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Polarization ratio determination with two identical linearly polarized antennas

July 9, 2017
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Conference Paper
Author:
Herbert M. Aumann
…
Published in:
2017 IEEE AP-S Symp. on Antennas and Propagation and USNC Radio Science Meeting, 9-14 July 2017.
Topic:
antennas
R&D area:
R&D group:

Summary

This paper describes a method for determining the complex polarization ratio using two identical, linearly polarized antennas. By Fourier transform analysis of s21 measurements with one of the antennas rotating about its axis a circular polarization ratio is derived which can be transformed into an equivalent linear polarization ratio. A linearly polarized reference antenna is not required. The technique was verified by electromagnetic simulations and illustrated by measurements in an anechoic chamber with two 3.3 GHz square patch antennas.
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Summary

This paper describes a method for determining the complex polarization ratio using two identical, linearly polarized antennas. By Fourier transform analysis of s21 measurements with one of the antennas rotating about its axis a circular polarization ratio is derived which can be transformed into an equivalent linear polarization ratio. A...

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Polarization ratio determination with two identical linearly polarized antennas

A polarization technique for mitigating low-grazing-angle radar sea clutter

June 4, 2017
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Conference Paper
Author:
Molly K. Crane
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Published in:
IEEE Int. Microwave Symp., 4-9 June 2017.
Topic:
radar
R&D area:
R&D group:

Summary

Traditional detection schemes in conventional maritime surveillance radars may suffer serious performance degradation due to sea clutter, particularly in low-grazing-angle (LGA) geometries. In such geometries, typical statistical assumptions regarding sea clutter backscatter do not hold. Trackers can be overwhelmed by false alarms, while objects of interest can be challenging to detect. Despite several decades of attempts to devise a means of mitigating the effects of LGA sea clutter on traditional detection schemes, minimal progress has been made in developing an approach that is both robust and practical. To supplement work exploring whether polarization information might offer an effective means of enhancing target detection in sea clutter, MIT Lincoln Laboratory (MIT LL) collected a fully polarimetric X-band radar dataset on the Atlantic coast of Massachusetts Cape Ann in October 2015. Leveraging this dataset, MIT LL developed Polarimetric Co-location Layering (PCL), an algorithm that uses a fundamental polarimetric characteristic of sea clutter to retain detections on objects of interest while reducing the number of false alarms in a conventional singlepolarization radar by as many as two orders of magnitude. PCL is robust across waveform bandwidths, pulse repetition frequencies, and sea states. Moreover, PCL is practical: It can plug directly into the standard radar signal processing chain.
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Summary

Traditional detection schemes in conventional maritime surveillance radars may suffer serious performance degradation due to sea clutter, particularly in low-grazing-angle (LGA) geometries. In such geometries, typical statistical assumptions regarding sea clutter backscatter do not hold. Trackers can be overwhelmed by false alarms, while objects of interest can be challenging to...

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A polarization technique for mitigating low-grazing-angle radar sea clutter

Wind turbine interference mitigation using a waveform diversity radar

April 27, 2017
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Journal Article
Author:
Steven I. Krich
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Published in:
IEEE Trans. Aerosp. Electron. Syst., Vol. 53, No. 2, April 2017, pp. 805-15.
Topic:
radar
R&D area:
R&D group:

Summary

Interference from the proliferation of wind turbines is becoming a problem for ground-based medium-to-high pulse repetition frequency (PRF) pulsed–Doppler air surveillance radars. This paper demonstrates that randomizing some parameters of the transmit waveform from pulse to pulse, a filter can be designed to suppress both the wind turbine interference and the ground clutter. Furthermore, a single coherent processing interval (CPI) is sufficient to make an unambiguous range measurement. Therefore, multiple CPIs are not needed for range disambiguation, as in the staggered PRFs techniques. First, we consider a waveform with fixed PRF but diverse (random) initial phase applied to each transmit pulse. Second, we consider a waveform with diverse (random) PRF. The theoretical results are validated through simulations and analysis of experimental data. Clutter-plus-interference suppression and range disambiguation in a single CPI may be attractive to the Federal Aviation Administration and coastal radars.
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Summary

Interference from the proliferation of wind turbines is becoming a problem for ground-based medium-to-high pulse repetition frequency (PRF) pulsed–Doppler air surveillance radars. This paper demonstrates that randomizing some parameters of the transmit waveform from pulse to pulse, a filter can be designed to suppress both the wind turbine interference and...

