A GPS Digital Phased Array Antenna and Receiver

NAVSYS High Gain Advanced GPS Receiver (HAGR) uses a digital beam-steering antenna array to enable up to eight GPS satellites to be tracked, each with up to 10 dBi of additional antenna gain over a conventional receiver solution. This digital, PC-based architecture provides a cost-effective solution for commercial applications where more precise GPS measurements are needed. The additional gain provided on the satellite signals by the HAGR enables sub-meter pseudo-ranges to be observed directly on the C/A code and also improves the accuracy of the GPS carrier phase observations. The directivity of the digital beams created from the antenna array also reduces multipath errors, further improving the accuracy of DGPS corrections generated by the HAGR and the navigation and timing solution computed. This paper describes the beam steering array and digital receiver architecture and includes test data showing the HAGR performance. HIGH GAIN ADVANCED GPS RECEIVER DESIGN The HAGR design is based on NAVSYS’ Advanced GPS Receiver (AGR) PC-based digital receiver architecture integrated with a digital beam steering array. Using a proprietary digital beam steering (DBS) board NAVSYS is able to combine data from as many as 16 antennas and create a multi-beam antenna pattern to apply gain to up to eight GPS satellites simultaneously. 2 The HAGR phased array antenna is shown in Figure 1 and the HAGR electronics includes the components shown in Figure 2. The multi-element antenna array is assembled using commercial antenna elements. The antenna outputs are fed to a Digital Front End (DFE) assembly that includes a custom RF-board that digitizes each of the received L1 signals. The digital output from the DFE assembly is then passed to a custom Digital Beam Steering (DBS) board installed in the AGR Personal Computer that performs the digital signal processing required to implement the digital beam steering operations. The AGR PC also includes a custom Correlator Accelerator card (CAC) that performs the C/A code correlation and carrier mixing on each satellite channel. Depending on the level of performance desired, the antenna array and DFE assembly can be populated with two, four, nine or sixteen antenna elements. The antenna elements are spaced 1⁄2 wavelength apart. The Digital Beam Steering board is operated through software control from the AGR PC. This applies the array spatial signal processing algorithms to form the digital antenna array pattern from the multiple antenna inputs, adjusts the antenna array pattern to track the satellites as they move across the sky, and applies calibration corrections to adjust for offsets between the individual antenna and DFE channels and alignment errors in the positioning of the antenna elements and array assembly. The GPS signal processing is performed by the HAGR Correlator Accelerator Card (CAC) also operated under software control from the PC. This performs the code and carrier tracking on each satellite signal. The HAGR PC-based software computes the navigation solution using the satellite data and can also be configured to record raw measurement data or generate differential GPS (DGPS) or kinematic GPS (KGPS) corrections. ANTENNA ARRAY BEAM PATTERNS