Performance of reduced size substrate lens antennas for Millimeter-wave communications

This paper presents the theoretical performance (input impedance, -10 dB return-loss bandwidth, radiation patterns and surface efficiencies) of reduced size substrate lenses fed by aperture-coupled microstrip patch antennas. The diameter of the extended hemispherical homogeneous dielectric (/spl epsiv//sub r,lens/) lenses varies between one and five wavelengths in free-space, in order to obtain radiating structures whose directivity is comprised between 10 and 25 dB. A lot of configurations of lenses are investigated using the finite-difference time-domain methods technique and compared in the 47-50 GHz band as a function of their diameter, extension length and dielectric constant. In particular, the analysis of internal reflections-in time and frequency domains-shows that the latter have potentially a strong influence on the input impedance of small lens antennas, even for low values of /spl epsiv//sub r,lens/(2.2), whereas the usual limit (beyond which anti-reflection coatings are required) is /spl epsiv//sub r,lens/=4. We also demonstrate that the diffraction limit of reduced size lenses is reached for extension lengths varying between 50% and 175% of the extension of synthesized ellipses, depending on the lens material and diameter. Finally, we show that superdirective structures with surface efficiencies reaching 250% can be obtained with small lens diameters, justifying the interest in reduced size lens antennas.     

Compound Fresnel Zone Lens Conformal to Truncated Cone: Antenna Application

A millimeter wave antenna consisting of two Fresnel zone plate lenses, plane and conical, is examined numerically by use of the vector diffraction theory. The lenses are of Wood-Wiltse (double-dielectric) or Soret (half-open) type, and are designed for the frequency of 117 GHz. The lenses are made conformal to a truncated circular cone with a base diameter of 500 mm and a plateau diameter of 250 mm. Designs for two opening semi-angles, 45° and 75° each of them with a particular lens thickness are presented. For the angle of 90° the cone lens becomes a plane ring lens, which in combination with the plateau zone lens forms a plane lens of size equal to the cone base diameter. Illuminated by directive feeds set at a focal distance of 525 mm from the cone apex, the double-dielectric and half-open compound and plane lenses, form three pairs of Fresnel zone lens antennas, the co-polar and cross-polar radiation characteristics of which have been compared numerically. The double-dielectric lens antennas examined are about 5 dB superior in gain to the half-open lens antennas, which has a gain of approximately 45 dBi. Because all lenses are of equal transverse aperture, the corresponding lens antennas exhibit the same ?3 dB beamwidth of about 0.33 degrees. The plane zone lens antenna is very thin and simple. Instead, the antenna comprising a 3-D compound Fresnel zone lens is thicker but can be made conformal to a specific surface shape and possesses more levels of design and optimization freedom.     

High-power constant-index lens antennas

The results of a study to develop a high temperature dielectric lens antenna for use in the microwave frequency range are presented. The design and fabrication of spherical and hemispherical constant-index lenses are described. Radiation patterns, gain, polarization, and VSWR characteristics of spherical and hemispherical constant-index dielectric lens antennas over the frequency range from 2 to 11 GHz are presented. The results from high-power testing of both spherical and hemispherical constant-index lenses at a 2 kW average power level indicate that this power level causes no degradation in the performance of the lenses.     

Shaped dielectric lenses for wireless millimeter-wavecommunications

Dielectric-lens antennas are effective at producing highly shaped beams that can enhance the performance of wireless broadband communication systems. Beam shaping is used to reduce multipath interference, which causes fading and decay spread, and to enhance gain, so that the received power level is compatible with the requirements of high-data-rate transmission. This paper presents an overview of the design and measured performance of some examples of dielectric lenses that can be used in typical scenarios of wireless broadband communication systems. The paper also addresses the radio coverage produced by these antennas. The lenses are based on a single basic configuration where the feed is embedded in the lens body. This antenna configuration is flexible enough to accommodate different target beam-shaping specifications     

