Direction Finding Research Articles

Design of a Tripod-Shaped Radiator Patch Antenna for Ultra-Wideband Direction Finding.

As UWB technology develops and devices become smaller, miniaturization techniques for an array antenna system are required. In addition, more in-depth research is needed for UWB direction-finding techniques using channel impulse response (CIR) data. This paper proposes an ultra-wideband (UWB) antenna using a single-radiator multiple-port (SRMP) design for the direction-finding systems of smart devices. The proposed SRMP antenna was designed using a single tripod-shaped patch that can replace the array system. The tripod-shaped radiator was optimized using the edge shape design function to improve its broadband and mutual coupling characteristics. For performance verification, the proposed antenna was fabricated, and the reflection coefficient, mutual coupling, and radiation patterns were measured in a fully anechoic chamber. The proposed antenna has an operating frequency band of 6.1 GHz (from 5.8 GHz to 11.9 GHz) for port 1 and a measured mutual coupling of -14.8 dB at 8 GHz. The SRMP antenna has measured maximum gains of 3.5 dBi for port 1 and 2.9 dBi for port 2. To examine the direction-finding performance, the fabricated antenna was connected to a circuit module with a DW3000 chip, which is widely employed in commercial mobile UWB systems. The direction of arrival (DoA) results using the measured CIR data show root-mean-square (RMS) errors of 1.57° and 4.58° at distances of 30 cm and 60 cm.

A high precision indoor positioning system of BLE AOA based on ISSS algorithm

This paper investigates the Bluetooth direction finding technique and combines it with the improved signal subtraction subspace (ISSS) algorithm for precise indoor positioning. First, the phase offset caused by the electronic switch is solved by the phase compensation algorithm. Then, the ISSS algorithm is proposed by combining the spatial smoothing techniques algorithm, the density-based spatial clustering of applications with noise (DBSCON) techniques and the signal subtraction subspace (SSS), which reduces the interference of coherent signals and caused by moving between people in the room. Finally, different placement methods for receivers in different spatial shapes are proposed. In this paper, the positioning accuracy of the algorithm is tested using Silicon Labs' Bluetooth device. The results show that the average positioning errors are 0.92 m for single receivers and 0.30 m for dual receivers in a room size of 3 m * 3 m. Therefore, the method has a promising application in achieving accurate indoor positioning.

Simultaneous Correlative Interferometer Technique for Direction Finding of Signal Sources.

In this paper, we propose a novel simultaneous Correlative Interferometer (CI) technique that elaborately estimates the Direction of Arrival (DOA) of multiple source signals incident on an antenna array. The basic idea of the proposed technique is that the antenna-array-based receiver compares the phase of the received signal with one of the candidates at each time sample and jointly exploits these multiple time samples to estimate the DOAs of multiple signal sources. The proposed simultaneous CI-based DOA estimation technique collectively utilizes multiple time-domain samples and can be regarded as a generalized version of the conventional CI algorithm for the case of multiple time-domain samples. We first thoroughly review the conventional CI algorithm to comprehensively explain the procedure of the direction-finding algorithm that adopts the phase information of received signals. We also discuss several technical issues of conventional CI-based DOA estimation techniques that are originally proposed for the case of a single time-domain sample. Then, we propose a simultaneous CI-based DOA estimation technique with multi-sample diversity as a novel solution for the case of multiple time-domain samples. We clearly compare the proposed simultaneous CI technique with the conventional CI technique and we compare the existing Multiple Signal Classification (MUSIC)-based DOA estimation technique with the conventional CI-based technique by using the DOA spectrum as well. To the best of our knowledge, the simultaneous CI-based DOA estimation technique that effectively utilizes the characteristics of multiple signal sources over multiple time-domain samples has not been reported in the literature. Through extensive computer simulations, we show that the proposed simultaneous CI technique significantly outperforms both the conventional CI technique in terms of DOA estimation even in harsh environments and with various antenna array structures. It is worth noting that the proposed simultaneous CI technique results in much better performance than the classical MUSIC algorithm, which is one of the most representative subspace-based DOA estimation techniques.

