Coaxial Antenna Research Articles

Mode-Matching Model for Electromagnetically Coupled Coaxial Dipole Array Antenna

A mode-matching model for an electromagnetically coupled coaxial dipole array antenna is presented. The Fourier transfor m/series technique is used to represent the continuous and discrete modes of scattered fields. The mode-matching is utilized to constitute a set of simultaneous equations for discrete modal coefficients. Numerical computation is performed to show its radiation behavior in terms of various antenna parameters.

DESIGN OF A 4X4 SQUARE MICROSTRIP PLANAR ARRAY

Wind profiling radars operating in Doppler beam swinging mode needs to have large antenna array in order to have a narrow beam for wind direction accuracy. To meet the above requirement, in the present work an array with 16 elements configured in a 4X4 square matrix is designed. The antenna inserted is a coaxial probe (Probe Feed) to the patch near its resonance in 'L' band is carried out. Principal plane 2-dimensional radiation patterns at 1.28GHz have been computed for single element and 4X4 planar arrays. The results of linearly polarized coaxial probe single element are generated by using IE3D software. Using this single element as basic building block, a2X2 and 4X4 planar arrays was designed. The results obtained are presented succinctly. The inferences from the design of coaxial probe antenna are presented. The Impedance Band-Width, 3-dB Beam Width and Gain for a single element as well as a 4X4 planar array are compared.

고출력 전자기파 발생 장치용 소형화 된 원뿔 계단형 COBRA

본 논문에서는 고출력 전자기파 발생 장치에 사용될 소형화 된 원뿔 계단형 COBRA(Coaxial Beam-Rotating Antenna)를 제안하였다. COBRA는 혼 안테나와 렌즈로 구성되는데, 일반적인 방법으로 설계할 경우 정전 파괴 방지를 위해 그 크기가 매우 커지게 된다. 소형화를 위해 안테나의 길이만 줄일 경우 위상 오류의 증가로 인해 안테나의 이득이 줄어들게 되는데, 이를 방지하기 위해 COBRA 렌즈를 원뿔 계단형으로 변형시켜 개구면에서의 위상 오류가 보정 되도록 하였다. 시뮬레이션 결과, 1,300 mm 길이의 안테나를 600 mm로 줄였음에도 불구하고 제안된 안테나는 더 높은 이득을 보였으며, 제작하고 측정된 원뿔 계단형 COBRA의 이득은 26.2 dBi로 나타났다. In this paper, miniaturized conically stepped COBRA is proposed. In order to prevent electrical breakdown, COBRA, which consists of hem and lens, has to get bigger if it is designed with conventional method. Because of the phase error increase, shortening the length of the antenna without changing the aperture size leads to the reduction of the antenna gain. To avoid this, the phase error at the aperture is compensated by transforming the COBRA lens into conically stepped form. The simulations result shows that the proposed antenna has higher gain than the conventional COBRA in spite of the size reduction from 1,300 mm to 600 mm. The fabricated and measured COBRA has the gain of 26.2 dBi.

Feasibility Study of Tumor Size Estimation Through Time Domain Peak Monitoring

A new ultrawideband (UWB) microwave method to estimate tumor size based upon detection of the tumor/liver interface is proposed. This method involves monitoring the response of a broadband pulse launched down a coaxial treatment antenna and radiated into the tumor. By monitoring the peak in the returned signal, and estimating the propagation velocity within the tumor, the location of the tumor/liver interface can be determined and the size of a spherical lesion estimated. The feasibility of this technique is demonstrated by finite element (FE) electromagnetic simulations of a spherical tumor in the liver. Robustness to noise is also investigated as well as the effects of insertion depth. The promising outcome of this feasibility study suggests that further development of this technique should be pursued.

