Log-periodic Dipole Research Articles

Development of a Log-Periodic antenna system

A 14-element log-periodic dipole antenna for VHF, UHF and SHF bands has been designed, constructed and characterized at a frequency band (300-5467)MHz. The experimentally measured values agree with the computed values with a standard deviation of 2.6. A gain of 20.33 ± 0.69 dB was achieved at a signal-to-noise ratio of 104.77 ± 1.04dB. The efficiency at frequencies above 500MHz is 97% and drops to 65% at frequencies below 200MHz. Keywords: Dipole antenna, radio communication and space loss Nigerian Journal of Physics Vol. 18 (1) 2006: pp. 81-90

A size-reduced Log Periodic Dipole Antenna

A rectangle capacity patch was adopted as the resonance unit of the Log Periodic Dipole Antenna (LPDA) so as to realize the miniaturization of this aerial in this paper. Fifteen rectangle capacity patch units of different parameters were analyzed in this paper and three design laws of size-reduction were found. According to these design laws, a 70% miniaturization ratio LPDA was designed and fabricated. The Voltage Standing Wave Ratio (VSWR) and pattern of the fabricated LPDA were measured. The results indicate that this size-reduction method do not deteriorate performance.

BROADBAND ANALYSIS OF ASKARYAN PULSES

A coherent radio emission from particle shower in a dielectric medium, so-called Askaryan pulse, has been recorded in a laboratory setting. In this report the analysis of measurement made with a broadband (1-18 GHz) log periodic dipole antenna (LPDA) is described. The properties of the observed radio pulses are compared with the current theoretical model. The radiation intensity as a function of frequency was found to agree well with the expectation, while the phase characteristics of pulses disagree with the theoretical work.

Log-Periodic Dipole Antenna Array-Type Optical Electric Field Sensor

In the microwave band, Optical Electric Field Sensors (OEFS) provide an attractive method to measure electromagnetic fields precisely. It is difficult however, to develop an OEFS that operates with both wide bandwidth and high sensitivity. In this paper, we propose a Log-Periodic Dipole antenna Array (LPDA)-type OEFS that achieves high sensitivity over a wide bandwidth. The LPDA-type OEFS has a large number of electrodes that are attached to each of the antenna elements. Not only the lengths of the antenna elements but also the lengths of electrodes vary log-periodically. The OEFS responds to microwaves by synchronizing the propagation direction of light with the propagation direction of the microwave. An OEFS constructed of y-cut z-propagation Lithium Niobate (LN) demonstrates good stability against temperature variation. Theoretical analysis with respect to the refractive index variation and optical modulator with the crystal orientation will be provided in this paper. In addition, the characteristics of the proposed LPDA-type OEFS will be shown over wide bandwidth in the microwave band.

Elimination of the effect of an ambient reflection in the measurement of S parameter between two log‐periodic dipole array antennas

AbstractThe transmission S parameter S21 of transmitting and receiving antennas can be used for site evaluation different from the normalized site attenuation. For instance, the effect of reflection from ambient objects can be removed by the Fourier transform and time domain gating process so that the transmission S parameter without ambient influence can be predicted. In this paper, a log‐periodic dipole antenna is used as a transmission and reception antenna that is a type of broadband antenna. It is shown for this antenna that the time domain gating becomes possible and the effect of reflection can be removed if the complex antenna factor indicating the antenna characteristic is taken into account. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(3): 35–43, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10042

Log‐periodic loop antennas with high gain and linear polarization

A log-periodic loop antenna (LPLA) is proposed and analyzed numerically and experimentally. This antenna has smaller transverse dimensions than the conventional log-periodic dipole antenna with comparable radiation properties. Radiation characteristics of an LPLA with six turns and a ground reflector (GR) are presented. The results indicate that the LPLA can provide high gain and linear polarization over a wide bandwidth. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 27: 66–68, 2000.

Log-periodic loop antennas with high gain and linear polarization

A log-periodic loop antenna (LPLA) is proposed and analyzed numerically and experimentally. This antenna has smaller transverse dimensions than the conventional log-periodic dipole antenna with comparable radiation properties. Radiation characteristics of an LPLA with six turns and a ground reflector (GR) are presented. The results indicate that the LPLA can provide high gain and linear polarization over a wide bandwidth. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 27: 66–68, 2000.