CRB-based comparative study of array signal processing direction finding methods supported with SDR platform implementation

Radio Direction-Finding (DF) is an extremely important process in numerous commercial and military applications. Array signal processing-based DF methods have been developed to improve estimation performance in recent applications that require higher resolution and accuracy. Practically, angle of arrival (AOA) estimation is challenging due to various intrinsic and extrinsic parameters that affect the results. Therefore, clarifying these parameters and researching their impact on various DF methods are considered important research topics. The Cramer-Rao Bound (CRB) for estimating AOA is calculated based on a model of a linear antenna array system. This bound identify the factors that significantly impact the estimation performance. The current study conducts a comparative analysis of the most widely used array-signal-processing-based direction-finding (DF) methods under different conditions of the CRB parameters. According to the simulation results, Multiple Signal Classification (MUSIC) AOA estimator provides more accurate and stable results. Accordingly, it is chosen for implementation using a prototype testbed based on Software Defined Radio (SDR) technology using National Instruments Universal Software Radio Peripheral (NI-USRP) platform version 2930. Experimental outcomes were tested at various AOA values. The appendix includes the complete derivation for the CRB relation applied on the system model.

Guiding an Unmanned Aerial Vehicle with a Thermal Imaging Correlation-Contrast Algorithm of Automatic Tracking in Conditions of Information Counteraction

The problem of constructing an algorithm for automatic tracking of a ground object for a guidance system (GS) for an unmanned aerial vehicle (UAV) is considered. The guidance system includes a thermal imaging target coordinator with a combined correlation-contrast direction finding algorithm and a strapdown inertial navigation system. Guidance takes place under conditions of information counteraction, which causes random interruptions in information and random changes in the power of interference, which are recorded by the corresponding indicators. A combined noise-resistant automatic tracking algorithm is obtained, using the readings of information interruption indicators, interference power, and measuring bearing angles, based on the theory of systems with a random jump structure. An example is given that illustrates the operation of the algorithm and demonstrates the satisfactory accuracy of automatic tracking.

Monopulse Leaky Wave Antennas for RSSI-Based Direction Finding in Wireless Local Area Networks

Monopulse Leaky Wave Antennas for RSSI-Based Direction Finding in Wireless Local Area Networks

Improving the accuracy of a digital spectral correlation-interferometric method of direction finding with analytical signal reconstruction for processing an incomplete spectrum of the signal

A method of correlation-interferometric direction finding has been improved, which effectively solves the problem of radio direction finding of radio emission sources under conditions of exposure to one or two masking interference. The problem was solved using the selection of an unmasked fragment of the spatial spectrum of the signal and the reconstruction of the missing samples of its signal group. As a result of the synthesis of the proposed method, estimates of signal samples were obtained as exact solutions to the proposed energy balance equations. The resulting solutions provide a significant increase in the signal-to-interference ratio and, accordingly, direction-finding accuracy without increasing the number of reception channels of the antenna array. As a result of the simulation, the dependences of the standard deviation of the bearing estimate on the signal-to-noise ratio in the presence of interference were built. Under the influence of one or two masking interferences and a signal-to-interference ratio of 0 dB, the use of the known direction-finding method without interference selection produces an anomalously large direction-finding error of more than 0.42 degrees, which is practically independent of the signal-to-noise ratio. The direction-finding method with selection of spectral signal samples masked by interference reduces the direction-finding error to 0.22 degrees when exposed to one interference and to 0.3 degrees when exposed to two interferences. This is due to the presence of power losses of the usable signal during the selection of its samples masked by interference. The proposed method of direction finding with reconstruction of signal samples provides a significant gain in accuracy by 3–30 times compared to the method of selection of masked samples in the range of changes in the signal-to-noise ratio (–20.5) dB. The direction-finding error of the proposed method decreases with increasing signal/noise according to a hyperbolic dependence. It is advisable to use the proposed direction-finding method when masking no more than two samples of the signal group

