Vertical Antenna Array Research Articles

The Influence of the A Priori Uncertainty of the Shallow Sea Sound Channel Model on the Vertical Array Gain

The purpose of this paper is to numerically demonstrate and comparatively analyze the critically strong and ambiguous impact of the a priori uncertainty of a shallow sea waveguide model in its main physical parameters on the output performance of model-based methods for spatial processing of multimode signals received by a vertical antenna array. The scenario is specified when a relatively weak signal of a remote underwater source is received against the background of intensive interference excited by a subsurface source (like a ship, for example) and ambient sea noise excited by wind waves. The considered array processing methods include matched-signal processing, optimal processing of the signal on the background of interference and noise, and suboptimal processing based on matched-mode array filtering of one of the signal-carrying modes with adaptive selection of its number. Quantitative estimates are obtained from above for the environment uncertainties, or model errors, with respect to the sound velocity in the water column and geoacoustic parameters of the underlying bottom, at which the array gain loss does not exceed a given level. It is shown that such estimates are very different both for different environmental parameters and for processing methods, with the determining role played by the conditions of useful signal reception, namely, the modal composition and intensity levels of the interference and sea noise at the array input. The problem statement and results are considered to be useful to detail the requirements for operational oceanography tools designed to support the effective operation of sonar antenna systems in real sea environments.

The Influence of the A Priori Uncertainty of the Shallow Sea Sound Channel Model on the Vertical Array Gain

The purpose of this paper is to numerically demonstrate and comparatively analyze the critically strong and ambiguous impact of the a priori uncertainty of a shallow sea waveguide model in its main physical parameters on the output performance of model-based methods for spatial processing of multimode signals received by a vertical antenna array. The scenario is specified when a relatively weak signal of a remote underwater source is received against the background of intensive interference excited by a subsurface source (like a ship, for example) and ambient sea noise excited by wind waves. The considered array processing methods include matched-signal processing, optimal processing of the signal on the background of interference and noise, and suboptimal processing based on matched-mode array filtering of one of the signal-carrying modes with adaptive selection of its number. Quantitative estimates are obtained from above for the environment uncertainties, or model errors, with respect to the sound velocity in the water column and geoacoustic parameters of the underlying bottom, at which the array gain loss does not exceed a given level. It is shown that such estimates are very different both for different environmental parameters and for processing methods, with the determining role played by the conditions of useful signal reception, namely, the modal composition and intensity levels of the interference and sea noise at the array input. The problem statement and results are considered to be useful to detail the requirements for operational oceanography tools designed to support the effective operation of sonar antenna systems in real sea environments.

RFGAN: RF-Based Human Synthesis

This paper demonstrates human synthesis based on the Radio Frequency (RF) signals, which leverages the fact that RF signals can record human movements with the signal reflections off the human body. Different from existing RF sensing works that can only perceive humans roughly, this paper aims to generate fine-grained optical human images by introducing a novel cross-modal RFGAN model. Specifically, we first build a radio system equipped with horizontal and vertical antenna arrays to transceive RF signals. Since the reflected RF signals are processed as obscure signal projection heatmaps on the horizontal and vertical planes, we design a RF-Extractor with RNN in RFGAN for RF heatmap encoding and combining to obtain the human activity information. Then we inject the information extracted by the RF-Extractor and RNN as the condition into GAN using the proposed RF-based adaptive normalizations. Finally, we train the whole model in an end-to-end manner. To evaluate our proposed model, we create two cross-modal datasets (RF-Walk & RF-Activity) that contain thousands of optical human activity frames and corresponding RF signals. Experimental results show that the RFGAN can generate target human activity frames using RF signals. To the best of our knowledge, this is the first work to generate optical images based on RF signals.