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Wind turbine interference mitigation using a waveform diversity radar

Learning to tutor from expert demonstrators via apprenticeship scheduling

February 4, 2017
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Conference Paper
Author:
Matthew C. Gombolay
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Published in:
AAAI-17 Workshop on Human-Machine Collaborative Learning, 4 February 2017.
Topic:
machine learning
R&D area:
R&D group:

Summary

We have conducted a study investigating the use of automated tutors for educating players in the context of serious gaming (i.e., game designed as a professional training tool). Historically, researchers and practitioners have developed automated tutors through a process of manually codifying domain knowledge and translating that into a human-interpretable format. This process is laborious and leaves much to be desired. Instead, we seek to apply novel machine learning techniques to, first, learn a model from domain experts' demonstrations how to solve such problems, and, second, use this model to teach novices how to think like experts. In this work, we present a study comparing the performance of an automated and a traditional, manually-constructed tutor. To our knowledge, this is the first investigation using learning from demonstration techniques to learn from experts and use that knowledge to teach novices.
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Summary

We have conducted a study investigating the use of automated tutors for educating players in the context of serious gaming (i.e., game designed as a professional training tool). Historically, researchers and practitioners have developed automated tutors through a process of manually codifying domain knowledge and translating that into a human-interpretable...

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Learning to tutor from expert demonstrators via apprenticeship scheduling

A rotating source polarization measurement technique using two circularly polarized antennas

October 30, 2016
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Conference Paper
Author:
Herbert M. Aumann
…
Published in:
38th Mtg. and Symp. of the Antenna Measurement Techniques Assoc., AMTA 2016, 30 October - 4 November 2016.
Topic:
antennas
R&D area:
R&D group:

Summary

This paper combines the standard two-antenna gain measurement technique with the rotating source method for measuring the polarization ratio and tilt angle of the polarization ellipse of a circularly polarized antenna. The technique is illustrated with two identical helical antennas, one for the source and one for the antenna-under-test (AUT), facing each other. Measurements of the voltage transfer ratio are made over one 360 degree on-axis rotation of the source while the AUT remains stationary. The rotation causes the phase of the electric field of the principal polarization to rotate in one direction and the phase of the cross polarization to rotate in the opposite direction. A Discrete Fourier Transform (DFT) of the data from a single rotation is insufficient to resolve the two polarization components. Leakage from the principal polarization will most likely cover up the low-level opposite polarization signal. However, the DFT resolution can be artificially increased by appending to the measured data, precisely M-1 copies of the data. Now the polarization components will be separated by 2M revolutions. Application of a heavy weighting function to the augmented data and a phase compensation to the DFT allows a clear determination of the amplitude and phase of the on-axis principal and cross polarization components. The technique was verified by electromagnetic simulations and by measurements in an anechoic chamber with two 6-turn 5.8 GHz helical antennas separated by 4 feet. There was very good agreement between the simulations and measurements of the polarization ellipse tilt angle and a -20 dB polarization ratio.
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Summary

This paper combines the standard two-antenna gain measurement technique with the rotating source method for measuring the polarization ratio and tilt angle of the polarization ellipse of a circularly polarized antenna. The technique is illustrated with two identical helical antennas, one for the source and one for the antenna-under-test (AUT)...

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A rotating source polarization measurement technique using two circularly polarized antennas

3D printed conformal array antenna: simulations and measurements

October 18, 2016
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Conference Paper
Author:
Alan J. Fenn
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Published in:
6th Int. Symp. on Phased Array Systems and Technology, PAST 2016, 18-21 October 2016.
Topic:
antennas
R&D area:
R&D group:

Summary

A conformal array antenna has been investigated using a combination of 3D printer and copper plating techniques. Circular patch antenna elements were copper plated onto a 3D printed dielectric substrate made of ABS-M30 material. Measured and simulated element reflection coefficient, element gain patterns, and array scanned beam radiation patterns at L band are in good agreement.
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Summary

A conformal array antenna has been investigated using a combination of 3D printer and copper plating techniques. Circular patch antenna elements were copper plated onto a 3D printed dielectric substrate made of ABS-M30 material. Measured and simulated element reflection coefficient, element gain patterns, and array scanned beam radiation patterns at...

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3D printed conformal array antenna: simulations and measurements

Biomimetic antenna array using non-foster network to enhance directional sensitivity over broad frequency band

October 1, 2016
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Journal Article
Author:
Aseim M. Elfrgani
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Published in:
IEEE Trans. Antennas Propag., Vol. 64, No. 10, October 2016, pp. 4297-4305.
Topic:
antennas
R&D area:
R&D group:

Summary

Biologically inspired antenna arrays that mimic the hearing mechanism of insects are called biomimetic antenna arrays (BMAAs). They are attractive for microwave applications, such as compact direction finding systems. Earlier, the BMAAs were designed for narrow frequency band phase enhancement, whereas we now propose to design them for use with a non-Foster coupling network (NFC). As the NFCs are not restricted by gain bandwidth product, their incorporation in the design can provide wideband phase enhancement. A method for designing BMAA, using a non-Foster coupling network (NFC-BMAA), and also for obtaining system stability, is presented. Simulated and measured results of the fabricated structure are also presented and discussed.
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Summary

Biologically inspired antenna arrays that mimic the hearing mechanism of insects are called biomimetic antenna arrays (BMAAs). They are attractive for microwave applications, such as compact direction finding systems. Earlier, the BMAAs were designed for narrow frequency band phase enhancement, whereas we now propose to design them for use with...

