Lobe Width Research Articles

Generalized Adaptive Polynomial Window Function

We present a novel method to design and optimize window functions based on combinations of linearly independent functions. These combinations can be performed using different strategies, such a sums of sines/cosines, series, or conveniently using a polynomial expansion. To demonstrate the flexibility of this implementation, we propose the Generalized Adaptive Polynomial (GAP) window function, a non-linear polynomial form in which all the current window functions could be considered as special cases. Its functional flexibility allows fitting the expansion coefficients to optimize a certain desirable property in time or frequency domains, such as the main lobe width, sidelobe attenuation, and sidelobe falloff rate. The window optimization can be performed by iterative techniques, starting with a set of expansion coefficients that mimics a currently known window function and considering a certain figure of merit target to optimize those coefficients. The proposed GAP window has been implemented and several sets of optimized coefficients have been obtained. The results using the GAP exemplify the potentiality of this method to obtain window functions with superior properties according to the requirements of a certain application. Other optimization algorithms can be applied within this strategy to further improve the window functions.

An array pairing method for localizing distributed sources by acoustic beamforming.

An acoustic beamforming concept is presented that alleviates some misrepresentation caused by deconvolution algorithms that can oversimplify distributed sources as a series of point sources. In the Array Pairing Method (APM) an initial array beamforms the acoustic source, then an iterative randomized array is calculated whereby the square-rooted product of the beamformer output possesses a minimum product of Maximum Sidelobe Level (MSL) and Main Lobe Width (MLW). A single and distributed source simulation and a single and dual speaker experiment using the APM reveal significant improvements in MSL and MLW and resolution in the distributed source region.

149: Effects of medications for opioid use disorder on the fetal brain and body measurements

Previous studies about maternal opioid use suggest a greater risk of fetal growth restriction. Limited literature was found about fetal brain and body growth and maternal prescription of medications for opioid use disorder (MOUD). We hypothesized that MOUD exposure was associated with reduction on fetal brain and body ultrasound measurements with an increased effect after co-exposure to alcohol. The ENRICH Prospective cohort study at the University of New Mexico included women who took MOUD, with or without alcohol co-exposure, and unexposed controls. Eligibility and group assignment were determined by alcohol and substance use questionnaires at enrollment and corroborated with biomarkers and assessments. Ultrasound examinations were performed at 18-22 weeks and 28-32 weeks. Measurements included standard biometric parameters and intracranial structures: frontal lobe width (FLW) and length (FLL), fronto-thalamic distance (FTD), and caval-calvarian distance (CCD). A total of 171 participants were found in the three groups (control n=56, MOUD n=75, MOUD+alcohol n=40). The sample included 166 participants who had performed an ultrasound in the second trimester and 144 in the third trimester. Compared with the control group, the MOUD only fetuses had a shorter OFD in the second trimester only, but none less than the 10th%ile. Co-exposure with alcohol was associated with several fetal brain and body measurements that were shorter than the control group in the second trimester (femur length, p=0.026; OFD, p=0.024) and third trimester (BPD, p=0.011; FTD, p=0.0084). Three participants were found to have fetal weight less than 10th%ile in their third trimester, all had alcohol co-exposure. Exposure to maternal medications for opioid use disorder does not appear to impact fetal brain and body measurements. Inquiring about maternal alcohol ingestion with these medications is recommended, because of the associated shorter lengths of several fetal brain and body measurements in the second and third trimesters.

Feasibility of quantitative tissue characterization using novel parameters extracted from photoacoustic power spectrum

Photoacoustic (PA) spectral parameters, obtained using conventional frequency domain analysis of photoacoustic power spectrum, bear complex relationship with absorber size, due to which it is difficult to recover quantitative information related to tissue microstructure accurately, using the conventional spectral parameters. In this study, we proposed to utilise two new spectral parameters namely number of lobes as well as average lobe width, which may change linearly with PA absorber radius, for recovering quantitative values of PA absorber size. Using an analytical model of PA power spectrum with bandlimited acquisition, we developed linear relationships between number of lobes and absorber radius as well as average lobe width and absorber radius for a wide range of radius values. These linear relationships were validated using simulations and experimentally acquired PA signal. The preliminary results of the simulation as well as phantom study showed that using the computed values of number of lobes as well as average lobe width in the linear relationships, absorber radius could be recovered with reasonable degree of accuracy. The proposed parameters were extracted from the multiwavelength PA data generated by freshly excised prostate tissue specimens from 30 human patients undergoing prostatectomy for biopsy confirmed prostate cancer. Statistical analysis showed that both the proposed parameters were significantly different between malignant and non malignant prostate as well as malignant and normal prostate. The preliminary findings showed that the proposed parameters can be used to differentiate diseased tissue pathology form normal tissue.

