Active Dipole Research Articles

Generation of cosecant squared pattern from linear array of active and parasitic dipole antennas

ABSTRACT This work uses the active and parasitic components in a linear antenna array composed of parallel dipoles to synthesize a cosecant squared pattern using the Quantum Particle Swarm Optimization approach. This pattern is obtained by the mechanical displacement of the parasitic array of the parallel dipole placed in front of an active dipole array. In addition to it, mutual coupling between the antenna elements is considered in this process. Two examples are presented to visualize the effect of this approach in the synthesis process. Moreover, obtained results from the simulation are also validated by the results produced from FEKO software.

Пригнічення післяімпульсних коливань в активних випромінюючих антенах типу Bow Tie

Subject and Purpose. This theoretical and experimental research is devoted to peculiarities of the ultra-wide bandwidth (UWB) pulse radiation from active bow-tie dipoles. The focus is on the relationship between the amplitude-time dependences of electromagnetic fields produced by active UWB pulsed antennas and the configuration of the conductive components for temporally short (less than 0.5 ns), ultra-wide-bandwidth pulse radiation. Methods and Methodology. Analysis of the radiator geometry action on the emitted pulse parameters is performed by numerical simulation with the use of the finite-difference time-domain (FDTD) method. The experiment involves specially made, variously shaped bow-tie radiators tested with different resistive loadings in radiation mode. The numerically simulated characteristic curves of the radiated field amplitude shape versus radiator geometry are confirmed by experiment. Radiation field parameters versus load resistance are experimentally studied, too. Results. Conditions for the effective pulse radiation with a largest-possible pulse amplitude have been determined, the post-pulse oscillation amplitude and duration reduced to a minimum. Conclusion. It has been shown that the resistive loading in the excitation area significantly reduces amplitudes and durations of post-pulse oscillations in signals radiated by active dipole antennas.

Glow discharge excited at low to high radio frequencies around active dipoles in the ionosphere

We present the first space-borne observation of optical emissions of both neutral and ionized argon atoms resulting from a radio-frequency glow discharge (RF-GD) from a sounding rocket payload. The Observations of Electric-field Distributions in the Ionospheric Plasma — a Unique Strategy-C (OEDIPUS-C) payload was designed to separate into two sub-payloads on its up-leg. This separation permitted a number of two-point measurements, including those on radio wave propagation from the active dipole antennas on the upper sub-payload to the synchronized receiving dipoles on the lower sub-payload. A white-light video camera on the lower sub-payload recorded strong luminosity around the active dipoles during the first 15 s after sub-payload separation, when argon gas jets were providing propulsion to separate the two sub-payloads. Parts of the ejected argon appeared as a glowing volume where the large radio-frequency (RF) fields from the two active dipoles excited the optical emission, as the sub-payload separation increased from 2 to 55 m. The shape and intensity of the luminosity were well repeated as a function of the swept frequency (0.025–8.000 MHz), but their frequency dependences were distinctly different from those of sounder-accelerated electrons measured onboard, and deduced to result from the nonlinearity of the glow discharge. The observation is to our knowledge the first of its kind, and is interpreted in terms of a RF-GD energized by the strong near electric fields of the transmitting dipoles.

Research of compromising USB interface electromagnetic emanations in the infocommunication networks control system

One of the key directions in the development of modern society is the formation of an integrated information space based on the latest information technologies. The widespread use of information technologies and infocommunication networks for the transmission, reception, processing and storage of information in various fields of activity, on the one hand, contributes to an increase in the efficiency of this activity, and on the other hand, it causes the emergence of threats of information leakage through technical channels, which are understood as the uncontrolled dissemination of information signal from its source through the physical environment to a technical means that intercepts information. In the list of threats, an important place is occupied by threats of information leakage through channels of compromising electromagnetic emanations, as well as a result of interference of information signals in power lines of technical means of information processing, connecting lines of auxiliary technical means and systems, ground circuits and extraneous conductors. To protect information from its leakage due to compromising electromagnetic emanations through communications connecting the system blocks of computing facilities with peripheral devices, it is important to analyze the formation of these signals and emissions. The article presents the results of the study of compromising electromagnetic emanations of the USB 2.0 interface, carried out to solve the problems of assessing the security of information at the objects of information activity. The processes of formation of technical channels of information leakage by compromising electromagnetic emanations at use of the USB-interface in structure of control system of information and communication networks are considered. The images of the signal levels of the compromising electromagnetic emanations of the USB 2.0 interface obtained with the spectrum analyzer ROHDE & SCHWARZ FSW 13 (Signal & Spectrum Analyzer) using the R & S Active Dipole Antenna HE527 are shown. As a result of the analysis of the form and spectrum of signals in the USB cable (test mode is off, test mode is on) it is established that in the USB interface there is a constant transmission of service packets to support the interface. When the test mode is turned on, additional pulse sequences appear on the spectrogram. The frequency of the first harmonic for the USB 2.0 interface is in the region of 240 MHz.

