Location Determination with Four Elements Antenna Using Matrix Pencil Method

It is shown that when a small bare circular loop antenna is buried in the ground it will respond to a vertically ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</tex> field) polarized ground-wave or sky-wave source with a directional azimuthal pattern. The response to a horizontally polarized skywave source is greatly enhanced by burying the antenna and is also shown to be far from omnidirectional in azimuth. These results depend upon the presence of a relatively small departure from a constant current distribution on the loop when it is regarded as a driven element. The current distribution formulas of Chen and King permit easy analytical estimates of these effects.

In ingestible systems, the antenna suffers from deterioration of performances due to surrounding dissipative tissues. A small circular magnetic loop antenna, whose diameter is equal to 1 cm and thickness is equal to 0.5 mm operating at the frequency of 315 MHz in the ISM band, is proposed to limit this degradation. The electric properties of the human body, having a high dielectric constant and low impedance, are considered to design and simulate the loop antenna. We found that the magnetic field is less attenuated than the electric field in the human body that improves the signal level received by near field magnetic coupling.

We propose a new calibration method for circular loop antennas. Generally, the standard field method is widely employed in loop antenna calibration, and a thermocouple is widely used as a current sensor on a transmitting loop antenna's element to calculate the magnetic field strength at an antenna under calibration. Therefore, it has certain disadvantages such as low accuracy of measurement, a fragile structure, and so on. However, the proposed method has the characteristics of the standard field method and reference antenna method, and it is simpler than these methods. In this study, a comparisons are made in simulations and experiments. The results show that the proposed method is simple and efficient for calibrating loop antennas.

Abstract: This paper is about the optimization of a small circular loop antenna using a Genetic Algorithm (GA) to significantly enhance its radiation efficiency for operation at 38.22MHz. Traditional small loop antennas are known for their poor radiation characteristics due to extremely low radiation resistance and high conductor losses, rendering them unsuitable for practical RF communication without a complex matching network. This research applies a Genetic Algorithm implemented in MATLAB to optimize two critical design parameters: the loop radius and the wire radius (thickness). An analytical electromagnetic model was developed to compute radiation resistance, conductor loss resistance (accounting for skin effect and radiation efficiency. The objective function was designed to maximize efficiency by minimizing its negative value. Results from the GA were analysed using convergence plots and two-dimensional contour maps, revealing the efficiency distribution across the design space. The optimized antenna achieved a loop radius of 0.02458m and a wire radius of 0.0099m, leading to a dramatic improvement in radiation efficiency from 0.02% (traditional design) to 99.4%. Additionally, gain and bandwidth performance were significantly improved, making the antenna suitable for terrestrial RF applications. The study demonstrates that evolutionary optimization techniques like GA can overcome the inherent limitations of traditional small loop antennas, by intelligently navigating the design space, the Genetic Algorithm identified configurations that would be difficult to obtain through manual tuning. These findings highlight the practical potential of computational intelligence in modern antenna design particularly for compact efficient and broadband systems in wireless and communication technologies.

A critical need in the evaluation of an ultrawideband (UWB) radio system is the calculation of the energy link loss between the source at the transmit antenna and the receiver load. While the rigorous calculation of link loss in a wideband pulsed system requires a full transient electromagnetic solution for the transmit and receive antennas, we show in this paper that accurate approximations for link loss can be obtained for the special cases of electrically small dipole or loop antennas, with Gaussian or Gaussian doublet (monocycle) generator waveforms. We also consider the error involved with applying the much simpler narrowband Friis transmission formula. It is found that the use of the basic Friis formula can result in link loss errors of more than 60 dB for a UWB system having severely (impedance) mismatched antennas, but may give results correct to within a few dB for well-matched narrowband antennas, or if the formula is augmented with an impedance mismatch correction factor. It appears that the dominant limitation of the Friis formula, when applied to UWB systems, is the broadband effect of mismatch between the transmit/receive antennas and their source or load impedances. Numerical examples are presented for electrically short dipoles, resonant dipoles, and broadband lossy dipoles for both Gaussian and monocycle input pulse waveforms.

Approximate expressions for the input impedances of small vertical and horizontal dipole and loop antennas above a conducting ground plane are developed. The formulas give increasingly accurate impedance estimates as [Formula: see text], where N is the refractive index of the ground. A comparison with the exact solution for a specific case, [Formula: see text] and varying antenna heights, is given.

In this paper, we propose two reference calibration methods (RCMs) for small circular loop antennas. Generally, the standard field method is widely employed in loop antenna calibration at many national metrology institutes and calibration laboratories. In this method, a thermocouple is employed as a current sensor on an antenna element of a transmitting loop antenna to calculate the magnetic field strength at an antenna under calibration. This method has certain disadvantages: The standard transmitting antenna is complicated, cumbersome, and fragile. On the other hand, a calibration method is necessary to be reasonably traceable to the standard of the magnetic antenna factor. Our proposed methods can establish and keep traceability to it. We also compare the two proposed RCMs and show that they are efficient in calibrating the loop antennas.

Implantable devices for wireless biotelemetry applications in the Medical Implant Communication Service (MICS) band ask for miniature, low-profile, broadband and insensitive to environmental changes antennas. Fundamental design techniques, if applied properly, can lead to optimum results. In this work, we discuss the appropriate approach for designing extremely small planar dipole antennas. As demonstrated, modifications on antenna structure driven by current vector alignment and conductor coupling factors affect antenna effective dimensions. Also, metallization proves to offer greater antenna performance compared to impedance matching with lumped elements. Finally, the quality factor of two small dipole antennas is evaluated.

