MF AM folded monopole characteristics

Folded monopole antennas have been used for many years in medium frequency amplitude modulation broadcast applications. These antennas offer a grounded radiating structure with a height approximating a quarter wavelength. Folded monopoles have been studied exhaustively during a previous effort in an attempt to characterize the input impedance and directivity characteristics as a function of monopole height. As a result it was observed that several impedance regions can be achieved as a function of antenna height and cage diameter: Some of these regions permit a bandwidth operation sufficiently broad to support a high fidelity response for analog or digital transmissions. This type of antenna can be useful at different heights including a self matching region at the standard 50 ohms impedance. By choosing the appropriate antenna physical dimensions, antenna tuners can be avoided and thus it increases efficiency. Measurements have been made on a full scale 72 meter tower with a 6 wire cage in order to validate the calculated antenna input impedance and directivity. The cage and supporting mast make up the equivalent of a transmission line. For this reason different standard triangular towers were analyzed in order to determine their effect on the input impedance. Tower effective radius is determined taking into account the tower width and the tower leg diameter. At the same time, a minimum antenna height with maximum efficiency has been analyzed to solve the hard problem for installations at places where antenna height is a challenge for the designer.     

MF AM asymmetric vertical-dipole-antenna measurements

A medium-frequency AM transmitting vertical dipole for a 50 kW broadcast station was constructed, during May and June, 1994, at Buenos Aires, Argentina. This kind of vertical dipole operates without the classic, 120-wire, buried artificial ground plane. In order to analyze its behavior, extensive measurements of the near and far fields were carried out. A comparison to standard monopoles gave a better understanding of the performance and efficiency parameters. The nocturnal service area was determined by measurements, in order to observe the antenna's high-angle radiation, and to compare it with the theoretical radiation pattern. Comparison with the previous monopole antenna confirmed that substantial improvements were obtained with this new installation, both antennas being of similar height. The measurements showed an improved coverage of both diurnal and nocturnal service areas, estimated to be four times the previous service areas     

MF digital AM station antennas

It is very important having the proper antenna, specially in the MF AM band where achieving the necessary bandwidth in the antenna impedance is a difficult task. This problem is critical in the lower frequencies were the antenna matching to the transmission line generally is very sharp and the best match is obtained only at the carrier frequency with an appreciable power reflection in the lateral frequency bands. This problem is not very important in the classical AM transmissions were the maximum transmitted power is located at the carrier frequency and only a fraction in the upper and lower lateral bands. Of course this produces some distortion in the AM transmission but in this case the quality of the audio is not really of high fidelity, like in an FM transmission, due to a lot of factors, one of them the lack of the full audio spectrum. This problem can be corrected with high fidelity audio transmitters and specially with digital transmission in order to achieve CD quality audio and here the transmitting antenna plays an important role. In this paper MF AM antenna systems are analyzed not only from the input impedance point of view, but with consideration of all the factors in order to determine the best system in bandwidth and radiation properties in different parts of the standard AM band. Cylindrical, type A, and Cantilever classical monopoles and the modern dipole type antenna systems are compared, to provide the criteria for choosing an optimum antenna for the future digital AM service. Examples of measured field strength as a function of distance in a flat region are presented in order to show the interesting MF AM possibilities for a digital service     

Height radius effect on MF AM transmitting monopole antenna

Measurements are made on ground electrical field intensity in order to obtain a coefficient for the shadow, or diffraction factor. This factor permits the determination, with good accuracy, of the ground E field from the transmitting antenna to a point well beyond the radio horizon. The ground E field is of paramount importance in obtaining the nocturnal service area of an AM broadcast station. Nocturnal service area depends on the antifading properties of the transmitting monopole antenna. Critical study of the height-radius (H/a) relationship effect is made in order to determine the performance of the transmitting monopole antenna. The results are of interest, since they permit evaluation of the best H/a relationship for a determined antenna height, in order to obtain maximum directivity and maximum diurnal and nocturnal service area. Improvements in existing MF AM antennas can be achieved for high-fidelity stereo transmissions choosing the optimum H/a relationship. Measured data from reduced-scale models are shown and compared with theoretical predictions. Good agreement between them has been achieved     

The modeling and measurement of HF antenna skywave radiationpatterns in irregular terrain