Wideband Antennas of Passive Seekers for Anti Radiation Missiles

Suppression of Enemy Air Defence (SEAD) is a fundamental element of Air Power application by means of in protecting friendly air attackers and destroying the enemy’s ability to defend against air attack. Most of the SEAD operation even today relies on Anti-radiation missile (ARM) which is an air-to-surface tactical missile designed to detect, seek, attack and destroy opponent’s radar. Passive seeker of ARM is a miniaturized ESM receiver which is capable of extracting the necessary angular data from the enemy radar emissions. Single head passive seeker covering wide frequency range from L to Ku band is the preferred choice. Wideband antennas have been designed and utilized for Direction Finding applications of ESM/ELINT receivers for ground, air and ship borne platforms. Unlike these platforms, there are several restrictions for passive seeker based compact ESM receiver for missile borne platform specially air to surface missile where lesser diameter is one of the preferred design parameter. This review paper mainly discusses the existing wideband antennas such as spiral, log-periodic, printed circuit vivaldi and all-metal vivaldi antennas and the comparison of their various parameters for passive seeker. The paper also suggests their suitability with respect to their placement on the missile for three configurations: concealed inside the radome, flush-mounted and conformal antenna based. The paper also brought about the specific test facility required for testing and evaluation of passive seeker to characterize it with missile radome which is the most challenging and time consuming task. Among the three passive seeker configuration discussed, conformal antenna based passive seeker using all-metal Vivaldi is the best option avoiding radome aberration correction which is being utilized in the present third generations of ARM. The second commonly and established passive seeker configuration is concealed inside the radome using spiral antennas where handling radome aberration correction is a limitation.

Information Entropy-Based Cooperative Surveillance in Areas with Obstacles

This paper solves the problem of searching a surveillance region and tracking possible radio emitters by multiple unmanned aerial vehicles cooperating through communication links in a decentralized manner. An innovative entropy-based approach is utilized to obtain the routes and tasks (search/track) for the vehicles. Another significant contribution of this research is the assumption of each vehicle being equipped with only one simple and cost-effective direction finding (DF) sensor. The routes and tasks are determined by minimizing a well-defined entropy-based cost function. The proposed surveillance scheme allows one to find a feasible and near-optimal solution. The algorithm’s efficiency is verified through various simulations.

Influence of radar direction finding errors
 of aerological radiosonds on the accuracy of wind sounding

Influence of radar direction finding errors
 of aerological radiosonds on the accuracy of wind sounding

The effect of lamppost scatterers on direction finding by cylindrical arrays of dipoles intended for smart antenna application in wireless communications

Smart antennas are widely used to enhance the capacity of the wireless communication systems in urban areas. To enhance the capacity by increasing the signal to noise ratio, one should estimate the angle of arrival precisely. In urban areas, the scattering from the lampposts in a boulevard or a highway is not negligible and its effect should be considered in direction finding algorithms. In this paper the lampposts are modelled by thick and long cylindrical scatterers and the scattered electric field is computed in terms of the cylindrical harmonics analytically. Then the total electric field is evaluated to estimate the angle of arrival by MUSIC direction finding algorithm. The computed total electric field with the proposed method shows a good agreement with precise HFSS simulation results for different incident angles. Monte-Carlo simulations are conducted to evaluate the RMS error values using cylindrical array of dipole antennas for direction finding and the results show that the proposed method can model the effects of the finite number of the lampposts in a wireless propagation scenario adequately, with reduced burden of computations. This fact contributes to a better planning of the beamforming in smart antennas with corresponding resolution.

Direct Immunofluorescence Findings and Factors Affecting Conjunctival Biopsy Positivity in Ocular Mucous Membrane Pemphigoid.