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Biomimetic antenna array using non-foster network to enhance directional sensitivity over broad frequency band

Apprenticeship scheduling: learning to schedule from human experts

July 9, 2016
  |
Conference Paper
Author:
Matthew C. Gombolay
…
Published in:
Proc. of the Int. Joint Conf. Artificial Intelligence (IJCAI), 9-15 July 2016.
Topic:
machine learning
R&D area:
R&D group:

Summary

Coordinating agents to complete a set of tasks with intercoupled temporal and resource constraints is computationally challenging, yet human domain experts can solve these difficult scheduling problems using paradigms learned through years of apprenticeship. A process for manually codifying this domain knowledge within a computational framework is necessary to scale beyond the "single expert, single-trainee" apprenticeship model. However, human domain experts often have difficulty describing their decision-making processes, causing the codification of this knowledge to become laborious. We propose a new approach for capturing domain-expert heuristics through a pairwise ranking formulation. Our approach is model-free and does not require enumerating or iterating through a large state-space. We empirically demonstrate that this approach accurately learns multifaceted heuristics on both a synthetic data set incorporating job-shop scheduling and vehicle routing problems and a real-world data set consisting of demonstrations of experts solving a weapon-to-target assignment problem.
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Summary

Coordinating agents to complete a set of tasks with intercoupled temporal and resource constraints is computationally challenging, yet human domain experts can solve these difficult scheduling problems using paradigms learned through years of apprenticeship. A process for manually codifying this domain knowledge within a computational framework is necessary to scale...

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Apprenticeship scheduling: learning to schedule from human experts

A modification of the two-antenna method to determine the phase center location as well as the gain of a wideband antenna

July 19, 2015
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Conference Paper
Author:
Herbert M. Aumann
…
Published in:
2015 IEEE Int. Symp. on Antennas and Propagation, 19-24 July 2015.
Topic:
antennas
R&D area:
R&D group:

Summary

A technique is presented for determining the amplitude center or phase center location of a wideband Vivaldi antenna at measurement distances of a few wavelengths. It is based on the well known two-antenna gain measurement technique but makes the antenna separation a variable. The phase center separation is shown to be proportional to the derivative of a transmission matrix loss parameter which is constant and independent of the antenna separation. A linear least squares fit to transmission loss parameters measured at several antenna separations is shown to yield the antenna gain and phase center location.
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Summary

A technique is presented for determining the amplitude center or phase center location of a wideband Vivaldi antenna at measurement distances of a few wavelengths. It is based on the well known two-antenna gain measurement technique but makes the antenna separation a variable. The phase center separation is shown to...

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A modification of the two-antenna method to determine the phase center location as well as the gain of a wideband antenna

Advisory services for user composition tools

February 7, 2015
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Conference Paper
Author:
Kevin K. Nam
…
Published in:
9th IEEE Int. Conf. on Semantic Computing, IEEE ICSC 2015, 7-9 February 2015.
Topic:
simulation
R&D area:
R&D group:

Summary

We have developed an ontology based framework that evaluates compatibility between processing modules within an end user development framework, using MIT Lincoln Laboratory's Composable Analytics environment as a test case. In particular, we focus on inter-module semantic compatibility as well as compatibility between data and modules. Our framework includes a core ontology that provides an extendible vocabulary that can describe module attributes, module input and output requirements and preferences, and data characteristics that are pertinent to selecting appropriate modules in a given situation. Based on the ontological description of the modules and data, we first present a framework that takes a rule based approach in measuring semantic compatibility. Later, we extend the rule based approach to a flexible fuzzy logic based semantic compatibility evaluator. We have built an initial simulator to test module compatibility under varying situations. The simulator takes in the ontological description of the modules and data and calculates semantic compatibility. We believe the framework and simulation environment together will help both the developers test new modules they create as well as support end users in composing new capabilities. In this paper, we describe the details of the framework, the simulation environment, and our iterative process in developing the module ontology.
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Summary

We have developed an ontology based framework that evaluates compatibility between processing modules within an end user development framework, using MIT Lincoln Laboratory's Composable Analytics environment as a test case. In particular, we focus on inter-module semantic compatibility as well as compatibility between data and modules. Our framework includes a...

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Advisory services for user composition tools
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