electronic digital beamforming implementation for radars

ELECTRONIC DIGITAL BEAMFORMING IMPLEMENTATION FORRADARSR. NEY, S. BONAIMÉ, F. DOLON , J.J. BERTHELIER,CETP/IPSL, 4 Avenue de Neptune, 94107 Saint-Maur Cedex, Francerichard.ney@cetp.ipsl.frR. CLAIRQUIN, D. NEVEJANSBIRA/IASB, Ringlaan 3, B-1180 Brussels, BelgiumC. DUVANAUDLAII, Université de Poitiers, IUT, 4 Avenue de Varsovie, 16021 Angoulême Cedex, FranceA. D’HERMIESESIEE, Cité Descartes, BP 99, 2 Bld Blaise Pascal, 93162 Noisy-le-Grand Cedex, FranceIntroduction.Beamformers are complex networks used to precisely control the phase and amplitude of RFsignals passing through them. They are used either in the transmission or the receiving modeand even in both modes. In RF transmitting systems for radars, beamformers are employedbetween the RF signal source and the radiating elements to shape the beam illuminating thetarget to be detected. In receiving systems beamformers are employed between the antennaarrays and the receiver to observe a specific region of space.Beamformers can be implemented either with analog or digital components. Figure 1illustrates the analog beamforming concept implemented on the Iceland and Kerguelen islandsradars of the SuperDarn network. The beamforming elements are inside the Phasing Matrixbox. Each antenna is associated to a power amplifier. Beamforming is performed in bothtransmitting and receiving mode.16 channelsPHASING MATRIXTo ReceiverFrom RF pulse generatorFigure 1: Analog beamforming on the Super DARN (Dual Auroral Radar Network)radars. Operating frequency band: 8-20 MHz, Frequency Agility capability

The main element of the unit (figure 3) is a FPGA programmed in VHDL language whichperforms the digital wave generation through a DDS scheme, the full control of the radaroperation and interface with a PC and the coherent integrations (up to 2 24 ) of 2500 range gatessignals. The frequency range is 0.2 to 5 MHz and the output peak power is 10W. The receiveris a standard analog unit. For the field tests, the ON/OFF, the data transfer, the controlparameters of the radar, are achieved through a wireless link between the PC and the radar.The data transfer is done according to a MIL STD 1553-like protocol.A digital beamforming implementation.Figure 4 illustrates the concept.Each antenna of an antenna network has to be associated to an electronic unit. Thisarchitecture is very flexible and allows Digital Beamforming for both transmission andreception, or if desired for reception only.This hardware can be applied to many radars in the HF and VHF bands. The analog receivercan be replaced by a digital receiver which implements the ADC at the HF or VHF level,digital demodulation and matched filtering on the I and Q baseband signals.Conclusions.The radar unit developed at CETP allows:• Digital beamforming in the receiving and transmitting modes.• A great number of range gates, a great flexibility (frequency generation, ability tooversampling, large range values for parameters…).• The VHDL program can be implemented in any FPGA.• Practical user interface.• Medium cost.• Extension to VHF frequency range, to higher transmitted power.• Use of digital receiver (better performances and flexibility).These features are likely to promote the use of digital beamforming at MF, HF, VHFfrequencies in several fields such as ionospheric radars, ST radars, oceanographic radars…References.Barton, P., (1980). Digital beam forming for radar. IEE Proceedings, Vol. 127, Pt. F, N°4,August, pp. 266-277.Berthelier,J.J., R. Ney, V. Ciarletti, A. Reineix, B. Martinat, M. Hamelin, F. Costard, W.Kofman, P. Paillou, C. Duvanaud, D. Nevejans, W. Kofman, J.G. Trotignon, G. Grandjean,M. Zamora and A. Nagy (2003). GPR, A Ground Penetrating Radar for the NetLandermission. J. Geophys. Res., 108, ( E4), 8027.Ney, R, J.J. Berthelier, V. Ciarletti, B. Martinat, M. Hamelin, M. Rodriguez-Cassola, F.Dolon, S. Bonaimé, A. Reineix, D. Nevejans, C. Duvanaud, F. Costard, and P. Paillou(2002). The Ground Penetrating Radar of the Netlander Misssion. Proceedings of the NinthInternational Conference on Ground Penetrating Radar, University of California, SantaBarbara, USA, Apil 29 – May 2, pp. 541-5 46.Steyskal, H. (1987). Digital Beamforming Antennas. Microwave Journal, January 1987, pp.107-124.

DDSFrequency Range : 0 - 25MHzPulse ModulationCW, Bi - phase, BPSKDACPowerAmplifierF0FPGA0Radar Controlπ/ 2ReceiverDemodulation at FoCoherent Integration sADCADCAcess-point PCMCIAWireless 802.11bFigure 3 : The NetLander GPR radar architectureRADAR-1Wireless802.11bRADAR-2RADAR-NFigure 4: Example of a digital beamforming radar architecture