The aim of this study was to describe the direct immunofluorescence (DIF) findings and factors affecting conjunctival biopsy positivity in patients clinically diagnosed with ocular mucous membrane pemphigoid (OMMP). This retrospective observational case series included patients with clinical OMMP who underwent conjunctival biopsy for DIF in at least 1 eye between 2018 and 2021 in an institutional setting. The primary outcome measures were association of age and chronic ocular complications with biopsy positivity. Of 61 patients, DIF positivity was seen in 33 (54.1%) clinically suspected cases of OMMP. Of 39 patients who underwent bilateral biopsy, 23 (59%) were positive, of which 12 (52%) were positive in both eyes while 11 (48%) were positive in 1 eye. Of 22 patients who underwent unilateral biopsy, 10 (45%) were positive. Of the 100 biopsied eyes, 45 (45%) were DIF positive. Among the immunoreactants studied, linear deposition of C3 was seen in all 45 positive eyes (100%). Increasing age was significantly associated with higher likelihood of biopsy negativity ( P = 0.032), whereas a greater Sotozono chronic ocular complication score, indicative of disease severity, was associated with low likelihood of biopsy positivity ( P = 0.0042) and lower overall expression of immunoreactants on DIF ( P = 0.0007). Older patients and patients with more severe ocular surface disease sequelae are likely to have negative DIF results. To optimize the chances of confirming the diagnosis of OMMP by DIF, both eyes should be biopsied early in the disease course. If 1 eye is being biopsied, the less affected eye must be chosen.

Methodology for processing information of a multi-base phase direction finder and assessing the quality of results, taking into account failures and deterioration in the operation quality of individual MPDF bases

When conducting radio-electronic monitoring (SEM) by systems of various types of basing, phase direction finding methods are widely used. To obtain both high accuracy and unambiguity of direction finding, a reusable phase direction finder (MBFP) is used. In the literature, quite a lot of works are devoted to methods for optimizing MBFP structures. In this paper, the issues of automation of accounting for failures or deterioration of the quality of work of individual MBPF databases in the process of processing direction finding information obtained during the management of SEM are considered. The determination of the bearing (guiding sine) on the radiation source with the phase direction finding method is carried out by a set of phase differences obtained at the output of a multi-phase phase direction finder (MBFP).

Алгоритм определения направления на источник радиоизлучения в двухканальном фазовом радиопеленгаторе

The article presents a block diagram of a two-channel phase direction finder with amplitude modulation of the signal. The features of the formation of a radiation pattern in the form of a cardioid using non-directional biconic antennas are considered. An algorithm for estimating the bearing using a limited number of antenna elements (two direction finding pairs) is proposed. A variant of increasing the number of bearing estimates for one contact with a radio source based on the use of a sliding buffer is presented.

Analysis of the electromagnetic availability of radio signal sources during propagation in the ionosphere radio channel

