Antenna Current Distribution Research Articles

Low-profile wideband miniaturized tag antenna mounted on the human body

Abstract In this study, a novel, cost-effective miniaturized tag antenna was developed for applications on the human body. To achieve impedance matching with the complex conjugate impedance of the Monza-4 tag chip (7.17–j74.22 Ω at 915 MHz), the proposed structure was configured by coarsely tuning the positions of vias and fine-tuning the small gaps of its coupled patches. For further reducing the profile and dimensions of the antenna, a design technique based on the three-dimensional dipole antenna current distribution was used. The proposed antenna configuration was not only miniaturized but also achieved a long stable reading distance (>5.0 m) and a wide impedance bandwidth of 71 MHz or 7.65% (covering the ultrahigh frequency radio frequency identification ranges in most regions), regardless of the location of the tag on the human body. Experiments were conducted to validate the simulated results, and adequate agreement was found between the simulated results and the measured results.

Impedance and Voltage Power Spectra of a Monopole Antenna in a Warm Plasma—Derivation and Application to CubeSats

AbstractThe impedance for a monopole antenna in a warm plasma is derived and compared with the cases for wire dipole and double‐sphere antennas. This derivation produces a new expression for the monopole antenna response function, Fm1(x), which is very similar to the double‐sphere antenna response function. The monopole, wire dipole, and double‐sphere response functions are compared by modeling an antenna in Earth's ionospheric plasma (i.e., electrostatic and collisionless) and predicting the antenna capacitance and voltage power spectra for quasi‐thermal noise (QTN) and shot noise. Specifically, we assume the antennas are part of a CubeSat, which has spurred this research as most interplanetary craft carry a dipole or more complicated antenna designs on board (Imbriale, 2006, https://doi.org/10.1002/0470052783.ch3; Imbriale, Gatti et al., 2006, https://doi.org/10.1002/0470052783.ch5). The monopole antenna current distribution is assumed to be a half‐triangular current distribution (considering only the positive half of the triangular distribution), which follows that of prior authors (Balmain, 1965, https://doi.org/10.6028/jres.069D.065; Kuehl, 1966, https://doi.org/10.1002/rds196618971; Couturier et al., 1981, https://doi.org/10.1029/JA086iA13p11127) and simplifies comparison. The predictions for the shot noise and capacitance presented problems, as the integral over wave number space or k space did not converge for large values of k. The derived expression therefore remains a current problem in these situations, and no alternative has been found in the existing literature, necessitating future work to determine a more general expression. In this paper we bring the problem of an appropriate analytic monopole antenna response function to the attention of the community and outline a number of tests that can be used to verify any future expression.

HOMOM/PE Hybrid Algorithm Based Calculation on Ground-Wave of the HF Antennas over Irregular Terrain

The parabolic equation model usually uses a gaussian pattern to fit the actual antenna’s pattern in free space to set the initial field, and then uses the image theory to deal with the effect of ground on the antennas. However, this method of setting the initial field cannot consider the specific HF antenna, and the image theory is only applicable to the radio wave propagation of antennas working in the microwave bands and above. The HF antenna is erected low, and the irregular terrain or the buildings around the antenna and their media parameters will affect the current distribution on the antenna, resulting in a large difference with the radiation pattern in the free space. The traditional method of fitting the pattern is no longer accurate. Aiming at the problem of radio wave propagation of HF antennas in the actual installation environment by parabolic equation method, a hybrid algorithm based on higher order-method of moment and parabolic equation method (HOMOM-PE) is proposed. The hybrid algorithm divides the whole calculation region into two regions, which is the inner zone and the outer zone. The inner zone is the zone that has a great influence on the antenna current distribution. In this area, HOMOM is used to model the antenna and the terrain together, and the influence of the complex terrain near the antenna on the antenna is strictly calculated. The PE algorithm is used to calculate the long-distance propagation, and the initial field data is derived from the electromagnetic vector distribution calculated in the inner region. The hybrid algorithm combines the antenna radiation and the wave propagation directly, which solves the problem of the initial field setting of the actual HF antenna under the complicated terrain conditions.

Metamaterial loads used in microstrip antenna for circular polarization: Review

The metamaterial elements and structures have been noticed for obtaining circular polarization (CP) while developing various procedures. In this paper, we have mentioned some of these cases and compared the metamaterial loads effect on antenna current distribution. We have classified them into four categories. The first case covers patch antenna based on composite right/left-handed method, where the metamaterial has been used for changing the current distribution in the loop form. The second case has been achieved by radome and metasurface. In the third model, the interaction between feed and metamaterial load has been considered and the last case has been made by the metamaterial load with truncated structure. The metamaterial loading has been modeled based on Nicolson-Ross or transmission/reflection techniques for extracting the permittivity and permeability. While the microstrip slot antennas are attractive for wider bandwidth, the truncated structure can change the current for achieving CP. Here, we have studied the antenna for wireless and WiMAX applications.

