双频基站天线中的反射板形状设计

蜂窝移动通信系统中的基站天线通常由直线阵列加反射板构成,而反射板的形状主要影响天线的前后比特性及水平面辐射方向图.该文对适合于基站天线的几种典型反射板形状进行优选,并采用矩量法线栅技术仿真计算了各种反射板形状对天线辐射性能的影响,根据仿真结果给出了满足基站天线双频辐射要求的反射板形状.     

Aperture-Sparsity Analysis of Ultrawideband Two-Dimensional Focused Array

We investigate the effects of aperture sparsity on the focusing performance and the angular-resolution capability of a two-dimensional focused array antenna excited by ultrawideband (UWB) impulse waveforms. The UWB-focusing array is characterized by a planar square aperture and a design parameter referred to as array spatial bandwidth. Spatial bandwidth is a function of the number of array elements, inter-element spacing, and frequency bandwidth. Performance analysis is carried out by generating computer plots of three-dimensional and two-dimensional antenna patterns for different values of array spatial bandwidth that hold for large aperture sparsity and large aperture density. The antenna patterns are peak-amplitude pattern, peak-power pattern, and energy pattern, whose narrow beamwidth and low sidelobe level are robust against aperture sparsity that may be caused by removed or failed elements. The half-power beamwidth (HPBW) of the antenna patterns, the focal distance, and the far-field distance of the UWB-focused array are expressed in terms of array spatial bandwidth. Computer simulation results show that UWB-focused-array beamforming based on impulse waveforms achieves efficient focusing of the radiation energy in the radiation-near-field region and beyond, and yields improvement in focusing performance and angular resolution for increased values of array spatial bandwidth. Such practical advantages are achieved without encountering grating lobes, large sidelobe level, or distortion of the radiation beam pattern that often limit the performance of the conventional narrowband phased array antennas.      

Signal correlations and diversity gain of two-beam microcellantenna

The motivation of the present study is to investigate the possibility of using two independently directed antenna beams in a mobile base station to provide diversity gain and reduce fading problems in a microcellular environment. The signal correlation of the individual antenna beams is studied, and it is shown that correlation depends on beamwidth, separation angle of the antenna beams, and the location of the base-station antenna array. Signal correlations have been computed using narrow- and wide-beam antennas in two separate base-station antenna locations. Diversity gains of both antenna types have been optimized by selecting the beam orientations which minimize the signal correlation. The numerical simulations show that a considerable diversity gain can be obtained using this approach     

On the efficiency and radiation patterns of mismatched shaped Cassegrainian antenna systems

Calculations are carried out with regard to the aperture illumination efficiency, spillover efficiency, and blockage efficiency of a shaped Cassegrainian antenna system whose feed pattern is not similar to that for which the antenna was designed. It appears that a maximum overall efficiency may be expected for antenna systems with a feed pattern having a slightly narrower beamwidth than those for which the systems were originally designed. It is further proved that the radiation pattern of mismatched systems is very unfavorable in the case of the beamwidth of the feed pattern being wider than the beamwidth of the feed pattern for which the system was designed. This is due to overillumination of the edges.     

Design of Cylindrical Conformal Millimeter-Wave Microstrip Antennas with Broad Beamwidth

This paper describes the design of a novel cylindrical millimeter-wave microstrip antenna (MA) with broad beamwidth by means of isotropic transformation (IT). A planar millimeter-wave antenna with broad beamwidth is designed first, and then IT is used to design a conformal one based on the planar structure. In addition, phased array with eight present elements has been designed as an example. Finally, numerical results are given to show that the present antenna possesses broad beamwidth and its array is of large scanning angle, which also verify the validity of the method of IT.     

A method of accurate determination of azimuthal distribution of received RF power

In this paper, we introduce a method for the determination of directional distribution of received RF power, with angular resolution independent of receiving antenna radiation pattern. The proposed method is based on a series of measurements taken while rotating, at fixed predefined steps, a usual directional antenna of known radiation pattern on the azimuthal plain. It is proved that the resolution accuracy of the measurement method depends only on the angular step of the antenna rotation and it is independent of the antenna beamwidth. As a result of this feature, the proposed method allows the determination of the RF power angular distribution with fine resolution using a directional antenna of much wider beamwidth for the measurements. Copyright © 2001 John Wiley & Sons, Ltd.     