Problem statement. Multi-channel automated short-wave radio communication networks are used to provide information support for the activities of critical facilities and the organization of information exchange between subscribers assigned to a large area, as well as the control of aircraft when flying at transcontinental ranges and sea vessels in remote areas of the world ocean. The probabilistic-temporal characteristics of the effectiveness of monitoring their dynamic states largely depend on the electromagnetic availability of radiation sources. The conditions of their electromagnetic availability must be determined by the values of the maximum applicable frequency and spatial-energy characteristics of the signals in the ionosphere radio channel. Time periods of stable reception must be set taking into account possible changes in ray trajectories and fading (fading) of signals due to refraction in ionized layers of the atmosphere during daily and seasonal fluctuations of electrical parameters. To determine the current values of the radio channel parameters, the International Reference Model of the Ionosphere and GOST 25645.146-89 “Earth's Ionosphere. Model of the global distribution of concentration, temperature and effective frequency of electron collisions”, which reflects the patterns of distribution of average values of the electron concentration in the Earth's ionosphere at different times of the year and day with changes in solar and geomagnetic activity. Goal. Evaluation of the electromagnetic availability of short wave emitters for monitoring posts based on a rational choice of operating frequencies and finding the spatial and energy characteristics of signal reception. Results. A predictive model has been developed for assessing the electromagnetic accessibility of radio signal sources by the values of the maximum applicable frequency and spatial and energy characteristics during propagation in the ionosphere radio channel. The profile of the ionized layers of the atmosphere and the structure of radio channel undergo changes depending on the mutual position of the Earth and the Sun, as well as solar activity and the latitude of the observation site. In the profile of the ionized structure of the atmosphere, four characteristic regions are conventionally distinguished – layers D, E, F1, F2. Due to the intrinsic fluctuations in the parameters of ionized layers under the influence of a large number of factors, ground-based complexes of vertical (inclined) sounding and a satellite system for observing the ionosphere do not provide the required reliability of data on its state in real time for the entire surface of the Earth. Based on certain values of the optimal operating frequencies and inclination angles of the ionosphere wave ray trajectories, the time intervals of the electromagnetic availability of transmitters located in different regions in the summer and autumn-winter periods were found. Based on the estimates of the maximum applicable signal frequencies in the ionosphere radio channel using an azimuth-elevation detector-direction finder located in the Central Federal District, the angles of inclination of the trajectories when receiving radio station signals meteorology information of airfield networks of the Russian Federation and neighboring countries were determined. The detector-direction finder used an active antenna array of 16 asymmetric vibrators 2.5 m high, located on an area of 200×200 m, and synchronized coherent radio devices with frequency conversion. Measurements were carried out in the Doppler ray separation mode when selecting signals at matching frequencies was carried out in accordance with the time schedule for the operation of radio stations. On routes with a length of about 1000 km, variations in the directions of arrival of signals along the elevation angle with 3 reflections from the ionosphere reach 15...20°, and in the azimuth plane - up to 4...5°. On routes with a length of more than 1000 km, the fading of signals is determined by the interference of beams commensurate in level; on routes with a length of more than 2000 km, as a rule, one beam prevails, and fading is due to a change in its heterogeneous-style in time. Practical significance. The predictive model for analyzing the electromagnetic availability of radio emission sources makes it possible to select the modes of operation of monitoring posts with the establishment of a period of time with the best conditions for receiving signals in given areas, based on the values of the maximum applicable frequency of radio channels and the angles of arrival of a sky wave with the highest power. The obtained results form the basis for improving the technology of monitoring the radio-electronic situation when receiving signals propagating over the ionosphere radio channel, and justifying the tactical and technical requirements for the characteristics of high frequency range direction finders.

Striation-based beamforming using a horizontal array

Conventional beamforming (CBF) based on plane waves is widely used for direction finding with a horizontal array deployed in ocean waveguides. However, CBF suffers from loss of spatial coherence due to the inhomogeneous field produced by constructive and destructive interference between multipath arrivals. Moreover, the grazing angle propagation leads to a bias in the estimated bearing. In this work, we revisit the striation-based beamforming (SBF) that exploits the waveguide invariant representing the complex wave propagation [Zurk and Rouseff, J. Acoust. Soc. Am. 132, EL264 (2012)]. Our approach involves a preliminary processing to restore the spatial coherence across the horizontal array, followed by CBF. Experimental results illustrate the performance improvement of SBF over CBF in terms of array gain, resolution, and bias.

Simulation of Spatial Polarization Characteristics of a Triorthogonal Antenna Element for the Tasks of HF Band Bearing