Plasma-Dielectric Traveling Wave Antenna

The paper investigates the efficiency of transformation of traveling wave into radiation in longitudinally inhomogeneous plasma cylinder. The plasma is limited by a dielectric shell of finite thickness. The investigation involves the use of the method of spectral field expansion in terms of a set of functions including the surface and spatial waves of plasma cylinder with dielectric shell. A system of integro-differential equations for expansion coefficients has been obtained. These coefficients determine the amplitudes of transmitted, reflected, and scattered waves and also radiation patterns (RP). The system of equations is solved for the case of strong longitudinal variation of plasma density. The relationships of the transformation coefficients of surface wave energy as a function of the plasma density gradient, electrical length of section of plasma inhomogeneity, the electric radius of plasma cylinder, dielectric permittivity, and the thickness of dielectric were calculated. The fraction of surface wave energy that is transformed into radiation at acute angles can amount to 35%. The resultant narrow-beam RPs have only one lobe. The radiation maximum fits into an angle of several degrees with respect to the direction of surface wave propagation. With an increase of plasma density gradient, the lobe width is reduced, while its position shifts to 0°. The impact of dielectric properties on radiation characteristics has been also investigated.

Proximity‐coupled feed patch antenna array for 79 GHz automotive radar

Autonomous driving is becoming a reality-but low-cost 79 GHz radar antenna technology is still imperfect. Here, the authors propose a kind of proximity-coupled feed patch antenna array. By reducing the non-linear mutual interference between the transmission line and the radiating elements, the antenna's operating bandwidth is improved and the antenna gain is increased. Moreover, the consistency of the antenna radiation pattern at different frequencies is also improved. The simulation results show that the antenna has a −10 dB impedance bandwidth from 76 to 81.4 GHz, and the gain is >14.8 dB. Within the operating frequency band, the antenna main lobe width is smaller than ±1.2°

Vectorial analysis of Airy-Airy bullets generated by high aperture binary micro zonal plate

Intense research has recently been carried out in the study of three dimensional light bullets. Based on the experimental approach for obtaining Airy-Bessel light bullets by Chong et al [1], we propose a theoretical methodology for obtaining and analyzing vectorial three dimensional bullets. First of all, we present the design criteria of binary micro zonal plates (BZP) that make it possible to obtain Airy-Airy bullets with sub-diffraction main lobe width. Following the vectorial diffraction theory, we analyze Airy-Airy vectorial bullets generated by illuminating the designed BZP with temporal Airy circular polarized pulses. The propagation dynamics of the resulting vectorial light bullets have been studied; the width of the resulting FWHM of the spatial main lobe at the focal plane being close to 0.75 λ0.

A Small Antenna Feeder System of an EHF Radio-Interferometer for Diagnostics of Gas-Dynamic Processes in Closed Volumes

This article presents the design of an antenna feeder system (AFS) for extremely-high-frequency radio interferometers equipped with a small transmitter, which is intended for diagnostics of fast gas-dynamic processes in closed volumes with a limited internal space . Numerical simulation and experimental studies proved the fundamental possibility of developing an AFS with an aperture size that does not exceed (3–5)λ. The designed AFS forms an axisymmetric radiation pattern of the probing field with a major lobe width of at most 30°–40° and a minimum level of lateral radiation. This research has shown that the required characteristics are achieved using transmitters with rod and conical dielectric inserts of a specific design.