The method of moments (MoM) was used in conjunction with the geometric theory of diffraction (GTD) for predicting the elevation-plane radiation patterns of simple high-frequency (HF) vertical monopoles and horizontal dipoles situated in irregular terrain. The three-dimensional terrain was approximated by seven connected flat plates that were very wide relative to the largest wavelength of interest. The plate length along the terrain profile was the longest possible that still adequately followed the shape of the path on the azimuth of the elevation pattern of interest and no shorter than 1 wavelength at the lowest frequency of interest. The MoM model was used to determine the antenna currents under the assumption that the terrain was planar (i.e., locally flat) over the distance pertinent to establishing the input impedance. The currents thus derived were used as inputs to the GTD model to determine the gain versus elevation angle of the antennas for HF skywave when situated in the irregular terrain. The surface wave solution for groundwave was not included since this does not appreciably contribute any effect to the skywave far-field patterns at HF in this case. The model predictions were made using perfect electric conducting (PEC) plates and using thin plates made of lossy dielectric material with the same conductivity and relative permittivity as measured for the soil. These computed results were compared with experimental elevation-plane pattern data obtained using a single-frequency helicopter-borne beacon transmitter towed on a long dielectric rope in the far field on a linear path directly over the antennas. The monopoles and dipoles were situated in front of, on top of, and behind a hill whose elevation above the flat surrounding terrain was about 45 m. The patterns of all of the antenna types and sitings exhibited diffraction effects caused by the irregular terrain, with the largest effects being observed at the highest measurement frequency (27 MHz)     

Stub-Loaded Long-Wire Monopoles Optimized for High Gain Performance

A technique to realize stub-loaded monopoles with enhanced gain performance is introduced in this paper. The omnidirectional high gain is achieved by combining an electrically long monopole with stubs attached at optimal locations along the antenna. In general, the lengths of the stub-loaded monopoles presented in this paper are significantly longer than conventional quarter-wave monopoles. Long wires alone do not provide the desired gain and VSWR performance; the stubs connected to the long monopole are vital in realizing simultaneous high gain and low VSWR at the intended operating frequency. A genetic algorithm (GA) is employed to optimize the locations and lengths of each of the stubs required to meet the design objectives. The results of this work show that between 11 and 12 dBi of gain can be obtained when the stub-loaded monopoles are placed over an infinite ground plane, whereas 8 dBi is obtained for one example when sited over a finite ground plane. A prototype of an optimized stub-loaded monopole was fabricated and tested. Excellent agreement was achieved between the measured and simulated results.     

MF AM transmitting asymmetric vertical dipole

An asymmetric vertical dipole is proposed as an MF AM-broadcast station transmitting antenna. This kind of vertical dipole antenna uses the supporting guys as part of the radiating structure permitting an efficient radiation with a strong surface wave. It produces less high-angle radiation compared to a classic buried-ground-plane monopole of similar height. Analysis data for near fields and power density of monopoles, elevated ground plane monopoles, and asymmetric vertical dipoles are presented graphically to explain why this last antenna can match the radiation efficiency of the classical monopole without a buried ground plane. Good agreement between calculation and measurements is achieved in all cases studied     

Miniaturization of the Biconical Antenna for Ultrawideband Applications

A miniaturized, ultrawideband antenna for the 3.1 to 10.6 GHz frequency band is presented. The antenna is designed to have a low profile to enhance integration onto existing structures and a low directivity pattern for body worn applications. A systematic process to miniaturize the well-known biconical antenna is illustrated by adding several different geometric features that reduce the size of the antenna. After miniaturization, the vertical height of the antenna was reduced by over 60% while maintaining electrical performance. Prototype antennas were manufactured using low cost plastic injection molding and dipping processes to facilitate transition to mass production and to enhance the durability of the antenna. The simulated and measured reflection coefficient of the antenna show good agreement. Measured antenna gain patterns verify that the manufacturing process employed is capable of producing low loss antenna structures. Lastly, time domain short pulse measurements of the antenna verify that it does not appreciably distort radiated signals in the azimuthal plane.      