Introduction. Achieving improved accuracy and sensitivity of the direction finding of radio signals represents a relevant research direction in the field of modern HF radio monitoring. HF radio waves propagate through ionospheric layers, which distorts the polarization parameters of the passing electromagnetic wave (EMW). One possible approach to improve the accuracy and sensitivity of the direction finding of HF radio signals consists in the use of an antenna element capable of accepting both components of the electromagnetic field in the antenna array.Aim. A comparative analysis of the proposed triorthogonal antenna element with existing solutions for the tasks of HF band bearing.Materials and methods. Antenna elements and their spatial polarization characteristics were simulated in the MATLAB environment using the Phased Array toolbox.Results. The spatial polarization characteristics of the triorthogonal antenna under study were constructed and compared with an asymmetric vertical vibrator and a biorthogonal antenna. The comparison showed that at small elevation angles, the triorthogonal antenna ensures an energy gain of up to 4.5 dB compared to a biorthogonal antenna and an asymmetric vertical vibrator. At elevation angles of 30…60° and over 60°, the increase in the quality of a signal received by the triorthogonal antenna element reaches 3 dB and 2 dB, respectively.Conclusion. According to the obtained spatial polarization characteristics, the triorthogonal antenna under study can be part of a large-base antenna array of the HF band. The use of this antenna will increase the accuracy and sensitivity of direction finding by means of matching the antenna element with the EMW polarization

Therapeutic Hypothermia and Cell Therapy Change Cognitive Functions of Spontaneously Hypertensive Rats

The paper presents the research results of spatial memory and learning processes for the comprehensive analysis of cognitive function of spontaneously hypertensive rats under the influence of independent and combined use of rhythmic craniocerebral hypothermia (RCH) and the introduction of cryopreserved cord blood nucleated cells (cCBNCs). It was shown that SHR rats have a cognitive deficit, which is manifested in reduced speed of the learning process and memory formation in the Morris water maze (MWM). The administration of therapeutic RCH and/or cell therapy (cCBNCs introduction) 30 days before training in the MWM improved the cognitive functions of SHR rats: the target search strategy changed, and the time to search for a platform hidden under water was significantly reduced. These changes indicated the acceleration of the processes of information perception, learning, and the formation of spatial memory. The preservation and reproduction of long-term memory and as a result of the formed strategy of direct finding of the target in the MWM was most influenced by certain therapy with the samples of cryopreserved cord blood in combination with the procedure of therapeutic hypothermia. It was established that this approach exerted a neuroprotective effect, contributing to the partial elimination of cognitive deficits in SHR by improving spatial memory and accelerating learning processes.

Using coherent processing algorithms for direction finding of UAV acoustic signals

Small UAVs are often used in a group, since their signals are highly correlated, their resolution is reduced when using non-coherent processing.
 The article analyzes the well-known methods of coherent processing of acoustic signals in order to increase the resolution in the direction finding of signals with a high degree of correlation. Obtaining qualitative indicators of the analyzed algorithms was carried out by the method of statistical computer modeling in the Matlab environment.
 Based on the simulation results, it is shown that coherent signal processing methods are the most stable in conditions of low signal-to-noise ratios, while non-coherent ones show the best results in the region of high signal-to-noise ratio, while coherent algorithms can potentially distinguish more targets. the WAVES coherent algorithm performs better in the high signal-to-noise ratio region, but loses to the CSSM algorithm in the low signal-to-noise region.
 To increase the efficiency of coherent processing of multipath signals, it applies spatial filtering of the inputsignal.

Assistant vehicle locating based on DOA estimation of deep unfolded network

In view of the decline in the positioning accuracy of the vehicles with small snapshots, this paper proposes a direction of arrival(DOA) estimation method based on deep unfolded network to assist the global positioning system to achieve high-precision locating. Firstly, the signal emitted from the on board unit installed on the vehicle is received by the array antenna of the road side unit(RSU), then RSU transmits the array data to cloud service platform, in which the traditional fixed point continuation algorithm is improved by using l1 norm instead of l2 norm, and the adaptive outlier point tracking algorithm is used to deal with the problem of symbol flipping caused by noise. Then we unfold the improved fixed point continuous algorithm for obtaining a neural network. In order to improve the DOA estimation performance and convergence speed, this paper uses the black widow optimization algorithm to determine the soft threshold shrinkage parameters. According to the mapping between the signal and the array manifold matrix, the DOA of the target is estimated, and its location can be evaluated from the geometry relation between vehicle and RSU. The simulation results show that the algorithm proposed in this paper has better direction finding performance and improves the vehicle positioning accuracy under small snapshots and high signal-to-noise ratio effectively.