Circularly polarized log-periodic dipole antenna for EMI measurements

Two types of broad-band antennas are widely used for electromagnetic interference (EMI) measurements in the frequency range from 30 to 1000 MHz. Log-periodic dipole antennas (LPDA) are mainly used for the range above 300 MHz and biconical antennas for the range less than 300 MHz. These two antennas have linear polarization. However, EMI measurements can sometimes be more conveniently made with an antenna having circular polarization and so we propose an improved LPDA, which has circular polarization. This LPDA has a second array of dipoles so arranged that each dipole of the second array has a quarter-wavelength phase difference from that of the corresponding dipole of the standard LBDA array for the given radiation field. For this reason, we named it a cross-element LPDA. The cross-element LPDA does not need a broadband 90/spl deg/ hybrid junction to produce circular polarization. We calculated the height pattern and the frequency characteristics of the classical site attenuation (CSA) for the cross-element LPDA when used for both transmitting and receiving, as well as the antenna factor. Moreover, we calculated the normalized site attenuation (NSA) when the cross-element LPDA is used for receiving or for both transmitting and receiving.

Compact electromagnetic test range using an array of log-periodic antennas

The design of an array of seven log-periodic dipole antennas is described: this is intended to generate an approximate plane wave in the near field. The array is used as an illuminating antenna for a compact range primarily intended for electromagnetic susceptibility or emission measurements, but is also potentially usable for antenna measurements. It is capable of operation at lower frequencies than reflector antennas, and achieves good-quality plane waves in the near-field region. The design procedure was based on a numerical near-field synthesis technique that produced a set of complex excitations for the seven elements. The magnitude-only synthesis technique was found to give better results than alternative methods. The resulting computed field distributions showed that acceptable approximations to a plane wave could be generated over a substantial quiet zone, and an experimental test of an array constructed in accordance with the design algorithm showed good agreement with the predicted performance.

Point-matching method for reduction of anomalous radiation of log-periodic dipole array

A point matching method is developed for the evaluation of the performance of the log-periodic dipole antenna (LPDA). Based on this method, the anomalous behaviour of the LPDA is studied and found to be improved at an optimum spacing factor and by selecting a small dipole length to diameter ratio; that is, an LPDA, operating over a given frequency band, must possess an optimum dimension that gives a pattern with eliminated anomalous backlobe peaks.

An investigation of the design of a log-periodic dipole array with low side-lobe levels for broadcast applications

The problem of cochannel interference is addressed. The ability of the Numerical Electromagnetics Code (NEC2) computer program to predict the radiation pattern of an antenna array on a mast is investigated. The evaluation and validation of NEC2 is undertaken by the comparison of measured and computed radiation patterns of log-periodic dipole antenna arrays. Emphasis is placed on the correspondence of the side-lobe levels -30 to -40 dB down from the main lobe. This is important in the synthesis of an array with predictable null positions and depths.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A multiradius, reciprocal implementation of the thin-wire moment method

An implementation of the moment method, entitled the multiradius bridge-current (MBC) moment method, for electromagnetic analysis of multiradius thin-wire structures (including multiwire, multiradius junctions) is presented. It is extension of the authors' uniradius bridge-current reformulation (see ibid., vol.37, p.1224-34, Oct. 1989) of Richmond's uniradius thin-wire theory (1974). The method features an exactly symmetric mutual impedance matrix ensuring reciprocity between sources, it is unconstrained with respect to both the length ratio and the radius ratio of adjoining segments (provided that the wires are electrically thin), and it permits the self-consistent inclusion of coaxial cable sections in the configurations under analysis. The method is validated through comparison with transmission-line theory for a two-wire line and a coaxial cable, and through comparison with measurements on a sleeve monopole antenna and a log-periodic dipole antenna. The MBC moment method program is shown to surpass the Numerical Electromagnetics Code (NEC) in terms of reciprocity and convergence for both an AM broadcast tower detuning stub problem and a bent two-wire transmission-line problem. >

On the suppression of asymmetric artifacts arising in an implementation of the thin-wire method of moments

The original version of the thin-wire frequency-domain moment-method program developed by J.H. Richmond (1974) has been modified to suppress the computation of nonphysical asymmetric fields. Richmond's implementation uses piecewise sinusoidal expansion and testing functions, along with filamentary current approximations. The modified version, termed the bridge-current version, is described. The original program and the modified version are compared with each other and with simplified theory, where applicable, on the following symmetrical structures: a rectangular wire loop, a two-wire transmission line, and a log-periodic dipole antenna. The bridge-current version is shown to eliminate the computation of nonphysical asymmetric fields, to be essentially invariant with respect to variations in segmentation for the above-mentioned structures, and to produce results that compare well with simplified theories where applicable. It is noted that the bridge-current version is particularly advantageous for structures that include close-spaced parallel wires connected by short wire segments. >

