Multi‐beam RF aperture using multiplierless FFT approximation

Abstract

Multiple independent radio‐frequency (RF) beams find applications in communications, radio astronomy, radar and microwave imaging. An N ‐point fast Fourier transform (FFT) applied spatially across an array of receiver antennas provides N ‐independent RF beams at N /2 log 2 N multiplier complexity. Here, a low‐complexity multiplierless approximation for the 8‐point FFT is presented for RF beamforming, using only 26 additions. The algorithm provides eight beams that closely resemble the antenna array patterns of the traditional FFT‐based beamformer albeit without using multipliers. The proposed FFT‐like algorithm was verified on‐chip using a Xilinx Virtex‐6 Lx240T field programmable gate array (FPGA) device. The FPGA implementation indicated bandwidth of 369 MHz for each of the independent receive‐mode RF beams.