Performance degradation due to the mutual coupling effect of antenna arrays in direction-of-arrival (DOA) estimations has been well known, and many mutual coupling compensation methods have been proposed throughout the years. In particular, the mutual coupling effect becomes significant when the antenna elements are closely spaced, which is difficult to compensate. In this paper, a new, accurate method is introduced to determine the receiving mutual impedances of antenna arrays with closely spaced omni-directional antenna elements. This new method uses a number of plane wave sources coming from different directions to determine the receiving mutual impedances of a particular antenna element with all other antenna elements in the array in a single step. This step is repeated for all the antenna elements in the array, and the full mutual impedance matrix of the array is thus obtained. Using the Matrix Pencil Method (MPM), DOA estimations using eight-element arrays were used to demonstrate the validity and accuracy of this new method.

In this paper, the accuracy of the singularity expansion method (SEM) used for antenna characterization is investigated. A well-known limitation of the SEM is that pole extraction is very sensitive to noise. A comparison between two main methods of pole extraction is presented. The matrix pencil (MP) method and the Cauchy's method are used to extract poles from the radiated fields of a dipole antenna and two bowtie antennas. Results are presented for simulated fields, and the robustness to a white Gaussian noise is also analyzed. We show that the MP method allows working with lower SNR than Cauchy's method and is more accurate for field reconstruction.

This paper presents an alternative vector analysis of the electromagnetic (EM) fields radiated from electrically small thin square and rectangular loop antennas of arbitrary length 2a and width 2b . This method employs the dyadic Green's function (DGF) in the derivation of the EM radiated fields and thus makes the analysis general, compact and straightforward. Both near- and far-zones are considered so that the EM radiated fields are expressed in terms of the vector wave eigenfunctions. Not only the exact solution of the EM fields in the near and far zones outside the region (where r > √a2 + b2 ) is derived by use of spherical Hankel functions of the first kind, but also the closed series form of the EM fields radiated in the near zone inside the region 0 r < b is obtained in series of spherical Bessel functions of the first kind. The two regions between the radial distances b and √a2 + b2 which are defined as intermediate zones are characterized by both the spherical Bessel and Hankel functions of the first kind. Validity of the numerical results is discussed and clarified.

The design of a two-element antenna for portable transceivers is considered. The antenna consists of a dipole terminated with a parallel loop-capacitor combination. The antenna has a single feed at a point on the loop opposite the junction and does not require external combining circuitry. The capacitor creates a phase shift between the dipole and loop currents, thereby greatly reducing the probability of deep nulls in the received signal when the antenna is deployed in free-space or in the vicinity of a fixed reflector, where standing wave patterns occur. Theoretical and simulation studies based on multiple incident/reflected plane wave fields typical of multipath environments are used to quantify the reduction in null probability. Simulation results are presented for three antenna types: a dipole antenna, a loop-dipole antenna without a capacitor, and the loop-dipole antenna with capacitor. The results are verified by field measurements on an automated outdoor test range, where the incidence angle and distance from the reflector are varied. With a single incident plane wave, the loop-dipole-capacitor (LDC) design reduces the probability of deep nulls in the received signal by up to two orders of magnitude at low signal-to-noise ratios (SNRs) when compared with the standard dipole antenna and the loop-dipole antenna without the capacitor. The performance advantage of the new design decreases as the number of incident waves increases; however, it performs at least as well as the dipole antenna in all cases studied.

Analysis of the near‐field irradiation of prolate spheroidal models of humans and animals by a small coaxial loop antenna is described. The near fields of the antenna are known exactly and hence are used to identify the suitable field parameters involved in the near‐field absorption in the spheroidal model. An integral equation is formulated in terms of the transverse dyadic Green's function, and the fields radiated by the current loop are expanded in terms of the vector spherical harmonics. The extended boundary condition method is then employed to solve the integral equation. The power distribution and the average specific absorption rate (SAR) are calculated and plotted, for different human and animal models, as a function of the separation distance from the loop. It is shown that for distances less than 5λ the average SAR values oscillate about the far‐field value. In particular, for d/λ &lt; 0.4 an increase in the average SAR values was generally observed. It is also shown that in spite of the complicated nature of the near fields the absorption characteristics can still be explained in terms of the incident radiation. Furthermore, from the calculated SAR distributions at different frequencies it is shown that at all frequencies, excessive heating occurs at the surface of the spheroid while a limited absorption occurs in the central region around the major axis. This result is of particular importance in hyperthermia, where extensive efforts are being directed toward achieving deep‐tissue heating by a coaxial coil carrying RF power at about 27 MHz.

Superconductive small loop antennas are investigated. The antenna radiator is a five turn spiral coil made of sintered 50%Ag–50%YBCO ceramics. The inner and outer diameters of the coil are 90 mm and 120 mm, respectively. Two serial capacitors are joined parallel to the coil and used for impedance matching between a radiator and a feed line. The antenna resonates at about 25 MHz and its gain at 77 K is 4.15 dB higher than a metal antenna at 300 K. This result shows that very small loop (diameter < λ/100) antennas with high efficiency can be realized by using superconductive radiators.

This paper deals with development of small loop antenna sensors with 10 mm in diameter for detecting electromagnetic (EM) waves emitted by partial discharges in the insulation system of inverter-fed motors. Partial discharges (PD) were generated with a pair of crossed enamel wires under ac voltage at 10 kHz for examining various fundamental properties of the small loop sensors; i.e. the frequency response, the distance dependence from the PD source to the sensor. The sensitivity of the small loop sensor was also measured. As a result, it was found that the developed small loop antenna allows detection of EM waves over the frequency range up to 4 GHz and can detect PD current pulse with its peak magnitude as small as 12.6pC. It is also suggested that the array of the developed loop sensors can be applied for PD localization in practical rotating machines under the so-called repetitive voltage impulse. It was found that the developed loop sensor can be also applied to detect and locate the PD source.