UWB microwave imaging of heterogeneous breast phantoms

UWB microwave imaging has potential for early-stage screening diagnostics of breast cancer. We present an experimental measurement setup for breast phantom trials based on M-sequence radar technology and active small dipole antennas as pre-stage for real in vivo measurements in a prone examination position. We describe current development steps as well as first experiences concerning the imaging of heterogeneous breast phantoms.

Design and Test of an Imaging System for UWB Breast Cancer Detection

Electromagnetic ultra-wideband (UWB) sensing and imaging provide perspectives for early-stage breast cancer detection. This paper deals with practical chal- lenges of real measurements. We present an experimental setup for breast phantom trials based on M-sequence radar technology and short active dipole antennas. It com- bines short impulse responses, appropriate fidelity and very small antenna dimension and allows array construc- tion with sufficient number of antennas around the breast. The basic approach and obtained imaging results are pre- sented. Furthermore, in this extended paper version con- tinuative development steps are described and measure- ment results reflecting specific performance aspects are discussed.

Antenna development for astroparticle and radioastronomy experiments

An active dipole antenna is in operation since five years at the Nançay radio Observatory (France) in the CODALEMA experiment. A new version of this active antenna has been developed, whose shape gave its name of “Butterfly” antenna. Compared to the previous version, this new antenna has been designed to be more efficient at low frequencies, which could permit the detection of atmospheric showers at large distances. Despite a size of only 2 m×1 m in each polarization, its sensitivity is excellent in the 30–80 MHz bandwidth. Three antennas in dual polarization were installed on the CODALEMA experiment, and four other have been recently installed on the Auger area in the scope of the AERA project. The main characteristics of the Butterfly antenna are detailed with an emphasis on its key features which make it a good candidate for the low frequency radioastronomy and the radio detection of transients induced by high energy cosmic rays.

Results of the radio-detection experiment CODALEMA

Measurements of the radio transients associated with Extensive Air Showers could provide a timely new effective method of detection of Ultra-High-Energy Cosmic Rays with interesting performances in terms of techniques and of accessible observables. The CODALEMA experiment at the Radio Observatory of Nançay, France, explores this possibility using an array of broadband active dipole antennas triggered by an array of ground particle detectors. The implemented detection techniques, the methods of analysis developed and the principal results achieved during the 5 years of upgrading will be recalled. This cursory glance will provide an opportunity to point out some new issues and to suggest some future challenges in this domain.

Geomagnetic origin of the radio emission from cosmic ray induced air showers observed by CODALEMA

The new setup of the CODALEMA experiment installed at the Radio Observatory in Nançay, France, is described. It includes broadband active dipole antennas and an extended and upgraded particle detector array. The latter gives access to the air shower energy, allowing us to compute the efficiency of the radio array as a function of energy. We also observe a large asymmetry in counting rates between showers coming from the North and the South in spite of the symmetry of the detector. The observed asymmetry can be interpreted as a signature of the geomagnetic origin of the air shower radio emission. A simple linear dependence of the electric field with respect to v ∧ B is used which reproduces the angular dependencies of the number of radio events and their electric polarity.

