Rigorous evaluation of the input impedance of a sleeve monopole bymodal-expansion method

A rigorous modal-expansion analysis is developed for obtaining the current distribution and input impedance of a sleeve-monopole antenna fed through an infinite ground plane by a coaxial line. A “perfectly matched boundary,” which is simply the combination of an electric wall and a magnetic wall, is initially proposed to facilitate the modal-expansion analysis. The walls are parallel to the ground plane at a variable height above it. Expansion coefficients of the electromagnetic fields are then determined by enforcing the boundary conditions at conducting surfaces and regional interfaces. Numerical results for the current distribution and input impedance of the sleeve monopole are presented and compared with available data in the literature. Very good agreement is observed. Also examined are the radiation pattern for different sleeve lengths and the effects of the length and finite thickness of the sleeve conductor on the antenna's input impedance     

Dielectric spectroscopy using monopole antennas of general electrical length

A procedure is developed for measuring the complex dielectric permittivity of a material over a broad range of frequencies using a monopole antenna. No restrictions are placed on the electrical size of the antenna. The antenna is calibrated one time by measuring the input admittance in a standard medium with known permittivity, such as air. Next, the admittance is measured with the antenna immersed in a material with unknown permittivity. These two sets of admittances are then used to determine the permittivity of the material. As an application of the procedure, the complex permittivity of the alcohol 1-butanol and saline solutions were measured using a cylindrical monopole antenna. The measured permittivities are in good agreement with those determined by previous investigators.     

Analysis of a wire antenna in the presence of a body of revolution

The problem of an arbitrarily oriented thin-wire antenna located near a body of revolution is analyzed. The usual integrodifferential equation for a thin wire in unbounded space is generalized to account for scattering from the nearby body. The presence of the body is accounted for by a numerical dyadic Green's function. The modified wire equation is solved by standard numerical techniques to obtain the current distribution on the wire. The effects of various bodies on input admittance are compared with results for an isolated antenna. Measured and theoretical input admittance data for a monopole near several different bodies of revolution are found to be in good agreement.     

The input impedance of a monopole antenna mounted on a cubical conducting box

An experimental investigation has been performed to determine the input admittance characteristics of a monopole antenna mounted on a conducting cubical box over a ground plane. Input admittances of monopoles from 2 to 6 cm long mounted on a 10 cm box were considered in the investigation so that effects of changes in the electrical size of the box could be evaluated. The monopoles were placed at various points to determine the functional dependence of input admittance on the position of the monopole antenna. A numerical analysis of the radiating structure was performed using the method of moments to compare the experimental data with the computed input admittance. This comparison and the observed empirical behavior of the input admittance were then utilized to predict the effects of the conducting box on the overall admittance of the radiator.     

Experimental study of an inductively loaded short monopole antenna

Theoretical studies have shown that the properties of electrically short monopole antennas are improved by placing an inductive load on the structure. The results obtained from the moment method are presented and compared with an experimental evaluation. The current distribution along the structure is computed and measured for various positions of the load. From this, the input admittance, efficiency, and bandwidth of the antenna are deduced. It is found that the efficiency and the bandwidth of the antenna increase as the load is moved from the base of the monopole until a maximum is reached. Simultaneously, the value of the inductance required to tune the monopole increases as the latter is moved away from the base.     

Permittivity measurements using a coaxial-line conical-tip probe

A conical-tip probe for the measurement of permittivity is presented which retains many of the advantages of the normal-plane probe including ease of sample preparation and moderate sample volume requirement, but which is mechanically better suited than monopole probes for the measurement of a wide range of biological materials since it does not promote free moisture regions resulting from cell rupture. The probe input admittance is found by modelling the probe as a short partially-sheathed monopole in free space and then a well-known antenna scaling theorem is used to determine the admittance and hence permittivity in the dielectric medium     

An experimental and theoretical study of the monopole embedded in a cylinder of anisotropic dielectric

The characteristics of a monopole antenna embedded in an anisotropic cylinder of semi-infinite length were studied. The anisotropic medium was created artificially by thin layers of lossless material whose dielectric constant alternated between two values, 15.0 and 1.06. A theoretical and experimental analysis was carried out for the axially anisotropic (uniaxial) orientation of the dielectric medium with curves shown for input admittance and current distribution. An experimental investigation was also carried out for the radially anisotropic orientation with measurements made for the input admittance, axial charge distribution, and the angular and axial current distributions.     

