Direction Finding Applications Research Articles

A Comparative Performance Analysis of Two Printed Circular Arrays for Power-Based Vehicle Localization Applications

A comparative study of the performance characteristics of a printed 8-element V-shaped circular antenna array and an 8-element Yagi circular array operating at 2.45 GHz for vehicular direction finding applications is presented. Two operating modes are investigated; switched and phased modes. The arrays were fabricated on FR-4 substrates with 0.8 mm thickness. Measured and simulated results were compared. Radiation gain patterns were measured on a 1 m diameter ground plane that resembles the rooftop of a vehicle. The HPBW of the Yagi was found to be about 3° narrower than its V-shaped counterpart when measured above a reflecting ground plane and operated in switched mode. The printed V-shaped antenna array offers 2.5 dB extra gain compared to the printed Yagi array.

Conformal antenna array for ultra-wideband direction-of-arrival estimation

The design and full-wave analysis of an antenna system for ultra-wideband radio direction finding applications is presented. The elliptical dipole antenna is selected as antenna element due to its robust circuital and radiation properties. The influence of the conformal deformation on the antenna performance has been studied in details. A suitable radome is designed to enhance the antenna front-to-back radiation ratio, as well as to increase the environmental durability of the structure. The considered antennas are optimized for their adoption in two different sub-arrays covering the [250, 950] MHz and [0.9, 3.3] GHz frequency bands, respectively. A uniform circular array (UCA) with five elements is used for the array topology. The full-wave analysis of the whole array structure is carried out in order to evaluate the coupling between the antenna elements. In particular, a novel calibration technique is developed in order to compensate for the mutual coupling between the array elements, possible variations in the antenna characteristics, and the effects of the array bearing structure. The performance of the designed array in terms of direction-of-arrival estimation is thoroughly analyzed and discussed.

Wire-Frame Monocone Antenna for Direction-Finding Applications on Unmanned Aerial Vehicle Platform

A detailed design for a loaded wire-frame monocone antenna for direction-finding applications on an Army UAV platform is presented. This was used to compare simulation and measurement results of radiation-pattern and gain measurements for a scaled prototype mounted on a UAV wing, using the FEKO electromagnetic-simulation software. The results indicated that this antenna design offers bandwidth and gain performance that is far superior to many other passive antenna candidates. The results also confirm the accuracy and efficiency of using FEKO for modeling candidate antennas integrated onto large-scale Army platforms.

A Beam Steering Radial Line Slot Array (RLSA) Antenna with Reconfigurable Operating Frequency

A beam steering radial line slot array (RLSA) antenna with reconfigurable operating frequency is proposed in this paper. The RLSA antenna is fed by an aperture coupled structure, which incorporates PIN diode switches that are integrated with the feed line. It is found that the beam steering ability and reconfigurable operating frequency are greatly influenced by the spiral and radius of feed line respectively. The activation of certain PIN diode switches configuration would then determine the beam steered angle and the frequency of operation. This novel antenna design is capable of steering its radiated beam to four different angles; 0°/360°, 90°, 180°, and 270°. Furthermore, the proposed antenna can be configured to operate from a single centre frequency, up to four operating centre frequencies concurrently, at each steered beam direction. The four frequencies are 2.3 GHz, 2.6 GHz, 2.9 GHz and 3.3 GHz. This antenna is a promising candidate to be installed for a smart antenna system, cognitive radio, radar or direction finding applications in the future.

Mutual Coupling Compensation for Direction-of-Arrival Estimations Using the Receiving-Mutual-Impedance Method

A short review of the receiving-mutual-impedance method (RMIM) for mutual coupling compensation in direction finding applications using linear array is conducted. The differences between the conventional-mutual-impedance method (CMIM) and RMIM, as well as the three different determination methods for receiving mutual impedance (RMI), will be discussed in details. As an example, direction finding with better accuracies is used for demonstrating the superiority of mutual coupling compensation using RMIM.

Utilization of antenna arrays in HF systems

Different applications of radio systems are based on the implementation of antenna arrays. Classically, radio di- rection finding operates with a multi channel receiving system connected to an array of receiving antennas. More recently, MIMO architectures have been proposed to increase the capacity of radio links by the use of antenna arrays at both the transmitter and receiver. The first part of this paper describes some novel experimental work carried out to examine the feasibility of ap- plying MIMO techniques for communications within the HF radio band. A detailed correlation analysis of a va- riety of different antenna array configurations is presented. The second section of the paper also deals with HF MIMO communications, focusing on the problem from a modelling point of view. The third part presents a sen- sitivity analysis of different antenna array structures for HF direction finding applications. The results demon- strate that when modelling errors, heterogeneous antenna arrays are more robust in comparison to homogeneous structures.