Cell Investigations Simultaneously with Exposure to 2.45 GHz Microwaves

The paper presents two microwave (MW) exposure systems (MWESs) that permit observations and measurements on cell cultures during their exposure to MW of 2.45 GHz: MWES-1 and MWES-2. MWES-1 is designed for the measurement of the cell membrane fluorescence anisotropies (MFA) simultaneously with MW exposure. MWES-2 is designed for the cells culture exploration under an inverted microscope before, during and after MW exposure. MWES-1 consists mainly of a 2.45 GHz microwave generator (MWG-2.45GHz-SAIREM) of 0–25 W, equipped withforwardpower and reflected power displaying, and an adjustable coaxial antenna immersed directly into the cuvette with the cellssuspension of a Spex type spectrofluorometer. The MW effect on membrane fluidity of B16F10 malignant melanoma (B16F10-MM) cells in suspension were investigated with MWES-1, by MFA measurements. We observed a MW induced transition temperature (ITT) rising strongly during the MW exposure as compared with ITT obtained by classical heating (CH). The MWES-2 consists of the MWG-2.45 GHz-SAIREM generator and a rectangular waveguide applicator with traveling wave placed between the condenser and the objective of a Zeiss Axiovert 200 microscope, equipped with a fluorescence device and image acquisition. The MW effects on shape and apoptosis of the B16F10-MM cells were investigate with MWES-2. The B16F10-MM cells exhibited visible shape changes during MW exposure up to 37°C. The MW exposure induced cells apoptosis/necrosis in several seconds after that MW are applied, beginning with SAR=1.5 W/sample, compared to CH controls exposed at the same temperature dynamics.

Radiation properties of an omnidirectional planar microstrip antenna

AbstractThe pattern and directivity of an ideal omnidirectional antenna, collinear coaxial, and omnidirectiontal microstrip antenna (OMA) are compared. The radiation of an OMA originates from the arraying of two radiating edges along each element. The width of the (OMA) elements determines omni‐plane pattern variation. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 55–58, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22995

Results of Field Tests on Radio-Wave Heating for Soil Remediation

After developing the radio-wave technique for various conditions in laboratory-scale and technical plant-scale experiments, field tests in combination with biodegradation and soil vapor extraction were carried out at three sites: (i) a bioremediation facility for ex situ cleaning of soil, (ii) in situ remediation of contamination at a former storage facility for organic solvents, and (iii) a polluted soil under a former petrol station. Various electrode arrangements such as parallel plates, rod arrays, and coaxial antenna were applied in order to meet the site-specific requirements optimally. Soil temperatures between 35 and 100 degrees C were established. The successful tests gave much insight into the engineering, physical, biological, and chemical aspects of radio-wave application. General conclusions on the appropriateness and competitiveness of the radio-wave method as well as on preferred application fields are drawn.

Simulation Investigation of an Improved MILO

Magnetically insulated line oscillator (MILO) is a gigawatt-class high-power microwave source whose behavior has been investigated experimentally and numerically. This paper presents an improved MILO model. A novel beam dump, a one-cavity RF choke section and a novel mode-transducing antenna are introduced into the improved MILO. The improved MILO is investigated in detail with particle-in-cell method (KARAT code). In simulation, high-power microwave of transmission electron microscopy (TEM) mode is generated with peak power of 4.2 GW, frequency of 1.76 GHz, and peak power conversion efficiency of 12%, when the voltage is 600 kV and the current is 52 kA. A novel plate-inserted mode-transducing antenna, which is composed of a plate-inserted mode converter and a coaxial horn, is introduced into the improved MILO. The TEM wave generated by the MILO propagates down the section of coaxial waveguide and is transformed into the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode by the novel plate-inserted mode converter, and then radiated by the coaxial horn antenna into air. The direction of the radiated microwave agrees with the axis of the MILO

X-band coaxial monopole antenna with an additional metal screen

The novel coaxial monopole antenna design with an additional metal screen is presented. The radiation char- acteristics of this antenna are investigated depending on a dis- tance between the ground plane and additional metal screens, as well as on a size of the latter. Measured and calculated ra- diation patterns are compared within limits of the operative frequency band and their revealed distinctions are discussed. The antennas characteristics allow pronounce that it can be considered as a promising candidate for various practical ap- plications both a single radiator and a composite element of antenna arrays.