折叠偶极子天线的设计

射频识别(RFID)应用中的天线设计需考虑的最重要因素是低价位、小剖面和小型化,而为了最大功率传输,天线的输出阻抗必须和其后的芯片的输入阻抗匹配。本文介绍一种新颖的简单结构折叠偶极子天线,所需的输入阻抗能通过选择合适的几何参数轻易获得,这对设计特殊阻抗的天线非常有用。     

A Circuit-Theoretic Approach to the Design of Quadruple-Mode Broadband Microstrip Patch Antennas

A novel method for the design of broadband patch antennas is described. The approach taken is to broadside couple two dual-mode patch antennas, resulting in a quad resonance antenna. The equivalent circuit of the antenna is similar to that of microwave filters, thus filter design techniques maybe employed to synthesize the antenna to obtain maximum return-loss bandwidth. This is the first time an increase in the bandwidth is achieved on a relatively thin substrate antenna as a result of coupling four resonant modes using two stacked circular microstrip patches. Electromagnetic simulation and measured results demonstrate bandwidth improvement of over four times that of a single-mode design.     

MF AM asymmetric vertical dipole measurements

A medium frequency AM asymmetric vertical dipole for a 50 kW broadcast station was constructed during June 1994. This kind of vertical dipole operates without the 120 wires classical artificial ground plane. In order to analyze its behavior extensive measurements of the near and far radiated fields were carried out. Those results were compared to standard monopoles to have a better understanding of the performance and efficiency parameters. The nocturnal service area was determined in order to observe the antenna high angle radiation. Comparison with the previous monopole served to confirm that substantial improvements are obtained with this new installation, being both antennas of similar height     

Integrated MIMO antenna with high isolation characteristic

A novel two-channel multiple input multiple output (MIMO) antenna for handset terminals is proposed. The antenna is basically composed of two folded monopoles and is designed to operate in WiBro (Wireless Broadband Internet; the Korean version of mobile WiMax) service band, 2.30-2.39 GHz. To decrease mutual coupling between the antennas, ground wall and connecting line are added. Good impedance matching and enhanced isolation performances are observed. Radiation patterns clearly show omnidirectional performance of the proposed antenna     

新型定向超宽带天线

基于圆片单极天线是一种结构简单的超宽带天线,研究了一种新型的超宽带天线,它将4个圆片单极天线垂直交叉放置作为馈源并采用平板反射面,实现定向以及双极化或圆极化特性。分析了2种变形形式:将平板反射器换为抛物面反射器,实现高增益特性;将圆片振子变形,实现更宽的低频端阻抗带宽。通过电磁仿真软件,计算了天线的S参量和辐射方向图随频率的变化规律。分析表明文中的天线对于传统的圆片单极天线有了有效的改进,实现了超宽带、定向辐射、双极化、圆极化、高增益等不同的特性,它们在卫星通信和移动通信中具有良好的应用前景。     

Multiple-tuned VLF antennas

Different approaches to feeding two multiple-tuned VLF antennas with regard to antenna performance and tuning are compared. Both antennas may be fed separately, or only one may be fed and the other grounded through a previously tuned coil. The antennas may either be connected or separated at their capacitive ends. The maximum bandwidth-efficiency product of all these arrangements is the same. Connected antenna systems achieve this maximum for all adjustments with in-phase base currents, and the most favorable tuning depends on the efficiency desired. If only one antenna is fed, the tuning procedure is quite simple, because only current magnitudes have to be adjusted. Retuning of the coils in the nonfed upleads is not necessary if changes are small compared with the magnitude of the antennas' coupling reactances. Connected element systems are particularly stable. These properties can be transferred to other multiple-tuned antenna systems of electrically short elements with top capacitances     

Analysis and size reduction of various printed monopoles withdifferent shapes

A simple analysis based on the transmission line model applied to printed dipole antennas, and the Babinet principle allows different shapes of printed monopole antennas to be easily optimised. A shortening ratio (ρ) of 48% (respectively 30%, 40%) is achieved for the monopole antenna by using a step change in line width (respectively a triangular monopole, and a line with a triangular cap). Theoretical input impedance of these various monopoles compare closely with experimental results     

Generalized co-phasing for multiple transmit and receive antennas

We propose and study a class of transmit beamforming techniques for systems with multiple transmit and multiple receive antennas with a per-antenna transmit power constraint. The per-antenna transmit power constraint is more realistic than the widely used total (across all transmit antennas) power constraint, since in practice each transmit antenna is driven by a separate power amplifier with a maximum power rating. Under the per-antenna power constraint, from an implementation perspective, it becomes desirable to vary only the phases (as opposed to both power and phase variation) of the signals departing from the transmit antennas. We name this class of techniques generalized co-phasing and formulate an optimization problem to calculate the transmit antenna phases. Furthermore, we propose five heuristic algorithms to solve the optimization problem. All the proposed algorithms except one are optimal for the case of two transmit antennas and an arbitrary number of receive antennas. For an arbitrary number of transmit and receive antennas, simulations indicate that the proposed algorithms perform very close to the optimal solution calculated through an exhaustive search of all possible transmit phases.     

