Performance and design procedure of dual parabolic cylindricalantennas

The radiation characteristics of dual parabolic cylindrical antennas are studied, and the dependence of the principal plane beamwidths and the peak cross-polarization on their geometrical parameters is determined. The antenna aperture is rectangular in shape and generates an elliptical beam pattern, with a beamwidth ratio that can be controlled by the main and subreflector focal lengths. The far-field patterns are determined by an extended aperture integration method that includes the contributions of the reflected and the main diffracted rays. It is found that the cross-polarization depends of the offset angle between the axis and the direction of the normal to the subreflector surface and can be minimized by optimizing the relative angle between the reflectors. Other pattern characteristics are controlled by the antenna geometrical parameters and the feed illumination. A procedure for the design of these antennas and the expressions for determining the reflector geometries are provided     

Gigabit/s indoor wireless systems with directional antennas

The design of a high speed (>150 Mb/s) wireless local area network (WLAN), requires that many factors be considered, including technical, economic, and regulatory. A major technical factor is the channel response behavior (multipath) in the indoor environment as a function of the frequency band, building type and radio system architecture. The consequences of designing indoor wireless systems with directional antennas at one or both ends of a line-of-sight (LOS) link are investigated. We determine how narrow the beamwidth must be so that the maximum data rate is not limited by multipath effects. For such beamwidths, simple unequalized two-level frequency shift keying (FSK) or phase shift keying (PSK) modems can be used in place of the more costly and complex “anti-multipath” modems, and data rates above 1 Gb/s may be achieved. The channel impulse response in an empty room is estimated using geometrical optics, observing that with directional antennas, multipath rays must arrive from the same direction as the LOS ray. The link outage probability is then estimated as a function of the antenna beamwidth, and guidelines are established for the selection of the frequency band and antenna placement. Experiments using a 19-GHz 622-Mb/s binary phase shift keying (BPSK) link and 15° beamwidth horn antennas in an office building with plaster walls and large metallized windows have demonstrated error-free performance on both LOS and non-LOS (NLOS) links     

Antenna beamwidth independence of measured rain attenuation on a 28-GHz Earth-space path

Rain attenuation measured at 28 GHz on an earth-space path is independent of antenna beamwidth for beamwidths as small as0.1degand for attenuations up to 30 dB. The measurements imply that angle-of-arrival fluctuations are less than0.02deg.     

口径天线方向性系数和增益的快速估算方法

导出了用天线方向图的半功率波束宽度快速计算口径天线方向性系数和增益的简单表达式，分析讨论了这些公式的应用范围。最后，给出了卫星通信天线的增益测量实例，实验结果表明：用半功率波束宽度快速计算的天线增益与其它方法测量的天线增益吻合很好，从而证明了这种方法的正确性。     

Range and antenna beamwidth dependencies in multidimensional fixed wireless channels

This paper describes a multidimensional model of the fixed wireless propagation channel, which is well suited to system-level simulations. The proposed method yields realistic predictions of various channel characteristic parameters as a function of the range and antenna beamwidths, in agreement with experimentally observed results. The originality of the approach is that the power-delay profile for omnidirectional antennas at the edge of the cell is used to predict the time-varying channel over the whole cell for any antenna beamwidth. The method is based on a set of spatially distributed scatterers, which can be scaled to any range within the cell. The time-varying channel impulse response is then calculated as the combination of all scattered contributions by means of a ray approximation. The multidimensionality of the channel model is explored through predictions of signal statistics, level-crossing rate, delay-spread and angle-spread. In contrast to most existing models, the impact of range and antenna beamwidth is clearly addressed and found to be close to experimentally observed behaviors.     

Analysis of Resource Assignment for Directional Multihop Communications in mm‐Wave WPANs

This paper presents an analysis of resource assignment for multihop communications in millimeter‐wave (mm‐wave) wireless personal area networks. The purpose of this paper is to figure out the effect of using directional antennas and relaying devices (DEVs) in communications. The analysis is performed based on a grouping algorithm, categorization of the flows, and the relaying DEV selection policy. Three schemes are compared: direct and relaying concurrent transmission (DRCT), direct concurrent transmission (DCT), and direct nonconcurrent transmission (DNCT). Numerical results show that DRCT is better than DCT and DCT is better than DNCT for any antenna beamwidths under the proposed algorithm and policy. The results also show that using relaying DEVs increases the throughput up to 30% and that there is an optimal beamwidth that maximizes spatial reuse and depends on parameters such as the number of flows in the networks. This analysis can provide guidelines for improving the performance of mm‐wave band communications with relaying DEVs.     

