Time delay digital beamforming for wideband pulsed radar implementation

Abstract

Radar system has been using a hybrid of analog and digital beamforming. Sub-arrays of phase shifters in the analog domain are digitized at the sub-array outputs for further digital beamforming processing. Such system suffers from limited bandwidth and is unable to create more than one simultaneous beam. Digital time delay beamforming brings many benefits such as wide bandwidth pulse waveform and simultaneous beams at different angles, wave forms and frequencies. Such capabilities may have been deemed too expensive in the past, but is now within reach due to the high density of multipliers in the FPGA and introduction of transceiver based ADC (Analog to Digital Converter)/ DAC (Digital to Analog Converter). This paper will present the design and implementation of a fractional delay (FD) filter used in time delay beamforming with Altera FPGAs and tools. Other beamforming issues like wide bandwidth, adaptive beamforming and high density interconnect architectures for phased arrays will also be investigated.

Impact: a low cost, reconfigurable, digital beamforming common module building block for next generation phased arrays

“…delays shorter than a single clock cycle), programmable fractional delay filters with group delays corresponding to the required beamforming time delay are employed ( [17]- [20]). This technique has been recently demonstrated in high-speed FPGA devices [21], however, the previous work relies on a substantially different digitization architecture apparent to the IMPACT common module. In our work, TTD structures are designed as bandpass FIR filters to maximize the bandwidth of the IF centered waveforms.…”

Efficient FPGA implementation of high speed digital delay for wideband beamforming using parallel architectures

“…When the beamforming involves narrowband signals, the delays can be realized with simple phase shifters, implemented with complex multipliers. Vice versa in case of wide-band signals, delay blocks must be implemented using more complex circuits [6][7]. A common solution consists in the use of fractional delay filters.…”

Implementation of wideband digital transmitting beamformer based on LFM waveforms

“…When wideband signals are applied to digital array radar, a time delay beam-steering method should be adopted to realise wideband digital beamforming because of aperture effect, i.e. the travelling time across the array antennas [11][12][13][14][15]. To compensate the aperture travelling time, digital time delay filters are employed at baseband.…”

“…To compensate the aperture travelling time, digital time delay filters are employed at baseband. With the help of FPGA and design tools, the implementation of fractional delay (FD) filters is described in [14,16]. However, all these proposed filters are implemented for a single waveform sample per processing clock and unable to be used in beamformer of wideband signals in polyphase structure.…”