Mike Roberts, (Slipstream Engineering Design) presenting at Interlligent UK's 2023 RF & Microwave Design Seminar.
Communication and radar systems consisting of antenna arrays conventionally use phase shifters in beamforming applications. This results in beam squint and dispersion (of wideband signals), limiting the capabilities of these systems to narrowband operation. An enhanced approach is the application of a true time delay (TTD) to each element of the array which enables beamforming with wideband signals. The key difference between a phase shifter and a time delay is that a phase shifter provides a constant phase shift with frequency whereas a time delay provides a linear variation of phase with frequency which automatically compensates phase for the delay experienced by signals arriving later at the antenna. Output phase for a given beam angle is always matched irrespective of frequency because delay is matched across the array. With systems employing high-speed data converters and digital front end interfaces including Field-programmable gate arrays (FPGAs), these time delays can also be used to account for and calibrate the discrepancies between channels and elements. One such device is the RF System-on-a-Chip (RFSoC) which combines programmable logic, hardened processors and high-speed data converters onto a unified chip which enables the digitisation of RF signals. This paper investigated a TTD beamforming algorithm implementation via a Farrow-structured Fractional Delay filter technology on Xilinx RFSoC. The performance of the beamformer was then assessed using continuous wave (CW) and wideband linear frequency modulated (LFM) chirp signals to confirm its suitability for wideband applications.