支持空时分复用无线Mesh网络的微带阵列天线

支持空时分复用的无线Mesh网络采用多方向天线阵列技术,使用多个高增益定向天线进行多方向覆盖,具备通信距离远和天线自动扫描与对准的特性,便于快速部署。但现有的多方向天线阵列的设计从扩大通信距离的角度考虑,侧重于提高天线增益,使其垂直主瓣宽度仅为6°,这对于通信距离较近并且节点之间高程差较大的情况来说,覆盖性能不够理想。对多方向天线阵列的组成单元——微带阵列天线进行了优化设计,提出了一种支持空时分复用无线Mesh网络的微带阵列天线设计,其垂直主瓣宽度可达30°,并对设计的微带阵列天线进行了性能仿真和实际测试。     

基于双基线比相测角的收发阵列天线设计

根据双基线比相测角的原理,规划出一条短基线与一条较长基线,经过仿真优化确定出三个接收天线之间的间距,最终设计出一款应用于24 GHz汽车防撞雷达且结构较为紧凑的一发三收的微带阵列天线。采用该收发天线进行测角,既可保证最大无模糊测角的范围,也可提高测角的精度。通过采用基于道尔夫-切比雪夫算法加权的串并联混合馈电网络,使该收发天线实现了高增益、低副瓣的特性。最终,对该一发三收天线进行了实物加工。根据实测结果可知:在中心频率24. 125 GHz处,该10×4 元发射天线与10×2 元接收天线的增益分别为23. 1 dB与19. 3 dB,方位面副瓣电平均小于-20 dB,并且方位面3 dB波束宽度均为8. 4°,满足设计需求。     

Joint estimation of the channel and I/Q imbalance for two-way relay networks

In modern day communication systems, the massive MIMO architecture plays a pivotal role in enhancing the spatial multiplexing gain, but vice versa the system energy efficiency is compromised. Consequently, resource allocation in-terms of antenna selection becomes inevitable to increase energy efficiency without having any obvious effect or compromising the system spectral efficiency. Optimal antenna selection can be performed using exhaustive search. However, for a massive MIMO architecture, exhaustive search is not a feasible option due to the exponential growth in computational complexity with an increase in the number of antennas. We have proposed a computationally efficient and optimum algorithm based on the probability distribution learning for transmit antenna selection. An estimation of the distribution algorithm is a learning algorithm which learns from the probability distribution of best possible solutions. The proposed solution is computationally efficient and can obtain an optimum solution for the real time antenna selection problem. Since precoding and beamforming are also considered essential techniques to combat path loss incurred due to high frequency communications, so after antenna selection, successive interference cancellation algorithm is adopted for precoding with selected antennas. Simulation results verify that the proposed joint antenna selection and precoding solution is computationally efficient and near optimal in terms of spectral efficiency with respect to exhaustive search scheme. Furthermore, the energy efficiency of the system is also optimized by the proposed algorithm, resulting in performance enhancement of massive MIMO systems.

     

Antennas for VHF/UHF personal radio: A theoretical and experimental study of characteristics and performance

A theoretical analysis of the characteristics of small personal radio antennas for the 68- to 470-MHz frequency range is given. Representing the human body by a simplified lossy dielectric structure, the influence of the body on the performance of the antenna is investigated in detail, and it is shown how antenna impedance, gain, and radiation patterns can be calculated taking the presence of the body into account. For very short antennas the results indicate that radiation from the body may dominate over the radiation contributed by the antenna itself, and that the presence of the body can increase the antenna efficiency considerably, indicating that even very short antennas may provide acceptable radiation efficiencies. The results of the theoretical work are supported by measurements on practical antennas. Quarter-wave and short antennas of the helical type are compared with respect to efficiency and radiation patterns at 80, 160, and 450 MHz, and it is demonstrated how the physical length of the antenna affects the antenna performance. The design of a very short and compact personal radio antenna is described.