Efficiency and Matching Tradeoffs for Inductively Loaded Short Antennas

Efficiency and input resistance of short monopoles (or dipoles) may be significantly improved through use of a loading coil in series with the monopole wire. The piecewise sinusoidal moment method is used to analyze the loaded monopole. When loaded to resonance, the current rises from the feed value to a peak slightly beyond the load point with decay to zero at the end. Radiation resistance improvement factors as large as 5 have been calculated. The resonant loading reactance is shown to vary inversely with the antenna length for most lengths. Efficiency varies slowly with load point and peaks at roughly 0.4 from the feed, in contrast to earlier approximate theory that predicted higher efficiency for loads farther out toward the end. The curves allow a tradeoff between slightly reduced efficiency and larger input resistance (to allow easier matching) to be made. For this case, a 2/3 loading point may be a good compromise. The length for which efficiency is 50 percent is a useful design guide. This length varies slowly withQandh/aand is in the range 0.06 to 0.09 λ. Thus shorter monopoles will have low efficiency. Bandwidth is improved due to loading coil losses at the expense of efficiency; lossless loading bandwidth is unchanged over the unloaded monopole as the radiation resistance and reactance slope increase commensurately. Extensive graphical data are presented.     

Efficiency transition point for inductively loaded monopole

Whip or monopole antennas less than a quarter wavelength long can be significantly improved through series inductive loading in the antenna wire, provided that the coil losses are less than the improved radiation resistance. However, if the antenna is too short or the coil too lossy, the performance may degrade instead of improve. The combination of antenna length, radius, and coil Q factor for which the efficiency is 50% is an important design guide. This transition point varies with Q1/3 and even more slowly with length/radius ratio. For Q = 300, the transition point occurs for monopole lengths between 0.05 and 0.07 wavelengths.     

Theoretical study of a Gunn diode in a resonant circuit

A computer simulation of a GaAs Gunn diode in a parallel resonant circuit has been made to determine the optimum device and circuit parameters. The maximum dc to RF efficiency, 5 to 8 percent, is obtained when the product of doping and length is between 10¹²and 2 × 10¹²cm^-2, the product of frequency and length is 10⁷cm/s, and the bias voltage divided by length is 8000 V/cm for a load resistance of30 R_{0}where R0is the low-voltage resistance of the diode. The product of output power and load resistance varies with frequencyfasC f^{2}whereCis 12,000 watt-ohm-GHz²for a load resistance of50 R_{0}. The frequency can be varied over an octave tuning range by the resonant circuit.     

短波宽带有源鞭天线设计

常用短波天线的尺寸一般较大,不适于在建筑物、运动载体等有限架设空间中使用.基于模型仿真计算短波垂直单极天线,理论分析其传输增益函数(Transducer Power Gain,TPG)对接收效率的影响.通过实测天线输入阻抗采用实频法设计天线匹配网络、有源放大电路.设计了一种小型的鞭状天线,其尺寸不大于波长的十分之一,通过加载匹配网络及有源放大后,实现小体积、超宽频带、高效率、高灵敏度、等特点,可灵活应用在各种移动载体的短波宽带有源鞭状接收天线.     

RC-loaded bow-tie antenna for improved pulse radiation

In this paper, a loading technique for improving pulse radiation from bow-tie antennas is introduced. This technique allows transmission of short transient pulses with very small late-time ringing and relatively high radiation efficiency. It makes use of a combination of a constant resistive loading along the antenna and a capacitive loading with linearly increasing reactance toward the antenna ends. The constant resistive loading is applied using volumetric microwave absorbers to cover one side of the antenna and the linear capacitive loading is realized by constructing narrow slots on the antenna surface. Relatively high radiation efficiency is achieved by choosing the location of the slot nearest to the feed point in such a way that radiation from it combines constructively with radiation from the feed point. Using a 0.8-ns monocycle for excitation, the technique results in a level of late-time ringing of lower than -40 dB and at the same time the peak value of the transmitted pulse is 54% higher than that of the same antenna without loading.     

