A Spatially Processed 3D Wideband Adaptive Conical Array System

This paper presents a novel structure for an adaptive fully spatially processed wideband conical antenna array. A major advantage of this configuration is the frequency invariance of the directional patterns of the array within a relatively large fractional bandwidth which makes this array a potential candidate for wideband and ultra wideband (UWB) technology applications. Furthermore, unlike conventional wideband antenna arrays which use delay lines or time-domain filters, this system relies on fully spatial processing of the incoming or transmitted signals using a single real multiplier for each antenna element, without utilising any phase shifters, digital filters or adjustable delays. Finally, due to the conical shape of the array configuration, beamforming in both azimuth and elevation angles is accomplished with symmetrical and uniform characteristics in all azimuth directions. © 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works

Memory-efficient approximate three-dimensional beamforming

Author Posting. © Acoustical Society of America, 2020. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 148(6), (2020): 3467-3480, doi:10.1121/10.0002852.Localization of acoustic sources using a sensor array is typically performed by estimating direction-of-arrival (DOA) via beamforming of the signals recorded by all elements. Software-based conventional beamforming (CBF) forces a trade-off between memory usage and direction resolution, since time delays associated with a set of directions over which the beamformer is steered must be pre-computed and stored, limiting the number of look directions to available platform memory. This paper describes a DOA localization method that is memory-efficient for three-dimensional (3D) beamforming applications. Its key lies in reducing 3D look directions [described by azimuth/inclination angles (ϕ, θ) when considering the array as a whole] to a single variable (a conical angle, ζ) by treating the array as a collection of sensor pairs. This insight reduces the set of look directions from two dimensions to one, enabling computational and memory efficiency improvements and thus allowing direction resolution to be increased. This method is described and compared to CBF, with comparisons provided for accuracy, computational speedup, and memory usage. As this method involves the incoherent summation of sensor pair outputs, gain is limited, restricting its use to localization of strong sources—e.g., for real-time acoustic localization on embedded systems, where computation and/or memory are limited.This work was partially supported by the Office of Naval Research, the Defense Advanced Research Projects Agency, and Lincoln Laboratory.2021-06-0

Design of an Ultra-Wideband Spiral Antenna for Ground-Penetrating Microwave Impulse Radar Applications

Radar systems that allow early detection of underground IEDs can save lives. The Microwave Impulse Radar (MIR) capable of IED detection requires antennas capable of transmitting sub-nanosecond pulses over ultra-wideband (UWB) frequency ranges. This thesis investigates the suitability of a novel MIR antenna for high-accuracy ground-penetrating radar (GPR) applications. Key GPR antenna considerations are pulse dispersion, size, and cost. UWB horn antennas provide excellent dispersion performance but limit system efficacy due to significant size and cost requirements. Micro-strip spiral antennas provide a low-cost alternative to UWB horn antennas, but common spiral designs demonstrate poor pulse dispersion performance. The article “Low-Dispersion Spiral Antennas” proposes using combination spirals, which combine the performance of multiple simple spiral antennas. This work investigates combination spiral suitability through 3D EM simulations and micro-strip fabrication. Testing results indicate that combination spirals possess improved pulse fidelity versus current spiral designs. Size and cost improvements are realized over horn antenna solutions. Updated simulation hardware and fabrication equipment could allow future combination spiral antennas to rival horn antenna performance

