Interference and Jammer Suppression of High Bandwidth Signals using an Array of Spatially Distributed Subarrays

Antenna arrays and spatial signal processing techniques have proven to be the most effective countermeasures against radio interference (RFI). Beamforming algorithms such as the prewhitening filter estimate the covariance matrix from a finite block of digitized raw antenna signals. Subsequently a scaled inverse of the covariance matrix can be applied to the same signal block to decorrelate the signals and hence, mitigate incident jammers. The application of this algorithms supposes that the narrowband assumption is met, which is the case for compact arrays, such as uniform rectangular arrays (URAs). Through the comparably large size of the latter, a hidden installation in cars produced for the consumer mass market is not possible, which is on the other hand a strict requirement by industry and customers, such that the aesthetic design of the car is not infringed. Therefore, the authors of this paper presented a new array concept consisting of two uniform linear arrays (ULAs), which can be spaced several wavelengths apart from each other. With that additional degree of freedom and the reduced footprint of a ULA compared to a URA, this array allows for a concealed installation in the front and/or rear bumpers as well as the side mirrors of a car. On the other hand, the narrowband assumption is violated through the increased spacing between the ULAs. Therefore each antenna receives the signals with a non negligible delay and, furthermore, a different Doppler frequency, if platform rotations are considered. Both effects decrease the correlation of the impinging signal and hence the beamformer performance. The authors demonstrated the possibility to utilize this new array using signals of the GPS L1 C/A band with a bandwidth of 2 ? 5 MHz. This paper demonstrates measured results of the array under consideration evaluated at a bandwidth of 12.5 MHz as incorporated in the new signals for GPS L5 or GALILEO E5a respectively. A novel approach to improve the performance for wideband signals will be presented which is capable of compensating the aforementioned differential delays as well. The approach will be developed, analyzed and the improvements in terms of interference mitigation capability will be assessed in comparison to the pure spatial state-of-the-implementation. The paper gives an insight into a novel technique for suppressing interference, jamming and spoofing using distributed antennas which is capable of also handling GNSS signals with high bandwidth (E5a/L5). Such signals are considered to be crucial for future automatically or autonomously driving cars. Real measurement data will be used to ensure realistic results and assessments.