An array processing GNSS (Global Navigation Satellite System) receiver may provide increased accuracy, reliability and integrity by forming beams towards satellites and nulls towards interference or reflective surfaces. Also, software defined receivers have proven themselves versatile and provide a convenient environment to implement novel algorithms.This paper first describes the gain/phase calibration of a seven element custom array antenna and proceeds to compare the single antenna performance to that of the performance attained by forming beams towards the satellites. IF (Intermediate Frequency) data, high rate samples representing the received signal in a narrow band around the GPS L1 frequency, from an array antenna have been recorded both in an environment with open sky conditions and also in more challenging areas (central Boulder, Colorado). Simultaneously, data from a high quality GPS based INS was recorded in order to obtain accurate estimates of position/ orientation. Calibration of the system (including antennas and front-ends) was performed using data from the benign environment, and based on this information, deterministic beams were formed towards the satellites using data from the semi-urban dataset. The single antenna accuracy was then compared to the position obtained by processing after forming beams.