A low-cost GNSS antenna array with raw data sampling of 40 units

Within the presented work, two very recent trends in research are intensively addressed. On the one side, software defined radio platforms (SDRs) are used, which are widely used to investigate novel receiver technologies and interference detection and mitigation techniques. On the other side, antenna arrays and array processing is commonly used in research projects and new products, thinking about satellite spot beams, 5G mobile communication, radar sensors and noise cancelling headphones. Antenna arrays are also more and more used for Global Navigation Satellite Systems (GNSS) applications, like controlled reception pattern antennas (CRPA) for anti-jamming and direction finding. There are various aspects and use cases, which benefit from an antenna array like interference detection and mitigation, GNSS signal quality monitoring and estimation of unknown code chips. The relevant literature reports about employment of large parabolic dish antennas [1] as well as antenna arrays [2][3][4]. With a multi antenna array, the raw data may be sampled from each individual unit and then be combined via software acting as a beam forming network. Such an approach is described by [2] and was also conducted in the herewith reported activity. Whereas previous international R&D activities in this field usually rely on a smaller number of antennas like 8 units [2] or already 25 units [3], the present work reports about an array using 40 antennas. Considering such big number of antennas and sampling units, economical considerations are not to be neglected. Hence, a major focus and challenge during the development of such a huge antenna array was the requirement using low to medium-cost commercial off-theshelf (COTS) products. Fortunately, the constantly decreasing prices of even high performance SDR platforms allow low-cost solutions. Recently, due to the COVID 19 and computer chip crisis unfortunately, the prices again increased. Summarising, of course, the whole system cannot be seen as a cheap system but comparably cost-efficient due to the proper selection of the components. The motivation behind this activity was creating an omnidirectional ultra-high gain antenna compared to dish antennas, which have a narrow directivity. This would allow receiving all visible satellites with a very high C/N0. One major point of understanding is that when talking about the antenna gain within this paper, we are talking about the passive antenna gain, usually described in an antenna pattern figure. This is different to the usually given gain value of the low-noise amplifier (LNA) of an active GNSS antenna. Manufacturers usually provide the passive gain information as a gain pattern figure. Sometimes, only the peak gain value (gain in dBic typical at zenith) gives a value of the maximum gain usually at 90° elevation. The composition of the paper looks as following: in the next chapter, the system requirements will be formulated, the selected components will be introduced and the derived system design will be presented. Afterwards, the mechanical development process will be described and the final setup will be shown, before the authors share the occurred challenges during the implementation process. Finally, shortly, results are given followed by a summary and outlook.