Parametric design and analysis of multiple-beam reflector antennas for satellite communications

This paper presents the parametric design and analysis of multiple-beam reflector-antenna systems employed for satellite communications. It is based on extending the earlier work of Rao (see IEEE Antennas and Propagation Magazine, vol.41, no.4, p.53-59,1999) by taking into account the efficiency of the horn and pointing error of the satellite in the design of the multiple-beam antennas (MBAs), and by analyzing the edge-of-coverage directivity and co-polar isolation (C/I) performance. Design and analysis equations are developed for the multiple-beam antennas using offset parabolic-reflector antennas by including various design parameters such as the number of reflectors, the number of frequency cells, the focal-length-to-diameter (F/D) ratio, the horn efficiency, and the pointing error. The analysis employs a quasi-Gaussian beam representation for the primary and secondary patterns in order to take into account the effect of the sidelobes. Results of the analysis given in this paper agree well with rigorous computations based on physical optics analysis of the antenna radiation. Design curves showing the impact of horn efficiency on the C/I performance of multiple-beam antennas are presented for various frequency-reuse schemes.     

An electromagnetic analysis of a cylindrical homogeneous lens

Radially symmetric lenses are ideally suited for use as multiple-beam antennas. In recent years, several investigations using a geometrical optics approach have indicated that simple lens structures such as homogeneous lenses might be suitable antennas. This paper presents an electromagnetic analysis of a cylindrical homogeneous lens as well as examining in detail the effect upon performance of parameter variations such that engineering and design evaluations can be made. It is shown that a lens with a relative dielectric constant of 3.5 gives the best performance. With the use of simple matching techniques, overall performance comparable to the more complex Luneburg lens is obtained.     

Design and characterization of single- and multiple-beam mm-wavecircularly polarized substrate lens antennas for wireless communications

Single- and multiple-beam circularly polarized ellipsoidal substrate lenses suitable for millimeter-wave wireless communications have been designed, implemented, and experimentally characterized at 30 GHz. The lenses are made out of low-cost low-permittivity Rexolite material. The single-beam lens achieves a directivity of 25.9 dB, a front-to-back ratio of 30 dB, and an axial ratio of 0.5 dB is maintained within the main lobe. The measured impedance bandwidth is 12.5% within a SWR⩽1.8:1. The single-beam antenna is well suited for broad-band wireless point-to-point links. On the other hand, the multiple-beam lens launches 31 beams with a minimum 3-dB overlapping level among adjacent beams. The coverage of the lens antenna system has been optimized through the utilization of a hexagonal patch arrangement leading to a scan coverage of 45.4° with a maximum loss in directivity of 1.8 dB due to multiple reflections. The multiple-beam lens antenna is suitable for indoor point-to-multipoint wireless communications such as a broad-band local area network or as a switched beam smart antenna. During the proposed design process, some fundamental issues pertaining to substrate lens antennas are discussed and clarified. This includes the depolarization properties of the lenses, the effect of multiple internal reflections on the far-field patterns and the directivity, the nature of the far-field patterns, the estimation of the lens system F/B ratio, and the off-axis characteristics of ellipsoidal lenses     

大气无线光通信系统中一种正交空时分组码编译方法

为了降低湍流对大气无线光通信的影响,提高无线光通信系统性能,提出了一种4发射天线、4接收天线的无线光多发射多接收系统模型,针对该模型设计了一种正交空时分组码(OSTBC)编译方法,并对该码的平均误比特性能进行了仿真分析。结果表明,该方案具有很大的分集优势,可获得的最大分集度为16,达到了4发4收系统所能获得的最大空间分集增益,同时该编码方法与传统的Alamouti方案一样能实现最大传输速率。通过对译码算法进行简单修改,OSTBC编译方法也可以应用在接收天线数目为1,2或3个的多光束发射和接收系统中。     

Offset-reflector antennas with offset feeds

The development of a simple mathematical model for the vector radiation fields from offset-parabolic-reflector antennas is outlined. The model permits the primary feed to be offset from the reflector geometric focus, and thus allows the study of multiple-beam antennas. Predicted results are shown and correlated with measurements made on a 30 GHz antenna system.     

