Multi-turn Loop Antenna Research Articles

Design of a Miniaturized Printed Multi-Turn Loop Antenna for Shielding Effectiveness Measurement

This paper proposes a novel miniaturized loop antenna consisting of a multi-turn printed strip and a ring-shaped ferrite core. The lateral surface of the ferrite core is tightly wrapped by the circular multi-turn strip, which is printed on a thin, ring-shaped Styrofoam. To verify the feasibility, the proposed antenna is fabricated, and the antenna factor (AF) levels are measured using the three-antenna method from the VLF to HF band. The AF levels by measurement, theory, and simulation are 36.14 dB, 34.01 dB, and 33.6 dB at 30 kHz, respectively. In the VLF band, the antenna has a diameter of 114 mm, which is miniaturized to less than 60% compared to previous research. In addition, the proposed antenna is employed in the shielding effectiveness (SE) measurement of a small commercial cabinet to observe its suitability for SE measurement of small shielding enclosures. The SE values averaged over the frequency range from 10 kHz to 3 MHz are 5.19 dB and 14.14 dB in the horizontal and vertical polarizations.

Type of active impulse noise suppressing method based on double‐loop antennas in very low frequency/ultra‐low frequency coupling communications

Very low frequency/ultra-low frequency coupling communication systems suffer from severe disturbance from non-Gaussian impulsive noises which producing significant long tails. Considering the significant in-band parts of the impulse, traditional noise-suppression methods are not adequate in improving the signal-to-noise ratio (SNR), and the performance of existing dipole–loop double antennas active noise suppression systems are limited to a low level due to the different directionality of the antennas. A new double-loop antennas active noise suppressing system was proposed, in which one multi-turn loop antenna was employed to receive the useful signals, and one single-turn loop was employed as the noise reference antenna. A mathematical morphology processor and a time-switch filter were employed to extract the impulsive noise, and the digital equivalent model of the multi-turn loop antenna was established filtering the extracted impulsive noise to obtain a duplicate transient, which is highly correlated with the transients received from the multi-turn loop antenna. The system SNR was improved by subtracting the transient duplicate from the received signals. Simulations were carried out with Monte Carlo method, showing that the SNR can be improved with the gain of about 18 dB with communication error rate extremely reduced by orders of magnitude. Experiment system was also designed and established to verify the feasibility and efficiency, and a 50 m communication experiment in an industrial environment showed that the error rate can be decreased from 0.2 to 0.06% while employing the proposed noise suppression method.

Wearable textile antennas

Owing to the rapid progress in fabrication technologies of conductive fibrous materials and the increasing demand for wireless communications in smart clothing systems, the potential application of wearable textile antennas in this field continues to increase. This article reviews a variety of wearable textile antennas in order to provide background information and application ideas for designing such antennas. The various materials used in the construction of wearable textile antennas, their fabrication methods, as well as the antenna types and their application fields are summarised. Owing to the high conductivity of metals, various metal composite yarns (MCYs) and fabrics have been used in the production of textile antennas. For inductively coupled near-field communication within smart clothing systems, woven or embroidered multiturn loop antennas are suggested. For far-field communication, a variety of broadband textile antennas were developed to counterbalance the detuning caused by the presence of a human body. Embroidered-folded dipole array antennas, metal-coated fabric patched bowtie and spiral antennas, a microstrip patch antenna array and a coplanar antenna made of metal-coated fabric patches and a ground plane, are the antennas that cover a broad spectrum and thus are capable of operating on the body.

Correction to "The electrically small multi-turn loop antenna with a spheroidal core"

In the above titled paper (ibid., vol. 48, no. 5, Oct 06), the authors used an approximation for the core loss resistance that was later found to be invalid for the magnetic-field distribution involved. After a brief outline if the problem, the correct loss resistance is derived and its impact discussed.

Comment on "The electrically small multi-turn loop antenna with a spheroidal core" [Letters to the Editor

Presents letters sent to the editor regarding previous articles from this publication or other relevant topics of discussion.

The Electrically Small Multi-Turn Loop Antenna with a Spheroidal Core

A complete analysis of the electrically small multi-turn loop antenna with a spheroidal core is presented, using quasistatic electromagnetic theory (QS). Its use as a primary design tool for later use in conjunction with a large finite-element (FEM) program for full-wave analysis of a practical loop with a cylindrical core is illustrated. Previously unavailable components of the equivalent circuit, including conductor and core losses, inductance, and capacitance, are derived. The accuracy of this circuit for practical use is demonstrated by comparison with results obtained from an FEM analysis of a cylindrical loop of equal volume and aspect ratio. All results are obtained in closed form: these include expressions for the dependence of the impedance, bandwidth, and efficiency upon the frequency, volume, aspect ratio, permeability, and number of turns. Although attention is focused on the design of a 2 MHz transmitting antenna, the theory is sufficiently general for application to the design of electrically small receiving or transmitting antennas at other frequencies

Design of loop antennas and matching networks for low-noise RF receivers: Analytic formula approach

A comprehensive procedure for designing loop antennas and matching networks for low-noise receivers, by using an analytical formula approach, is presented. The effective length l/sub effect/ of an equivalent transmission line, for a single-turn loop antenna, and the effective coupling coefficient /spl rho/, for a multiturn loop antenna, are introduced in the approximate formulas for the impedances of single loop as well as multiturn loop antennas, which are valid up to the first resonant frequency. Hence, an accurate design of loop antennas and matching networks of receiving systems can be achieved by using circuit analysis. The theoretical results are compared with the measured results.