An Adaptive Hybrid Beamforming Approach for 5G-MIMO mmWave Wireless Cellular Networks

Hardware complexity reduction is a key concept towards the design and implementation of next generation broadband wireless networks. To this end, the goal of the study presented in this paper is to evaluate the performance of an adaptive hybrid analog-digital beamforming approach in fifth-generation (5G) massive multiple input multiple output (MIMO) millimeter wave (mmWave) wireless cellular orientations. In this context, generated beams are formed dynamically according to traffic demands, via an on-off analog activation of radiating elements per vertical antenna array, in order to serve active users requesting high data rate services without requiring any expensive and mechanical complex steering antenna system. Each vertical array, which constitutes a radiating element of a circular array configuration, has a dedicated radio frequency chain (digital part). The performance of our proposed approach is evaluated statistically, by executing a sufficient number of independent Monte Carlo simulations per MIMO configuration, via a developed system-level simulator incorporating the latest 5G-3GPP channel model. According to the presented results, the adaptive beamforming approach can improve various key performance indicators (KPIs) of the wireless orientation, such as total downlink transmission power and blocking probability. In particular, when studying/analyzing a MIMO configuration with 15 vertical antenna arrays and 10 radiating elements per array, then, depending on the tolerable amount of transmission overhead, the proposed adaptive algorithm can significantly reduce the number of active radiating antenna elements compared to the static grid of beams case. In the same context, when keeping the number of radiating elements constant, then the total downlink transmission power as well as the blocking probability can be significantly reduced. It is important to note that all the KPIs have been extracted when deploying the developed array configuration in complex cellular orientations (two tiers of cells around the central cell).

Multiport Vector Network Analyzer Radar for Tomographic Forest Scattering Measurements

We describe a P-, L- and C-band radar, BorealScat, designed for polarimetric time-series measurements of forests. Radar tomography is implemented with a vertical antenna array, which provides measurements of the vertical scattering distribution. To minimize temporal decorrelation, the radar performs simultaneous measurements of the reflected signals using all array elements. The system is implemented using a 20-port vector network analyzer (VNA) and a stepped-frequency waveform. It has two 20-element arrays: one array optimized for P- and L-bands and one for C-band. The arrays are installed on a 50-m high tower and radar measurements are collected over a hemiboreal forest stand. We discuss several design issues and demonstrate some tomographic imaging capabilities. The multiport VNA tomography results are compared with results from the system operating in the slower 2-port VNA measurement scheme.

Projection Techniques for Altitude Estimation Over Complex Multipath Condition-Based VHF Radar

In very high-frequency (VHF) radar, the performance of low-angle target tracking is strongly affected by multipath phenomenon, especially in the case of complex terrain where exact information of reflection paths is unknown. To deal with this problem, a practical multipath signal model for VHF radar in complex terrain is presented, where both curved earth geometry and actual ground surface reflection coefficient are considered. Then, a novel altitude estimation technique based on alternating projection is proposed, where the motion or Doppler shift of a target is neglected during the observation time of one coherent processing interval. The technique applies to vertical antenna arrays which perform an interferometric estimation of the target elevation angle. Simulation results and real data analysis show that the target tracking accuracy can be efficiently improved by using the proposed algorithm under both simple and complex multipath scenarios.

Estimation of efficiency of vertical antenna arrays in underwater sound channels

The gain of the vertical antenna array in a randomly inhomogeneous ocean waveguide is numerically simulated on the assumption that the useful signal is generated by a finite set of mutually uncorrelated discrete spectrum modes and is received against the ocean noise background. It is shown that the choice of themost effective weight distribution of the array and the thus obtained gain strongly depend on both the modal spectra of the signal and noise and the number and position of the receiving elements in the channel. The critical factor is the mutual orthogonality of the waveguide modes at the array input, which indicates the possibility of specially arranging the elements for the known (expected) mode spectrum of the signal.

Handoff Study of Ring Shaped Cellular Configuration Designed for High Altitude Platform Communications

In this paper, the concentric ring shaped cellular configuration is designed for High Altitude Platforms (HAPs). An one dimensional (1D) vertical linear antenna array is used to generate this configuration. The effect of different types of HAP mobility models, e.g. drift, random walk, and reflection has been examined. The possibility of reducing the need for mechanical stabilization via handoff techniques is demonstrated through the study of handoff, dropping, and blocking probabilities. General Terms Handoff probability, blocking probability, and dropping probability.