基于光学保角变换的电磁器件设计

保角变换是基于解析函数的一种非常重要的解析方法,利用保角变换可以将虚拟空间中复杂的边界曲线转化为物理空间中简单的边界曲线,从而求解二维平面场问题。文章主要综述并介绍保角变换在几何光学中的应用,通过控制光线传播来设计完美隐身衣、中继透镜、波导弯角和透镜天线等新型电磁器件。最后利用射线追踪仿真和全波仿真对设计加以证明。     

A Plane-Wave Beam-Steering Lens Design Using Microstrip Switched-Line Phase Shifters

A compact beam-steering lens design appropriate for millimeter-wave and submillimeter-wave applications is experimentally verified with an X-band test model. The lens achieves coupling to plane-wave beams through arrays of patch antennas placed on its two outer surfaces. The isolation between input and output antennas is accomplished by inserting a metal ground plane in the middle of the lens. The two closest patch antennas on the front and the backside are connected together with microstrip circuits that include switched-line phased shifters and interconnecting vias through the lens substrate. Three different X-band 100-element plane-wave microstrip lenses that use passive delay lines instead of actual phase-shifters were fabricated to successfully demonstrate the beam-steering angles of 20 and 40 degrees. From a separate waveguide measurement on the unit-cell element only, the insertion loss of the lens was estimated to be approximately 3.5 dB with bandwidth of 2% at 10 GHz.     

Array of hexagonal Fresnel zone plate lens antennas

An array of overlapping single-zone hexagonal Fresnel zone plate lens antennas was designed and tested at 30 GHz. By arraying smaller-diameter lenses, a significantly lower overall profile can be achieved compared to a single lens of equivalent diameter. These arrays can also find use in spatial power combining or in imaging applications.     

Ion-milled waveguide lenses and lens arrays in GaAs

The authors discuss ion-milled planar waveguide lenses in GaAs which exhibit a considerably higher efficiency than that previously reported for those lenses and near diffraction-limited spot size. The authors also report the performance characteristics of these latest lenses, including single lenses and lens array of analog Fresnel, chirp grating, and hybrid types as well as a collimation-Fourier transformation lens-pair, together with the detailed design and fabrication procedures. A simple theoretical model for the lens efficiency is also formulated to assist in the lens design. Ion milling has been shown to be a simple and versatile technique for fabrication of waveguide lenses in GaAs and applicable to any other substrate material. Such ion-milled waveguide lenses should facilitate realization of a variety of monolithically integrated optic device modules and circuits in GaAs and other related substrates with applications to communications, signal processing, and computing     

Conical Double-Dielectric Fresnel Zone Lens and Antenna

A conical double-dielectric phase-reversal Fresnel-zone plate (FZP) lens is introduced. We present the lens design equations as functions of cone opening angle. As an example, the phase-reversal lens has been applied to four millimeter-wave antennas with different lens opening semi-angles: 45deg, 60deg, and 75deg (conical lenses) and 90deg (plane lens). The radiation characteristics of these antennas have been calculated and contrasted one-to-another, and to those with the same semi-angles and linear dimensions binary (half-open) FZP lens antennas. The double-dielectric FZP conical arrangement can serve as a conical antenna lens and a radome simultaneously     

Focusing properties of small lenses

The potential use of small substrate lenses for coupling to antennas at millimeter wave frequencies is investigated by analyzing the focusing properties of dielectric spheres with quarter-wave matching layers. The fields and the power density are calculated at various points within the sphere to learn how the focusing deteriorates as the lens is made smaller. The absorption loss of the lens is also calculated. The calculations show that quartz spheres with quarter-wave matching layers, can exhibit good focusing properties down to a radius of about half a free space wavelength. This minimum radius was found to increase almost linearly with the refractive index of the lens. The calculations also indicate that at 94GHz the absorption losses of fused quartz, silicon and gallium arsenide lenses, with radii of one free space wavelength or less, are less than 0.2 dB. As the minimum diameter of a quartz lens is comparable with the spot size in free space, it should be possible to build an imaging lens array in which each lens will act as a separate imaging element.     