Modal Proportion Analysis in Antenna Characteristic Mode Theory

The characteristic mode theory (CMT) can provide physically intuitive guidance for the analysis and design of antenna structures. In CMT applications, the antenna current distribution is decomposed into the superposition of multiple characteristic modes, and the proportion of each current mode is characterized by the modal weighting coefficient (MWC). However, different characteristic currents themselves have different radiation efficiencies reflected by the eigenvalues. Therefore, from the perspective of the contribution to the radiation field, the modal proportion should be more accurately determined by the combination of the modal weighting coefficient and the mode current itself. Since the discrete mode currents calculated using the electromagnetic numerical method are distributed on the whole conductor surface, we can actually use the radiation field to quantify the modal proportion or estimate it using the far field in the maximum radiation direction. The numerical examples provided in the paper demonstrate that this modal proportion can effectively evaluate antenna performance.

Design of wireless contact-lens antenna for intraocular pressure monitoring

Intraocular pressure is an important aspect in the evaluation of patients at risk from glaucoma. Glaucoma is an ocular disorder that results in the damage of optic nerve, often associated with increased aqueous pressure in the eye. Wireless technology reduces discomfort, risk of infection and monitor patients in remote places by providing timely health information. In order to transmit the ocular pressure through the wireless media a proposed design of wireless contact-lens antenna has been designed. The contact-lens coupled structure antenna was designed for the betterment of reflection co-efficient and for minimising the density of materials by gap-coupled configuration in comparison with the conventional on-lens loop antennas. The return loss of the designed contact lens antenna was 21 dB at 2.6 GHz with a diameter ranging from 14 to 15 mm. The simulation result of designed antenna return loss was obtained using advanced design system. The measured antenna return loss, radiation pattern and current distribution will be demonstrated in this paper, which are suitable for application of wireless ocular physiological monitoring.

Design of wireless contact-lens antenna for intraocular pressure monitoring

Intraocular pressure is an important aspect in the evaluation of patients at risk from glaucoma. Glaucoma is an ocular disorder that results in the damage of optic nerve, often associated with increased aqueous pressure in the eye. Wireless technology reduces discomfort, risk of infection and monitor patients in remote places by providing timely health information. In order to transmit the ocular pressure through the wireless media a proposed design of wireless contact-lens antenna has been designed. The contact-lens coupled structure antenna was designed for the betterment of reflection co-efficient and for minimising the density of materials by gap-coupled configuration in comparison with the conventional on-lens loop antennas. The return loss of the designed contact lens antenna was 21 dB at 2.6 GHz with a diameter ranging from 14 to 15 mm. The simulation result of designed antenna return loss was obtained using advanced design system. The measured antenna return loss, radiation pattern and current distribution will be demonstrated in this paper, which are suitable for application of wireless ocular physiological monitoring.

Design and analysis of stepped reconfigurable rectangular patch antenna for LTE, vehicular and ultra wideband applications

A stepped rectangular patch antenna having partial ground loaded with parasitic element is analyzed in this article. The Proposed antenna is connected to a diode on the flip side of the structure that is in between the parasitic element and the partial ground, the two cases ON, OFF are studied and analyzed. In OFF case the antenna got rejected at 3 bands (2 to 2.3 GHz, 2.6 to 3 GHz and 5.8 to 7.9 GHz). On the other hand, in ON case antenna got rejected at single band (3.6 to 4.4 GHz). The maximum gain of 5.5 dB is observed at 7.8 GHz frequency in ON case and the maximum gain of 4.4 dB is observed at 9 GHz frequency in OFF case with an average gain of 3.3dB in ON case and 2.9dB in OFF case. The proposed antenna works in almost at all ultra wideband applications having single rejection at 3.6GHz-4GHZ.The proposed antenna E-Field, Current distribution and radiation patterns have been analyzed using CST microwave studio in this article.

Wide band SRR-inspired slot antenna with circular polarization for wireless application

In this paper, wideband slot antenna based on SRR-inspired structure with circular polarization in 2–3.8GHz for WLAN and WiMAX applications is designed. Metamaterial are highly attractive in antenna and microwave applications because of their negative permittivity and permeability. In this paper, SRR-inspired are employed to miniaturize and modify the antenna frequency and obtain CP (circular polarization). In order to achieve this CP characteristic by controlling the antenna current distribution, SRR-inspired loads are used and for improving axial ratio, a special shape of slot and corner truncation are implemented. The final antenna has bi-directional pattern with circular polarization and wideband in range of 2–3.8GHz for WLAN applications with gain of 2–3.5dBi. The size of prototype patch antenna is 40×40mm which is fabricated on FR-4 low cost substrate with εr=4.4 and thickness of 1.6mm. It is simulated by HFSS and CST microwave studio commercial full wave software’s. In addition, the designing process of the prototype antenna is explained completely and the experimental results are compared with the simulation one. The efficiency of final antenna is more than 90%.