CFO sensitivity and efficient joint estimation for the short filter multicarrier system FBMC-PAM

Sensitivity to carrier frequency offset, due to oscillator inaccuracy and terminal mobility, is a key issue that modern multicarrier systems have to face. In that respect, FBMC-PAM holds a specific position due to its short prototype filter: the overlapping factor is K=2 and the width of the main lobe of its frequency response is 3 times the sub-carrier spacing, while OFDM and FBMC-OQAM schemes have frequency response whose main lobe width is 2 times the sub-carrier spacing. As a consequence, it is shown in the present paper that FBMC-PAM outperforms other multicarrier techniques in terms of CFO sensitivity. In order to best exploit this property in burst transmission, an efficient and accurate approach for joint symbol timing and CFO estimation is proposed, based on a specific preamble. A theoretical in-depth analysis of the scheme is provided as well as performance validation in multipath channel through simulations.

Target Motion Parameters Estimation in Forward Scatter Radar

This paper is devoted to the estimation of target motion parameters with a forward scatter radar (FSR). To provide an upper bound for the estimation performance, a closed-form expression of the Cramer–Rao lower bound (CRLB) is provided for the main target signal parameters, namely Doppler rate, baseline crossing instant, and main lobe width parameter of the target amplitude modulation pattern. This is performed by operating on the signal at the output of the standard FSR processing scheme, namely on the crystal video detector signal: the received signal, which is passed through a square-law envelope detector followed by a DC removal filter. The estimate of the kinematic parameters of moving targets that follow a linear trajectory can be obtained by inverting the relationship between these parameters and the previously estimated target signal parameters. Especially, two FSR configurations are investigated: single-node FSR configuration and dual-baseline FSR configuration with a small angular separation between the two baselines. The closed-form expression of the corresponding CRLB is derived by using a linearized version of the same inverse transformation. Finally, a practical estimator is presented, based on a two-dimensional filter bank, and its performance is compared with the derived CRLB. The results show that unbiased and highly accurate estimates of the kinematic parameters are obtained. The feasibility and the effectiveness of this estimation scheme is demonstrated by applying this technique to recorded live data acquired with a dual-baseline FSR configuration exploiting FM signals as a waveform of opportunity.

Ultra-Wideband Dielectric Resonator Antenna Design Based on Multilayer Form

In this paper, an ultra-wideband dielectric resonator antenna (DRA) is investigated. It basically covers the bandwidth from 6 GHz to 16 GHz and achieves a relative bandwidth of 90.9%. It is found that a wide bandwidth can be reached with a small DRA by adopting multilayer form. Thus, the dimension of the designed DRA element which is composed of nine-element phased-scanning linear array is as small as 6.9mm x 8.2mm x 11 mm. While the maximum stable zenith gain is 6.2dB, the lobe width is 3 dB. The operating frequency range of the antenna array is from 5.42GHz to 16.5GHz, achieving a 101.1% relative bandwidth. A large scanning angle of ±60° is realized within the operating frequency band, with good scanning pattern and cross polarization. To verify the design and simulation, a 1 × 9 DRA array is fabricated, and measurements are carried out.

Efficient signal separation method based on antenna arrays for GNSS meaconing

As an effective deceptive interference technique for military navigation signals, meaconing can be divided into two main types: those that replay directly and those that replay after signal separation. The latter can add different delays to each satellite signal and mislead the victim receiver with respect to any designated position, thus has better controllability and concealment capability. A previous study showed there to be two main spatial processing techniques for separating military signals, whereby either multiple large-caliber antennas or antenna arrays are used to form multiple beams that align with all visible satellites. To ensure sufficient spatial resolution, the main lobe width of the antenna or beam must be sufficiently narrow, which requires the use of a large antenna aperture or a large number of array elements. In this paper, we propose a convenient and effective signal separation method, which is based on an antenna array with fewer elements. While the beam of the array is pointing to a specified satellite, the other satellite signals are regarded as interference and their power is suppressed to a level below the receiver's sensitivity. With this method, the number of array elements depends only on the number of visible satellites, thus greatly reducing the hardware cost and required processing capacity.

On the use of modified phase transform weighting functions for acoustic imaging with the generalized cross correlation.