Optimized three-dimensional lenses for wide-angle scanning

Three-dimensional bootlace lens antennas with two and four focal points can be optimized to produce high-quality scanned beams over a wide field of view. For two-dimensional scanning, the planar feed locus is replaced by a curved feed locus designed to minimize path length errors. Comparisons with previous bootlace lens designs demonstrate the advantages of this focal distribution. The bifocal lens shows good scanning performance in both principal and orthogonal planes. The quadrufocal lens performs better in its principal plane than in its orthogonal plane. It is also shown that the quadrufocal lens can be realized with a planar outer surface and a circular focal arc, and improved scanning performance is still achievable. Further optimization of the focal arc and/or relaxation of the planar outer surface condition results in quadrufocal lenses with negligible phase errors in the principal plane.     

Curvilinear Fresnel-Zone Plate Lens Antenna: Vector Radiation Theory

A generalized vector diffraction theory of the half-open curvilinear Fresnel zone plate (FZP) tens antenna that is valid for any lens profile shape is presented. It is an extension to the vector Kirchhoff diffraction theory for the plane half-open FZP lens antenna and is based on the conical-segment lens profile approximation. An equation for the electric far-field vector is derived from which follow the expressions for the co- and cross-polarization radiation patterns and directive gain. The proposed theory is utilized for a numerical analysis and comparison of 140-GHz curvilinear half-open FZP lens antennas grouped in two distinct sets:

1. (a)
   Set I: antennas with different in shape FZP lenses (plane, conical, parabolic and spherical) having the same number of zones. All eurvilinear FZP antenna lenses are designed for similar gain, co- and cross-polarization performance and bandwidth, regardless of the lens-profile.
    
2. (b)
   Set II: antennas with different in shape FZP lenses and different number of zones. Since this affects gain, polarization and bandwidth performance, to make the characteristics of these FZP lens antennas practically equal to those of Set I, antenna feeds with different gain patterns have been used.
    

     

A new accurate design method for millimeter-wave homogeneous dielectric substrate lens antennas of arbitrary shape

The synthesis and the optimization of three-dimensional (3-D) lens antennas, consisting of homogeneous dielectric lenses of arbitrary shape and fed by printed sources, are studied theoretically and experimentally at millimeter(mm)-wave frequencies. The aim of the synthesis procedure is to find a lens profile that transforms the radiation pattern of the primary feed into a desired amplitude shaped output pattern. This synthesis problem has been previously applied for dielectric lenses and reflectors. As far as we know, we propose, for the first time, to adapt and implement it for the design of substrate lens antennas. The inverse scattering problem is solved in two steps. In the first one, the geometry of the 3-D lens is rigorously derived using geometrical optics (GO) principles. The resulting second-order partial-differential equation is strongly nonlinear and is of the Monge-Ampe/spl grave/re (M.A) type. The iterative algorithm implemented to solve it is described in detail. Then, a surface optimization of the lens profile combined with an analysis kernel based on physical optics (PO) is performed in order to comply with the prescribed pattern. Our algorithms are successfully validated with the design of a lens antenna radiating an asymmetric Gaussian pattern at 58.5 GHz whose half-power beamwidth equals 10/spl deg/ in H plane and 30/spl deg/ in E plane. The lens is illuminated by a microstrip 2/spl times/2 patch antenna array. Two lens prototypes have been manufactured in Teflon. Before optimization, the measured radiation patterns are in very good agreement with the predicted ones; nevertheless, the -12 dB side lobes and oscillations appearing in the main lobe evidence a strong difference between the desired and measured patterns. This discrepancy is significantly reduced using the optimized lens.     

