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Ultra-wideband step notch array using stripline feed

Published in:
IEEE Antennas and Propagation Society Int. Symp., 2007 Digest, 9-15 June 2007, pp. 3361-4.

Summary

Electronically scanned array (ESA) antennas capable of efficiently radiating over an octave of bandwidth provide system designs with more flexibility in multiple mode operation. Communication and radar bands occupy different frequency allocations and the growing research in Ultra-Wideband (UWB) communications make the use of a single ESA to cover these frequencies an area of interest. Array antennas constructed of tapered-slot antennas and TEM horns have been investigated and shown to operate successfully over an octave bandwidth. These antennas use vertical feeds which make them optimal for brick architectures, but less than desirable for tile architectures. Conventional notch antennas require a feed extending vertically away from the notch antenna which makes a flat 2-D connection between antennas difficult. In this work an Ultra-Wideband Step Notch Array (UWSNA) was designed for ESA applications. The array operates over a 6-12 GHz range using a flat, tile-based 2-D feed network making this array optimal for conformal applications with a minimum of vertical distance. Simulation results and measurements on a small prototype demonstrate the concept.
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Summary

Electronically scanned array (ESA) antennas capable of efficiently radiating over an octave of bandwidth provide system designs with more flexibility in multiple mode operation. Communication and radar bands occupy different frequency allocations and the growing research in Ultra-Wideband (UWB) communications make the use of a single ESA to cover these...

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Design of overlapped subarrays using an RFIC beamformer

Published in:
IEEE Antennas and Propagation Society Int. Symp., 2007 Digest, 9-15 June 2007, pp. 1791-4.

Summary

Electronically scanned arrays require a minimum number of controls, Nmin, given by the number of orthogonal beams that fill a prescribed scan sector. Most practical antenna arrays require considerably more than Nmin control elements, but overlapped subarray architectures can approach this theoretical limit. Figure 1 shows a block diagram of an overlapped subarray architecture. The overlapped subarray network produces a flattopped sector pattern with low sidelobes that suppress grating lobes outside of the main beam of the subarray pattern. Each radiating element of the array is connected to multiple subarrays, creating an overlapping geometry. It is possible to scan one beam, or a fixed set of contiguous beams, over the main sector of the subarray with a set of Nmin phase shifters. Alternatively, digital receivers can be connected to the Nmin subarrays and multiple simultaneous beams can be formed digitally. Digital subarray architectures using a combination of element level phase shifters and subarray level receivers makes it possible to scan multiple beam clusters over all space. The conventional approach to the design and manufacturing of the overlapped subarray network shown in Figure 1 is challenging and costly due to the complexity of the microwave network. However, the design of the overlapped subarray beamformer using Radio Frequency Integrated Circuits (RFIC) represents a novel approach for implementing an efficient trade-off between the agility and capability of fully digital arrays and the cost effectiveness of analog arrays.
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Summary

Electronically scanned arrays require a minimum number of controls, Nmin, given by the number of orthogonal beams that fill a prescribed scan sector. Most practical antenna arrays require considerably more than Nmin control elements, but overlapped subarray architectures can approach this theoretical limit. Figure 1 shows a block diagram of...

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A component model approach for the RCS validation of an electrically large open-ended cylindrical cavity

Published in:
IEEE Antennas and Propagation Society Int. Symp., 2007 Digest, 9-15 June 2007, pp. 2275-2278.

Summary

A novel RCS component prediction model approach to producing both fast and accurate scattering from an electrically large open-ended cylindrical cavity (circular cross section) is presented. The component model is a hybrid approach which easily permits individual scattering mechanisms to be coherently combined to produce a high fidelity signature. For this problem, the component model included scattering produced from the interior of the cavity calculated via the waveguide modal approach combined with the scattering produced from the cavity's finite thick rim opening (i.e., annulus) computed via the Method of Moments (MoM) and finally combined with the cavity's external base ring edge diffraction computed via PTD. Narrowband and wideband signature analysis for the circular cylindrical cavity configuration are presented to validate the component prediction model with static range measurements, and another prediction result computed using MoM for X- band frequencies and linear polarization. Excellent agreement is achieved among the data sets: measurement and prediction (component and MoM model).
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Summary

A novel RCS component prediction model approach to producing both fast and accurate scattering from an electrically large open-ended cylindrical cavity (circular cross section) is presented. The component model is a hybrid approach which easily permits individual scattering mechanisms to be coherently combined to produce a high fidelity signature. For...