Virtual SATCOM, Long Range Broadband Digital Communications

The current naval strategy is based on a distributed force, networked together with high-speed communications that enable operations as an intelligent, fast maneuvering force. Satellites, the existing network connector, are weak and vulnerable to attack. HF is an alternative, but it does not have the information throughput to meet the distributed warfighting need. The US Navy does not have a solution to reduce dependency on space-based communication systems while providing the warfighter with the required information speed. Virtual SATCOM is a solution that can match satellite communications (SATCOM) data speed without the vulnerable satellite. It is wireless communication on a High Frequency (HF) channel at SATCOM speed. We have developed an innovative design using high power and gain, ground-based relay systems. We transmit extremely wide-wideband HF channels from ground stations using large directional antennas. Our system starts with a highly directional antenna with a narrow beam that enables increased bandwidth without interfering with other spectrum users. The beam focus and power provide a high SNR across a wideband channel with data rates of 10 Mbps; 1000 times increase in HF data speed. Our modeling of the ionosphere shows that the ionosphere has more than adequate bandwidth to communicate at 3000 km and high speeds while avoiding detection. We designed a flexible structure adjustable to the dynamic ionosphere. Our design provides a high-speed communications path without the geo-location vulnerability of legacy HF methods. Our invention will benefit mobile users using steerable beam forming apertures with wide bandwidth signals. This dissertation will focus on three areas: an examination of the ionosphere’s ability to support the channel, design of a phased array antenna that can produce the narrow beam, and design of signal processing that can accommodate the wideband HF frequency range. Virtual SATCOM is exciting research that can reduce cost and increase access to long-range, high data rate wireless communications

Robust vector sensor array processing and performance analysis

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.Includes bibliographical references (p. 179-186).Acoustic vector sensors, which measure scalar pressure along with particle motion (a vector quantity), feature many advantages over omnidirectional hydrophone sensors. A sizable literature exists on the theory of processing signals for many vector sensor array applications. In practice, however, mismatch (the difference between the assumed and actual system configurations), several noise processes and low sample support can pose significant problems. Processing techniques should be robust to these system imperfections and practical complexities. This thesis presents analytical results which quantify the effect of system mismatch and low sample support on acoustic vector sensor array performance. All arrays are susceptible to perturbations in array element locations; vector sensor arrays, however, are also sensitive to changes in sensor orientation. This is due to the fact that the particle motion vector measurement must be placed in a global reference frame. Gilbert and Morgan (1955) developed a statistical analysis with system mismatch for an array of scalar, omnidirectional elements. This thesis includes a vector sensor extension to their analysis by including sensor orientation perturbations. Theoretical expressions for the mean and variance of the vector sensor array spatial response are derived using a Gaussian perturbation model, with excellent comparisons between theory and simulation. Such analysis leads to insight into theoretical limits of both conventional and adaptive processing in the presence of system imperfections. One noteworthy result is that the vector aspect of the array "dampens" the effect of array mismatch, enabling deeper true nulls. This is accomplished because the variance of the vector sensor array spatial response (due to rotational, positional and filter gain/phase perturbations) decreases in the side lobes, unlike arrays of omnidirectional hydrophones.(cont.) As long as sensor orientation is measured within a reasonable tolerance, the beampattern variance dominates the average side lobe power response. Results from random matrix theory are used to characterize the effect of low sample support on signal detection using a vector sensor array. When using vector sensors, the effects of low sample support potentially increase by a factor of four since each element in a vector sensor array consists of a scalar hydrophone and up to three spatially orthogonal particle motion sensors. Also presented is an analysis of vector sensor array performance in ocean noise given an arbitrary spatial array configuration, sensor orientation and particle motion sensor type (velocity or acceleration). Several different ocean noise models exist, including isotropic noise, directional noise and realistic surface generated noise. Theoretical expressions are derived for array data covariance matrices in these different noise models for arbitrary array configuration and sensor orientation, which can in turn be used with optimal MVDR beamforming weights to analyze array gain. Using Monte Carlo simulations, we present examples of signal, noise and array gain variability as a function of mismatch intensity. Our analysis suggests that vector sensor array gain performance is less sensitive to rotational than to positional perturbations in the regions of interest. Hydrophones and particle motion sensors have very different response and noise characteristics. For instance, particle motion sensors are more sensitive to non acoustic, motion-induced noise than hydrophones. In a towed line array configuration, those sensors orthogonal to the direction of motion are exposed to higher intensities of flow noise at low frequencies than those coincident to the array axis.(cont.) Similarly, different dipole sensors may be exposed to varying degrees of rotational mismatch. Sensors may also rest on the seafloor, creating asymmetries. Recognizing these practical issues, we derive a new adaptive processing method customized to the unique characteristics of vector sensors and robust to mismatch and finite sample support. This new approach involves using multiple white noise gain constraints. During the past couple of decades, stationary vector sensor arrays have been built and tested, demonstrating improved gain and ambiguity lobe attenuation. Up until recently, however, very few towed vector sensor arrays had been built and tested. As such, many of the advantages of vector sensor arrays had only previously been shown in theory and/or with stationary arrays. We present results from sea trials in Monterey Bay, CA (2006) and Dabob Bay, WA (2007) towing a relatively short vector sensor array. Results highlight several of the distinct practical advantages of vector sensor arrays: resolution of spatial ambiguity (e.g., port/starboard and conical ambiguity), the ability to "undersample" an acoustic wave without spatial aliasing, quiet target recovery via clutter reduction, immunity to mismatch, improved array gain and enhanced detection performance.by Andrew Joseph Poulsen.Ph.D

