Digital Phased Array Research Articles

60GHz single-chip CMOS digital radios and phased array solutions for gaming and connectivity

In this paper, we present four examples of highly integrated 60 GHz single-chip CMOS 90 nm digital radios and phased array solutions. These solutions include for the first time digital-to-analog/analog-to-digital conversion and embedded multi-gigabit mixed signal modem requiring no external processing. This convergence of 60 GHz CMOS digital radio, low power multi-gigabit mixed-signal processing and digital signal processing on a single chip offers the lowest energy per bit transmitted wirelessly at multi-gigabit rate to meet the very stringent low-power specifications for battery operated consumer electronic portable devices. Layout and temperature dependent 60 GHz CMOS 90 nm model development and critical high performance analog and mixed building blocks are presented as fundamental enablers for single chip integration. The designs have been optimized for robustness against process variation and temperature, and verified by measurement results.

High resolution fast digital photoacoustic CT for breast cancer diagnosis

Photoacoustic imaging combines advantages of both ultrasound imaging and optical imaging to provide high ultrasonic resolution and high optical contrast in noninvasive medical images. A photoacoustic computer tomography （PCT） system with a focused digital phased array transducer is proposed. In particular each element of the transducer array has a thin cylindrical ultrasonic lens to select 2D image plane and suppress the out-of-plane signals to realize photoacoustic computed tomography. A fast full-view photoacoustic imaging system for visualizing tissue structures using a linear transducer array with combined scan, whies; detects photoacoustic signals by combined electronic and mechanical scanning. An improved limited-field filtered back projection algorithm with directivity factors was applied to reconstruct the optical absorption distribution and further improve the lateral resolution. In the experiment, the spatial resolution of this imaging system is determined as 0.2mm, and the slice resolution of Z axis is 1.5mm. Mechanical step scanning was performed, leading to a measurement time of 6.4 seconds per position, and a total scan duration of 150 seconds to obtain the two-dimensional photoacoustic image. High spatial resolution of 2D photoacoustic vascular image and quasi-3D photoacoustic CT for breast cancer imaging are achicned. The experimental results demonstrate that this method and imaging system can realize the high resolution photoacoustic tomography wtich can be applied to noninvasive detection of early breast cancer.

Low-power Tx module for high-resolution continuous programmable phase shift

A novel phase shifter topology for digital phased antenna arrays based on a low-power phase control block joint with an innovative PLL design is presented. Experimental results obtained by a prototype are reported validating the architecture capabilities.

Performance characterization of FPGA techniques for calibration and beamforming in smart antenna applications

A field-programmable gate array (FPGA) implementation is presented for a smart antenna application employing digital beamforming. The digital beamforming is performed at the RF signal carrier frequency by means of bandpass (IF) sampling, using high-speed 8-b analog-to-digital converters. The digital phased array receiver presented in this paper consists of an eight-channel system with back-end FPGAs for calibration and digital beamforming processing. The system operates in the L-band (1.8-2 GHz) with various bandwidths depending on the application and FPGA processing requirements. This paper focuses on two main topics, calibration methodologies and FPGA implementation for calibration and digital beamforming, and includes several performance trades. Results presented include real measured data that were collected with the system and processed via FPGAs.

Digital phased array beamforming using single-bit delta-sigma conversion with non-uniform oversampling.

Digital beamforming based on oversampled delta-sigma (delta sigma) analog-to-digital (A/D) conversion can reduce the overall cost, size, and power consumption of phased array front-end processing. The signal resampling involved in dynamic delta sigma beamforming, however, disrupts synchronization between the modulators and demodulator, causing significant degradation in the signal-to-noise ratio. As a solution to this, we have explored a new digital beamforming approach based on non-uniform oversampling delta sigma A/D conversion. Using this approach, the echo signals received by the transducer array are sampled at time instants determined by the beamforming timing and then digitized by single-bit delta sigma A/D conversion prior to the coherent beam summation. The timing information involves a non-uniform sampling scheme employing different clocks at each array channel. The delta sigma coded beamsums obtained by adding the delayed 1-bit coded RF echo signals are then processed through a decimation filter to produce final beamforming outputs. The performance and validity of the proposed beamforming approach are assessed by means of emulations using experimental raw RF data.