On the improvement of the mutual coupling compensation in DOA estimation

A new and exact calculation method for the mutual impedance matrix of receiving arrays is proposed. The mutual impedance matrix is derived from electromagnetic boundary conditions and can be used to relate the coupling free open-circuit voltages, instead of the conventional ones, to the measured voltages. A remarkable improvement on compensation for the coupling effects is shown in the direction finding applications, while a simple relationship between measured terminal voltages and the coupling free voltages is remained.

A Multi-Channel Correlative Vector Direction Finding System Using Active Dipole Antenna Array for Mobile Direction Finding Applications

A fast correlative vector direction finding(CVDF) system using active dipole antenna array for mobile direction finding(DF) applications is presented. To develop the CVDF system, the main elements such as active dipole antenna, multi-channel direction finder, and search receiver are designed and analyzed. The active antenna is designed as composite structure to improve the filed strength sensitivity over the wide frequency range, and the multi-channel direction finder and search receiver are designed using DDS-based PLL with settling time of below 35 us to achieve short signal processing time. This system provides the capabilities of the high DF sensitivity over the wide frequency range and allows for high probability of intercept and accurate angle of arrival(AOA) estimation for agile signals. The design and performance analysis according to the external noise and modulation schemes of the CVDF system with five-element circular array are presented in detail.

Disk-Loaded 다이폴과 Folded 다이폴로 동작하는 Reconfigurable 안테나

본 논문에서는 PIN 다이오드를 사용하여 disk-loaded 다이폴 안테나와 folded 다이폴 안테나로 형상이 변화하는 새로운 구조의 소형 안테나를 개발하였다. 개발된 안테나는 PIN 다이오드의 RF on/off 특성을 이용하여 안테나의 전기적 길이를 변화시켜 이중 대역에서 동작하며, 저주파 대역에서는 높은 복사 저항 값을 가지는 folded 다이폴 안테나로 동작하고 고주파 대역에서는 수평 방향으로 무지향성의 복사 패턴과 수직 방향으로 도넛 형태의 복사 패턴을 가지는 disk-loaded 다이폴 안테나로 동작한다. 제안된 안테나는 <TEX>$20{\sim}300$</TEX> MHz에서 30cm 다이폴 안테나에 비해 크기가 소형화 되었음에도 높은 이득을 가진다. 또한, <TEX>$300{\sim}1,300$</TEX> MHz에서 <TEX>$80^{\circ}$</TEX> 이상의 넓은 빔 폭을 가짐으로써 방향 탐지 안테나로 사용이 가능하다. In this paper, we propose a reconfigurable antenna which operates as a disk-loaded dipole antenna and a folded dipole antenna alternatively using RF on/off switches. The antenna can change its effective length to achieve dual-band operation; operates as the folded dipole antenna for stepping up the radiation resistance in low frequency band of <TEX>$20{\sim}300$</TEX> MHz, and as the disk-loaded dipole antenna for an omni-directional radiation pattern (horizontal plane) and a donut-shaped radiation pattern (vertical plane) in high frequency band of <TEX>$300{\sim}1.3$</TEX> GHz. In the low band, the proposed antenna shows higher gain than a conventional dipole antenna with a reduced antenna size. In the high band, the antenna maintains a broad beamwidth of about <TEX>$80^{\circ}$</TEX>, thus the antenna can be applicable to antennas for direction finding applications.

방향 탐지용 소형 안테나 설계

본 논문에서는 새로운 구조의 방향 탐지용 소형 안테나를 제안하였다. 제안한 안테나는 800 MHz 이상의 고주파 대역에서도 안테나의 복사 패턴이 일그러지지 않도록 끝이 구부러진 스커트 모양의 디스크가 연결되었으며, 200 MHz 이하의 저주파 대역에서 증폭기와의 임피던스 매칭이 가능하도록 다단 구조의 매칭 스터브가 삽입되었다. <TEX>$20{\sim}700 MHz$</TEX>에서 제안된 안테나는 60cm 다이폴 안테나에 비해 크기가 1/2로 축소되었음에도 불구하고 유사한 성능을 가진다. 또한, 다이폴 안테나와 달리 <TEX>$700{\sim}1,300 MHz$</TEX>에서 복사 패턴이 크게 일그러지지 않고 주 빔 방향으로 널이 발생하지 않으며 넓은 빔 폭을 가진다. In this paper, we propose a novel small antenna for direction finding applications. The proposed antenna employs a skirt type disk to eliminate the radiation null on the broad-side direction in the high frequency range. Additionally, the multi-section matching stub is used for impedance matching in the low frequency range, The size of the proposed antenna is reduced as a half of the 60cm dipole which has a same resonance frequency of 200MHz. The antenna maintains a donut shape radiation pattern with a broad beam width for a wide range of frequency while the 60cm dipole shows radiation nulls on the broad-side direction and the high side-lobe level from 700MHz to 1,300MHz.