The generalized cross correlation (GCC) is an efficient technique for performing acoustic imaging. However, it suffers from important limitations such as a large main lobe width for noise sources with low frequency content or a high amplitude of side lobes for noise sources with high frequencies. Prefiltering operation of the microphone signals by a weighting function can be used to improve the acoustic image. In this work, two weighting functions based on PHAse Transform (PHAT) improvements are used. The first adds an exponent to the PHAT expression (ρ-PHAT), while the second adds the minimum value of the coherence function to the denominator (ρ-PHAT-C). Numerical acoustic images obtained with the GCC and those weighting functions are compared and quantitatively assessed thanks to a metric based on a covariance ellipse, which surrounds either the main lobe or the side lobes. The weighting function ρ-PHAT-C provides the smallest surface ellipses especially when the arithmetic of the GCC is replaced by the geometric mean (GEO). Experimental measurements are carried out in a hemi-anechoic room and a reverberant chamber where two loudspeakers were set in front of microphone array. The acoustic images obtained confirm that the ρ-PHAT-C with the GEO outperforms the GCC, GCC-PHAT, and GCC ρ-PHAT.

Adaptive array reduction method for acoustic beamforming array designs.

This letter presents a modification to a very recent iterative microphone removal array design process, called the Array Reduction Method (ARM). The ARM iteratively reduces an array based on the product of sidelobe and main lobe criteria, yet the main lobe may become distorted and the beamformer output can disproportionately favor one of the criteria. The Adaptive Array Reduction Method presented here uses the derivative estimates of the maximum sidelobe level and main lobe width with respect to the number of microphones removed, and the distortion of the main lobe during iteration, to produce an improved source image map.

Design and Statistical Analysis of Tapered Coprime and Nested Arrays for the Min Processor

Coprime and nested arrays are sparse sensor arrays that provide $\mathcal {O}(MN)$ degrees of freedom using only $\mathcal {O}(M+N)$ sensors. The signals sampled by these sparse arrays contain the aliasing artifact; the min processor is used to disambiguate this aliasing artifact. The min processor beampattern has the same main lobe width and resolution as the beampattern of a full uniform linear array (ULA) with many more sensors. However, the peak side lobe (PSL) height of the min processor beampattern is higher than the PSL height of a full ULA with the same taper and resolution if the sparse arrays are not extended. Extending the sparse arrays, while keeping the intersensor spacing fixed, can reduce the PSL height to the level of the full ULA. Until now, the analytical expressions of the extension factor required to match the PSL height have not been found for the min processor. Also, the analytical expressions of the probability density function (PDF), mean, and variance of the min processor output for non-uniform tapers have not been derived. In this paper, we derive both of these analytical expressions. We consider the uniform, Hamming, Hann, Blackman-Harris, and Dolph-Chebyshev tapers for both coprime and nested arrays. We use the derived PDF in evaluating detection performance metrics such as receiver operation characteristic, Kullback Leibler divergence, and symmetric Kullback Leibler divergence. Our results show that min processing is superior to conventional beamforming and product processing in Gaussian signal detection for a given extended coprime or nested array.

Range Coherence Factor for Down Range Sidelobes Suppression in Radar Imaging Through Multilayered Dielectric Media

In radar imaging applications through layered dielectric media, an antenna array with a limited operating frequency bandwidth at the low end of the microwave band is usually employed to probe the target space of interests. As a result, the focused radar imagery is characterized by severe sidelobes in the down-range direction, which leads to the degradation of the image quality. Several techniques, such as windowing and apodization filtering combined with phase coherence factor (PCF) filtering, have been reported to suppress the down-range sidelobes. However, these approaches either expand the main lobe width or are sensitive to parameter tuning. In this paper, by investigating the distribution characteristics of the down-range sidelobes among sub-frequency radar imageries, a robust and efficient range coherence factor (rCF) technique is proposed to suppress the down-range sidelobes in the focused radar imagery. The performance of the proposed approach is assessed by the finite-difference time-domain (FDTD)-based numerical simulations as well as onsite experiments to verify its sidelobes' reduction capabilities.

