Small Phased Array Research Articles

Portable ultrasound-guided keyhole evacuation of intracerebral hemorrhage: a detailed case report highlighting technical nuances.

Intracerebral hemorrhage (ICH) is a common neurosurgical emergency that is associated with high morbidity and mortality. Minimally invasive or endoscopic hematoma evacuation has emerged in recent years as a viable alternative to conventional large craniotomies. However, accurate trajectory planning and placement of the tubular retractor remains a challenge. We describe a novel technique for handheld portable ultrasound-guided minimally invasive endoscopic evacuation of supratentorial hematomas. A 64-year-old male diagnosed right hematoma (48.5 mL) at the basal ganglia was treated with emergent ultrasound-guided endoscopic transtubular evacuation through a small craniotomy. Ultrasound-guidance facilitated optimal placement of the tubular retractor into the long axis of the hematoma, and allowed for near-total evacuation, reducing iatrogenic tissue damage by mitigating the need for wanding or repositioning of the retractor. The emergence of a new generation of small portable phased array ultrasound probes with improved resolution and clarity has broadened ultrasound's clinical applications.

Development of a Front End Array for Broadband Phased Array Receiver

The receiver is a signal receiving device placed at the focus of the telescope. In order to improve the observation efficiency, the concept of phased array receiver has been proposed in recent years, which places a small phased array at the focal plane of the reflector, and flexible pattern and beam scanning functions can be achieved through a beamforming network. If combined with the element multiplexing, all beams within the entire field of view can be observed simultaneously to achieve continuous sky coverage. This article focuses on the front-end array of phased array receiver at 0.7–1.8 GHz for QiTai Telescope, and designs a Vivaldi antenna array of PCB structure with dual line polarization. Each polarization antenna is designed to arrange in a rectangle manner by 11 × 10. Based on the simulation results of the focal field, 32, 18, and eight elements were selected to form one beam at 0.7, 1.25, and 1.8 GHz. An analog beamforming network was constructed, and the measured gains of axial beam under uniform weighting were 19.32, 13.72, and 15.22 dBi. Combining the beam scanning method of reflector antenna, the pattern test of different position element sets required for PAF beam scanning was carried out under independent array. The pattern optimization at 1.25 GHz was carried out by weighting method of conjugate field matching. Compared with uniform weighting, the gain, sidelobe level, and main beam direction under conjugate field matching have been improved. Although the above test and simulation results are slightly different, which is related to the passive array and laboratory testing condition, the relevant work has accumulated experience in the development of the front-end array for the phased array receiver, and has good guiding significance for future performance verification after the array is installed on the telescope.

A Transmit-Receive Phased Array for Microbubble-Mediated Focused Ultrasound Brain Therapy in Small Animals.

This study aimed to design, construct, and evaluate a dual-mode phased array for MB-mediated FUS brain therapy in small animals. A 256-element sparse hemispherical array (100 mm diameter) was fabricated by installing 128 PZT cylinder transmitters (f0 = 1.16 MHz) and 128 broadband PVDF receivers within a 3D-printed scaffold. The transmit array's focal size at the geometric focus was 0.8 mm × 0.8 mm × 1.7 mm, with a 31 mm/27 mm (lateral/axial) steering range. The receive array's point spread function was 0.6 mm × 0.6 mm × 1.5 mm (1.16 MHz source) at the geometric focus, and sources were localized up to 30 mm/16 mm (lateral/axial) from geometric focus. The array was able to spatially map MB cloud activity in 3D throughout a vessel-mimicking phantom at sub-, ultra-, and second-harmonic frequencies. Preliminary in-vivo work demonstrated its ability to induce localized BBB permeability changes under 3D sub-harmonic MB imaging feedback in a mouse model. Small form factor transmit-receive phased arrays enable acoustic imaging-controlled FUS and MB-mediated brain therapies with high targeting precision required for rodent studies. Dual-mode phased arrays dedicated for small animal use will facilitate high-throughput studies of FUS-mediated BBB permeability enhancement to explore novel therapeutic strategies for future clinical application.

