Digital Architectures for UWB Beamforming Using 2D IIR Spatio-Temporal Frequency-Planar Filters

A design method and an FPGA-based prototype implementation of massively parallel systolic-array VLSI architectures for 2nd-order and 3rd-order frequency-planar beam plane-wave filters are proposed. Frequency-planar beamforming enables highly-directional UWB RF beams at low computational complexity compared to digital phased-array feed techniques. The array factors of the proposed realizations are simulated and both high-directional selectivity and UWB performance are demonstrated. The proposed architectures operate using 2's complement finite precision digital arithmetic. The real-time throughput is maximized using look-ahead optimization applied locally to each processor in the proposed massively-parallel realization of the filter. From sensitivity theory, it is shown that 15 and 19-bit precision for filter coefficients results in better than 3% error for 2nd- and 3rd-order beam filters. Folding together with Ktimes multiplexing is applied to the proposed beam architectures such that throughput can be traded for K-fold lower complexity for realizing the 2-D fan filter banks. Prototype FPGA circuit implementations of these filters are proposed using a Virtex 6 xc6vsx475t-2ff1759 device. The FPGA-prototyped architectures are evaluated using area (A), critical path delay (T), and metrics AT and AT2. The L2 error energy is used as a metric for evaluating fixed-point noise levels and the accuracy of the finite precision digital arithmetic circuits

Broadband multiple cone-beam 3-D IIR digital filters applied to planar dense aperture arrays

A digital beamformer that can synthesize array factors (AFs) with multiple, ultrawideband (UWB), frequency-independent beams at lower computational complexity is proposed. The beamformer is based on a novel 3-D infinite impulse response (IIR) transfer function H(z) having multiple cone-shaped passbands in the 3-D spatio-temporal (ST) frequency-domain ω ε R. The magnitude frequency response and the AF of H(z) are simulated for dual- and single-passband cases. An element pattern of a broadband Vivaldi antenna is simulated at 1.4 GHz and is used to obtain the total array pattern. Computational complexity of H(z) for single-passband (1Cone) case and that of the conventional phased array (PA) beamformer are derived. The magnitude frequency response of the proposed beamformer for 1Cone case and that of the PA beamformer are compared using the mean square error (MSE). For the given selectivity specified by the half cone angle ε = 5°, proposed beamformer provides around 60% lower MSE for the same complexity and around 90% lower complexity for the same MSE compared with the PA beamformer

Hexagonal Multi-Beam Analog RF Aperture Array

A spatially discrete temporally continuous antenna array analog signal processing scheme that can produce highly selective hexagonal beams is proposed. A three dimensional (3-D) infinite impulse response (IIR) filter transfer function having hexagonal beam shaped passabands in the 3-D space-time frequency domain omega is introduced. A hexagonal beam passband in w produces a hexagonal radio beam in the array pattern, and having closely packed multiple hexagonal beams, one can optimally sense a given sky area in a typical radar/microwave imaging application. The proposed array processing scheme employs analog RF circuits for achieving scaling, summing and time delay as building blocks for the signal processing operation. The 3-D IIR filter transfer function is derived by considering an example 10th-order 1-D Butterworth prototype polynomial

Digital Architectures for UWB Beamforming Using 2D IIR Spatio-Temporal Frequency-Planar Filters

A design method and an FPGA-based prototype implementation of massively parallel systolic-array VLSI architecturesfor 2nd-order and 3rd-order frequency-planar beam plane-wave filters are proposed. Frequency-planar beamforming enables highly-directional UWB RF beams at low computational complexity compared to digital phased-array feed techniques. The array factors of the proposed realizations are simulatedand both high-directional selectivity and UWB performance are demonstrated. The proposed architectures operate using 2's complement finite precision digital arithmetic. The real-time throughput is maximized using look-ahead optimization applied locally to each processor in the proposed massively-parallel realization of the filter. From sensitivity theory, it is shown that 15 and 19-bit precision for filter coefficients results in better than 3% error for 2nd- and 3rd-order beam filters. Folding together with Ktimes multiplexing is applied to the proposed beam architectures such that throughput can be traded for K-fold lower complexity for realizing the 2-D fan filter banks. Prototype FPGA circuit implementations of these filters are proposed using a Virtex 6 xc6vsx475t-2ff1759 device. The FPGA-prototyped architectures are evaluated using area (A), critical path delay (T), and metrics AT and AT2. The L2 error energy is used as a metric for evaluating fixed-point noise levels and the accuracy of the finite precision digital arithmetic circuits.Peer Reviewe

Systolic-array architecture for 2D IIR wideband dual-beam space-time plane-wave filters

A spatio-temporal 2D IIR broadband plane-wave filter having 2 user-selectable passbands is proposed using the concept of 2D network resonance. The plane-wave filter is capable of the highly-selective directional enhancement of 2 far-field plane-waves in the presence of undesired waves at different directions of arrival. A massively-parallel systolic-array processor architecture is proposed for the real-time VLSI implementation of the filter. The architecture is designed, simulated, and implemented as a prototype clocked at 50 MHz, using a Xilinx Virtex-4 Sx35-10ff668 FPGA device. The proposed systolic-array delivers a real-time throughput of one-frame-per-clock-cycle (OPFCC) which implies 50 million linear frames per second. The design is simulated (for a 32 element array) and tested on-chip (for an 18-element array) using 2D impulse- and frequency-responses, and using multi-directional broadband plane-wave test sequences

Electronically steerable directed energy using space-time network resonant digital systems

The ability to electronically steer a radio frequency (RF) beam to 'illuminate' a target is fundamental to radar. Transmit beamformers are also needed in wireless communications. Wideband systems, based on direct bits-to-RF apertures, where digital streams are converted to RF using high-bandwidth data converters, that in turn, drive power amplifiers at each array element, is important for emerging wideband, multi-frequency multi-waveform applications. An electronically steerable transmit-beamformer based on space-time network-resonant infinite impulse response discrete systems is proposed for wideband directed energy applications. The proposed method leads to an order-of-magnitude lower digital multiplier count compared to the FIR filter based transmit arrays. Single-beam architectures are introduced. Simulations demonstrate the space-time domain and 2-D frequency domain behavior of the transmit beamformer for example input signals

Space-time spectral white spaces in cognitive radio: theory, algorithms, and circuits

Space-time spectral white spaces in a cognitive radio environment are defined based on multidimensional spatio-temporal spectral properties of radio waves received by a planar array of antennas. Spectral occupancy of a given carrier frequency pertaining to a particular direction in space is expressed by the volume of a semi-cone shaped geometrical region in the 3-D spatio-temporal frequency space ω. A combined approach employing low complexity array processing and conventional time-frequency spectrum sensing is proposed towards the detection of space-time white spaces in ω. The detection scheme employs four subsystems; antenna array, front-end processing, 3-D spatio-temporal array processing, and 1-D spectrum sensing. Key components in the antenna array and front-end processing subsystems are described including an example of a broadband Vivaldi antenna simulated in the frequency range 1.25-2 GHz. The array processing subsystem employs 3-D infinite impulse response digital beam filters, as a low complexity alternative to conventional phased arrays. One potential realization of the 1-D spectrum sensing subsystem is described by using a tunable bandpass filter followed by an energy detector. Simulation examples are provided by considering different directions of arrival, effect of multi-path replicas, signal to noise ratio changes and both narrow band and wideband signals in the normalized temporal frequency range (0,π)