An iterative microphone removal method for acoustic beamforming array design

This paper presents a beamforming array design method that uses a large array of microphones and systematically reduces it to a predetermined number of microphones. The microphone, while included in the array, that results in the smallest (defined as Φ in this paper) product of frequency-averaged Main Lobe Width (MLW) and Maximum Sidelobe Level (MSL) of the point spread function using the cross-spectral beamforming algorithm is identified and removed. The reduction method is implemented in two ways: one-by-one microphone removal and an accelerated procedure that removes several microphones per iteration, where the removed number of microphones decreases in an exponential manner with increasing iterations. Multi-frequency array reductions, using 841 and 961-channel equi-and-non-equispaced grid initial arrays, are conducted over the frequency range of 2000 Hz–8000 Hz to replicate typical conditions in a small scale anechoic facility. These reduced arrays are compared against several logarithmic spiral and randomised pattern arrays and in most cases, reveal superior values of MSL, MLW and Φ. Single-frequency array reductions, using both 961 and 169-channel initial arrays, at the best-case frequencies for the logarithmic spirals, also display superior performance. Both the multi-and-single-frequency arrays can be used practically: the multi-frequency arrays possess an even performance across the simulated frequency range, whereas the single-frequency arrays possess excellent performance over narrowband frequency ranges and can be modified within an array stencil for each acoustic experiment.

Leaf Area and Its Relationship with Leaf Descriptors Elements in Liquidambar styraciflua L.

This study aimed at determining the leaf area in Liquidambar styraciflua L. and at characterising the relationship between leaf area and leaf descriptors. The biological material was the species Liquidambar styraciflua L. We determined leaf area in 100 leaves (Figure 1) based on the size of median rib (L), leaf width at higher (W1) and lower (W2) lobe level, and on area constants (KA). The size of elements L, W1 and W2 were found by measuring with a precision of ±0.5 mm. Area constants in the species Liquidambar styraciflua L. were KA1 = 0.63, determined depending on leaf width at upper lobe width (W1), and KA2 = 0.81 in relation to the width W2 of the lower lobes. Between the scanned leaf area (SLA) and measured leaf area (MLA) and leaf descriptors (L, W1 and W2) we identified relations of interdependence statistically ensured: r = 0.960 to r = 0.971 for SLA; r = 0.951 to r = 0.981 for MLA W1, and r = 0.933 to r = 0.972 for MLA W2, respectively. Leaf descriptors L, W1 and W2 had a differentiated contribution in determining SLA and MLA. SLA was influenced by leaf length (L) with higher statistic safety (R2 = 0.963, p << 0.001, F = 1277.2) than leaf width at upper lobe width W1 (R2 = 0.943; p<<0.001; F = 797.7) and leaf width at the extremities of the lower lobes W2 (R2= 0.927, p << 0.001, F = 620.59).

Cylindrical Plasma Antenna with Large Longitudinal Density Irregularity

The efficiency of operation of a cylindrical plasma antenna as a function of the degree of longitudinal nonuniformity of the plasma density is examined. The study is based on the method of spectral field expansion into a complete set of functions comprising surface and pseudosurface waves of the plasma column. The system of integrodifferential equations for expansion coefficients determining radiation patterns and the amplitudes of transmitted, reflected, and scattered waves is solved in the case of rapid variation in the plasma density. Dependences of the coefficients of conversion of the surface-wave energy on the plasma-density gradient, the electric length of the section of plasma nonuniformity, and the electric radius of the plasma cylinder are calculated. It is demonstrated by examples that the portion of energy of the surface wave converted into radiation may exceed 50%. It has been found that the radiation patterns are narrow with a single lobe whose maximum is at an angle of several degrees to the direction of propagation of the surface wave. As the plasma-density gradient increases, the lobe width decreases and the lobe itself shifts toward 0°.

Subspace Rejection for Matching Pursuit in the Presence of Unresolved Targets

Unresolved scatterers (separated by less than a 3-dB matched filter main lobe width) are known to degrade the matching pursuit performances in radar: It tends to generate spurious detection or miss weaker targets, hidden in strong sidelobes. In this paper, we propose a new matching pursuit algorithm performing a subspace radar resolution cell rejection. The philosophy is the following: As it is usually not possible to distinguish several unresolved scatterers, we do not try to distinguish them, but when a scatterer is detected, then every contribution in the corresponding resolution cell should be cleaned. For that, the continuous cell interval is approximated by a subspace and the corresponding orthogonal projector is build. The projector basis is chosen so that it minimizes the projection residue inside the interval and a method is proposed to select its dimension according to the rejected target SNR. We show that it enables to control the sidelobe level after rejection (orthogonal projection) so that the sidelobe detection probability can be maintained low. It allows matching pursuit to work well even if the target parameter distribution differs from a delta Dirac distribution inside the matched filter resolution cell.