The multiturn half-loop antenna

The multiturn half-loop antenna consists of a coaxial array of N circular, half loops mounted perpendicular to a conducting image plane and interconnected beneath the image plane by a set of N-1 coaxial transmission lines. This antenna is analyzed using a Fourier series expansion for the current in the loops and a new, accurate model for the excitation of the loops by the TEM field in the coaxial apertures at their ends. When this structure is electrically small, the currents in all of the loops are approximately equal; hence, it has the well-know characteristics of an electrically small multiturn loop antenna. For a structure of general electrical size, both the radius of the loops and the lengths of the transmission lines can be adjusted to optimize the performance of the antenna for a particular application. Surprisingly, proper phasing of the excitations can make a multiturn half-loop antenna of moderate electrical size have a simple toroidal pattern, a pattern that can be obtained for a single-turn, half-loop antenna only when it is electrically small. This result is verified experimentally for a two-turn loop. Examples are shown where electrically large loops are phased with the interconnecting transmission lines to produce nearly optimum end-fire and broadside patterns.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Impedance measurements on a VLF multiturn loop antenna in a space plasma simulation chamber

The Space Sciences Laboratory of The Aerospace Corporation is presently defining an experiment to test a loop antenna configuration for a VLF transmitter in the ionosphere. The primary objectives of the experiment are to validate existing models for radiation by a loop antenna and to study the performance of the antenna in the ionospheric plasma. A one‐third scale model of the antenna has been constructed. Impedance measurements have been made on the model in a 5‐m diameter space plasma simulation chamber at NASA Lewis Research Center. The measurements confirm that the reactance of the antenna in an ionospheric plasma is essentially identical to its free space self‐inductance. The effective series resistance of the circuit increases with frequency. The losses are attributed to power transferred to plasma turbulence.

A hybrid technique for wire antennas in a cavity

Two numerical techniques for solving the current distribution on wire antennas, namely point matching and reaction matching, have been combined in a particular fashion to yield a new technique termed the "hybrid method." The hybrid method is well suited for a wire antenna mounted in a cavity. Over the antenna, piecewise sinusoidal basis functions with reaction matching are used, and on the support structure, point matching is used with pulse basis functions. The hybrid method has been applied to calculate the input impedance and the radiation efficiency of the three-turn loop antenna in an open circular cavity. Calculated input resistance of the antenna is found to agree quite well with measured data. Effects of varying the extent of recession of the antenna and varying the radius and the material of the antenna wire on the bandwidth, the efficiency, the antiresonance frequencies, and the general input reactance level of the antenna have been examined for a specific antenna geometry. The results are considered to be indicative of the general characteristics of a multiturn loop antenna with nearby support structure. The computer program that has been developed may be applied to a systematic parametric study of this type of antenna in order to optimize it for a particular application.

The electrically small magnetically loaded multiturn loop antenna

An analytical model of a class of electrically small multiturn loop antennas has been formulated and compared with experimental measurements over a frequency range of 3 to 86 MHz. Both air core and magnetically loaded eases were examined. Transmitted signal enhancement as high as 10 dB was predicted and observed by magnetic loading. Several interesting properties of the transmitting antenna were investigated experimentally and by analysis based upon the model. It is concluded that transmitted signals can be enhanced in the 2-30 MHz range, at reasonable power levels, as much as 10 dB with state-of-art ferrite materials. Secondly, the analytical model described in this paper should prove an effective design aid for a volumetrically constrained antenna of the class.

Two methods for the measurement of antenna efficiency

Two methods for measuring antenna efficiency are described. The two methods, referred to as the Wheeler method and the Q method, are used to find the efficiency of electrically small multiturn loop antennas. The principal advantage of both methods is that they can be quickly and easily applied. Further, both methods relate the antenna efficiency to the input impedance rather than a far-field pattern integration. Thus, the methods are applicable at VHF and frequencies below where the design of an antenna range or anechoic chamber becomes increasingly difficult and expensive.

Characteristics of body-mounted antennas for personal radio sets

The development of a multiturn loop antenna for a police officer's personal radio set is described. The antenna is small, low profile, lightweight, with dimensions of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2.7 \times 2.7 \times 0.7</tex> in high ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.06 \times 1.06 \times 0.28</tex> cm), and is tunable over the 150- to 170-MHz band. VSWR and radiation patterns are presented with the antenna mounted on a man's shoulder. The shoulder-mounted antenna characteristics are described with conditions where the man is in standing, stooping, and prone positions, with various head and arm movements, and with light and heavy clothing. Radiation patterns are referenced to a 6-in helical whip commonly used by police officers. Radiation patterns also indicate body absorption loss for loop and whip antennas mounted at waist level as compared with shoulder levels. The instantaneous bandwidth is 1.4 MHz for a VSWR <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\leq 3:1</tex> . A dual-frequency model for use in a two-frequency push-to-talk mode, is also shown to be practical.

On thin-wire multiturn loop antennas

A general theory of thin-wire multiturn loop antennas is presented. For convenience the windings of the loop are considered to form a circular helix. An integral equation is derived and solved numerically for the current distribution on the antenna. The antenna impedance, efficiency, and pattern are obtained.

Radiation efficiency of electrically small multiturn loop antennas

The radiation efficiency of electrically small multiturn loop antennas is calculated using an ohmic resistance which includes both the normal skin effect and the additional loss due to the proximity effect.