Resonance phenomena of log-periodic antennas: characteristic-mode analysis

The method of characteristic modes is implemented in the form of a general-purpose computer program based on an established moment-method program using piecewise sinusoids. Application of the method to the log-periodic dipole antenna (LPDA) yields characteristic modes that are insensitive to changes in moment-method segmentation and are revealing with regard to parasitic resonance phenomena. A study of the modes on the LPDAs shows that the asymmetry resonance is dominated by a mode that is not restricted to one cell, although the single-resonant-cell postulate remains a good first-order explanation. On the other hand, the symmetric termination resonance is shown to involve more than one mode. A numerical study of various antenna deformations shows that only length extensions cause strong asymmetry resonances. The E-plane array is analyzed, and the results are shown to compare favorably with experiment. >

Design of log-periodic dipole antennas

The goal of the paper is to improve the log-periodic dipole antenna (LPDA) design procedure introduced by Carrel (1961). A computer-aided design technique is introduced, providing an easy-to-use design method of LPDAs. Corrections to Carrel's design contours, and new constant input resistance and truncation coefficients diagrams are presented. The influence of the feeder characteristic impedance, and dipole length-to-diameter ratio on LPDA parameters is studied. Design diagrams for LPDA's typical of HF communications are included.< >

Approach to a suitable directional antenna for UHF radio positioning applications

The phase centre properties of log-periodic dipole (LPD) arrays are examined for suitability in UHF radio positioning systems and are compared with phase properties of commonly used Yagi arrays. LPD arrays offer gain nearly comparable to that obtained from short Yagis, exhibit nearly 180° main lobe coverage with no front quadrant nulls and show very small phase centre movement over the entire front hemisphere.

Reduction of the anomalous resonances of symmetric log-periodic dipole antennas

Computer analysis reveals that the anomalous behavior of symmetric log-periodic dipole antennas (LPDA) is mainly due to the radiation of the dipole elements in the anomalous radiating region which is excited by the transmission line resonance of the feed structure. By replacing the cylindrical dipole elements in the LPD antennas with wide-angle triangular-outline dipoles with central wires, the computed anomalous back lobe peaks are reduced to negligible levels. LPD antennas were constructed using wide-angle triangular-outline dipoles with central wires, and they were found to exhibit satisfactory performance.

Log-periodic flat short-circuited dipole array with a squinted beam

A new class of microstrip travelling wave antenna of large bandwidth is described. The log-periodic array is composed of flat short-circuited half dipoles acting at quarter-wave resonance and fed in series by means of a high characteristic impedance microstrip line. A model has been constructed and tested. A large squinted main beam is obtained between 0.75 and 4.5 GHz. The constant experimental radioelectric properties are in good agreement with the theoretical predictions.

Analysis of the loop-coupled log-periodic dipole array

A simple theoretical model is described to analyze the loop-coupled log-periodic dipole antenna (LPDA). Computed and experimental data are presented, comprising an investigation into both the far field and the dipole and feeder currents, for a wide range of antenna parameters. Particular attention is paid to a class of parasitic resonances characterized in the swept-frequency radiation pattern by a narrow-band reduction in front-to-back ratio. The calculations show that these resonances involve high out-of-phase currents in adjacent dipole elements, and also predict correctly their dependence on the nature and location of the feedline termination. Design data are presented showing how gain and front-to-back ratio can be optimized and parasitic resonance effects minimized.

Effects of lossy and perfectly conducting ground on the time and frequency behavior of a log‐periodic antenna using the singularity expansion method

This paper presents an insight into the transient behavior of a vertical log‐periodic dipole antenna (LPDA) above a lossy ground and over a perfectly conducting half space. Mathematically, the problem is formulated in the Laplace domain by a singularity expansion representation of the solution of an electric field integral equation using a Sommerfeld integral kernel. The influence of the feeding network and of the mutual coupling of the elements as well as the influence of the element thickness on the natural resonances of the LPDA is studied. The modes of the antenna elements are presented and the current in frequency and time domain is computed for free space. Dependent on the ground parameters and the antenna height, we show the resonance migration in the complex frequency plane and determine the appropriate modes. Starting with the free space current distribution, we compute the transient far fields of the vertical LPDA over ground for various ground parameters and antenna heights.