Null steering in adaptive arrays is usually achieved by controlling the complex weights of all or most of the array elements. This study explores an alternative approach, where only the two side elements of the array are used for null... more
Null steering in adaptive arrays is usually achieved by controlling the complex weights of all or most of the array elements. This study explores an alternative approach, where only the two side elements of the array are used for null steering. By suitably adjusting the amplitude and phase excitations of these elements, it is possible to modify the overall array pattern to place a wide angular null in the direction of undesired interfering signals. Unlike the adaptive arrays, the proposed method is much simpler in practical implementation.
Dual Apodization with Cross-correlation (DAX) is a novel adaptive beamforming technique that utilizes two distinct receive apodizations in suppressing clutter to enhance ultrasound image contrast. Previous studies have shown that its... more
Dual Apodization with Cross-correlation (DAX) is a novel adaptive beamforming technique that utilizes two distinct receive apodizations in suppressing clutter to enhance ultrasound image contrast. Previous studies have shown that its performance in terms of contrast enhancement diminishes with increasing level of phase aberration and has a tendency to create image artifacts. In this work, we propose a modified version of DAX, known as Phase Apodization with Cross-correlation (PAX), which utilizes sinusoidal phase apodization to further enhance image quality. Our preliminary simulation and experimental results presented in this work showed that PAX performs in a more robust manner than DAX, especially with increased level of phase aberration, to further improve image contrast and reduce image artifacts.
3D USCT II is a new imaging method aimed at early detection of breast cancer. Synthetic aperture focusing technique is used for reconstructing images which requires unfocused ultrasound emission and reception. Thus the SNR received is... more
3D USCT II is a new imaging method aimed at early detection of breast cancer. Synthetic aperture focusing technique is used for reconstructing images which requires unfocused ultrasound emission and reception. Thus the SNR received is low. Coded excitation (CE) and match filtering techniques are used to increase the SNR. The Currently applied CE is a linear chirp.
The received A-scans contain multiple superimposed reflections which are difficult to separate due to the system's limited bandwidth side lobes. Literature suggests Huffman sequence (HS) as CE to gain more control over side lobe distribution. Since the system has limited bandwidth, the HS is received band limited and which does not produce satisfactory results.
A method is presented here to design HS under limited bandwidth preserving their good properties. The evaluation has been carried out with well established metrics like MSR and SLD. The results show better performance than using a chirp for side lobe suppression by trading-off main lobe energy.
—A sidelobe cancellation over a wide angular range for the uniformly excited planar array is proposed. The approach is to readjust the amplitude and phase excitations of the boundary elements only, while keeping the rest of elements... more
—A sidelobe cancellation over a wide angular range for the uniformly excited planar array is proposed. The approach is to readjust the amplitude and phase excitations of the boundary elements only, while keeping the rest of elements unchanged. Simple expressions for computing the required amplitude and phase exci-tations of these boundary elements are given. The technique simplifies the feed network as it requires only one attenuator and two phase shifters. Simulation results show that cancellation of side-lobes across a wide angle can be obtained.
Sidelobes in dish reflector antennas are wasted energy in unwanted directions making the antenna more susceptible to noise. They represent security vulnerability since an unintended receiver may pick up the classified communication and... more
Sidelobes in dish reflector antennas are wasted energy in unwanted directions making the antenna more susceptible to noise. They represent security vulnerability since an unintended receiver may pick up the classified communication and most importantly yield to interference. Therefore reducing the near-in sidelobes which is desirable in parabolic reflectors and can be achieved by adding metallic stripes to scatter and diffract the unwanted radiation. The amount of reduction that can be attained ranges from 15 to 20 dB.
—Generally, the null steering is performed by controlling the amplitude and/or phase weightings of all element excitations or only a small number of them. In such cases, a need for extra RF components such as variable attenuators and... more
—Generally, the null steering is performed by controlling the amplitude and/or phase weightings of all element excitations or only a small number of them. In such cases, a need for extra RF components such as variable attenuators and variable phase shifters with each element in the array is inevitable. In this paper, an alternative method is introduced where the null steering is performed by thinning (or turning off) only a small subset of the elements in the uniform linear arrays. To find an optimum combination of active (on) and inactive (off) elements, a binary genetic algorithm is used. In large arrays, the number of required nulls is much smaller than the total number of array elements, thus only a small subset of the array elements could be sufficient for producing the required nulls rather than optimizing all the array elements. By this way, a faster convergence speed of the optimizer and lowest peak sidelobe level can be obtained. The effectiveness of the proposed method with various subset configurations will be demonstrated and compared with some standard null steering methods.
This paper introduces an array with a new element structure to achieve asymmetric sidelobe pattern nulling which is a much desired feature in many applications such as communication systems, tracking radars, and imaging. The proposed... more
This paper introduces an array with a new element structure to achieve asymmetric sidelobe pattern nulling which is a much desired feature in many applications such as communication systems, tracking radars, and imaging. The proposed element structure is built by combining two simple wire dipoles in the horizontal and vertical positions to form a crossed dipole element. The array patterns of the horizontal and vertical dipoles share some common radiation features such as angular null positions which are exploited to provide the required sidelobe nulling. By properly scaling the array pattern of the horizontal dipoles and adding or subtracting its array pattern from those of the vertical dipoles, a new array pattern corresponding to the crossed dipoles elements with controlled sidelobes pattern is obtained. The proposed method is equally applied to the uniformly and nun-uniformly excited arrays. Moreover, the proposed idea is verified by simulating an array with 10 half wavelength crossed dipoles using computer simulation technology microwave studio, and the obtained resultswhich are compared to the theoretical Matlab findings-confidently validate the presented idea.
Dual Apodization with Cross-correlation (DAX) is a novel beamforming technique that utilizes a pair of complementary receive amplitude apodizations for ultrasound image contrast enhancement. The effectiveness of DAX in vivo is often... more
Dual Apodization with Cross-correlation (DAX) is a novel beamforming technique that utilizes a pair of complementary receive amplitude apodizations for ultrasound image contrast enhancement. The effectiveness of DAX in vivo is often reduced because of the strong reverberation clutter signals caused by near-field structures. In this work, we propose a modified version of DAX, known as Multi-Phase Apodization with Cross-correlation (MPAX), which utilizes multiple pairs of complementary phase apodizations for robust suppression of reverberation clutter. Our experimental sponge phantom results and initial clinical results from a healthy volunteer show that MPAX achieves CNR values higher than or comparable to DAX with much more uniform reverberation clutter suppression throughout the field-of-view. Hence, MPAX results in a large improvement in image quality and shows great potential for more accurate diagnosis in clinics.
—In this letter, a novel multiwide null steering method for uniformly excited large arrays by only adjusting the amplitude and phase of a relatively small number of elements on the extremes of the array is presented. These adjustable... more
—In this letter, a novel multiwide null steering method for uniformly excited large arrays by only adjusting the amplitude and phase of a relatively small number of elements on the extremes of the array is presented. These adjustable elements are optimized by means of genetic algorithm (GA) to construct a specific cancellation pattern that can be used to produce multiple wide nulls in the radiation patterns of the uniformly excited linear arrays. To simplify the feeding network as well as to increase the convergence speed of the optimization algorithm, the excitations of the majority of the array elements are kept constant. Results of applying the GA to optimize 10 out of 100 elements are shown. Index Terms—Antenna arrays, genetic algorithm (GA), multi-null steering, uniformly excited arrays.
