Design and Implementation of a Dual-Mode Digital Backend for the GZNU Small Antenna Array

Abstract

Small-aperture radio antenna arrays provide flexible platforms for high-time-resolution searches of bright radio transients, such as pulsar giant pulses and fast radio bursts, as well as for long-duration monitoring and technical validation of array observing modes. To support the GZNU small-aperture antenna array under construction, we developed a dual-mode digital backend based on the Xilinx RFSoC 47DR. The backend is designed to serve two complementary observing requirements. In Baseband Mode, the backend digitizes analog signals at a sampling rate of 1024 MHz and streams the raw voltage data with VDIF header to a server via a 100 Gbps interface for further processing. In PSRFITS Mode, dual-polarization signals from a single antenna are channelized using a polyphase filter bank and Fourier transform, integrated, gain-adjusted, quantized, and converted into AABBCRCI polarization products before being encapsulated into PSRFITS files. System characterization show that the relative timing offsets among four ADC channels are on the order of 10 -2 -10 -1 ns for a reference signal at various frequencies. Packet-transmission tests show no packet loss during a four-hour PSRFITS-mode run, while a short-duration Baseband-mode test gives a packet loss rate of approximately 0.04%, limited mainly by the current storage system. Validation was completed via observations of the pulsar B0329+54 in PSRFITS Mode, resulting in well-defined waterfall plots and integrated profiles. These results demonstrate the initial end-to-end functionality of the RFSoC-based backend and provide a basis for future long-duration baseband recording, multi-antenna interferometric verification, and fast-transient searches.