (2) bandwidth
decorrelation of broadband RFI. Here, we propose a new technique to improve RFI
suppression of interferometers by replacing the fringe-frequency averaging
process with a different filtering process. In the digital implementation of
the correlator, such a filter should have cutoff frequencies $< 10^{-6}$ times
the frequency at which the baseband signals are sampled. We show that filters
with such cutoff frequencies and attenuation $>$ 40 dB at frequencies above the
cutoff frequency can be realized using multirate filtering techniques.
Simulation of a two element interferometer system with correlator using
multirate filters shows that the RFI suppression at the output of the
correlator can be improved by 40 dB or more compared to correlators using a
simple averaging process.