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

Direction Finding With Mutually Orthogonal Antennas

Estimating the direction-of-arrival of incident electromagnetic plane waves (a.k.a. direction finding or DF) has typically been accomplished in the past using arrays of spatially separated antennas. The spatial separation produces a delay in each antenna\u27s measured voltage due to the finite propagation time as the wave strikes each antenna in succession. In this thesis, we approach the problem differently by using three antennas that have been oriented in orthogonal directions but are co-located at the origin of a coordinate system. Being co-located, this mutually orthogonal arrangement of antennas cannot detect the propagation phase delay and must rely solely on the polarization properties of the incident waves. Using the vector effective height concept, three algorithms are formulated. The first algorithm estimates the direction-of-arrival by computing a vector that is perpendicular to the locus of the instantaneous electric field vector. The second and third algorithms are based on the well-known maximum likelihood and MUSIC algorithms. Simulation results show that each algorithm can estimate the direction-of-arrival with a root-mean-squared error within 1° or less when the incident wave is circularly polarized, the antennas are small compared to wavelength, and the signal-to-noise ratio is above 20dB

Characterization of an Impulse Radiating Antenna in the Near Field

The biological effects of intense sub-nanosecond pulses on tissues or cells are in the dielectric domain and not based on thermal loading as in the conventional microwave radiation, which may lead to an entirely new approach of modifying cell functions. Moreover, the resulting cell functional change may be detected with higher resolution by broadband, sub-nanosecond pulses than conventional narrowband systems. The delivery of intense sub-nanosecond pulses to near-field biological tissues, however, has not been studied, not mentioning the focal depth and volume. In this dissertation, for the first time, an impulse radiating antenna with a balanced feed structure is studied for focusing electromagnetic fields in the near-field for the purpose of therapy and target detection. This antenna has the potential of radiating sub-nanosecond pulses up to 100 kV. It is a travelling wave antenna with the conical transmission lines as the wave launcher. The electric field distribution is studied both through experiment and simulation studies. Results show a close agreement between experimental and simulated results. The antenna focal spot is found to be 32cm wide in axial direction and 10cm wide in lateral direction near the focal point, which is 16cm from the aperture plane. Enhancement of focal spot size and increase of field at the focal point is studied with a dielectric lens. The use of a dielectric lens to match the waves to the target medium increases coupling between the antenna and the target medium, thereby increasing the field strength at focus and decreasing the focal spot size. Experimental study shows an increase in electric field at focus by a factor of 3 and an increase in resolution by a factor of 1.5. The delivery of sub-nanosecond pulses to tissues is studied with the antenna and the combination of the lens and antenna. While a lossless lens may enhance the coupling of the radiation to the tissue, the trend of decreasing in intensity as the wave penetrates remains the same as the case where only an antenna is used. However, the trend can be reversed or modified by a lossy lens, which contains some resistive materials as part of its structure. With a lossy lens, a local maximum forms in the deep region (6cm in depth) of the tissue. The design of such lossy lens is novel and provides an extra means to control the electric field distribution in the target