Towards optimal phased-array tile configurations for large new-generation radio telescopes and their application to NenuFAR

Context. Recent instrumental developments have aimed to build large digital radio telescopes made of ~100k antennas. The massive data rate required to digitise all elements drives the instrumental design towards the hierarchical distribution of elements by groups of 𝒪(10) that form small analogue phased arrays that lower the computational burden by one to two orders of magnitude. Aims. We study possible optimal layouts for a tile composed of five to 22 identical elements. We examine the impact of the tile layout on the overall response of an instrument. Methods. We used two optimisation algorithms to find optimal arrangements of elements in the tile using: (i) a deterministic method (Kogan) based on beam pattern derivative properties; and (ii) a stochastic method (modified simulated annealing) to find global optima minimising the side-lobe level while increasing the field of view (FOV) of the tile, a required condition for all-sky surveys. Results. We find that optimal tile arrangements are compact circular arrays that present some degree of circular symmetry while not being superimposable to any rotated version of themselves. The ‘optimal’ element number is found to be 16 or 17 antennas per tile. These could provide a maximum side-lobe level (SLL) of −33 dB (−24 dB) used with dipole (isotropic) elements. Due to constraints related to the analogue phasing implementation, we propose an approaching solution but with a regular arrangement on an equilateral lattice with 19 elements. By introducing random relative rotations between tiles, we compared and found that the 19-element equilateral tile results in better grating lobe mitigation and a larger FOV than that of rectangular tiles of 16 antennas. Conclusions. Optimal tile arrangements and their regular versions are useful to maximise the sensitivity of new-generation hierarchical radio telescopes. The proposed solution was implemented in NenuFAR, a pathfinder of SKA-LOW at the Nançay Radio Observatory.

Rainbow-Link: Beam-Alignment-Free and Grant-Free mmW Multiple Access Using True-Time-Delay Array

The millimeter-wave (mmW) communications is a key enabling technology in 5G to provide ultra-high throughput. Current mmW technologies rely on analog phased arrays to realize beamforming gain and overcome high path loss. However, due to a limited number of simultaneous beams that can be created with analog/hybrid phased antenna arrays, the overheads of beam training and beam scheduling become a bottleneck for emerging networks that need to support a large number of users and low latency applications. This paper introduces rainbow-link, a novel multiple access protocol, that can achieve low latency and massive connectivity by exploiting wide bandwidth at mmW frequencies and novel analog true-time-delay array architecture with frequency dependent beamforming capability. In the proposed design, the network infrastructure is equipped with the true-time-delay array to simultaneously steer different frequency resource blocks towards distinct directions covering the entire cell sector. Users or devices, equipped with a narrowband receiver and either a single antenna or small phased antenna array, connect to the network based on their angular positions by selecting frequency resources within their rainbow beam allocation. Rainbow-link is combined with a contention-based grant-free access to eliminate the explicit beam training and user scheduling. The proposed design and analysis show that rainbow-link grant-free access is a potential candidate for latency-critical use cases within massive connectivity. Our results show that, given less than 1e-5 probability of packet loss, a rainbow-link cell, over 1 GHz bandwidth using 64 element antenna array, attains sub-millisecond user-plane latency and Mbps user rates with an approximate 400m line-of-sight coverage and a density of up to 5 active single antenna users per second per meter square.

ACPR Improvement in Large Phased Arrays With Complex Modulated Waveforms

Phased array transmit systems use a number of antennas to combine RF power amplifiers (PAs) in free space. If all the RF channels are identical, then the transmit spectrum in the far field, including both linear and nonlinear components, would be a scaled version of the output spectrum of each channel. However, it is found that random variations in the nonlinear components (AM–AM and AM–PM) between the channels improve the nonlinearity of the overall array as the number of elements increases. In this article, detailed measurements are done on an 8- to 256-element phased array and show that the adjacent channel power ratio (ACPR), which is one metric of linearity, improves with the number of elements at a fixed backoff from the 1-dB compression point. Also, for a100-Mbaud 64-QAM signal and a fixed ACPR of −32 dBc, a 256-element phased array can be operated at $P_{1\,\text {dB}} - 2$ dB, while an eight-element phased array needs to be operated at $P_{1\,\text {dB}} - 4$ dB to achieve the same ACPR level. These improvements were found to occur at broadside (no scan) for any scan angle and for different modulated waveforms (64-QAM, 16-QAM, QPSK, and so on). This result has great implications on the overall efficiency of 5G phased arrays since it implies that large phased arrays can be operated at less backoff than the small phased arrays (or single antennas with high-PAs). Thus, in practical implementations and taking the ACPR as the figure of merit, large phased arrays are ~2 dB more efficient than what is predicted by standard system simulations that assume the same nonlinear response for all the phased array channels.

