Direction of Arrival Estimation with an Analog Null Steering Controlled Reception Pattern Antenna System

Mai Hassan, Ali Massoud, Mohamed K. Emara, Haidy Elghamrawy, Aboelmagd Noureldin

Abstract:	Controlled Reception Pattern Antenna (CRPA) systems are becoming increasingly common in Global Navigation Satellite System (GNSS) receivers for their adaptability and effectiveness in mitigating jamming signals. Analog null-steering is commonly used in these systems due to its low complexity and power efficiency. It operates by applying variable attenuators and phase shifters at each antenna element to shape the reception pattern and suppress interference, without requiring prior knowledge of the desired signal structure. By adjusting complex weights across antenna elements, spatial nulls are formed toward the direction of strongest interference. The Power Inversion (PI) algorithm is often employed for this purpose, making use of the fact that GNSS signals are significantly weaker than jamming signals. However, due to array geometry and mutual coupling between antenna elements, which inevitably occurs in practical antenna radiation patterns, other nulls can be introduced in different directions, in addition to the intended null direction. We define these inadvertent nulls as ghost nulls. These ghost nulls can suppress jamming signals even when the antenna weights are targeting a different direction, leading to ambiguity in estimating the jammer’s true direction of arrival (DOA). This ambiguity can lead to less effective countermeasures against the jammer or incorrect positioning in tracking systems. To overcome this issue, we propose a modified PI-based null-steering approach that explicitly accounts for ghost nulls. Our method identifies the finite set of ghost nulls associated with each DOA and constructs a lookup table (LUT) of antenna weights that minimizes received power while also reducing null depth at ghost directions. Using real radiation patterns from a 4-element uniform circular antenna array operating in the L1 band, designed by Calian GNSS, simulation results show a 95.8% reduction in LUT entries that have associated ghost nulls compared to the standard PI algorithm. This leads to around 30% improvement in DOA estimation accuracy and significantly enhances jamming mitigation effectiveness in GNSS receivers.
Published in:	Proceedings of the 38th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2025) September 8 - 12, 2025 Hilton Baltimore Inner Harbor Baltimore, Maryland
Pages:	756 - 764
Cite this article:	Hassan, Mai, Massoud, Ali, Emara, Mohamed K., Elghamrawy, Haidy, Noureldin, Aboelmagd, "Direction of Arrival Estimation with an Analog Null Steering Controlled Reception Pattern Antenna System," Proceedings of the 38th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2025), Baltimore, Maryland, September 2025, pp. 756-764. https://doi.org/10.33012/2025.20367
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