등가 모델을 이용한 광대역 수신용 능동 다이폴 안테나 설계

VHF 대역에서 능동 안테나는 작은 크기로 인하여 많이 사용되고 있다. 능동 안테나는 안테나와 증폭기가 직접 연결되어 있으며, 수신 시스템의 초단부에 위치하고 있으므로, 능동 안테나의 이득 및 잡음 지수 특성은 좋은 감도를 위하여 중요하다. 본 연구에서는 5:1 대역폭(100<TEX>${\sim}$</TEX>500 MHz)에서 동작하며, 다이폴과 P-HEMT 증폭기로 구성되는 능동 다이폴 안테나를 개발하였다. 능동 다이폴 안테나의 요구된 성능을 얻기 위하여, 안테나와 증폭기를 동시에 설계되어야 한다. 이를 위하여, 1-포트 다이폴 안테나를 등가의 2-포트 시스템으로 모델링하는 등가 포트 개념을 도입하였다. 이러한 제안된 등가 포트를 이용하여 ADS로 능동 다이폴 안테나의 성능에 대한 시뮬레이션 하였다 안테나의 이득과 잡음 지수 특성을 측정하기 위하여, 2-포트 등가 임피던스 모델을 이용하였다. 제작된 능동 다이폴 안테나의 측정된 평균 이득, 잡음 지수 및 VSWR은 각각 8dBi, 9dBi, 1.7:1이다. 방사 패턴은 다이폴 안테나와 같은 특성을 얻었다. 시뮬레이션 결과와 측정된 결과를 비교 시, 제안된 방법의 타당성을 확인하였다. In the VHF range, active antennas are widely used for wideband applications due to their small size. Active antenna consists of antenna elements and amplifiers, which are directly connected to each other. Gain and noise-figure characteristics are very important for good sensitivity performance, because it is located at the front end of a receiving system. In this study, we developed an active dipole antenna with 5:1 bandwidth(100<TEX>${\sim}$</TEX>500 MHz), which consists of a dipole antenna and a P-HEMT amplifier. To obtain required performances, the antenna and the amplifier should be designed simultaneously. In order for that, we introduced an equivalent port concept to model the 1-port dipole antenna as an equivalent 2-port system. Using the proposed equivalent port, the performance of the active dipole antenna was simulated by the ADS. In order to measure the gain and noise-figure characteristics of the antenna, we utilized the same concept of the two-port equivalent impedance model. The measurement results for typical gain, NF and VSWR in the required frequency band were 8dBi, 9dB and 1.7:1, respectively. The radiation patterns at the principal planes were same as the typical radiation pattern of a dipole antenna. By comparing the simulation results with measured ones, it is confirmed that the proposed methods works well.

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.

The influence of electromagnetic singularities on an active dipole antenna within a cavity

Abstract. We study the influence of both the electromagnetic source singularity and electromagnetic cavity resonances on the current distribution of a dipole antenna within a rectangular cavity. These two types of electromagnetic singularities are triggered by the radius of the dipole antenna and the quality factor of the enclosing cavity, respectively. The key element of our investigation is a novel representation of the electromagnetic Green’s function for a lossy rectangular cavity. It allows to directly obtain the current distribution on the antenna by means of the method of moments. As a result it is recognized that a dominating source singularity, i.e., a small antenna radius, can inhibit resonating effects, even if a cavity resonance is excited and the quality factor of the cavity is high.

CPW fed active dipole antenna for television receivers

A coplanar waveguide fed active dipole antenna for a television receiver is fabricated on a thin dielectric film by using photoetching techniques. A transistor amplifier is integrated between the feeding point of the dipole and CPW. Actual gains of more than 8 dBd are obtained at frequencies from 470 to 770 MHz.

Asymmetry of an electrical field meter with an active dipole antenna

Asymmetry of an electrical field meter with an active dipole antenna

Active dipole antennas to measure radio interference field intensities in the near zone

Active dipole antennas to measure radio interference field intensities in the near zone

Resonant length of the active loop dipole antenna

ABSTRACT A modification is introduced to the previous circuitry of Maclean for an active loop monopole antenna in order to obtain resonance for a significantly lower wire length. For the fed-emitter collector loop (FECL), it is proposed to connect the collector to either the base or the emitter through a resistor.

Frequency response of active dipole antennas†

Abstract The paper presents a simple technique for improving the bandwidth and receiving gain of a passive dipole antenna by introducing a special transistor circuit at the feed point. The circuit utilizes the inductive property of a transistor amplifier, thus providing a good impedance match over an appreciable portion of the frequency range in which the dipole is capacitive. The base resistor of this amplifier has a significant effect on the gain and bandwidth as well as lowering the centre frequency at which the gain is maximum. It is shown that the improvement in gain due to this circuit of a 44-8 cm long dipole operating at 220 MHz is 9 dB while the VSWR becomes 1.54 as compared to 29-6 for the passive antenna.