Deployable cylindrical phased-array applicator mimicking a concentric-ring configuration for minimally-invasive delivery of therapeutic ultrasound

A novel design for a deployable catheter-based ultrasound applicator for endoluminal and laparoscopic intervention is introduced. By combining a 1D cylindrical ring phased array with an expandable paraboloid or conical-shaped balloon-based reflector, the applicator can be controllably collapsed for compact delivery and deployed to mimic a forward-firing larger diameter concentric ring array with tight focusing and electronic steering capabilities in depth. Comprehensive acoustic and biothermal parametric studies were employed to characterize the capabilities of the applicator design as a function of transducer dimensions, phased array configuration, and balloon reflector geometry. Modeling results indicate that practical balloon sizes (43–57 mm expanded diameter), transducer array configurations (e.g. 1.5 MHz, 10 mm OD × 20 mm length, 8 or 16 array elements), and sonication durations (30 s) are capable of producing spatially-localized acoustic intensity focal patterns and ablative thermal lesions (width: 2.8–4.8 mm; length: 5.3–40.1 mm) in generalized soft tissue across a 5–100 mm depth range. Larger focal intensity gain magnitudes and narrower focal dimensions are attainable using paraboloid-shaped balloon reflectors with natural geometric focal depths of 25–55 mm, whereas conical-shaped reflectors (angled 45–55°) produce broader foci and extend electronic steering range in depth. A proof-of-concept phased array applicator assembly was fabricated and characterized using hydrophone and radiation force balance measurements and demonstrated good agreement with simulation. The results of this study suggest that combining small diameter cylindrical phased arrays with expandable balloon reflectors can enhance minimally invasive ultrasound-based intervention by augmenting achievable focal gains and penetration depths with dynamic adjustment of treatment depth.

Deep Learning for Tuning Optical Beamforming Networks

In communication between planes and satellites, Optical Beamforming Networks (OBFNs), which rely on many small and flat Phased Array Antennas (PAAs), need to be tuned in order to receive signals from specific angles. In this paper, we develop a deep neural network representation of tuning OBFNs. The problem of tuning an OBFN is in many aspects similar to training a deep neural network. We present a way to exploit the special structure of OBFNs into deep neural network and an algorithm for tuning OBFNs based on feedback that can be easily measured in real system. Training data, which consists of full signals, can be measured, and therefore is used in this paper. For pilot signals, the desired signal is known explicitly. Given the configuration of OBFNs and all nominal parameters required, it was verified in simulation that the deep neural network can be used to tune large scale OBFNs for any desired delays.

An Integrable SIW Phase Shifter in a Partially Magnetized Ferrite LTCC Package

There is a growing need for small size integrable phased antenna arrays for emerging satellite communications on-the-move applications. Traditional ferrite-based phase shifters are generally bulky due to the need of electromagnets for biasing, yielding them unsuitable for this kind of application. In this paper, a novel compact light-weight substrate integrated waveguide (SIW) based phase shifter realized in a multi-layer ferrite low-temperature co-fired ceramic package with embedded bias windings is reported. By using embedded windings and operating the material in a partially magnetized state, the required bias magnetic field could be significantly reduced from typically about 1000 Oe to less than 50 Oe. Moreover, the presented phase shifter has two modes of operations corresponding to two different biasing scenarios of the SIW, namely, symmetric and anti-symmetric bias. Under anti-symmetric bias, the phase shifter can achieve high nonreciprocal phase shift, whereas under symmetric bias, the phase shift is reciprocal, but the available phase shift is less than the anti-symmetric case. The fabricated prototype operates in the 11.5–13.5-GHz range and has a peak figure of merit (phase shift per decibel of loss) of 102 $^{\circ}/{\hbox{dB}} $ and a maximum phase shift per unit length of 153 $^{\circ} /{\hbox{cm}}$ , which are more than five times the previously reported figures for this technology. Due to the use of embedded windings, the presented phase shifter offers a huge size reduction from the order of ${\hbox{cm}}^{3}$ to ${\hbox{mm}}^{3}$ , making it particularly useful for mobile phased-array applications.