Design and development of a unit element microstrip antenna for aircraft collision avoidance system

Aircraft/traffic alert and collision avoidance system (ACAS/TCAS) is an airborne system which is designed to provide the service as a last defense equipment for avoiding mid-air collisions between the aircraft. In the existing system, four monopole stub-elements are used as ACAS directional antenna and one blade type element is used as ACAS omnidirectional antenna. The existing ACAS antenna has some drawbacks such as low gain, large beamwidth, frequency and beam tuning/scanning issues etc. Antenna issues like unwanted signals reception may create difficulties to identify the possible threats. In this paper, the focus is on the design and development of a unit element microstrip antenna which can be used for ACAS application and to overcome the possible limitations associated with the existing techniques. Two proposed antenna models are presented here, which are single feed and dual feed microstrip dual patch slotted antenna. These are designed and simulated in CST Microwave Studio tool. The performance and other antenna characteristics have been explored from the simulation results followed by the antenna fabrication and measurement. A good reflection coefficient, Voltage Standing Wave Ratio (VSWR), narrow beamwidth, perfect directional radiation pattern, high gain and directivity make this proposed antenna a good candidate for this application.     

Ground plane impact on quadrifilar helix antenna performance with respect to deployment heights

Quadrifilar helix antenna (QHA) has its applications in satellite communications. This paper presents the performance optimisation of input and radiation characteristics of QHA in the presence of infinite and finite metallic ground planes. For the infinite ground plane, it has been observed that input parameters such as impedance and voltage standing wave ratio (VSWR) are stable, and the antenna has broader half power beamwidth (HPBW). Smaller metallic platforms that act as finite ground planes produce better 3‐dB axial ratio beamwidth and boresight axial ratio. Deployment of QHA on smaller metallic platforms such as nanosatellites and CubeSats enhances the circularly polarised beamwidth of the antenna with improved boresight axial ratio. However, on large low earth orbit (LEO) satellites, stable input characteristics and broader HPBW have been achieved at the cost of narrow circularly polarised beamwidth and degraded boresight axial ratio.     

FM wide band panel dipole antenna

It is very common that when a broadcaster needs to install an FM transmitting antenna within a large metropolitan area he places it on the tallest structure or building available. When the rooftop is already occupied by a large number of other types of transmitting and receiving antennas, the panel dipole antenna should be chosen. This antenna is secured to the side walls of the upper floors with the panel oriented to obtain full coverage of the most desirable areas of the city. For the Buenos Aires area this orientation avoids radiating toward Uruguay and specifically toward Montevideo, some 140 miles away. A wide band antenna operation permits placing the station on the air and at the same time allows future stations to share it without the installation of new antennas. Details of model and full model impedance and radiation pattern measurements during the antenna development are presented in order to show its technical characteristics. The radiation patterns were measured on a scale model in an anechoic chamber. The full scaled model was measured in an outdoor antenna range. Both E and H plane radiation patterns were measured along the FM band in order to observe pattern variations on both planes. Practically no difference in a panel radiation beamwidth from 88 to 108 MHz was observed and at the same time good input impedance was maintained. A really wide band antenna in pattern and VSWR is obtained. Power division for the antenna system is obtained designing an eight port power divider using the microstrip line technique. In this case, however due to high power operation the ground plane and strip are contained in a sealed metallic box and are separated by high pressure dry air like into the 3" feeding coaxial line.     

