T-matched dipole antenna integrated in electrically small body-worn wireless sensor node

A 2.4 GHz antenna for an electrically small body-worn sensor node is presented. Usually, unbalanced antennas are used in such applications. Implementing a balanced antenna in a small node deployed on the body is problematic from the points of view of both design and characterisation. A solution using a T-matched dipole integrated in the node housing is presented. Techniques for characterisation both in free space and on the body are described. Besides antenna port impedance and radiation efficiency, radiated power and radiation patterns of the active antenna fed by a transceiver in a fully functional sensor node are measured. The benefits and drawbacks of the chosen antenna design and characterisation techniques are discussed.     

Compact ultrahigh-frequency antenna designs for low-cost passive radio frequency identification transponders

Compact planar antennas for low-cost radio frequency identification (RFID) passive transponders are disclosed. The proposed ultrahigh-frequency antenna takes advantage of its unique topology to assure conjugate matching with essentially complex impedance of the electronic chip directly embedded into the radiator. Rectenna design issues are also emphasised. An original method to characterise IC chips and antennas as taken in its entirety of transponders is presented. The characterisation of the chip takes into account the impact of connecting antennas to the rectifier by flip-chip bonding process. The proposed experimental method allows finding chip impedance exactly as it seen by antennas. Refined rectifier circuitry effectively overcomes dependence of transponder performances on the type deviation of the connected antennas. Very good antenna performance is predicted theoretically and validated experimentally over an operating bandwidth of actual RFID systems.     

Finite-difference time-domain model for the feeding gap of coaxial probe driven antennas

In the finite-difference time-domain (FDTD) method, a simple and realistic feed model for coaxial probe driven antennas is proposed here. The feed zone of the antenna may be considered as an equivalent source in view of the antenna theory and a load port in view of the transmission line theory. The proposed feed model is constructed by combining the infinitesimal-gap source condition of the antenna and the equivalent load condition of the feed line. It leads to perform no additional FDTD cell modelling of the line. The transient reflected voltage and the input impedance of cylindrical monopole antennas fed by coaxial lines are calculated numerically and then compared with the accurate measurement and a full fine-grid. The FDTD results of the proposed model have a good agreement with the measured data and the fine-grid results.     

Superstrate effects on slot-coupled microstrip antennas

An analysis for studying the superstrate (cover) effects on the slot-coupled microstrip antennas is presented. The approach is based on the reciprocity theorem and uses the grounded double- and single-layer dielectric slab Green's functions in a moment method solution for the unknown slot fields and patch currents. From these fields and currents, various characteristics of the antenna can be extracted, such as the radiation efficiency, directivity, input impedance, and resonant frequency. Numerical calculations showing superstrate effects on these antenna characteristics are presented. The input matches obtained from proper adjustment of the slot and patch dimensions are discussed.<>     

Space Electromagnetic and Plasma Sensor (SEAPS): A Laboratory Prototype for a Space Payload

Space electromagnetic and plasma sensor is a proposed space payload consisting of an electric field vector sensor—a tri-axial arrangement of monopoles in a mutually orthogonal configuration—and a magnetic field vector sensor, which is a tri-axial arrangement of mutually perpendicular loop antennas. Both operate between 0.5 and 20 MHz in order to acquire the complete 3D polarization matrix. The antennas, which are meant to be electrically short, are matched with a high input impedance amplifier, followed by gain blocks, filters and a six-channel data acquisition system. Some of the proposed goals of the project include study of the low frequency Sun, plasma interactions between the solar wind and Earth’s magnetosphere, lunar atmosphere, and radio emission from other planets within the solar system. This article describes the construction of a laboratory prototype and preliminary calibration results.     

High-temperature superconductor antennas: Utilization of low rf losses and of nonlinear effects

The low radio frequency (r.f.) losses in epitaxial HTS thin films allow the realization of novel antenna structures which have to be excluded in conventional antenna techniques with normal conductors because of the highly reduced radiation efficiency. Thus, the design of miniaturized but nevertheless highly efficient antennas down to a lower limit determined by both the required order of radiation pattern and the frequency bandwidth becomes possible. For a bandwidth of more than about 1%, a considerable margin for a size reduction below the critical size is restricted to the case of electrically small antennas and of superdirective antennas with a relatively low order of the radiation pattern, e.g. antennas with a beam of less than 15 dB maximum gain. If the size approaches the lower limit, the antennas show a sharp bandpass frequency response. This is demonstrated by means of experimental results for a novel HTS meander antenna. These bandpass characteristics can be utilized in compact multiport antenna systems in order to decouple subantennas for adjacent frequency bands. Besides the low losses in HTS's, their nonlinear properties can be used in order to realize current-controlled HTS switches for antenna systems.     