Temporal Survey of Polarimetric P-Band Scattering of Tropical Forests

This paper deals with the temporal survey of the tropical forest electromagnetic scattering with a ground-based radar equipment. Installed on the top of a 55 m flux tower overlooking the Paracou forest in French Guiana, a dense primary tropical forest, the radar system uses a vertical antenna array and it is able to provide every 15 minutes P-band complex scattering matrix coefficients. The experiment has been successfully set up and it is operating since October 2011. The main goal of this campaign is to investigate the evolution of the backscattering coefficient and the temporal coherence of the tropical forest at different time scales range. Data are calibrated in relative and processed to take advantage of the largest number of independent looks. Three months of data are exploited in terms of polarimetric temporal coherence and backscattering coefficient in the rainy season and about two months in the dry period. The temporal coherence exhibits daily cycles during the consecutive dry days, whatever the period, and these cycles are perturbed by the presence of rain. Its overall time series appear clearly dependent on the period, dry or rainy, and also on the polarization. The backscattering coefficient time series exhibit also a daily cycle during consecutive dry days, very clearly in the dry period but less pronounced or absent during the rainy period. The backscattering coefficient presents an overall relatively high stability over the full period.

A correlation leak detector with a vertical antenna array for seeking leaks in underwater pipelines

A correlation method for localizing leaks in underwater pipelines using a two-element vertical antenna is considered. The main calculation relationships were obtained and estimates of the error of this method are presented.

Optimization of mode composition of the acoustic field excited by a vertical antenna array in a shallow sea

The problem statement is described, and the solution to the problem of optical tuning of the radiating antenna array providing for the optimal mode composition of the field radiated to a waveguide is determined. Matlab software is developed based on the proposed algorithms, and the optimal fields for shallow sea waveguides are calculated.

Measurement of the parameters of the natural waveguide mode

The possibilities of using the decomposition of natural waveguide modes in a shallow-water sea in case there is a sound velocity gradient into sinusoidal modes of an ideal waveguide is grounded. The applicability range of such decomposition is shown. Dispersion in signals of the modes presented in such a way is determined by mathematical reversal without a test source. The structure of discrete modes in a natural waveguide is determined without utilizing the bottom parameters and sound velocity’s distribution over the waveguide depth. The coefficient of the mode signal’s correlation with the measured parameters of the mode signal and a real signal, introduced into it, is shown to be 0.973. The signals from a point emitter positioned at the depth of 50 m in the frequency range of 90–280 Hz in a shallow-water sea (the Barents Sea, a 120 m depth, a 7 km distance), received by a vertical antenna array comprising 32 receivers spaced equidistantly with a 3-m step are used in the experiment. A real signal has been successfully reversed using a mathematical model.

Modal time reversal of waves for shallow-water sea

A method is proposed for calculating the time-reversed wave field generated by a point source in a waveguide by using signals received by a vertical antenna array. The procedure of time reversal is based on representing the wave field in the form of the decomposition into modes of the ideal waveguide. In contrast to the earlier proposed simplified numerical method of time reversal of waves, the method presented here allows one to obtain the reversed field for the entire thickness of the waveguide. The method is successfully applied to a shallow-water sea with a depth of 120 m, at distances of 7, 10.5, and 12 km. It is shown that an opportunity arises to increase the gain of the array; to determine the parameters of the medium, including its stability in the presence of currents; and to match the point of transmission of an arbitrary received signal and the point of transmission of the reversed signal.

Adaptive beamforming applied to underwater acoustic measurements

In many applications, such as measuring the underwater noise level of moving ships, underwater acoustic measurements face serious difficulties related to several factors, including low signal‐to‐noise ratio, effects of surface and bottom on signal, as well as complicated spatial structure of the sea interference. The increase of the measurement interference resistance, compared to the case of a single receiver (hydrophone), can be provided by the use of spatially distributed receiving systems (antenna arrays), which are able to suppress the interference due to their spatial selectivity. The present work is aimed at developing adaptive methods for underwater acoustic measurements with the use of vertical antenna arrays. The method must provide the maximum reduction of external interference keeping the given measurement accuracy, i.e., the result must coincide with the output of a single receiver in the absence of interference. From the point of view of synthesis of array systems, the originality of the pre...

