A modular resistivity sensor disposable in a drillstring having a drill bit on a distal end for drilling a wellbore in a formation, includes a sensor body having a longitudinal axis radially offset from a longitudinal axis of the drillstring, one or more transmitting coil antennas disposed along a length of the sensor body, one or more receiving coil antennas disposed along a length of the sensor body, and a calibrating device configured to calibrate signals generated from the receiving coil antennas.