Ultrawideband Band-Notched Folded Strip Monopole Antenna

We propose a new band-notched folded strip monopole antenna for ultrawideband applications. This antenna is composed of a forked-shape radiator and a 50 Omega microstrip line. To achieve band-rejected filtering property at the WLAN bands, the forked-shape strips are folded back and result in a pair of coupled lines on the radiator. The length and gap width of the coupled lines primarily determine the notched frequency of the antenna. Based on the band-notched resonance, an equivalent circuit model is proposed for the antenna and the calculated antenna input admittance agrees with the full-wave simulation data. With the help of the dimensionless normalized antenna transfer function, the radiation characteristics are investigated thoroughly. The transmission responses of a transceiving antenna system and their corresponding transient analysis are discussed at the end of this paper.     

Loaded monopole antenna: Fourier series and admittance coefficientanalysis

A Fourier series method is presented for determining the self and mutual admittance between two generators driving a monopole antenna. It is shown that the admittances are useful in practical problems involving a monopole with a lumped load. They are applied to the loading of a base driven monopole to produce an outgoing travelling wave between generator and load     

Two-stage Parany monopole antenna with triangular complements

A new multiband and broadband antenna based on the traditional fractal equilateral Parany monopole is presented. In general, Parany and Sierpinski monopoles are resonant, log-periodic and multi-band antennas. For example, a traditional two-stage Parany monopole antenna provides three bandwidths. In this Letter, the input impedance behaviour of this antenna is improved by adding two conductor triangles to a traditional two-stage Parany monopole and eliminating two connections between the conductor triangles that shape such an antenna. For VSWR<3, the resultant fractal two-stage Parany monopole antenna with triangular complements shows bandwidth improvements compared to the traditional two-stage Parany monopole antenna. Good agreement between simulated and measured results was observed.     

Design of a Multiresonator Loaded Band-Rejected Ultrawideband Planar Monopole Antenna With Controllable Notched Bandwidth

We present a new multiresonator loaded band-rejected planar monopole antenna for ultrawideband applications. The proposed microstrip-fed antenna is composed of a flared metal plate, a truncated ground plane, and two pairs of folded strips. By applying the resonance nature of the folded strips and the associated cross coupling effects, the proposed antenna demonstrates bandstop-filter-like response with bandwidth controllability at the targeted rejection band. To illustrate the antenna operating mechanism more clearly, an equivalent circuit model consisting of RLC lumped resonators and J-inverters is discussed and extracted. The antenna input admittance calculated with the help of the equivalent circuit model agrees reasonably well with the simulated one obtained by the full-wave simulator. The design concept and the simulated and experimental results including the return losses, radiation patterns, and gain responses versus frequencies are carefully investigated throughout the paper. A parametric study in terms of the bandwidth tunability of the proposed design at the notched band is performed. The effects of the finite size ground plane are studied in this paper as well.      

Integral equation analysis of a sheet impedance coated window slotantenna

Presents an integral equation and method of moments analysis of a window slot antenna. The antenna is modeled by a sheet admittance coated rectangular aperture in an infinite ground plane. It is shown that the sheet admittance coated aperture is complementary to a sheet impedance plate, which permits the window slot antenna to be analyzed with existing computer programs. Numerical results are compared with measurements for input impedance and radiation efficiency     

An experimental investigation of dielectric-coated antennas

The characteristics of a monopole antenna embedded in a cylinder of low-loss dielectric have been measured. A cylinder of infinite length was approximated by extending the length of a finite cylinder until the admittance did not change. Admittance and current distribution data are represented as a function of antenna length for various diameters and dielectric constants of the cylinders. The results compare well with a theoretical analysis by Ting. The effect of the cylinder is to increase the electrical length of the antenna and decrease the bandwidth.     