Array-Fed Partially Reflective Surface Antenna With Independent Scanning and Beamwidth Dynamic Control

In this communication we present a concept of a partially reflective surface (PRS) antenna capable of independent beam-scanning and beamwidth dynamic control. The beamwidth is controlled by reconfiguring the PRS reflectivity via embedded varactor diodes, while the beam is steered by using a small phased array in the H-plane as a source antenna exciting the Fabry-Pérot cavity. A fully operational prototype is fabricated and measured upon reconfiguration, demonstrating the viability of the concept and good agreement between simulated and measured results. The achieved beamwidth variation is from 18.7° to 22.4°, with the scanning range of 15° and 20° for the narrowest and the widest beamwidth, respectively.

Effect of feed array configuration on the Field-of-View of radio telescope antenna

Phased Array Feed (PAF) is a small two-dimensional phased array antenna, playing a role as the multi-beam feed for the reflector antenna. The prominent capability of large continuous Field-of-View (FoV) coverage and fast survey speed makes PAF the promising feed for radio telescopes. In this paper, the effect of feed array of PAF on the gain fluctuations over FoV is analyzed on a simplified model of the Five-hundred-meter Spherical Aperture radio Telescope (FAST), including illumination pattern edge taper, element spacing, element arrangement and element amount. And the differences between rectangular and hexagonal array arrangements are compared. The relationship between the FoV and array configuration are concluded at last.

A Small Ku-Band Polarization Tracking Active Phased Array for Mobile Satellite Communications

A compact polarization tracking active phased array for Ku-band mobile satellite signal reception is presented. In contrast with conventional mechanically tracking antennas, the approach presented here meets the requirements of beam tracking and polarization tracking simultaneously without any servo components. The two-layer stacked square patch fed by two probes is used as antenna element. The impedance bandwidth of 16% for the element covers the operating frequency range from 12.25 GHz to 12.75 GHz. In the presence of mutual coupling, the dimensional parameters for each element of the small 7 × 7 array are optimized during beam scanning and polarization tracking. The compact polarization tracking modules based on the low-temperature cofired ceramic (LTCC) system-in-package (SiP) technology are proposed. A small active phased array prototype with the size of 120 mm (length) × 120 mm (width) × 55 mm (height) is developed. The measured polarization tracking patterns of the prototype are given. The polarization tracking beam can be steered in the elevation up to 50°. The gain of no less than 16.0 dBi and the aperture efficiency of more than 50% are obtained. The measured and simulated polarization tracking patterns agreed well.

Intelligent z -plane boundary condition-particle swarm optimiser for small array pattern synthesis

This study concerns the radiation performance improvement of small periodic linear phased arrays in the presence of mutual coupling. An approach using a particle swarm optimiser (PSO) coupled with Schelkunoff's z-plane unit circle is proposed, with z-plane zeros constrained using adaptive boundary conditions (termed the intelligent z-plane boundary condition-PSO). It is shown that the proposed optimisation scheme has successfully achieved the target results for a range of problems presented including low-sidelobe scanned beam, and sector-beam pattern synthesis. The approach has consistent and faster convergence when compared with competitive techniques. Results showing significant improvement are presented using a Bowtie dielectric resonator antenna and uniform hemispherical elements.