An antenna coupling model for cross-polarized antennas for radarelectromagnetic compatibility analysis

A statistically based antenna coupling model for linearly polarized, cross-polarized antennas is presented. The antenna gains are defined as random variables. It is assumed that the probability density functions of the gains can be estimated from the antenna patterns. From the density functions, a method is developed to calculate the combined density function. This method accounts for angular motion that the antennas would experience if they were mounted on ships subject to roll. The probability of interference is defined, and a method is developed to calculate it based on the combined density function. The results of this analysis for two selected antennas are presented, and the limits of applicability, are discussed     

Subreflector shaping to improve multiple-beam performance of a Cassegrain antenna

A method of designing multiple-beam antennas based on shaping the subreflector of an offset Cassegrain antenna is described. It is applied to a compact system having a diameter of 300? that is required to produce beams up to 4-6°either side of boresight. The performance is shown to be only slightly less than that obtainable by also shaping the main reflector, indicating that efficient multiple-satellite-access antennas can be designed without specially shaped main reflectors.     

CPW-fed oscillating microstrip antennas

Operating with a low-cost FET, oscillating CPW-fed microstrip antennas working at ~4 GHz have been presented. Because the design is based on slot or slot loop apertures, no via holes are required, These oscillating antennas are compact, easy to fabricate while providing uniform radiation patterns with cross-polarisation levels below -17 dB. Active integrated power combining arrays or active integrated phased arrays are possible future applications of these radiating elements     

Adaptive nulling with multiple-beam antennas

Some of the more prominent features of an Applebaum-Howells type adaptive nulling processor when used in conjunction with a multiple-beam antenna operating over the earth field of view at synchronous altitude are discussed. Incorporation of this scheme with a multiple-beam antenna allows for the use of a large filled aperture in order to obtain pattern shaping capabilities over a limited field of view while keeping the number of antenna output ports at a tractable number. It also leads to a partial decoupling of the adaptive feedback loops, a property which can be exploited to provide significant improvements in the dynamic performance of the control system. Three techniques for accomplishing this improved dynamic performance particularly applicable to multiple-beam antennas are considered.     

Analysis of yagi-uda-type antennas

A method of analyzing Yagi-Uda-type antennas is presented. Since the Yagi-Uda array is a fairly well-known antenna, it is used as an example to demonstrate the application and accuracy of the method. However, the method of solution is not limited to a planar array, such as the Yagi, but can be applied to arrays of nonplanar linear elements. The approach taken in analyzing Yagi-Uda antennas is based on rigorous equations for the electric field radiated by the elements in the array. All interactions are taken into account. Calculated results are presented for the Yagi-Uda array that show excellent agreement with experimental results reported in the literature. In addition, the dependence of the far-field patterns on the phase velocity is shown. It is also demonstrated that the phase velocity is generally nonuniform along the array.     

Efficient implementation of multiple-beam sampler for continuously scanned array antennas

A multiple-beam sampler is described for continuously scanned array antennas using time modulation or frequency modulation. It is shown that, for the special case of an array antenna with a number of elements equal to an integer power of two, the multiple-beam sampler can be implemented using a minimum number of phase shifters and adders.     

Off-axis scanning of cylindrical lenses

Two aspects of cylindrical lens antennas excited by off-axis transform feeds are explored. First, the properties of the subarrays formed by the feeds at various off-axis locations are investigated to evaluate their potential for forming sector coverage patterns. Secondly, the use of transform feeds is investigated for the purpose of providing multiple scanning beams with low sidelobes and high directivity. The basic equations are presented without derivation because the method of analysis for antennas of this type with on-axis feeds is well established. The contribution of this paper is to investigate how the pattern characteristics are modified by moving the feed-axis, along a prescribed curve.     