Constant flux illumination of square cells for millimeter-wavewireless communications

The use of highly shaped-beam base-station antennas in millimeter-wave wireless communication systems may contribute to significantly enhance system performance. Previously proposed axial symmetric dielectric lenses provide a most useful constant-flux circular footprint, but they may fail to cover the regions near the vertices of square or rectangular cells, unless excessive wall illumination is allowed. This paper presents a simplified procedure to design shaped three-dimensional dielectric lenses that produce constant-flux illumination with square or rectangular footprints, suitable for indoor cells. The procedure is based on circular symmetric dielectric-lens design formulation, yet very sharp rectangular-cell boundary is obtained. Calculated and measured antenna performance is presented, not only in terms of radiation pattern, but also in terms of coverage and time-dispersion characteristic. The procedure is demonstrated for a square-cell lens and is extended for the rectangular-cell case     

The design of radially symmetric lenses

For scanning over wide angles at millimeter wavelengths, an antenna incorporating a radially symmetric lens is an attractive solution if the lens can be realized in a practical form. It is shown that suitable lenses can be constructed very simply, from natural dielectrics if desired, and a design technique for the optimal antenna is presented. Some results are given of analytical and experimental studies of a number of actual antennas operating at wavelengths near 4 mm. These confirm that practical solutions are available. Homogeneous lenses may be used up to antenna gains of about 35 dB, and a lens consisting of a single shell and a core is sufficient for most other practical requirements.     

Planar three-dimensional constrained lenses

A new design for a beamforming lens is presented. Both faces are planar arrays of radiating elements interconnected by transmission lines whose length varies as a function of radius. While the front face elements are regularly spaced, the back face elements are displaced radially from their corresponding front face elements, the amount of displacement also being a function of radius. We show that such a lens is capable of forming low sidelobe beams over an angular sector 36 beamwidths across in all planes ofphiby switching between clusters of only seven feed elements. Because both faces are planar, construction of lightweight lenses for multibeam antennas should be feasible.     

Wide-scan spherical-lens antennas for automotive radars

A new approach to wide scan-angle antennas at millimeter-wave frequencies is introduced with special focus on ease of manufacturing and reliability. The system is composed of planar feed antennas (tapered-slot antennas), which are positioned around a homogeneous spherical Teflon lens. Beam scanning can be achieved by switching between the antenna elements. The spherical-lens system is analyzed through a combined ray-optics/diffraction method. It is found that a maximum efficiency of 50%-55% can be achieved using Teflon, Rexolite, or quartz lenses. The efficiency includes taper, spillover, and reflection loss. Calculations also indicate that the maximum lens diameter is 30-40 λ₀, which results in a maximum directivity of 39.5-42 dB. Measurements done on a single-element feed and a 5-cm Teflon lens agree very well with theory and result in a 3-dB beamwidth of 5.5° and better than -20-dB sidelobe levels at 77 GHz. Absolute gain measurements show a system efficiency of 46%-48% (including dielectric loss). A 23- and 33-element antenna array with a scan angle of ±90° and a -3.5- and -6-dB crossover, respectively, in the far-field patterns was also demonstrated. The 23-element array resulted in virtually no gain loss over the entire 90° scan angle. This represents, to our knowledge, the first wide scan-angle antenna at millimeter-wave frequencies     

Dielectric lens shaping and coma-correction zoning, part I: Analysis

Shaping techniques are applied to the design of dielectric lens antennas. By shaping the lens to serve as an optical transformer for aperture distribution control, many special antenna patterns can be achieved. For multiple beam applications, the cubic phase error for off-axis beams can be significantly reduced by a unique method of coma-correction zoning. Such shaped lenses are excellent candidates for low-cost, lightweight and high-performance antennas for extremely high frequency (EHF) systems. In this communication, the design principles and numerical techniques are given. Examples with parametric trade-offs are also discussed.     

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     

Design of aplanatic waveguide Fresnel lenses and aberration-freeplanar optical systems

A modification of the waveguide Fresnel lens design that has phase-shifting zones placed on the curved contour is suggested. It is shown that the selection of a suitable shape for this contour allows coma aberration to be eliminated. Computer simulation results are presented to demonstrate the significant improvement of the optical characteristics for curved contour lenses. The aplanatic homogeneous refracting waveguide lenses are also considered. It is found that thick aplanatic refracting lenses and the proposed Fresnel lenses have field curvature aberration of opposite sign. This fact allows planar optical systems free from low-order aberration to be designed by combining refracting and Fresnel lenses. An algorithm for producing such a system is presented