# Improved 2D Ground Target Tracking in GPS-Based Passive Radar Scenarios
## 6 Results with Real Data  
### Radar Scenario  
A real radar data acquisition campaign was carried out to evaluate the ground target detection and localization performance of the proposed GPS-based PR. An area of the external campus of the University of Alcala, near the Faculty of Physiotherapy and Nursing, was selected as the radar scenario. Figure 10 shows a Google Earth image of the Area of Interest (AoI). The radar scenario is composed of a 390-m straight road with several buildings and sports facilities at both sides. The biggest building is mainly made of metal (shown in Figure 10 in the yellow area), and the numerous metal fences and high lampposts distributed throughout the sports facilities. During the experiments, the PR receiver was placed on the pavement near the road and a cooperative vehicle was driven along the road starting its movement from the back of the PR location. The PR receiver deployment and the cooperative target are depicted in Figure 10.  
Figure 8: Results for the simulated radar scenario: (**a**) confirmed detections and associated tracks in the measurement space (range-Doppler); (**b**) Cartesian space tracking results (+ marker) and reference targets’ path presented in Figure 7 (solid line).  
Figure 9: Localization error in the simulated scenario.  
An updated version of the IDEPAR technological demonstrator, developed at the University of Alcala [17] was employed to acquire the real radar data. The PR demonstrator was composed of a commercial active GPS antenna, right hand circularly polarised with 3 + 30 dB gain and hemispherical pattern, for the reference channel acquisition. The surveillance channel was composed of a uniform five-element linear array whose individual elements were linearly polarised antennas with an azimuthal beamwidth of 80 degrees and a gain of 6.8 dB.  
For the tests, the GPS satellite constellation was selected as IoOs, and the civil GPS signal in the L1 band was selected as the illumination signal. The PR demonstrator was configured to acquire 40 s of continuous signal at GPS L1 band (1575.42 MHz). The illumination signal was oversampled up to an acquisition rate of 25 MHz to increase the bistatic range accuracy and to allow ground target localization at low ranges. The acquired data were divided into 160 non-overlapping Coherent Processing Intervals (CPI), each of 250 ms duration, that were processed following the scheme described in Section 2 and 3. For the first stage of the spatial filtering, 3 different orthogonal beams were generated (\(-25^{\circ}\), \(0^{\circ}\), \(25^{\circ}\)), the set of simultaneous beams was complemented with two additional beams at the first intersections of the orthogonal ones (\(-15^{\circ}\), \(15^{\circ}\)).  
A search of available GPS satellites was performed, identifying seven satellites, with PRNs 2, 6, 12, 25, 29, 31, and 32. The GPS signals associated with these PRN codes were reconstructed and considered in the adaptive filtering process to reduce their interference contributions in the RDMs. The satellite transmitting PRN 32 was selected as IoO due to its higher power at ground level.  
Some tests have been performed on the radar scenario with moving cooperative targets to evaluate the performance of the system. The cooperative targets started from the rear of the passive radar. A straight road trajectory of 390 m was defined, with the targets moving at a nearly constant speed of 30 km/h along the trajectory on the AoI. Nevertheless, the variation of the bistatic geometry produced an accelerated motion in the bistatic range-Doppler domain.