A statistical model for the error bounds of an active phased array antenna for SAR applications

A model for the theoretical error bounds for the radiometric calibration of SAR imagery is described. The model is then applied utilizing the radar system parameters that will be used in the project PHARUS (Phased Array Universal SAR), a Dutch polarimetric airborne C-band universal SAR, which is currently under construction. An error model for the phased array antenna pattern is presented. This model was applied to a 16*8 phased array antenna to determine the influence of errors in the T/R modules and angle variations of the beam direction. For a wide range of variances the model is in good agreement with the exact solution, but with far less computer effort. Other, more complicated, antennas can be analyzed in a straightforward way. The model can be used as a design tool for digital phased array radar. >

A New Digital Phased Array System for Dynamic Focusing and Steering with Reduced Sampling Rate

In order to enhance the resolution of the ultrasonic B-mode image, digital techniques for dynamic focusing and steering have been receiving a great deal of attention for a long time. In this paper, we present the theory and preliminary experimental results for a new architecture of a fully digital B-mode imaging system with this desired feature. The system employs the Pipelined-Sampled-Delay-Focusing (PSDF) scheme to eliminate the bulky memory addressing and interpolation circuits which are needed in conventional digital imaging systems. To reduce hardware requirements and the bandwidth required for digital processing, we describe an efficient method to generate the sampling clocks for dynamic focusing and steering and some modified bandwidth sampling techniques to reduce the sampling rate for signal digitization. Using these methods, it is possible to achieve dynamic focusing and steering in real-time sector imaging using a linear phased array.

A new digital phased array system for dynamic focusing and steering with reduced sampling rate

In order to enhance the resolution of the ultrasonic B-mode image, digital techniques for dynamic focusing and steering have been receiving a great deal of attention for a long time. In this paper, we present the theory and preliminary experimental results for a new architecture of a fully digital B-mode imaging system with this desired feature. The system employs the Pipelined-Sampled-Delay-Focusing (PSDF) scheme to eliminate the bulky memory addressing and interpolation circuits which are needed in conventional digital imaging systems. To reduce hardware requirements and the bandwidth required for digital processings, we describe an efficient method to generate the sampling clocks for dynamic focusing and steering and some modified bandwidth sampling techniques to reduce the sampling rate for signal digitization. Using these methods, it is possible to achieve dynamic focusing and steering in real-time sector imaging using a linear phased array.

Nonlinearities in digital manifold phased arrays

In digital beamforming (DBF), the phase shifter is functionally replaced with a receiver and digital phase rotation. A Taylor series expansion of mixer nonlinearities is used to generate receiver intermodulation spectrums respective of the element position and the iso-Doppler wavefront directions of signal arrival across the array. The dominant intermodulation distortion at each element experiences linear phase errors across the array proportional to the harmonic number and the desired steering direction phase gradient. The array distortion signals are reduced relative to the desired signal by the array factor sidelobe isolation when desired collimation directions exceed a few beamwidths of scan off the array normal vector. The result of the nonlinear down conversion analysis is extended to inphase and quadrature imbalances and batch manufacturing tolerances for element receivers.

Computer simulation of synthesizing images by digital phased arrays

A method of synthesizing images by digital phased arrays is proposed. Following this method a numerical experiment of image synthesis is conducted to simulate arrays of 64 × 64 by computer. Each array element is assigned a binary digit, that is, it is either excited or nonexcited.

Granularity of beam positions in digital phased arrays

Many phased arrays are designed to use digital or digitalized phase shifters in which the phase shift varies in discrete steps rather than continuously. In such cases, the beam can be steered only in discrete steps. Granularity, defined as the finest realizable increment between adjacent beam positions, is an important parameter in the description of the performance of a phased array antenna using digital phase shifters. Two approaches to the problem of determining granularity are developed in this paper. The first is based upon the expansion by its moments of complex aperture distribution functions; the second is based upon approximating the actual discrete phase distribution by a linear continuous one. Results of the two approaches are shown to be in excellent agreement, with a variation of less than 3.6 percent being obtained. Arrays employing binary digital phase shifters are explicitly considered, but the techniques can be generalized to other types of digital, or digitalized, phase shifters. For other than the first beam position, there are alternate phase distributions which might be used to obtain a given beam position. The selection of a specific phase distribution depends, at least in part, upon the computer logic and round-off procedures. It is shown that these alternate phase distributions do not produce large differences in the beam position. The spread in beam position is between 2 and 3 percent for the alternate distributions. The effect of an amplitude taper on granularity is also considered. It is found that when the edge elements are less intensely illuminated than those at the center, the first beam position off-broadside is nearer broadside than for an array having the same phase distribution but uniform amplitude. The average granularity of a phased array has been determined, and is plotted against the number of elements with the number of phase bits as a parameter.