Summation of modes of a sound signal in a shallow sea

Results of an experiment on the summation of selected modes of a sound signal in a shallow sea (the Barents Sea, a sea depth of 120 m, a 17-km-long path) are presented. The experiment is performed with the use of a point source generating a broadband pulsed signal with a duration of 5 s and a linear frequency modulation within 100–300 Hz. The mode selection in the in-sea experiment is achieved using a vertical antenna array (32 hydrophones, length of 96 m). It is shown that the mode signals selected at the end of the path are formed with a part of the path. The modes are summed coherently (with the use of two methods) and incoherently. The noise immunity of the mode summation is estimated.

Null Steering Approach With Minimized PCV and GD for Large Aperture Vertical Antenna Arrays

A novel null-steering method that minimizes the effect of radio frequency interference (RFI) and the effect of antenna phase center variation (PCV) and group delay (GD) is proposed. PCV and GD are important to characterize for global navigation satellite system (GNSS) antenna arrays used in satellite based landing architectures, since they directly affect the pseudo-range and accumulated Doppler observables. The proposed method is denoted as the beam subtraction method (BS). The BS method is compared against a conventional null-steering (CNS) method applied to a large aperture antenna array. Simulation results reveal noticeable improvement in both the PCV and GD curves as a function of azimuth and elevation angles when using the BS method compared to the CNS thus reducing the error on the range measurements as well as improving system availability in the presence of RFI.

Use of the Coupling Between Elements of the Vertical Antenna Array of LCRs to Gain Radiation Efficiency for UWB Pulses

The inductance of large current radiators (LCRs) can be reduced by stacking several of them as a vertical array. The reduced inductance permits a shorter rise time for the driving current. Both theory and experimental data show that the radiated field strengths are increased considerably for a fixed, small driving voltage.

Modified null broadening adaptive beamforming: constrained optimisation approach

A constrained optimisation approach for null broadening adaptive beamforming is proposed. This approach improves the robustness of the traditional MVDR beamformer by broadening nulls for interference direction and the mainlobe for the desired direction. This optimisation is efficiently solved by semidefinite programming. The proposed approach, when applied to high altitude platform communications using a vertical linear antenna array, provides significantly better coverage performance than a previously reported null broadening technique.

Selection of modes in a shallow sea by using a vertical antenna array

The experimental data on selecting the modes in a shallow sea (the Barents Sea) on 17-and 8-km-long paths are presented. The data are obtained with the use of a 93-m-long vertical receiving array of 32 hydrophones and a point sound source transmitting a pulsed signal with linear frequency modulation in a frequency band of 100–300 Hz. The experimental selection of modes is based on the structure of normal waves in a waveguide with a perfectly reflecting impedance bottom. The bottom impedance for different modes is determined from the experiment. A pressure-release bottom and a bottom with an impedance that is intermediate between the pressure-release and rigid cases correspond to the first mode and the higher modes, respectively. The amplitudes of the modes and their directivity are determined. On the basis of the mode dispersion data and the comparison of the mode contents observed at distances of 8 and 17 km, it is concluded that higher modes are generated at the distances from 8 to 17 km.

Boundary element modeling of radio base station antennas

The paper presents an accurate and efficient boundary element procedure for the analysis of radiation from base station antennas. The base station antenna system is represented by the vertical antenna array in front of perfectly conducting (PEC) ground plane reflector. The formulation of the problem is based on a set of coupled Pocklington integro-differential equations for vertical antenna array. This set of coupled equations has been numerically treated by the indirect Galerkin–Bubnov boundary element method (GB-IBEM). The numerical results for the currents induced along the wires obtained via GB-IBEM are compared to the results computed via numerical electromagnetic code (NEC). Knowing the current distribution along the antenna array the corresponding radiated field is calculated. Some illustrative numerical results are presented in the paper.