A Low-SWaP 16-Beam 2.4 GHz Digital Phased Array Receiver Using DFT Approximation

• Published in: IEEE transactions on aerospace and electronic systems Vol. 56; no. 5; pp. 3645 - 3654
• Main Authors: Coutinho, Vitor A., Ariyarathna, Viduneth, Coelho, Diego F. G., Pulipati, Sravan Kumar, Cintra, Renato J., Madanayake, Arjuna, Bayer, Fabio M., Dimitrov, Vassil S.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.10.2020; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Analog to digital conversion; Approximation; Approximation algorithms; Array signal processing; Beamforming; Complexity theory; DFT approximation; Discrete Fourier transforms; Filter banks; low-complexity beamforming; low-complexity FFT; Mathematical analysis; Microwave antenna arrays; multibeam beamforming; Phased arrays; Radio frequency; Receivers; Sidelobes
• ISSN: 0018-9251; 1557-9603
• DOI: 10.1109/TAES.2020.2987094

A low-complexity approximation for the 16-point DFT and its respective multiplierless fast algorithm is proposed. A receive mode multibeam phased-array experiment was realized at 2.4 GHz employing a 16-element IQ receiver array that uses the proposed approximate spatial DFT in real-time in order to achieve multibeam digital beamforming. The 16-beam digital receiver experiment uses a ROACH-2 based Xilinx Virtex-6 FPGA platform for both digital beam computation as well as to perform the multireceiver analog-to-digital conversion. Receive mode RF beams were measured and compared to the exact DFT (realized with fixed-point multipliers with 8-bit twiddle factors). The measured approximate DFT closely followed the measured beams resulting from the fixed-point conventional DFT implementation. The approximate DFT achieves RF beam performance (mainlobe gain, sidelobes) similar to the DFT at the cost of a small error which would be tolerable for the majority of multibeam phased-array receivers. The 16-point approximate DFT provides a hardware reduction of \sim70% with respect to FFTs, setting up a low size, weight and power (SWaP) system.The maximum magnitude error of the filter bank response is 0.106 (\approx -20 dB).