Rigorous modal-expansion analysis of asymmetrical dipole antennas

This paper describes a rigorous analysis of asymmetrical cylindrical dipole antennas by the modal-expansion method. The analysis is facilitated by introducing two parallel conducting plates to enclose the dipole antenna. Field expressions for all the subregions of the resulting structure can be readily derived, and the expansion coefficients are found by enforcing the continuity conditions of tangential field components across the regional interfaces. Comparison of computed results with experimental data shows an excellent agreement. Numerical results are also presented for the input impedances, current distributions, and radiation patterns of various dipole antennas     

基于矩量法对导体板上单极天线特性研究

利用矩量法对有限大导体板上单极天线的阻抗特性进行了研究。基于Pocklington积分方程和Galerkin法，采用分域基正弦函数展开模式，得出了有限尺寸导体板上单极天线的电流分布和输入阻抗，并对单极天线在不同长度及不同导体板上的情况进行了研究。结果表明，单极天线的长度及导体板的形状及大小在一定程度上影响了单极天线的特性。     

An experimental study of a monopole over a grounded hemisphere

Very little quantitative information is available on the behavior of an antenna over a nonplanar surface. A monopole over a metal hemisphere on a ground plane is a simple configuration which has possible applications to spacecraft antennas [1] and to broadcasting antennas erected on a hill. Measurements have been made of the driving-point admittance of a monopole with electrical lengthsbetah = pi/2, pi, 2pias a function of the radiusbof the hemisphere. A traveling-wave monopole withbetah=2piandbetah_{T} = pi/2was also investigated. The current distribution on the hemisphere was measured by means of a movable probe.     

Miniaturised self-resonant split-ring resonator antenna

A self-resonant miniaturised antenna composed of a broadside-coupled split ring resonator (SRR) and an excitation arc-shaped monopole is presented. The size of the antenna and its resonance frequency is essentially defined by the SRR dimensions and geometry, while the input resistance at the resonance is governed by the arc length of the monopole. Numerical and experimental results are presented for an antenna configuration of 1/23.4 wavelength in diameter (ka ˜ 0.134). The antenna is tuned to 50 Ω without any matching network, and its efficiency is measured to be 17.5%.     

Internal antenna with modified monopole type for DVB-H applications

An internal modified monopole antenna for DVB-H band is presented. By extending the feeding line of the modified monopole and locating it over a ground plane, a wideband input impedance of 328 MHz within 6:1 VSWR is achieved. The proposed antenna has an approximately omnidirectional radiation pattern and yields greater than -3 dBi antenna gain covering DVB-H band. These features are suitable for DVB-H applications     

Frequency Notched UWB Planar Monopole Antenna Optimization Using a Finite Element Method-Based Approach

The objective of this work is the design and optimization of an ultrawideband (UWB) planar monopole antenna with frequency-notched behavior intended to get rid of the 5–6 GHz frequency band for WLAN compatibility purposes. An optimized profile UWB planar monopole designed by means of a Simulated Annealing algorithm and full three-dimensional finite element method, detailed in a companion paper, was considered as the design starting point. In order to design the band-notched rejection no full finite element analysis is carried out on each profile modification as is usual. The procedure is based on a genetic algorithm and a multipurpose admittance matrix approach instead. Artificial ports are allowed in the computational domain and an admittance-type matrix comes up. As a result, a multiport network describes the electromagnetics within the analysis domain. Circuit manipulations of this network efficiently outperform full-wave analyses for different monopole modifications, thus making it possible to use this strategy in a computer aided-design scheme.