MINIATURIZED MICROSTRIP PATCH ANTENNA WITH DEFECTED GROUND STRUCTURE

The aim of this work is to miniaturize a microstrip patch antenna resonating at 3 GHz. For this purpose, defected ground structure (DGS) has been employed to shift the resonance frequency of an initial microstrip antenna from 5.7 GHz to 3 GHz by disturbing the antenna's current distribution. The proposed DGS is incorporated in the ground plane under the patch antenna to improve its performances. Finally, a miniaturization up to 50%, with respect to the conventional microstrip antenna, is successfully accomplished. A prototype of the antenna was fabricated with the FR4 substrate and tested. The measurements results were in good agreement with simulation results.

Summary and results of the study of the hybrid matching option implementation of the ITER ICRH system

The hybrid option has been chosen for the load-resilient matching of the ITER ICRH system. The corresponding 3dB hybrid matching circuit has been developed and fully implemented on a low-powered scaled mock-up at the LPP-ERM/KMS. The circuit features 23 simultaneously active feedback loops to minimize reflections on the 8 triplet lines, reduce the mutual coupling between the triplets and control the antenna array strap current distribution. The article discusses the employed methods for the implementation on a test-bench of the matching system including the derivation of closed-form analytical matching solutions for the tuners, the development of real-time control algorithms and the feedback systems. Furthermore, the achieved results are compared to numerical simulations of the ideal transmission line model of the matching system and the significance of these results for the extrapolation to the ITER case is discussed.

Maximum Gain of a Lossy Antenna

An upper bound on the achievable gain of a lossy antenna is derived. This limit depends on the antenna size and a newly defined “loss merit factor,” which is shown to be a measure of the antenna material loss. The derived limit extends the well-known upper limit on the ratio of antenna directivity to its quality factor to the lossy antennas. Optimal antenna current distribution for the maximum gain is found, and the radiation pattern and antenna efficiency are also presented.

Terminal Impedance and Antenna Current Distribution of a VLF Electric Dipole in the Inner Magnetosphere

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The current distribution and input impedance of an electric dipole antenna operating in a cold magnetoplasma at very low frequency (VLF) is determined through numerical simulation. A full wave solution of Maxwell's equations using a finite-difference frequency-domain (FDFD) method is implemented to simulate electromagnetic wave propagation in this highly anisotropic medium. The classical perfectly matched-layer (PML) boundary condition is found to exhibit instabilities in the form of nonphysical wave amplification in this environment. To circumvent these difficulties, a PML is developed that is tailored to the cold plasma environment at VLF frequencies. It is shown that the current distribution for antennas with length <formula formulatype="inline"> <tex>$≪$</tex></formula> 100 m is approximately triangular for magnetospheric conditions found at <formula formulatype="inline"><tex>$L = 2$</tex></formula> and <formula formulatype="inline"><tex>$L = 3$</tex></formula> in the geomagnetic equatorial plane. Calculated variations of input impedance as a function of drive frequency are presented for two case studies and compared with predictions of existing analytical work. </para>

Impedance and quality factor of mutually coupled multiport antennas

AbstractIn this study, expressions for the radiation quality factor Q and the input impedance seen at any terminal of a multiport antenna are derived. It is shown computationally that because of the possibility to adjust the antenna current distribution through suitable feeding/loading a multiport antenna can perform lower Qs than a similar single‐port antenna. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2034–2039, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23564

Simplified calculation of ground losses in low- and medium-frequency antenna systems

Calculations of ground losses are paramount in obtaining the best performance of a monopole antenna in the low- (LF) and medium-frequency (MF) bands. Ground losses are usually computed numerically, due to difficulties in the mathematical formalism. The novel approach here permits obtaining simple analytical expressions for ground-loss calculations that can be useful for determining the behavior of the ground plane. As a first approximation, the monopole antenna is placed on a perfect electrically conducting (PEC) ground plane in order to obtain the antenna current distribution and the near magnetic field, taking into account the non-zero-radius effect of the monopole. Next, the near magnetic field is used to determine the surface-current density on the ground plane below the antenna. This is divided into two zones: (1) the artificial ground plane, where either a radial-wire ground screen or a metallic layer is used to increase the soil's conductivity; and (2) the natural ground plane or bare soil up to a circular boundary a half wavelength from the antenna's base. The power dissipation is calculated from the artificial and natural ground-plane surface-current densities, and the ground-plane loss resistance is obtained. Also, an effective conductivity is defined as a measure of the ground plane's effectiveness, and the cases of quarter-wave monopoles and short top-loaded antennas are analyzed. Some results are validated by means of numerical computations and moment method simulations