常用短波鞭天线性能优化工程技术研究

短波天馈线系统是短波通信系统中的重要组成部分,天线的效率直接关系到短波通信的质量,在实际开展短波通信时,加强对短波天线的工程应用研究和优化改进,才能充分发挥短波通信的总体效能。通过对鞭状天线较为全面的性能分析,从提高鞭状天线辐射效率的角度出发,分别在加顶负载、加电感线圈、埋设地线或地网等几个方面给出性能优化的具体实现方法,切实有效地改善了短波通信（话音、数据）传输性能。     

对数周期天线特征参数对电性能的影响分析

提出了通过优化馈管间距、馈电点位置和馈管长度三个特征参数,实现对数周期天线驻波比最佳化的方法,并对四个不同频段的天线进行了理论仿真分析和实测验证.实验结果表明：当馈管间距为馈管边长的1.45倍,馈电点位置为最短振子长度与天线间隔常数乘积的2倍,馈管端部到最短振子的长度为馈电点到最短振子长度的1.15倍时,天线的驻波比达到最优状态.这些理论分析与实验结果为对数周期天线的工程应用提供了重要依据,也为最优化设计提供了一种更有效的方法.     

Transient response of thick axially symmetric monopoles

The steady-state results for thick hemispherically capped monopoles with or without conical feed sections are used to construct the transient response of such monopoles. For a voltage pulse excitation, file transient waveforms for the transmitted-reflected feed currents, the radiated fields in different directions, and the instantaneous currents on the monopoles are calculated and presented. Steady-state results are obtained by solving the scalar potential integral equation with the axis extended boundary condition using the moment method.     

Matching of an impedance to a feeder with the help of Γ sections consisting of reactive LC elements with finite Q factors

Relationships for calculation of the elements of ?? sections, which consist of reactive LC elements with finite Q factors and are used for matching of the load impedance to the resistance of a generator are derived. Recommendations on the choice of a particular type of the ?? section out of eight possible design versions for an arbitrary position of the point representing the load impedance on the Smith chart are given. It is shown that, in the case of a high level of the load standing-wave ratio (more than 100), the dissipative insertion loss of a matching ?? section with imperfect elements experiences substantial oscillations, which depend on the phase of the reflection coefficient and the relationships between the Q factors of reactive LC elements. As an example, the results on matching of small electric and magnetic monopoles with lengths of (0.2?C0.9)??/4 to a circuit with a characteristic impedance of 50 ?? are presented.     

船载短波鞭状天线的设计

在分析电小天线理论的基础上,设计了一款适用于船载通信的短波鞭状天线。天线体高度为2 m,内径为100 mm,利用HFSS电磁仿真软件建立了仿真模型。通过电抗加载来改善天线低频段阻抗特性,并在天线馈电端进行匹配网络设计,使天线在5 MHz~15 MHz频段内阻抗平稳,有效增加了带宽;通过天线结构的改进,有效提高了天线效率,增益达到-15 dB(5 MHz~9 MHz)和-10 dB(9 MHz~15 MHz),电压驻波比小于1.8,交叉带宽大于500 KHz。并且其结构紧凑,体积小,抗风能力强,符合船载环境下天线的设计需求。     

Cylindrical antennas with constant capacitive loading

Experimental and theoretical values of admittance are presented for a monopole antenna made in the form of a row of identical conducting, mutually insulated cylinders. The influence of the number of cylinders making monopoles of equal length and with equal total gapwidths between the cylinders is analysed. It was found that such antennas exhibit broadband properties similar to those of antennas with tapered capacitive loading.     