Comparison between the conventional method of extraction of essential oil of Laurus nobilis L. and a novel method which uses microwaves applied in situ, without resorting to an oven

A novel microwave method has been applied to the hydrothermal extraction of essential oil from plants. An insulated microwave coaxial antenna was introduced inside a 1000ml glass flask containing dry Laurus nobilis L. leaves and tap water. Microwave power up to 800W at 2450MHz was emitted in continuous wave regime (CW) or in pulsed regime (PR) at 8kW peak power. Stirring with a magnetic bar and a Clevenger refrigerator connected to the flask enabled to complete the extraction in 1h. The results of the in situ microwave extraction were compared with those obtained by heating the same reactor with a conventional electric mantle by gas chromatography–mass spectrometry (GC–MS) analysis. Differences were observed both in the composition of the essential oil and from the energetic point of view. The essential oil obtained with microwave (MW) methods contained substantially higher amounts of oxygenated compounds and lower amounts of monoterpenes than conventional method. The in situ microwave heating is safe and versatile; it presents time and energy saving advantages, and therefore it can be considered useful also for industrial applications.

Design and numerical simulation of miniaturised COBRA lens horn

Proposed is a novel miniaturisation method of a coaxial beam-rotating antenna (COBRA) lens horn for high power application. Generally, a miniaturised horn increases the phase error at the aperture because of large flare angle which causes gain decrease. However, since the proposed COBRA lens horn compensates phase error with a modified COBRA lens, radiation characteristics such as gain and radiation pattern of the miniaturised COBRA lens horn are similar to the conventional one while the length of the horn is reduced by more than 50%.

Modal-Expansion Analysis of Electromagnetically Coupled Coaxial Dipole Antennas

This paper presents a modal-expansion analysis of the electromagnetically coupled coaxial dipole antenna. The analysis of the antenna problem is initially simplified using the even-odd mode excitation and then the resultant half structure is divided into two parts; one is the characterization of a coaxial feeding network and the other is the modeling of a sleeve monopole antenna driven by a coaxial line. The formally exact modal-expansion method is employed to analyze both parts. The analysis of the sleeve monopole antenna is facilitated by introducing a perfectly conducting boundary at a distance from the monopole's top end. The current distribution and input impedance of the electromagnetically coupled coaxial dipole antenna are obtained by finding expansion coefficients through enforcing the continuity of tangential field components across regional interfaces and cascading the two parts together. Numerical results for the coaxial dipole antenna's radiation characteristics are presented and discussed.

A Floating Sleeve Antenna Yields Localized Hepatic Microwave Ablation

We report a novel coaxial antenna for hepatic microwave ablation. This device uses a floating sleeve, that is, a metal conductor electrically isolated from the outer connector of the antenna coaxial body, to achieve a highly localized specific absorption rate pattern that is independent of insertion depth. This floating sleeve coaxial dipole antenna has low power reflection in the 2.4-GHz IMS band. Ex vivo experiments confirm our numerical simulation results. Index Terms-Ablation, coaxial aperture antennas, finite element methods, floating sleeve, microwave heating.

Broadband coaxial antenna for WiMAX access‐point application

AbstractA broadband coaxial antenna mainly comprising an upper square cylindrical plate and a lower square cylindrical ground is presented. The antenna functions like a two‐wire dipole antenna, and furthermore provides a wide operating bandwidth of about 4 GHz (about 1.9 to 5.9 GHz in the study), making it very promising for application in Worldwide Interoperability for Microwave Access Forum (WiMAX) access points. The antenna has been successfully implemented, and experimental results are presented. The effects of the lower square cylindrical ground on the antenna performances are also analyzed. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 641–644, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21432

An Analysis of Coaxial Line Slot antenna for Hyperthermia Treatment by Spectral Domain Approach

An extended spectral domain approach (ESDA) is applied to evaluate the scattering parameter of laterally slotted coaxial antenna for hyperthermia treatment. The results calculated by ESDA are in good agreement with that by Finite Element Method (FEM) simulation. Computational labor of the present method is far lighter than that of FEM, and the method is suitable for the iterative computation that is required for the optimization of antenna design. The present method can afford to consider the effect of the metallization thickness in the outer conductor.