Direction finding system for automotive applications using small phased antenna array

Direction finding technique for car location in large parking lots is presented.Method uses compact phased antenna array with two-bit phase shifters. Proposed array operates as an intermediary between a car owner hand-held unit and car electronic circuit with small omnidirectional antenna. Only one antenna array for all cars is that utilized for car finding service. Experimental results confirm math estimations and MATLAB simulation. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:2441–2446, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26275

A New Transesophageal Probe for Newborns

Current transesophageal probes are designed for adults and are used both in the operating theatre for monitoring as well as in the outpatient clinic for patients with specific indications, like obesity, artificial valves, etc. For newborns (<5 kg), transesophageal echocardiography (TEE) is not possible because the current probes are too big for introducing them into the esophagus. There is a clear need for a small probe in newborns that are scheduled for complicated cardiac surgery and catheterization. We present the design and realization of a small TEE phased array probe with a tube diameter of 5.2 mm and head size of only 8.2–7 mm. The number of elements is 48 and the center frequency of the probe is 7.5 MHz. A separate clinical evaluation study was carried out in 42 patients (Scohy et al. 2007). (E-mail: n.dejong@erasmusmc.nl)

In vivo high‐resolution imaging of the injured rat spinal cord using a 3.0T clinical MR scanner

To investigate the feasibility of obtaining high-resolution MR images for the detection of pathological changes occurring in the injured rat spinal cord with a routine clinical 3.0T imaging system. Adult female Fischer 344 rats received thoracic spine contusion injuries. In vivo MR imaging was performed on days 1 and 43 postinjury with a clinical head 3.0T imaging system equipped with a dedicated small animal 4-channel phased array spine surface coil using T2-weighted turbo spin-echo and T1-weighted spin-echo sequences. The acquired images provide good spatial resolution allowing reliable gray/white matter differentiation in the intact spinal cord as well as detection of hemorrhage, edema, and cystic degenerative changes in the injured rat spinal cord as confirmed by correlation with structural alterations in histological sections. Results from the present study demonstrate that a routine clinical MR imaging system can be employed for noninvasive analysis of pathological changes occurring in the injured rat spinal cord and thus might represent a more broadly available, powerful tool to monitor the effects of experimental therapeutic interventions in vivo.

An L‐band, circularly polarised, dual‐feed, cavity‐backed annular slot antenna for phased‐array applications

AbstractThe results of a parametric study for the development of an L‐band, circularly polarised, dual‐feed, cavity‐backed annular slot antenna is presented. The study includes detailed numerical simulations and measurements on a prototype with different ground planes in order to assess the antenna's applicability as an element in a small phased array antenna. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 873–878, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21504

Small Ku-band phased array antenna system

A four-element phased array antenna prototype with varactor tuning has been constructed. The design employs aperture-fed quarter-wave patch elements and loaded-line phase shifters, having a phase adjustment range of about 50/spl deg/, which enables beam steering up to 13/spl deg/ from the array boresight. The system is suitable as a building block for larger arrays and shows as such a maximum gain of 7.7 dBi and an impedance bandwidth of 1 GHz. The sidelobe level is better than -13 dB. Problems encountered include parasitic resonances which disturb matching, and partially deteriorate the radiation pattern. Additionally, mechanical manufacturing tolerances of the microstrip boards were not always adequate, whereby a 6% shift in the center frequency, some impedance errors, and phasing inaccuracies were observed.

Retrodirective beams and their application to low sidelobe pattern synthesis in small planar phased arrays

Beam synthesis remains one of the most difficult problems for an antenna array designer, this task being made more difficult when one limits the number of elements to a handful. Pattern synthesis in planar arrays is often achieved by the sampling of a continuous aperture distribution at the element locations. In the case of arrays of limited numbers of elements this produces errors that can unacceptably distort the radiation pattern. When one also then considers the effects of mutual coupling between the antenna elements, the application of ideal element weights derived in this way are no longer valid. In the paper a technique is presented, using the concept of retrodirective beams, that can achieve a low sidelobe beam from a continuous distribution on a circular aperture. The theory is then extended to include a planar array of antenna elements. This is achieved by the addition of retrodirective beams to the uniform beam pattern of the array. Measured data is presented for a small planar array antenna using the derived method. A method for correction of the element weights, to minimise the effects of mutual coupling, producing low sidelobe radiation patterns is then applied. No knowledge of the antenna array&apos;s coupling coefficients are required.

Real-time null steering by the CLEAN technique

The main attraction of the CLEAN technique is its simple algorithm, but in its previously existing form it is still too complex to be implemented in real time in a small phased array. A more effective CLEAN version is proposed for small realtime phased array systems based on relatively low-performance digital signal processors, and it is shown how real-time null steering may be achieved.