Monopole with inductive loading

This paper presents the results of a study undertaken to determine the electrical characteristics of a base-driven inductively loaded monopole, shorter than self-resonant length, oriented normal to an infinite perfectly conducting ground screen. The antenna may be tuned by a combination of two lumped coils of finiteQ. One is in series with the generator at the base; the other is in series with the antenna conductor some distance above the feed point. In some installations the use of two loading inductors may be a convenience in that this arrangement permits final tuning adjustments to be made at the base of the antenna. Sufficient information is available to permit determination of the reactance of the lossy loading coils to achieve resonance, the voltage rise across the coils, the impedance presented to the generator, and the antenna efficiency in the absence of antenna ohmic and ground system losses. Simple ancillary studies, as proposed by an illustrative example, permit decisions to be made regarding the merit of a particular inductively loaded monopole of small dimensions in terms of the operating wavelength-whether the application is for VLF transmission from a shore radio station, or for transmission from a moving motor vehicle at shorter wavelengths. An interesting by-product of the present analysis is a formula for the impedance of a monopole grounded at its base, and driven some distance above the earth plane.     

On the performance properties of the Koch fractal and other bent wire monopoles

Koch fractal monopole antennas are known to exhibit lower resonant frequencies than Euclidean monopoles of the same height. It has been concluded that there exists a unique relationship between the antenna's fractal geometry and its electromagnetic behavior. Here, the performance properties of the Koch fractal monopole are examined and compared with the performance properties of other bent wire geometry monopoles having the same total wire length and overall height. It is demonstrated that monopoles with less complex shapes exhibit lower resonant frequencies because they are more effective at increasing the electrical volume of the antenna. When these antennas are made to be resonant at the same frequency, they exhibit virtually identical performance properties independent of differences in their geometric shape and total wire length. It is also demonstrated that the effective height of these monopoles converge to that of an electrically small Euclidean monopole near the small antenna limit and they exhibit virtually identical radiation resistance properties at low frequencies. Finally, it is shown that the fractal limit in lowering of resonant frequency is related to the limit in the increase in the antenna's effective volume.     

An analysis of the performance of a handset diversity antennainfluenced by head, hand, and shoulder effects at 900 MHz .I. Effectivegain characteristics

A diversity antenna for portable telephones, which Is composed of a whip antenna and a planar inverted F-antenna (PIFA) operating at 900 MHz, has been analyzed. The analysis includes the electromagnetic effects of a human operator. Wire-grid analysis yielded the radiation efficiency, mean effective gain, correlation coefficient, and diversity gain characteristics under various incident wave propagation environments with whip length, head-to radio separation, and inclination of the radio from the vertical as parameters. The analysis has been carried out using a homogeneous human phantom model, which includes a head, a hand, and a left shoulder. The effective gain characteristics in multipath propagation environments is described. The analytical results indicate the structural and environmental requirements for designing the diversity antenna with a high diversity effect under practical use conditions     

Determination of reactance loading for circularly polarized circular loop antennas with a uniform traveling-wave current distribution

A simple theory is presented to predict the lumped reactance loading for circularly polarized circular loop antennas with a uniform traveling-wave current distribution. The reactive load is located on a circular wire loop of one-wavelength circumference at a position of 45/spl deg/ away from the feed point. To achieve a uniform traveling-wave current distribution, the loading reactance and the input impedances of the loaded and unloaded loop antennas need to satisfy certain conditions. First, the input resistance and the input reactance of the unloaded loop antenna should have the same absolute value. Second, the input impedance of the loaded loop must be purely resistive and its value needs to be two times of the input resistance of the unloaded loop. Third, the loading reactance should be chosen to be two times in value and opposite in sense of the input reactance of the unloaded loop. These conditions can be approximately met when the circular loop is placed above a ground plane. The loading reactance is determined from the input impedance of the unloaded loop and is optimized for an optimal performance of circular polarization. It is found that the reactive load must be capacitive and its value depends on the height of the loop above the ground plane and the thickness of the wire. The characteristics of the circular polarization and the input impedance of the capacitance-loaded circular loop antennas are investigated. An experimental example is presented to verify the theoretical prediction.     