A novel compact and wideband shorted patch antenna

AbstractA novel compact shorted patch antenna with the bowtie‐type patch and the dual triangle portion to obtain a large bandwidth (790–970 MHz) is presented in this paper. Using shorted patches with via holes, a size reduction of 95.7% is achieved, as compared to that of the conventional half‐wave patch antenna. Moreover, it has 10‐dB return‐loss bandwidth of 20.4% for the GSM and CDMA bands. This proposed antenna exhibits not only a compact and a thin profile, but also wideband characteristics. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 46: 4–6, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20884

Improved input impedance of a coaxial-slot antenna for interstitial heating by loading a matching circuit

Recently, research on medical applications of the thermal effects of microwaves, such as microwave treatment, on biological bodies has been carried out extensively. One example is hyperthermic treatment of cancer. In particular, in the treatment of cancer deep inside the human body, interstitial hyperthermia is effective. The most important characteristic of the antenna for interstitial hyperthermia is its heating properties. However, when clinical use is considered, impedance matching also must receive attention. In the present paper, with a view to impedance matching of the interstitial hyperthermia antenna, a coaxial slot antenna with a matching circuit of simple configuration is proposed. The reflection coefficient (S11) of the antenna is used as an evaluation guideline, and numerical simulation by the FDTD method and measurement are carried out. From these examinations, it is confirmed that the reflection characteristics can be improved drastically. It is further confirmed that the proposed antenna can supply a power of at least a certain level regardless of the electrical parameters of the biological tissue to be heated and of the antenna insertion length. Hence, this antenna is demonstrated to be practical. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(12): 11–19, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20218

Coaxial Antenna for Microwave Hyperthermia

We present in this paper a coaxial applicator in which the radiating source is a circular slot realised by exterior conductor interruption of a coaxial guide. The guide is immersed in a strong dissipated medium. A dielectric material girdle without losses or an air layer is inserted among the radiating slot and the load. In this paper, we study a single slot radiation and analyse the radiating field distributions in the load, the approaching field influences and the role of dielectric girdle on the dissipated power distribution in the load.

Application of Perfectly Matched Layer Absorbing Boundary Conditions for Propagation of Surface Wave on the Long Plasma Cable

We have developed a computer code for the simulation of large scale SWP plasma excited by a long coaxial antenna with a VHF wave of 300 MHz, this antenna is located along the center axis of a cylindrical chamber. The antenna used in this model structure is so long that the computational region has become very large. Therefore, for the calculation of the electromagnetic field profile in order to design a long and large scale SWP plasma, it is necessary to apply a proper boundary condition to truncate the computational region, and from this viewpoint we have introduced the PML absorbing boundary conditions and have studied the effectiveness of this boundary conditions for our purposes.

Measurement of electric-field intensities using scanning near-field microwave microscopy

In this paper, we propose methods for the measurement of electric intensities of a microwave field above the surface of microwave circuits. Using miniaturized coaxial antennas, we measure all spatial components of the induced field above device-under-test. A special position/signal difference method is used to better localize the measured field and increase the spatial resolution of the field mapping. During the scanning process, the antenna is driven at the defined distance above the sample surface according to previously acquired topographic data. For measurement of the tangential-field components parallel to the sample surface, the antenna is tilted by approximately 45/spl deg/ relative to the sample surface. By its rotation about the vertical axis, various components of the field are measured, and vertical and horizontal electric-field intensities are recalculated. The probes are calibrated in a well-defined field standard and allow good quantitative characterization of the measured field.