Spatial Interference Nulling Before RF Frontend for Fully Digital Phased Arrays

Fully digital arrays offer huge advantages in terms of flexibility and performance; however, they may suffer from dynamic range issues when used in the presence of in-band interferers. Higher dynamic range components can be used, but are more costly and power hungry, making the implementation of such technology impractical. This paper presents a way to mitigate those interferers by creating a spatial notch at the RF front-end with an antenna-agnostic circuit placed at the feeding network of the antenna array. This circuit creates a steerable null in the embedded element pattern that mitigates interferers at a specified incoming angle. A full mathematical model and closed form expressions of the behavior of the circuit are obtained and compared to simulated and measured results, where up to a 20 dB null in the embedded element pattern of an 1$\times$ 8 array is achieved with less than 1.5 dB of insertion loss. Finally, a real case scenario is set up with a desired signal and an interferer, which is initially saturating the receiver. The receiver successfully demodulates the signal after the null is placed in the direction of the interferer.