Novel Dual Band Resonant Cylindrical Hat-Covered Monopole for Personal Communications

A cylindrical hat-loaded method is employed to make monopoles behave as dual band resonators. The two frequency bands are obtained by perturbing higher propagation modes by modifying the hat length. The longer the cylindrical hat is, the lower the resonant frequencies are obtained. The hat length behaves as an inductive load, also increasing the electric length of the monopole. As a result, a compact resonant structure is got, working at two different frequencies without modifying the omnidirectional radiation pattern at both bands.     

Multiple-polarization microstrip reflectarray antenna with highefficiency and low cross-polarization

This paper presents the study and prototype demonstration of the concepts of antenna focusing, cross-polarization reduction, and multiple-polarization capability of a planar microstrip reflectarray antenna. A square patch with two equal microstrip delay lines connected to its two orthogonal feeding points is used as the antenna element of the planar reflectarray. The length of the delay lines, which varies from patch to patch, is schematically designed to focus the plane wave to the feed point. The measured overall efficiency of the prototype antenna is above 50% in the normal operating band, and in some frequency ranges the efficiency has reached 70%. The experimental patterns show that the measured cross polarization due to special arrangement of the delay lines is quite low at the direction of the main beam. X-polarization and Y-polarization measured data show that the antenna is suitable for multiple-polarization applications (dual linear and dual circular). Surprisingly, the antenna has achieved approximately greater than 7% of gain bandwidth (-3 dB gain drop). These results demonstrate the feasibility of such an antenna for radar and communication system applications     

基于LCC-S补偿结构无线电能传输的阻抗匹配的研究

无线电能传输效率的优化具有重要研究意义,无线充电系统中存在着系统最佳阻抗。充电过程中,电池阻抗并非在最佳阻抗点,传输效率偏低。为了实现效率的优化,将LCC-S型拓扑结构与DC-DC变换器结合,实现宽范围调节的阻抗匹配。首先从理论分析了最佳阻抗点的数值,然后通过仿真软件MATLAB验证了效率的提升与宽范围的调节,最后搭建了无线电能传输的实验平台。实验表明,加入阻抗匹配的系统传输效率达到83%以上,证了上述方案的正确性与可行性。     

Coil‐Capacitor Circuit Design of a Transcutaneous Energy Transmission System to Deliver Stable Electric Power

A new transcutaneous energy transmission (TET) system was developed for transmitting electrical power to an implanted device, such as an artificial heart in a patient's body. This new design can maintain a stable output voltage independent of the load resistance. The system includes a compensation capacitor to reduce energy loss and increase power transfer efficiency. Experimental results show that the output voltage of the receiving coil changes very little as the load resistance varies from 14.8 Ω to 15 kΩ, which corresponds to a change in output power from 0.1 to 97 W.     

Megasonic transducer drive utilizing MOSFET DC-to-RF inverter withoutput power of 600 W at 1 MHz

This paper describes MOSFET power inverter systems, each provided to drive a megasonic transducer with an output power of 600 W at a frequency of 1 MHz. Since the megasonic transducer is used as a resonant load with a series resistance of approximately 1 Ω, the impedance characteristic of the megasonic transducer used as an inverter load is analyzed and compared with measured data. A new method is developed to match the inverter output impedance to the load impedance of as low as 1 Ω at the resonant frequency using a high-performance output transformer which can feed RF power to the load at high efficiency. The output transformer having a primary-to-secondary winding ratio of 2 to 1 was used by the inverter to drive the megasonic transducer. Based on the analysis of the impedance characteristics of the load, two types of MOSFET dc-to-RF power inverters, a full-bridge version and a single-ended version, were designed and built. These power inverters were put into practical use in cleaners. The power conversion efficiency was greater than 80% for the full-bridge version at an output of approximately 600 W and 50% for the single-ended version at an output power of approximately 600 W. When the megasonic transducer was operated with an input power of 600 W. the operation was satisfactory