An Investigation and Solution to Spatial Interferers Before RF Front End for Phased Arrays

Fully digital arrays offer significant advantages in terms of flexibility and performance, however they suffer from dynamic range issues when used in the presence of in-band interferers. Higher dynamic range components may be used, but are more costly and power-hungry, making the implementation of such technology impractical for large arrays. 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. 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. Up to 20 dB null in the embedded element pattern of a 1x8 array is achieved with less than 1.5 dB of insertion loss. A steerable null using phase shifters is shown to prove real-time changes in the null placement. Phase shifters are substituted by tunable filters and enable a significant boost in the overall performance. To further validate the concept, a real case scenario is set up with a desired signal and an interferer that is initially saturating the receiver. The receiver successfully demodulates the signal after the null is placed in the direction of the interferer. The circuitry is then expanded to a planar array to fully optimize the interferer-free scanning volume.