Hybrid Applications of RF Lens and Absorbing Material to Optimize the Radiation Patterns of Four-arm Spiral Antennas in the Direction Finding System

The broad radiation patterns of the four-arm spiral antenna can potentially cause difficulties in the practical direction finding applications. For example, the patterns might be interfered with multi-path signals, which will cause errors in the angle estimation, when installed in an aircraft structure. This paper proposes a hybrid application of RF lens and absorbing materials to optimize the radiation patterns so that the antennas may retain their advantageous characteristics in the applications of direction finding system. The characteristics of the impact on the angle estimations with this hybrid structure will be examined by numerical simulations and validated by experimental measurements.

Fast Direction Finding Using Modified Pseudocovariance Matrix

A modified pseudocovariance matrix is described which can improve the performance of Kim 's (Fast DOA estimation algorithm using pseudocovariance IEEE Trans. Antennas Propagat., vol. 53, no. 4, pp. 1346-1351, Apr. 2005) algorithm to realize the fast direction finding with single snapshot in coherent or uncorrelated case. By adding the backwards formulation of pseudocovariance matrix, the rank of pseudocovariance matrix is enhanced. Then a set of pseudocovariance matrices are constructed by circularly shifting the matrix. By weighted averaging, a modified pseudocovariance matrix is reconstructed whose noise is reduced. The proposed matrix has less array element loss than that of the original matrix. Moreover, this algorithm can be applied in the lower signal-noise-ratio (SNR) through noise preprocessing. The new matrix has expanded the application of high-resolution direction finding to nonuniform linear array (NLA), since traditional methods usually assume the array is uniform linear when handling coherent sources. Simulations are conducted to compare the performance of the modified method and the original method. The results illustrate that the high performance of DOA estimate could be obtained rapidly

High-Resolution Direction Finding From Higher Order Statistics: The$2rm q$-MUSIC Algorithm

From the beginning of the 1980s, many second-order (SO) high-resolution direction-finding methods, such as the MUSIC method (or 2-MUSIC), have been developed mainly to process efficiently the multisource environments. Despite of their great interests, these methods suffer from serious drawbacks such as a weak robustness to both modeling errors and the presence of a strong colored background noise whose spatial coherence is unknown, poor performance in the presence of several poorly angularly separated sources from a limited duration observation and a maximum of N-1 sources to be processed from an array of N sensors. Mainly to overcome these limitations and in particular to increase both the resolution and the number of sources to be processed from an array of N sensors, fourth-order (FO) high-resolution direction-finding methods have been developed, from the end of the 1980s, to process non-Gaussian sources, omnipresent in radio communications, among which the 4-MUSIC method is the most popular. To increase even more the resolution, the robustness to modeling errors, and the number of sources to be processed from a given array of sensors, and thus to minimize the number of sensors in operational contexts, we propose in this paper an extension of the MUSIC method to an arbitrary even order 2q (qges1), giving rise to the 2q-MUSIC methods. The performance analysis of these new methods show off new important results for direction-finding applications and in particular the best performances, with respect to 2-MUSIC and 4-MUSIC, of 2q-MUSIC methods with q>2, despite their higher variance, when some resolution is required

Implementation of physical optics analysis of spiral antenna radiations in the presence of Bor radome structure for the application of direction finding

A practical physical optics (PO) implementation procedure is employed to study the radiations of multi‐arm spiral antennas in the presence of a body of revolution (BOR) radome structure in direction finding applications. This procedure potentially simplifies the geometrical optics ray tracing procedure based on characteristics of spiral antennas, which is required to define the equivalent currents of PO, and provides efficient formulations to compute the radiation fields due to PO currents that are equivalent to the radiation of spiral antennas in the presence of the same type radome structure.

