Digital beamforming receiver architectures for microwave remote sensing applications

Abstract

Digital beamforming radar systems, capable of generating multiple antenna beams simultaneously, are now being used for high spatial resolution studies of the ocean surface and atmospheric boundary layer. This paper describes several receiver architectures applicable to digital beamforming systems and compares their relative merits. The simplest and lowest-cost architecture, comprised of a single receiver sampling a large array of antenna elements, is applicable to situations where some receiver inefficiencies can be tolerated. The second architecture described attaches a complete low noise receiver to each antenna element in the array to achieve the highest possible sensitivity. The Turbulent Eddy Profiler (TEP) utilizes this architecture to study clear air turbulence intensity and motions within the atmospheric boundary layer. A third architecture, employing a high accuracy digital receiver to sample each antenna output, is applicable to systems requiring the highest degree of antenna pattern control. SWITCHED RECEIVER DESIGNThe Focused Phased Array Imaging Radar is a digital beamforming array radar developed by Quadrant Engineering and the University of Massachusetts for oceanographic research [l]. FOPAIR produces coherent radar images of an extended area of ocean surface (typically 60 m x 90 m) resolved to 1.5 m resolution. An X-band array of 128 elements, shown in Figure 1, provides the .25" beamwidth necessary for fine-scale imaging. All array elements share a single receiver through a high-speed switching network that samples the elements sequentially, analogous to the sequential scan of a synthetic aperture radar. For short to medium range applications, a 100 kHz PRF ensures rapid image capture (typically within 1 ms), and array scans can be repeated up to 180 scans per second. Figure 2 shows a block diagram of FOPAIR. The receiving arrays consist of linear tapered slots, which are low-cost printed circuit antennas. The receiver outputs are baseband I-and Q-channels, each with a bandwidth of up to 100 MHz. These outputs are digitized by a high-throughput sampling system capable of burst mode This work was supported by the Office of Naval Research, Army Research Office, and the Air Force Research Laboratory.Fig. 1. FOPAIR's X-band receiver array of 128 elements.sampling rates up to 400 MS/s at 12 bits.Two-dimensional radar imagery is generated from the unfocused array data, either through post-processing on a computer workstation or by an embedded DSP processor capable of real-time imaging at rates up to 72 frames/s. Radar "motion pictures" of ocean surface backscatter clearly show wave propagation and intermittent scattering events. These moving images can be viewed by opening the following web site: www.quadeng.com/ocean/fopair/fopair . html. HIGH SENSITIVITY DIGITAL BEAMFORMING ARRAY FOR TURBULENCE IMAGINGThe Turbulent Eddy Profiler (TEP) is an example of a highly sensitive clear-air turbulence sensor requiring a dedicated receiver for each antenna [2], [3]. TEP's 90 element array provides a focused beam...

RF Analog Beamforming Fan Filters Using CMOS All-Pass Time Delay Approximations

“…7 can then be obtained by combining (15) and (16) (17) where , , , and . Assuming , , and , (17) can be simplified as (18) As indicated above, besides a left-hand plane pole and righthand plane zero, the transfer function also has an extra pole associated with the output loading capacitance , which includes both the parasitic capacitance coming from the second stage itself and its following stage.…”

“…7, by merging the parasitic gate-drain capacitance of into , the transfer function of the first stage, from to , can be expressed as (15) Similarly, the transfer function of the second stage, from to , can be given by (16) In (16), the parasitic gate-drain capacitance of is neglected for simplicity.…”

“…Ultra-wideband (UWB) beamforming on a uniform linear array (ULA) of broadband antennas [7] enables the directionally-selective enhancement of propagating far-field uniform plane wave (PW) signals having a specified directional of arrival (DOA) . UWB beamforming facilitates front-end instrumentation in various applications including wireless communications [4], [8], [9], next-generation radio telescopes such as the square kilometer array (SKA) [10]- [14], microwave imaging [15], [16] and radar [17]- [19]. Current methods are based on analog delay-and-sum, filter-and-sum, complex correlation and digital phased array feeds [2], [5], [20]- [29].…”

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

“…Beamforming enables array factors (AFs) [15] with steerable directional sensitivities which are used to enhance/reject plane-wave signals [16][17][18][19][20][21][22]. Real-time UWB beamforming benefits both engineering and scientific applications such as radar [23][24][25][26], navigation [27], wireless communications [18,[28][29][30][31], cognitive radio [32,33], frequency-agile antennas [34], radio astronomy and RF space imaging [35][36][37][38][39][40][41][42][43][44][45], microwave imaging and remote sensing applications [46][47][48]. Radio telescopes [49][50][51][52] such as the square kilometer array (SKA) [53][54][55] requires algorithms for real-time UWB beamforming (70 MHz-1.4 GHz) with multiple beams [56].…”

Fast FPGA-architecture for fan/beam-steering in wave-digital RF aperture arrays

“…Two-dimensional (2-D) infinite impulse response (IIR) beam-and fan-filters are capable of directional enhancement of ultra wideband (UWB) propagating electromagnetic plane waves based on their directions of arrival (DOA), using a uniform linear array (ULA) of N -wideband antennas (Madanayake et al 2008;Mead 1998;Madanayake and Bruton 2010;Madanayake et al 2013). Such electronically-steerable beamforming is highly desirable in the receiving of radio signals from fast-moving sources (Erturk et al 2014;Owen et al 2012;Acedo et al 2011).…”