CPW-fed passive and active microstrip antennas

A numerical modelling based on the solution of coupled integral equations is used for the design ofCPW-fed microstrip antennas. This type of antennas shows properties close to those of aperture-coupled antennas fed by microstrip lines. Oscillating antennas and large bandwidth antennas working in the C-band are realized with the help of the theoretical model. Various shapes of excitation slots are studied and the slot-loop is shown to be a convenient feeding for the insertion of active devices.     

Offset dual-reflector multiple-beam antennas using circularly symmetric main reflectors

An investigation into the multiple-beam capability of offset antennas using circularly symmetric main reflectors is described. The efficiency and sidelobe performance of systems designed to produce beams up to 4.6° either side of boresight with reflector diameters ranging from 100 to 300 wavelengths are shown to make the antennas suitable for multiple-satellite-access earth stations. Comparison is made with a nonsymmetrical main-reflector antenna designed for the same requirements.     

A design procedure for classical offset dual reflector antennaswith circular apertures

A geometrical optics procedure for designing electrically optimized classical offset dual reflector antennas with circular apertures is presented. Equations are derived that allow the size and spacing of the main and subreflectors of the antenna system, along with the feed horn subintended angle, to be used as input variables of the design procedure. The procedure, together with these equations, yields an optimized design, starting from general system requirements. The procedure is demonstrated by designing both an offset Cassegrain and an offset Gregorian antenna, and is validated by analyzing their radiation patterns using physical optics surface current integration on both the main and subreflectors     

Optimum Design of Millimeter-Wave Double-Dielectric Fresnel Zone-Plate Lens and Antenna

The microwave/millimeter-wave Fresnel-zone plate (FZP) lenses differ substantially in construction, technology and applications from their optical analogs and require specific design equations and methods of electromagnetic analysis. In this paper, optimum design equations for double-dielectric lossless FZP lens are derived. The best and worst choices of the permittivity ratio for lossless dielectrics are discussed in detail. In addition, the influence of dielectric losses on the lens thickness for given wavelength and permittivities is examined. Two versions of a 57.5-GHz double-dielectric phase-reversal zone plate are used as focusing elements of FZP lens antenna. The antenna co-polar and cross-polar radiation patterns, aperture efficiency and frequency bandwidth are analyzed numerically and contrasted with those of half-blocked FZP and horn lens antennas.     

A numerical technique for calculating mutual impedance and element patterns of antenna arrays based on the characteristics of an isolated element

A numerical technique for calculating mutual impedance and element patterns of antenna arrays based on the characteristics of an isolated element is presented. The basis for this technique is the theory of minimum-scattering (MS) antennas and, in particular, the interpretation of the mutual impedance between two canonical minimum-scattering (CMS) antennas as the first term in a perturbation series of the mutual impedance of arbitrary antennas. For the computation of the mutual impedance via the CMS approximation this pattern must be continued analytically into the complex domain. However, numerical codes provide radiation patterns only for real observation angles. To overcome this problem, the numerically calculated patterns are expanded in terms of spherical modes and the computation over complex angles is carried out analytically. Numerical results for collinear and linear arrays of parallel electric dipole antennas and rectangular probe-fed patch antennas are presented and a comparison is made with direct calculations using the WIPL-D code. Results presented show the good agreement between the CMS approximation and the WIPL-D code.     

CAD of waveguide array antennas based on "Filter" concepts

In this paper, an alternative approach for the design of open-ended waveguide array antennas is presented. The approach is based on microwave filter concepts. The exploitation of this alternative viewpoint has been made possible by the availability of a very efficient computer-aided design (CAD) tool which is based on a full-wave modal analysis technique. In this paper, we first outline the technique for the efficient analysis of open-ended waveguide array antennas. Using the software developed and following the alternative design approach, two different application examples are then shown, indicating how the alternative viewpoint introduced gives indeed significant additional degrees of freedom.