An 8-Beam 2.4 GHz Digital Array Receiver Based on a Fast Multiplierless Spatial DFT Approximation

A low-complexity receive-mode 8-beam multi-beamformer in the digital domain has been realized at 2.4 GHz using an 8-element IQ receiver array. The proposed beamformer is based on a new low-complexity approximation for the 8-point DFT, which is used to perform the spatial DFT operation to achieve multi-beams. The presented DFT approximation is multiplierless and thus achieves low-complexity hardware realizations. The ROACH-2 FPGA platform was used for the analog-to-digital conversion and performing the digital computation. Beams resulting from the approximate transform were measured using digital circuits and were compared to the corresponding beam patters arising from the exact DFT implementation (using 8-bit twiddle factors). The measured beam patterns corresponding to the approximate transform closely followed the pattern of the measured beams resulting from the exact DFT implementation and from the Matlab simulation. The proposed approximate transform based method achieves a performance similar to the exact DFT-based beamformer at a hardware reduction of ~150% at a cost of up to 1.2 dB deviation in the highest side lobe with respect to the measured exact DFT beams.