Optimizing an array of antennas for cellular coverage from a high altitude platform

In a wireless communications network served by a high altitude platform (HAP) the cochannel interference is a function of the antenna beamwidth, angular separation and sidelobe level. At the millimeter wave frequencies proposed for HAPs, an array of aperture type antennas on the platform is a practicable solution for serving the cells. We present a method for predicting cochannel interference based on curve-fit approximations for radiation patterns of elliptic beams which illuminate cell edges with optimum power, and a means of estimating optimum beamwidths for each cell of a regular hexagonal layout. The method is then applied to a 121 cell architecture. Where sidelobes are modeled as a flat floor at 40-dB below peak directivity, a cell cluster size of four yields carrier-to-interference ratios (CIRs), which vary from 15 dB at cell edges to 27 dB at cell centers. On adopting a cluster size of seven, these figures increase, respectively, to 19 and 30 dB. On reducing the sidelobe level, the improvement in CIR can be quantified. The method also readily allows for regions of overlapping channel coverage to be shown.     

Scheme for enhancing performance of smart antennas in variableprocessing gain packet CDMA systems

Owing to the finite beamwidths of smart antenna systems, interference exists between signals belonging to different beams in CDMA systems. A new scheme is proposed for reducing the interference between the signals of smart antennas for variable processing gain packet CDMA systems. Numerical results show that the proposed scheme considerably improves the system performance     

Approximate SIR and BER formulas for DS-CDMA based on radiationpattern characteristics of adaptive antennas

Approximate formulas are presented for the signal to interference gain and the bit error rate when radiation pattern characteristics such as the beamwidth and average sidelobe level are considered for adaptive antennas in DS-CDMA. These formulas can be used to produce results easily for a range of ideal or effective values and hence provide a fast and simple way to evaluate the performance of an adaptive antenna in a DS-CDMA system     

The Characteristics of Iris-Fed Millimeter-Wave Rectangular Microstrip Patch Antennas

The fabrication of various iris-fed millimeter-wave rectangular microstrip patch antennas is described. A mathematical model is proposed to describe the iris-fed antenna. An iris having 15 percent of the area of the patch is used to couple energy into the antenna. Resonance of the antenna is observed to be insensitive to the size of the iris for irises up to 115 percent of the size of the patch. A study is also made of the coupling to the antenna as a function of position of the iris with respect to the transverse plane of the waveguide, the iris always being centered with respect to the patch. In general, the antenna has a VSWR in the waveguide feed of roughly 5:1 at resonance, except for the fully open waveguide which gives rise to a VSWR of 2.9:1 at resonance. Far-field antenna power patterns are observed to be quite broad with H-plane beamwidths about 130°. Maximum antenna gain observed was 4.5 dB relative to an isotropic source (dBi), with 2 dBi typical. An initial study is made of the microstrip patch antenna fed from a longitudinal waveguide wall. Results indicate that this feed structure is likely to prove valuable for microstrip patch antennas, with coupling at least as good as for the transverse-fed patch, added to the possibility of feeding multiple patches from a single waveguide.     

Delay spread reduction effect of beam antenna and adaptively controlled beam facing access system in urban line-of-sight street microcells

The paper presents theoretical and experimental investigation results of the delay spread reduction effect of beam antennas in urban line-of-sight (LOS) street microcells. The 95% delay spread cumulative probability in a 600 m LOS cell length is reduced to 70% when the 3 dB beamwidth of the base station (BS) antenna is in the range from 80/spl deg/ to 140/spl deg/, compared with that (420 ns) in omnidirectional antennas. An adaptively controlled beam facing access (ABFA) system in which the beam antennas are used in both the base and mobile stations is further proposed. The beam direction of the BS antenna is fixed along the street, but that of the mobile station (MS) antenna is adaptively controlled as the maximum received power is obtained. Using ABFA, the 95% delay spread cumulative probability in the 300 m LOS microcell is reduced to less than 70 ns, when the antenna beam-width lies in the range from 20/spl deg/ to 140/spl deg/ in the BS and about 80/spl deg/ in the MS.     

High-power, broad-bandwidth HF dipole curtain array with extensivevertical and azimuthal beam control

The design, construction details, and performance of a prototype high-power HRS 12/6/.5 antenna system covering the 6 to 26 MHz international broadcast bands are presented. The antenna has been developed, erected, and tested as part of the Voice of America modernization program to demonstrate the feasibility of controlling the horizontal and vertical apertures and beam directions of high-power, broad-bandwidth (2:1 frequency ratio) antennas. The antenna system provides 11 vertical slews, 15 azimuthal slews, and five azimuthal widths. The peak of the elevation pattern can be steered to angles of 4° to 20° above the horizon and the azimuthal beam can be steered up to ±30° with respect to boresight. Gains range from 16 to 31 dBi. Azimuthal beamwidths between -6 dB points range from 8° to 75°. The antenna is designed to handle the input power of one or more 500-kW double-sideband, amplitude-modulated transmitters. The antenna system has been designed using basic dipole and antenna switching modules from which smaller subarrays (HRS 2/6/.5, HRS 4/6/.5, HRS 8/6/.5, etc.) can be readily developed. The extensive beam control provided by the antenna system enables a shortwave broadcaster to use fewer antennas to reach the same audience. This reduces the land area of the station as well as its acquisition and operating costs     

Minimum Sidelobe Levels for Linear Arrays

A method of finding the optimum sidelobe-minimizing weights for an arbitrary linear array is derived that holds for any scan direction, beamwidth, and type of antenna element used. Optimum linear array positions are then determined via the particle swarm optimization method. Hence, the two together can give a global bound on antenna array performance with regards to sidelobe minimization. Results are presented for linear arrays of 2-6 elements for different scan angles, beamwidths and antenna elements.     