Structural properties and stability of metastable phases in the Zr-Nb system: Part II. Aging of bcc (β) alloys and assessment of β-Zr

The lattice parameters (LPs) of the bcc (β) phase occurring metastably in a series of Zr-rich Zr-Nb alloys have been determined at and above room temperature (T R ) using neutron diffraction techniques. LP values at T = T R were determined in alloys with Nb contents in the range 8.4 ≤ at. pct Nb ≤ 23 using both standard and high-resolution neutron diffractometry. These results support the applicability of Vegard’s law at T R . In addition, a neutron thermodiffractometric technique is used to establish the LP vs T relation of the β phase in two Zr-Nb alloys with 18 and 23 at. pct Nb up to 700 K. Such high-temperature data are used in a generalized Vegard’s law approach to gain insight into the LP vs T relation of the β phase in pure Zr, which is metastable in this temperature range. With these new LP values, an assessment is performed of the thermal expansion coefficient of β-Zr covering both stable and metastable states. As a direct application of the present findings, the results of an aging experiment are discussed, which provide information on the composition of the β phase taking part in the bcc-hcp equilibrium in the Zr-Nb phase diagram at 900 K. Such composition has been the subject of contradictory reports in recent literature. The composition value arrived at in the present analysis agrees well with the results of a thermodynamic calculation of the Zr-Nb phase diagram (A. Fernandez Guillermet: Z. Metallkd., 1991, vol. 82, p. 478)

Hypothesis of Natural Radar Tracking and Communication Direction Finding Systems Affecting Hornets Flight — Abstract

—The hypothesis of a natural sophisticated RADAR tracking system affecting hornets flight was described, analyzed and developed in previous papers [1, 2] considering their (cuticle) skin complex spike elements arrays shown by electronic microscope pictures. The existence of different spike length arrays and their disposition lead, by analogy with antenna, and radio theory and practice, to the hypothesis of transmitting and receiving phased arrays antennae operating at three different wavelengths in the sub-millimetric bands. The natural photo-and piezo electric generation of energy in the hornets reported previously explain how is generated the Radio Frequency (RF) energy required for the operation of the sub-millimeter wavelength natural RADAR system. However, similar to bats, new computation results show that the operation range of hornets RADAR system is limited to less than 100 m. Recently, investigations have shown that also in the hornet two antennae are located hundreds of spikes which may radiate and detect significant radio energy from their internal photo electric sources and piezoelectric effect. Thus, the existence of three separate sources of radiation and detection enable the application of Direction Finding (DF) communication additional hypothesis. The DF concept can contribute

Simulation of mutual coupling effect in circular arrays for direction-finding applications

The effect of mutual coupling on direction finding in circular arrays is simulated using rigorous electromagnetic computation and the MUSIC superresolution algorithm. The various scenarios studied include element spacing, noise level, antenna gain and delay, and platform effects. Our results show quantitatively the effect of mutual coupling on the direction-of-arrival estimates. The compensation of the coupling effect using the coupling matrix approach is also examined. This approach is found to be quite satisfactory in most cases, except when the array calibration data contain a high noise level or when strong platform effects are present. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 26: 331–336, 2000.

DOA estimation of wide-band signals based on time-frequency analysis

A numerical study on an approach based on the time-frequency analysis is performed for the high-resolution direction finding applications of wide-band signals. In this method, the direction of arrival (DOA) is estimated using a subband of the incoming signal instead of the whole signal spectrum. This treatment forces the DOA of the wide-band signals to be similar to that of the DOA of the narrow-band signals. The reason behind this can be thought of as the after effects of reducing the signal bandwidth, which constrains the signal subspace. An empirical analysis of the performance of the DOA estimator Is also investigated. This is done to compare the correct and estimated angles of separation between the targets, and it is demonstrated that there is a good agreement which implies that the use of prefiltering does not affect the resolution of the DOA estimator.

Short leaky-wave antennas of sum and differencepatterns

A set of differential feed short (~0.7 λ0) leaky-wave antennas with sum (Σ) and difference (Δ) patterns is presented. Rigorous field-theory analyses show that the radiation characteristics of these antennas agree well with the measurements. The performance of these antennas is well suited for direction finding applications.

Ethics and the assessment of quality of life

The topic of quality of life (QoL) has attracted substantial research in the past decade. In this period the development of measurement strategies has not only been supported, but to a large extend driven, by those requiring the direct application of findings. This is particularly true of QoL research as an aspect of health outcomes. Ethical considerations for QoL researchers in the health context are outlined. Two general questions are considered: whenand what aspects of QoL are important in health settings and what psychosocial consequences follow for indi viduals from the investigation of their QoL? Many of the considerations raised relate to generic issues for research with a range of psychosocial phenomena. Some particular issues pertain to the popularity of the concept of QoL and the demand to apply methodologies which are in development, and to the competing perspectives on QoL across disciplines. The outline of ethical issues across the range of concerns of the QoL researcher illustrates that ethical practice requires active consideration at every stage of the research process.