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SiGe IC-based mm-wave imager

Published in:
2007 IEEE Int. Symp. on Circuits and Systems, 27-30 May 2007, pp. 1975-1978.

Summary

Millimeter-wave radiation and detection offers the possibility of detecting concealed weapons. Passive imaging measures the mm-wave radiation emitted from target objects. A passive mm-wave imager and the designs affecting the overall system performance are discussed. With low power receiver architecture and SiGe ICs, a focal plane based full staring array is feasible and can provide a high thermal resolution, ~1.1K at >10Hz frame rate.
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Summary

Millimeter-wave radiation and detection offers the possibility of detecting concealed weapons. Passive imaging measures the mm-wave radiation emitted from target objects. A passive mm-wave imager and the designs affecting the overall system performance are discussed. With low power receiver architecture and SiGe ICs, a focal plane based full staring array...

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Using filter banks to improve interceptor performance against weaving targets

Author:
Published in:
AIAA Guidance, Navigation, and Control Conf., 21-24 August 2006.

Summary

It is well known that interceptor performance against a weaving or spiraling target can be improved by use of a special purpose weave guidance law. However the weave guidance law requires knowledge of the target weave frequency. When the target weave frequency is unknown an extended Kalman filter is usually considered for the problem because it can be used to estimate the target weave frequency. However, the performance of the extended Kalman filter is sensitive to initialization errors. This paper offers an unusual linear Kalman filter bank approach, where each filter is tuned to a different target weave frequency, as a potential solution for estimating the target weave frequency. Rather than combining individual filter outputs in some probabilistic sense, a straightforward algorithm is presented for choosing the filter that is most closely tuned to the actual target weave frequency. This paper demonstrates that this filter bank approach is superior to that of the extended Kalman filter for the weaving target problem.
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Summary

It is well known that interceptor performance against a weaving or spiraling target can be improved by use of a special purpose weave guidance law. However the weave guidance law requires knowledge of the target weave frequency. When the target weave frequency is unknown an extended Kalman filter is usually...

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Enhanced detection and classification of buried mines with an UWB multistatic GPR

Published in:
IEEE Antennas and Propagation Society Int. Symp. 2005 Digest, Vol. 3B, 3-8 July 2005, pp. 88-91.

Summary

In this paper we present a resonance-based classification technique for the identification of plastic-cased antipersonnel (AP) land mines buried in lossy and dispersive soils under rough surfaces by a stepped-frequency ultra-wideband (UWB) downward-looking ground penetrating radar (GPR) with an array of receivers. For this application the multistatic ground probing sensor is positioned just above the ground surface and operates from UHF to C-Band frequencies. Novel physics-based models based on the finite difference frequency domain (FDFD) technique simulate the characteristic resonating multi-aspect target frequency responses for several realistic buried land mine detection scenarios. Matched filter detection results are presented which assess the GPR's performance in identifying a simulated mine buried under a rough surface at varying depths in dry sand and a dispersive clay loam soil from other false targets such as buried rocks.
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Summary

In this paper we present a resonance-based classification technique for the identification of plastic-cased antipersonnel (AP) land mines buried in lossy and dispersive soils under rough surfaces by a stepped-frequency ultra-wideband (UWB) downward-looking ground penetrating radar (GPR) with an array of receivers. For this application the multistatic ground probing sensor...