Impact of antenna radiation pattern variation on the performance of SPMA at 28 GHz

The target of this paper is to analyze the impact of variation in antenna radiation pattern on the performance of Single Path Multiple Access (SPMA) in urban/dense-urban environment. For this study, an extended 3GPP antenna model, and 3D building data from an urban area of Helsinki city is used. The simulations are performed at 28 GHz frequency using “sAGA” a MATLAB based 3D ray tracing tool. The variables considered for the series of simulations are Front to Back Ratio (FBR), Side Lobe Level (SLL), and Half Power Beamwidth (HPBW) of an antenna in horizontal and vertical plane. Network performance is compared in terms of metrics like signal strength, SINR, and capacity. This paper also presents the spectral efficiency and power efficiency analysis. The performance of SPMA was found susceptible to the change in antenna radiation pattern, and the simulation results show a significant impact of radiation pattern on the capacity gain offered by SPMA. Interestingly, SPMA was found a fairly power efficient solution with respect to the traditional macro cellular network approach. However, the level of power efficiency heavily depends upon the antenna beamwidth and on other beam parameters.     

改进折叠导电墙结构的宽波束圆极化微带天线

利用折叠导电墙结构可以有效减小微带天线的尺寸,展宽辐射波束。对折叠导电墙结构进行改进,将导电墙分解为3部分,各个部分分别加工完成后,进行装配组合,并加载到微带天线。改进后的导电墙结构的加工费用远小于一体化折叠导电墙。在L1频段设计加载改进导电墙的右旋圆极化微带天线结构,Ansys HFSS软件仿真结果和实测数据表明,所设计的天线仍具有小尺寸和宽波束的优点。     

Radiation performance of high efficiency dual reflector antenna fed by beam waveguide

Equations for calculation of the radiation performances of modified high efficiency dual reflector antenna fed by beam waveguide are derived. Using them, one can predict the performance of the antenna, such as the radiation patterns, the peak values of copolarization and depolarization, the factor of half power beamwidth, the phase loss and so on. These equations have been modified to meet the requirements of general engineering computation. A large number of calculations for general engineering use has been made, and the conclusion is that they are convenient, for engineering use.     

Beam-Switching Antenna Based on Plane Dipole Structure

A novel method for designing a beam-switching antenna with the plane dipole is presented. The antenna is composed of double dipoles placed at the center of an active square structure that is divided in four equal sectors by metallic sheets. Metallic patches at the outside of the structure are used to enhance the radiation performance of the antenna. In each step, the diodes in one sector are on, whereas other diodes are off. The sector with off-state diodes defines the direction of the radiation pattern. An antenna model is designed on the substrate of FR4. The proposed antenna operates from 4.8 GHz to 5.5 GHz with gain of 6.3 dBi and F/B (front to back ratio) of 13.2 dBi when the operating frequency is 5.2 GHz. The antenna radiation pattern can be swept in the entire azimuth plane in four steps with a 3 dB beamwidth of 90. The results reveal that the antenna could be used in the base station of the wireless communication systems.     

Comparative study of high-performance GPS receiving antenna designs

The FAA decision allowing the use of the global positioning system (GPS) as a radio navigation and landing help system in the United States commercial airports boosts the need for a high-performance GPS receiver which provides the demanded precision. The design of the receiving antenna is one of the most important parts in the design process, as it has to face significant challenges including uniform coverage of all satellites and the rejection of the multipath signals. The rejection of the multipath signals is accomplished by specifying restrictive criteria to the GPS antenna. This includes a high rejection of the cross-polarized signals and a radiation pattern with a sharp slope for low-elevation angles; that is, near the horizon. The feasibility of using different types of antennas to satisfy restrictive criteria such as dual-frequency coverage (L1 and L2 frequencies), -15 dB cross-polarization rejection, and a beamwidth of more than 130° is discussed. The antenna designs examined in this study include patch antennas, helical antennas, and conical spiral antennas. Two different receiver designs were also examined including a single-antenna system with a hemispherical coverage and an antenna array which may provide independent sectoral coverage or the desired beamwidth. It is shown that a design based on a conical spiral antenna backed with absorbing material may be used to satisfy all the desired specifications. This result was confirmed experimentally     

Radiation characteristics of a spherical array of circularly polarized elements

The radiation properties of a spherical phased-array antenna with circularly polarized elements are studied. Each antenna element is assumed to have a cosine type of field pattern. It is found that such an array is capable of providing complete hemispherical coverage without appreciable loss of gain. The radiation produced by the array stays circularly polarized in all directions, and the state of polarization is independent of beam steering. A special distribution of elements on a spherical surface is developed. This considerably suppresses the grating lobes in the pattern and thereby makes the antenna array broadband. Numerical calculations are made to determine the directivity and half-power beamwidth for the radiation patterns produced under various situations.     