Application of gain-bandwidth bounds on loaded dipoles

Physical limitations based only on antenna volume, form factor and material parameters are applied to electrically small antennas in the form of single dipoles. The upper bound on the gain-bandwidth product is solely determined by the polarisability matrix that characterises the antenna when it is immersed in a uniform applied static field. The polarisability, and hence the bandwidth, is increased by loading the dipole arms close to their ends. The half-power impedance bandwidth is increased from 5 to 13% by moving the coils from the centre to the ends of the dipole arms. The introduction of a stub-matching further improves the bandwidth but the physical limit is not reached. Finally, a dual-resonance dipole antenna is analysed. It is observed that a second resonance hardly reduces the bandwidth of the first resonance if the resonances are separated more than 1.7 times in frequency.     

Application of dual-mode filter techniques to the broadband matching of microstrip patch antennas

Structures such as square or circular microstrip patch antennas may support two orthogonal resonant modes. The paper presents a new method of utilising the dual-mode property to increase the bandwidth of microstrip antennas. The input impedance of such a dual-mode antenna may be represented as a second-order ladder network of coupled resonators, where each resonator is coupled to a load resistor. A theoretical method for evaluating the coupling values in the network is presented, enabling the bandwidth of a dual-mode antenna to be maximised. A theoretical bandwidth improvement of up to 3:1 is achieved when compared to a single-mode antenna. This is confirmed with an experimental dual-mode circular microstrip patch antenna     

Antenna/sensor multifunctional composites for the wireless detection of damage

Wireless structural health monitoring (SHM) techniques generally rely on the integration of sensors, transmitters, and antennas into structures; however, the ideal solution would entail the material itself acting as a monitoring system. The current work investigates the application of antenna/sensing multifunctional composites. In this technique, carbon fiber reinforced plastic (CFRP) structures are modeled as half-wavelength dipole antennas. The electrical or antenna property varies in accordance with damage occurrence and can be monitored wirelessly at a remote location. The feasibility of wireless SHM using the self-sensing antenna technique is investigated analytically and experimentally using unidirectional CFRP laminates and rotor blades of woven CFRP. The CFRP radiates radio energy well when it is used as a half-wavelength dipole antenna, and damages to the CFRP can be wirelessly detected by monitoring an increase in the resonant frequency of the CFRP antenna.     

Amplitude calibration of a digital radio antenna array for measuring cosmic ray air showers

Radio pulses are emitted during the development of air showers, where air showers are generated by ultra-high energy cosmic rays entering the Earth's atmosphere. These nano-second short pulses are presently investigated by various experiments for the purpose of using them as a new detection technique for cosmic particles. For an array of 30 digital radio antennas (LOPES experiment) an absolute amplitude calibration of the radio antennas including the full electronic chain of the data acquisition system is performed, in order to estimate absolute values of the electric field strength for these short radio pulses. This is mandatory, because the measured radio signals in the MHz frequency range have to be compared with theoretical estimates and with predictions from Monte Carlo simulations to reconstruct features of the primary cosmic particle. A commercial reference radio emitter is used to estimate frequency dependent correction factors for each single antenna of the radio antenna array. The expected received power is related to the power recorded by the full electronic chain. Systematic uncertainties due to different environmental conditions and the described calibration procedure are of order 20%.     

High-resolution measurements of the specific absorption rateproduced by small antennas in lossy media

We describe a thermistor-based technique for measurement of the specific absorption rate (SAR) of radio frequency energy from a small antenna in lossy matter with high spatial resolution. The apparatus employs a small thermistor probe, that is moved about the antenna using a computer-controlled positioning system. The antenna is excited by pulses of radio frequency energy, and the SAR is obtained from the measured rate of temperature increase. We present a simplified thermal model to account for heating of the thermistor by the applied electromagnetic energy, which is a major potential artifact in the method. The apparatus is useful for studies of radio frequency ablation of tissue or near-field exposure in models of the body by transmitters     

Matching radio frequency identification tag compact dipole antennas to an arbitrary chip impedance

A method for matching dipole antennas to capacitive or inductive arbitrary complex impedances is proposed for ultra high frequency radio frequency identification (RFID) tag antenna designs. It can be applied to straight, capacitive-loaded, meander or any small high-Q dipole topology. For this purpose, design stages are provided with the corresponding formulas. The reflection coefficient simulations and measurements of four implemented prototypes show the expected output when the RFID frequency band, bandwidth, chip impedance and maximum tag size are required as inputs for the method. The eventual S11 < 10 dB bandwidth depends on the chip impedance Q factor and the antenna size. How this bandwidth is manifested in terms of the read range is also discussed. A length ratio of up to 31.1% regarding the standard Λ/2 dipole at resonance is obtained.     

