A 16-Element 2.4-GHz Digital Array Receiver Using 2-D IIR Spatially-Bandpass Plane-Wave Filter
A receive-mode digital-RF beamformer based on spatially bandpass 2nd order 2-D IIR beam filters has been designed, built and tested. These 2-D IIR filters have been derived using multi-dimensional space-time network resonance, and consume less hardware resources compared to FIR filter based realizations leading to lower chip area and power consumption. For a similar performance/selectivity, implementing a 2nd order 2-D IIR SBP beam filter leads to 83.7% reduction in computational hardware complexity when compared to an FIR filter implementation. The beamformer operates at 2.4 GHz, supporting 120 MHz of bandwidth. The microwave front-end consists of a 16-element patch antenna array feeding 16 direct conversion receiver chains. Downconverted signals from the chains are sampled at 240 MHz and processed using a ROACH-2 platform, which employs a Xilinx Virtex 6 FPGA. The filter was implemented on FPGA and the filter coefficients were used to set the beam directions to measure the resulting RF beam pattern of the beamformer. The measured beam patterns have been reported for beam directions of 15° and 30°. Measured beam patterns are in well accordance with the simulated beam patterns. Thus the real time performance of the 2-D IIR SBP beamfilters have been verified demonstrating their low-complexity usage in beamforming applications for the first time.