An apparatus for calibrating a global navigation satellite system (GNSS) receiver system for group delay errors in GNSS transmitter signals, the apparatus comprising: a controlled reception pattern antenna (CRPA) (10, 42) comprising a plurality of receiving elements (12, 14) and configured to sense a plurality of signals from a plurality of GNSS transmitters using one or more transmitter frequencies; a signal conditioner configured to convert a plurality of sensed GNSS signals to a plurality of time domain digital signals; and a processor configured to: convert the time domain digital signals into a plurality of frequency domain digital signals; access group delay calibration correction data for combinations of the plurality of receiving elements (12, 14), a plurality of transmitter orientations with respect to the CRPA (10, 42), and the one or more transmitter frequencies; compensate the frequency domain digital signals by the group delay calibration correction data to obtain a plurality of compensated frequency domain digital signals; combine for each GNSS transmitter and frequency the compensated frequency domain digital signals by using a beam forming technique to obtain a plurality of frequency domain filtered signals; convert the frequency domain filtered signals into a plurality of time domain filtered signals; and track code modulations of the time domain filtered signals and convert the time domain filtered signals into GNSS pseudorange measurements for the plurality of GNSS transmitters at the one or more transmitter frequencies. a controlled reception pattern antenna (CRPA) (10, 42) comprising a plurality of receiving elements (12, 14) and configured to sense a plurality of signals from a plurality of GNSS transmitters using one or more transmitter frequencies; a signal conditioner configured to convert a plurality of sensed GNSS signals to a plurality of time domain digital signals; and a processor configured to: convert the time domain digital signals into a plurality of frequency domain digital signals; access group delay calibration correction data for combinations of the plurality of receiving elements (12, 14), a plurality of transmitter orientations with respect to the CRPA (10, 42), and the one or more transmitter frequencies; compensate the frequency domain digital signals by the group delay calibration correction data to obtain a plurality of compensated frequency domain digital signals; combine for each GNSS transmitter and frequency the compensated frequency domain digital signals by using a beam forming technique to obtain a plurality of frequency domain filtered signals; convert the frequency domain filtered signals into a plurality of time domain filtered signals; and track code modulations of the time domain filtered signals and convert the time domain filtered signals into GNSS pseudorange measurements for the plurality of GNSS transmitters at the one or more transmitter frequencies. convert the time domain digital signals into a plurality of frequency domain digital signals; access group delay calibration correction data for combinations of the plurality of receiving elements (12, 14), a plurality of transmitter orientations with respect to the CRPA (10, 42), and the one or more transmitter frequencies; compensate the frequency domain digital signals by the group delay calibration correction data to obtain a plurality of compensated frequency domain digital signals; combine for each GNSS transmitter and frequency the compensated frequency domain digital signals by using a beam forming technique to obtain a plurality of frequency domain filtered signals; convert the frequency domain filtered signals into a plurality of time domain filtered signals; and track code modulations of the time domain filtered signals and convert the time domain filtered signals into GNSS pseudorange measurements for the plurality of GNSS transmitters at the one or more transmitter frequencies.