Comparative robustness study of planar antennas

Is it possible to produce a planar dipole-like antenna with a reduced conductive area without any loss in either robustness or performance? The objective is to reduce the amount of expensive conductor to be used when applying a meshing technique to the printing of antennas. In this context, robustness means that the characteristics are maintained when the antenna is damaged, for example if it is scratched. This is particularly important for radio frequency identification tags in logistic systems. A general antenna robustness evaluation methodology, based on numerical simulations of a large number of randomly damaged antennas, is used for the antenna comparisons. The antenna performance degradation, based on the return loss (S₁₁) at 868 MHz, is monitored for some basic planar antennas. Finally, we show that it is possible to produce robust low-cost antennas using wire replacements for the solid planar antennas and thus, provided that the robustness requirement is moderate, replace the solid antenna with a thin conductor analogue     

Rectangular microstrip antennas

Abstract

The theory of rectangular microstrip antennas based on the line resonator model and the cavity model are summarized. The theoretical and experimental values of input impedance and radiation patterns are compared, and the discrepency between these two values are explained. A parallelogram microstrip antenna is constructed, and the input impedances are compared to those of the rectangular microstrip antenna.     

RFID天线的丝印工艺研究

为分析优化RFID天线的丝网印刷过程并提高其印刷质量,对丝网印刷工艺对天线印刷精度的各种影响因素进行了分析,包括网目数、印版特性、刮刀角度等各项参数。通过优化丝印工艺参数,印刷了RFID天线并测量了作为主要参数之一的阻抗,结果表明其阻抗波动较小,丝印工艺可满足天线印刷的质量要求。     

Broadband flexible comb-shaped monopole antenna

A broadband comb-shaped monopole antenna is proposed. The antenna has dimensions of 19 mm x 12 mm. The measured results show good agreement with the numerical prediction, and broadband operation with 10 dB impedance bandwidth of 44.75% (1.7-2.68 GHz). The antenna is built on one side of a flexible-printed circuit board (PCB) dielectric substrate. Folded and rolled antenna structures, which are transformed by the proposed planar antenna structure, are presented. Each antenna has a broadband impedance bandwidth that covers the PCS, UMTS, WiBro, WLAN and SDMB bands. Also, omni-directional radiation patterns over the operating bands have been obtained. The proposed antennas are suitable for mobile communication applications requiring a small antenna.     

Lambda/4 resonance of an optical monopole antenna probed by single molecule fluorescence

We present a resonant optical nanoantenna positioned at the end of a metal-coated glass fiber near-field probe. Antenna resonances, excitation conditions, and field localization are directly probed in the near field by single fluorescent molecules and compared to finite integration technique simulations. It is shown that the antenna is equivalent to its radio frequency analogue, the monopole antenna. For the right antenna length and local excitation conditions, antenna resonances occur that lead to an enhanced localized field near the antenna apex. Direct mapping of this field with single fluorescent molecules reveals a spatial localization of 25 nm, demonstrating the importance of such antennas for nanometer resolution optical microscopy.     

A Holographic Surface Measurement of the Texas 4.9-m Antenna at 86 GHz

An instrument has been built which allows the electromagnetic measurement of the surface accuracy of a large millimeter-wavelength antenna. The University of Texas 4.9-m radio telescope has been measured with this technique at 86.1 GHz to an accuracy of 4 ?m at the surface. Our technique is an interferometric one which is fast, accurate, and able to measure the whole antenna surface at once. While the technique is illustrated by its use on a large antenna, it could be used in a near-field measurement of a smaller antenna. Several antenna surface maps are presented. A comparison of run-to-run repeatability was made. The technique itself was tested by deforming the antenna surface in a known way and subsequently detecting the deformation.     

一种利用S参数测量平衡RFID标签天线阻抗的优化方法

针对测量平衡RFID标签天线阻抗的准确性问题,提出了一种利用s参数测量的优化方法。该方法将平衡RFID标签天线等效为双端口网络,通过联合使用端口短路、开路延伸方法测量S参数,根据拐点选取最邻近数据并进行区间的数据拟合,从而计算出天线阻抗。首先 h1 进行了测量理论分析．然后设计了实物测量场景（915MHz频段的RFID天线）,并将该优化方法与传统的Bahm方法、无延伸单端口方法、延伸单端口方法进行了对比。结果表明,在工作频段内,该优化方法所测的标签天线的阻抗实部,虚部与仿真结果基本一致,比传统的Balun2及单端口等测摄方法准确;在工作频段外,所测阻抗实部仍然与仿真结果接近,尽管阻抗虚部与仿真结果存在一定的偏差。     

Infrared and Optical Properties of Carbon Nanotube Dipole Antennas

The characteristics of armchair carbon nanotube dipole antennas are investigated in the infrared and optical regime. The analysis is based on a classical electromagnetic Halleacuten's-type integral equation, and an axial quantum mechanical conductance function for the tube. It is found that, within a certain frequency span in the GHz-THz range, finite-length carbon nanotube dipoles resonate at approximately integer multiples of one-half of a plasma wavelength. Outside of this range, current resonances are strongly damped. In the optical regime, antenna properties are strongly modulated by interband transitions. General antenna characteristics of finite-length carbon nanotube dipoles are presented, such as input impedance, current profile, gain, and efficiency, and radiation patterns are discussed