Pillbox antenna design for millimeter-wave base-station applications

A pillbox antenna is a linearly polarized, waveguide-fed, cylindrical reflector, sandwiched between parallel plates. It is well suited to be a base-station antenna for the millimeter-wave, local-to-multipoint distribution service (LMDS). We can form the reflector-surface profile to provide a shaped radiation pattern, such as a cosecant-squared pattern in elevation, and we can design the radiating aperture to provide a broad-beam azimuth pattern. In this article, we begin by discussing LMDS requirements for base-station antennas, and we then briefly compare pillbox antennas with other antennas. Next, we describe in detail a highly accurate and efficient procedure for designing a pillbox antenna, using a combination of ray-tracing theory and commercially available three-dimensional electromagnetic analysis software. In particular, we discuss methods for designing the reflector surface, the waveguide feed horn, the radiating aperture, the polarizer, and the radome. Measured results of a prototype antenna at 29.4 GHz compare very well with our predictions.     

Hybrid-coupled broadband triangular microstrip antennas

Two broadband configurations consisting of three hybrid-coupled equilateral and isosceles triangular microstrip antennas have been proposed. Both configurations yield more than four times the bandwidth as compared with the corresponding single triangular microstrip antenna. The radiation pattern of a hybrid-coupled isosceles triangular microstrip antenna is in the broadside direction with very small variation over the entire bandwidth. In addition, this antenna has wide half power beamwidth, making it suitable as an element for the large scan broadband antenna array.     

Design of a Six-Sector Switched Parasitic Planar Array Using the Method of Genetic Algorithms

Switched parasitic planar arrays, as possible implementations of smart antennas, and an efficient method of designing them are presented in this paper. The radiation pattern of an array can be controlled by a digital word, the insertion of which in the antenna feeding circuit achieves electronic beam steering. The 1s and the 0s in the digital word represent the active and short-circuited elements in the array, respectively. The aim of the design is to cover the azimuth plane with six radiation patterns, each one having 3 dB beamwidth equal to 60° and relative sidelobe level not more than –3 dB. The well-known genetic algorithms are used tooptimize the antenna performance, determining the element positions and voltage phase values. This is made feasible by selecting the digital words, among the 2^N–1 available (N-number of elements), which maximize theobjective function containing the pattern requirements of the design. The numerical results presented show a possible application of this idea. An array of seven identical dipoles /2 offers diagrams, with an average 3 dB beamwidth equal to 63°. Relative sidelobe levels lower than –3 dB are obtained. Simulations at different frequencies prove that thearraydesigned here is a narrowband one and its bandwidth is 2.5% of the carrier frequency.     

An efficient moderate-size vertical-incidence ionosonde antenna for 2-20-MHz polarization studies

A wide cone-angle conical spiral antenna which has been developed for use as a circularly polarized vertical-incidence ionosonde antenna is described. It exhibits an 80-degree beamwidth, 5-dB gain, axial ratio of 1.2:1 and SWR less than 2:1 typically over the band 2-20 MHz. The entire structure is only 38 meters high and 52 meters in diameter. Extensive measurements on models and the full-size antenna are presented which show that the polarization and radiation patterns are quite uniform over the entire operating band. In particular, the radiation pattern shows no evidence of sidelobes at low elevation angles which could cause unwanted oblique returns. The discovery of a beam-reversing phenomenon in spiral antennas is described along with its elimination by geometry control. An example of ionosphere mode selection by means of polarization control with the full-size antenna is presented.