Effects of Cavities on Monopole Antenna Current Distribution and Decoupling From Mounting Structure

The effects of cavities located near the base of a ground plane-mounted coax-driven monopole antenna are investigated. The cavities are either embedded in the tubular antenna itself or in the region below the conducting surface. Coupled integral equations are formulated and solved to determine the distribution of current on the structure. Two primary functions of the cavities are discussed. 1) At certain frequencies the input impedance of the cavity is infinite and the current at the base of the antenna is forced to zero. A single structure may contain several cavities, each cavity having unique resonant frequencies. It is demonstrated that superposition of these cavities may provide multiple resonant frequencies within a large frequency band. The utility of base cavities in the design of an antenna that is decoupled from the ground plane on which it is mounted is discussed. 2) Regardless of frequency, the cavities affect the distribution of current on the structure and, concomitantly, the standing wave ratio and gain of the antenna. The cavities are shown to be efficient and physically-rigid tools for current-shaping and tuning coax-fed antennas. Results computed from solutions of the coupled integral equations are compared with those from physical measurements

Current distribution of a VLF electric dipole antenna in the plasmasphere

In a recent paper (Inan et al., 2003) a method of remediating enhanced energetic electron fluxes in the radiation belt was proposed in which injection of VLF whistler mode waves from spacecraft within the radiation belts would dramatically increase the pitch angle scattering of the relativistic electrons and cause these particles to be rapidly lost from the belts, thereby mitigating the flux enhancement. The VLF wave transmitting system discussed by Inan et al. (2003) involves electric dipole antennas. One of the most important characteristics of such an antenna is the current distribution along the length of the dipole, since it is this current which ultimately determines the amount of VLF power which can be radiated from the antenna into the plasma. In past work it has been assumed without proof that the dipole current has a triangular distribution. In the present work we determine the dipole antenna current distribution from first principles, constructing an integral equation of the Hallén type relating the current distribution to the wave vector potential. In this development it is assumed that the length of the thin cylindrical dipole antenna is small compared to the wavelength of whistler mode waves which propagate parallel to the Earth's magnetic field Bo. In the case of the dipole antenna oriented parallel to Bo, it is found that the assumption of a triangular current distribution is reasonable for antenna lengths up to hundreds of meters. For the case of the antenna perpendicular to Bo, it is found that the current decays exponentially along the antenna from the feed points to the antenna ends. In this case we find the conditions under which a triangular current distribution is still a reasonable approximation. We also give the conditions under which the quasi‐static model of Balmain (1964) reasonably describes the electric fields associated with the dipole antenna.

Current and Near Field Calculations for Cellular Base-Station Collinear Array Antennas

In this paper, we present a new formulation for the evaluation of the electromagnetic field levels in the near zone of a cellular radio base-station collinear array antenna. The algorithm allows to determine the real current distribution along each half-wave dipole forming the array for a given exciting function and it enables to take into account the effects of mutual coupling among array elements. Once the antenna current distribution has been determined, the radiated field in the near zone is reconstructed using the integro-differential equation relating field and current. The developed algorithm, tested respectively on a 4-element and 8-element collinear array antenna operating at 900 MHz, allows to accurately analyze the response of dipole arrays with a computational cost significantly lower than that of a classical method of moments.

On inductively coupled plasmas for next-generation processing

The electron heating mechanism in ICP is briefly reviewed in the collisionless regime. We suggest a parallel resonance antenna (PRA) that by varying capacitance in a capacitor ( C v) as an external parameter can control not only the antenna current distribution, but also plasma uniformity. Radial plasma uniformity can be controlled and optimized by controlling coil currents between the coil segments, operating pressure, and chamber geometry in a recently developed antenna system. These results are consistent with the previous modeling paper [Appl. Phys. Lett. 77 (2000) 492].

Polarization agile circular wire loop antenna

We show that the inclusion of a pin diode suitably positioned in a circular wire-loop antenna mounted over a ground plane can be used to electronically control the polarization radiation properties of the antenna. Specifically, we use a gapped circular wire loop of circumference 1.13/spl lambda//sub o/ at 1 GHz positioned 0.3/spl lambda//sub o/ above a 33 cm /spl times/ 33 cm ground plane. Inclusion of a pin diode into a 2.7-mm gap, suitably positioned with respect to the generator, allows the antenna current distribution to be electronically controlled such that the loop produces linearly polarized radiation VSWR of 1.8 or circularly polarized radiation VSWR of 2.5, boresight axial ratio less than 2.5 dB.