We present a new GPU-accelerated signal processing pipeline for real-time beamforming, correlation, and radio frequency interference (RFI) mitigation through spatial filtering on densely packed aperture arrays and phased array feeds. Developed as an instrument-agnostic pipeline, we demonstrate the pipeline's application to the Low-frequency Australian Megametre-Baseline Demonstrator Array (LAMBDA), a new 50–350 MHz VLBI-capable array presently commissioning 36 antennas at the Paul Wild Observatory, Narrabri, New South Wales, Australia.

While the theory of spatial-filtering-based RFI mitigation is well established, building a working real-time system raises genuine systems engineering questions: how to structure a pipeline flexible enough to support rapid iteration on detection and mitigation strategies; how to cleanly inject a priori information, such as sky models or known interferer locations, into a high-performance pipeline; and how to balance flexibility against the throughput demanded by real-time operation. LAMBDA's current modest scale and short baselines make it an ideal testbed for iterating on these implementation problems before deployment at larger arrays. We discuss the design of the pipeline and the trade-offs involved in making it both flexible and fast. We also benchmark its GPU throughput, showing performance sufficient for processing 25 MHz of bandwidth on one NVIDIA A100 for both the current and full 256-antenna LAMBDA array. Using LAMBDA data, we demonstrate the pipeline's RFI mitigation on real interfering signals.