A versatile leaky-wave antenna based on stub-loaded rectangularwaveguide .I. Theory

A new leaky-wave antenna is presented that possesses many desirable features and is suitable for application to both the millimeter-wave and microwave ranges. These desirable features, some of which are unusual, include a simple configuration, a wide flexibility in the range of available beamwidths, the ability to control the beamwidth and the direction of the beam essentially independently, and negligible cross polarization at all scan angles. The antenna structure consists of a parallel-plate stub guide of small height, less than a half wavelength, located off center on the top of rectangular waveguide. The beamwidth is easily controlled from very wide to very narrow by adjusting the stub width or location. The article presents the principle of operation and the theory, employing a new transverse equivalent network that is accurate, but also simple, so that it permits rapid and inexpensive numerical calculations     

Performance evaluation of a cellular base station multibeam antenna

Experimental test results are used to determine the performance that can be achieved from a multibeam antenna array, with fixed-beam azimuths, relative to a traditional dual-diversity three-sector antenna configuration. The performance tradeoffs between the hysterisis level, switching time, and gain improvement for a multibeam antenna are also examined. The multibeam antenna uses selection combining to switch the signals from the two strongest directional beams to the base station's main and diversity receivers. To assess the impact of beamwidth on overall system performance, the following two multibeam antennas were tested: a 12-beam 30° beamwidth array and a 24-beam 15° beamwidth array. Both multibeam antennas were field-tested in typical cellular base station sites located in heavy urban and light urban environments. Altogether, the system performance is evaluated by investigating three fundamental aspects of multibeam antenna behavior. First, the relative powers of the signals measured in each directional beam of the multibeam antenna are characterized. Then, beam separation statistics for the strongest two signals are examined. Gain improvements achievable with a multibeam antenna compared to the traditional sector configuration are determined in the second phase of the analysis. Results indicate that in excess of 5 dB of gain enhancement can be achieved with a 24-beam base station antenna in a cellular mobile radio environment. Finally, the effects of hysterisis level and switching time are characterized based on gain reductions relative to a reference case with no hysterisis and a 0.5-s switching decision time. Useful approximations are developed for the gain effects associated with varying hysterisis levels and switching times. The resulting design curves and empirical rules allow engineers to quantify multibeam antenna performance while making appropriate tradeoffs for parameter selection     

a broad-band constant beamwidth corrugated rectangular horn

Using aperture field theory to predict the far-field radiation from a rectangular horn, a horn with substantially constantE- andH-plane beamwidths of17degand10degrespectively, is designed to operate over a 2.4:1 bandwidth. Assuming a cosine aperture field distribution in both theE- andH-planes of the horn, the general conclusion is first made that an aperture phase error of 0.37 wavelengths at the lowest operating frequency produces the least beamwidth variation (3 dB) over the band. A general design curve showing "constant" beamwidth as a function of horn throat length is produced, furthering the design of such horns with beamwidths in the range approximately9degto27deg. TheE-plane walls of the horn are corrugated, and to cover the bandwidth corrugations are comprised of "T-section" slots which are designed from a simple transmission line model. To realize the specified beamwidths, a compound horn configuration is adopted. Some experimental results obtained from a prototype horn are given.     

MM-Wave integrated phased arrays with ferrite control

A new class of electrically scanned antenna arrays for the millimeter wave range is described. The antenna is based on a planar integrated ferrite travelling wave structure and is controlled by the magnetization of ferrite elements. Experimental antennas operating in the 8-mm wave range have the following electrical parameters: beamwidth 2 to 4°, two dimensional scanning ±20°, loss about 3 to 4 dB     

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.     

On the use of a conical cornucopia antenna to reduce EMI

The wide-angle radiation form a prime-fed parabolic reflector antenna and the associated EMI (electromagnetic interference) it produces can be greatly reduced by constructing the antenna in the form of an absorber-lined conical cornucopia (CC). Measured RPEs (radiation pattern envelopes) are inspected for the case where all antennas have about a 10-ft diameter and 43-dBi gain at 6 GHz and typify the type of WAR (wide-angle radiation)-RPE improvement achievable if scaled to other bands/sizes. It is shown that the CC's RPEs for angles from about 10 full half-power beamwidths (here 10°) and beyond, and most especially from about 30 full half-power beamwidths (here 30°) and beyond, are vastly superior to those of either the standard or improved (UHX/UMX) parabolic dishes. Indeed, it is seen that the CC's RPE levels are about 95 dB down from on axis for angles greater than about 90°. In other words, the CC's wide-angle RPE is about 40 dB lower than that of a standard parabolic-dish antenna of the same gain. These very low WAR levels then greatly mitigate the EMI to adjacent microwave routes in terrestrial radio relay applications