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Design considerations and results for an overlapped subarray radar antenna

Summary

Overlapped subarray networks produce flattopped sector patterns with low sidelobes that suppress grating lobes outside of the main beam of the subarray pattern. They are typically used in limited scan applications, where it is desired to minimize the number of controls required to steer the beam. However, the architecture of an overlapped subarray antenna includes many signal crossovers and a wide variation in splitting/combining ratios, which make it difficult to maintain required error tolerances. This paper presents the design considerations and results for an overlapped subarray radar antenna, including a custom subarray weighting function and the corresponding circuit design and fabrication. Measured pattern results will be shown for a prototype design compared with desired patterns.
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Summary

Overlapped subarray networks produce flattopped sector patterns with low sidelobes that suppress grating lobes outside of the main beam of the subarray pattern. They are typically used in limited scan applications, where it is desired to minimize the number of controls required to steer the beam. However, the architecture of...

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MIMO radar theory and experimental results

Published in:
38th Asilomar Conf. on Signals, Systems and Computers, Vol. 2, 7-10 November 2004, pp. 300-304.

Summary

The continuing progress of Moore's law has enabled the development of radar systems that simultaneously transmit and receive multiple coded waveforms from multiple phase centers and to process them in ways that have been unavailable in the past. The signals available for processing from these Multiple-Input Multiple-Output (MIMO) radar systems appear as spatial samples corresponding to the convolution of the transmit and receive aperture phase centers. The samples provide the ability to excite and measure the channel that consists of the transmit/receive propagation paths, the target and incidental scattering or clutter. These signals may be processed and combined to form an adaptive coherent transmit beam, or to search an extended area with high resolution in a single dwell. Adaptively combining the received data provides the effect of adaptively controlling the transmit beamshape and the spatial extent provides improved track-while-scan accuracy. This paper describes the theory behind the improved surveillance radar performance and illustrates this with measurements from experimental MIMO radars.
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Summary

The continuing progress of Moore's law has enabled the development of radar systems that simultaneously transmit and receive multiple coded waveforms from multiple phase centers and to process them in ways that have been unavailable in the past. The signals available for processing from these Multiple-Input Multiple-Output (MIMO) radar systems...

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Wideband aperture coherence processing for next generation radar (NexGen)

Summary

This report develops robust signal processing architectures and algorithms specifically designed to achieve multi-aperture coherence on transmit and receive. A key feature of our approach is the use of orthogonal radar waveforms that allow the monostatic and bistatic target returns to be separated at each receiver's matched filter output. By analyzing these returns, we may determine the appropriate transmit times and phases in order to cohere the various radar apertures using both narrowband and wideband waveforms. This process increases the array gain on receive to N2 instead of N for the single transmitter case. Furthermore, when hll coherence on transmit is achieved, the array gain is N3. The performance of our coherence algorithms is quantified using Monte Carlo simulations and compared to the Cramer-Rao lower bound. A computational complexity study shows that our aperture coherence algorithms are suitable for a realtime implementation on an SGI Origin 3000 multi-processor computer.
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Summary

This report develops robust signal processing architectures and algorithms specifically designed to achieve multi-aperture coherence on transmit and receive. A key feature of our approach is the use of orthogonal radar waveforms that allow the monostatic and bistatic target returns to be separated at each receiver's matched filter output. By...

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Power-law scattering models and nonlinear parametric estimation for super-resolution radar

Published in:
MIT Lincoln Laboratory Report TR-1095

Summary

This paper introduces a direct solution of the frequency-dependent, GTD-based, scatterer-model parameters leading towards a new modern spectral-estimation technique to be used for enhanced, super-resolution radar analysis. The overcomplete nature of the full GTD scatterer-model basis (positive and negative half-integer power laws) is recognized and overcome by introducing the vector-channel method, well known from communication theory. This physically motivated discretemodel- based analysis eliminates the need for computationally intensive and potentially nonconvergent local optimization procedures. Each scatterer is assigned a half-integer power law that identifies its cross-section frequency dependence and hence restricts the possible underlying physical feature geometries. This analysis opens the possibility for vector-attribute-based feature processing for target recognition that offers the potential for significant improvement in target identification performance.
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Summary

This paper introduces a direct solution of the frequency-dependent, GTD-based, scatterer-model parameters leading towards a new modern spectral-estimation technique to be used for enhanced, super-resolution radar analysis. The overcomplete nature of the full GTD scatterer-model basis (positive and negative half-integer power laws) is recognized and overcome by introducing the vector-channel...

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