Double-slot antennas on extended hemispherical and elliptical quartz dielectric lenses

In this paper, the theoretical far-field patterns and Gaussianbeam coupling efficiencies are investigated for a double-slot antenna placed on quartz hemispherical lenses with varying extension lengths. The radiation patterns of the double-slot antenna are computed using ray-tracing inside the lens and electric and magnetic field integration on the spherical dielectric surface. The theoretical results are equally valid for double-dipole, log-periodic, and spiral antennas, and are presented in extension length/radius and radius/λ. Therefore, the results yield universal design curves for quartz lenses of different diameters and at different frequencies and using different antennas. The results indicate that forsingle units, there exists a wide range of extension lengths (ext. length/radius=0.61 to 0.76) which result in high Gaussian-coupling efficiencies to moderately highf/# systems. Forimaging array applications with high packing densities, an extension length/radius=0.82 to 0.93 (depending on frequency) will result in peak directivity and highest packing density but lower Gaussian-coupling efficiencies.     

Off-axis properties of silicon and quartz dielectric lens antennas

The theoretical far-field patterns and Gaussian-beam coupling efficiencies are investigated for a double-slot antenna placed off aids on extended hemispherical silicon and quartz lenses. Measured off-axis radiation patterns at 250 GHz agree well with the theory. Results are presented that show important parameters versus off-axis displacement: scan angle, directivity, Gaussicity, and reflection loss. Directivity contour plots are also presented and show that near-diffraction limited performance can be achieved at off-axis positions at nonelliptical extension lengths. Some design rules are discussed for imaging arrays on dielectric lens antennas     

Far-field pattern analysis of 94 GHz extended hemispherical lens monopulse antennas

In this paper, the far-field patterns are investigated for double-slot antenna array placed on extended hemispherical lenses. The radiation patterns of the extended hemispherical lens fed by single double-slot antenna or double-slot antenna array are computed using ray-tracing inside the dielectric lens and electric and magnetic field integration on the spherical dielectric surface. The computation results show that the sharp null of the difference pattern is below -37dB.     

Ray tracing on extended hemispherical and elliptical silicon dielectric lenses

In this paper, extended hemispherical and elliptical silicon dielectric lenses are compared by means of ray tracing. It is shown that the optical focuses of two lenses are not at same position though the elliptical lens is synthesized from an extended hemispherical lens by carefully choosing a particular extension length as stated in ref[1]. It may be used to explain why the best compromise between alignment, directivity and Gaussian-coupling effciency will be obtained if the feed antenna is placed at the region between 2.2 mm and 2.4 mm of extension length (for 13.7 mm diameter lens, dielectric contant = 11.7).     

Planar Log-Periodic Antennas on Extended Hemishperical Silicon Lenses for Millimeter/Submillimeter Wave Detection Applications

In this paper, the radiation properties of log-periodic (LP) antennas on extended hemispherical dielectric lenses are investigated. The starting point is the far field pattern for the log-periodic antenna on a semi-infinite silicon substrate obtained from numerical simulation. Then the effects of extended hemispherical silicon dielectric lenses on this far field pattern are evaluated using ray tracing and field integration techniques. The far fields patterns out of the lenses are derived as a function of the extension length (L), from which the optimum L can be determined. The coupling efficiencies of the pattern to Gaussian beams are also calculated. The computation results show that the log-periodic antennas have good performance in terms of impedance and pattern and can be used in many submillimeter/THz systems. The simulation methods are verified by comparing the simulation results with experimental data from literature. The utilized approach represents an effective method for log periodic antenna-lens system design at millimeter/submillimeter wavelengths.     

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.     

An improved solution for integrated array optics in quasi-opticalmm and submm receivers: the hybrid antenna

A dielectric lens antenna that is a special case of an extended hemispherical dielectric lens and is operated in the diffraction-limited regime is considered. The dielectric lens antenna is fed by a planar antenna that is mounted on the flat side of the dielectric lens antenna, using it as a substrate, and the combination is termed a hybrid antenna. Beam pattern and aperture efficiency measurements were made at millimeter and submillimeter wavelengths as a function of the extension of the hemispherical lens and of lens size. An optimum extension distance for which excellent beam patterns and simultaneously high aperture efficiencies can be achieved is found experimentally and numerically. At 115 GHz the aperture efficiency was measured to be (76±6)% for a diffraction-limited beam with sidelobes below -17 dB. Results for a single hybrid antenna with an integrated superconductor-insulator-superconductor (SIS) detector and a broadband matching structure at submillimeter wavelengths are presented. The hybrid antenna is space efficient in an array due to its high aperture efficiency, and is easily mass produced, thus being well suited for focal plane heterodyne receiver arrays     

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     

A 140-170-GHz low-noise uniplanar subharmonic Schottky receiver

A 150-GHz Schottky diode subharmonic receiver based on a coplanar-waveguide-fed double-folded-slot (DFS) antenna is presented in this paper. The DFS antenna is placed on an extended hemispherical high-resistivity silicon substrate lens to achieve a high directivity and a high coupling to a Gaussian beam efficiency. The uniplanar receiver results in a 12±0.5-dB measured double-sideband conversion loss at 144-152 GHz for a 8-10 mW local-oscillator power at 77 GHz, and has a wide-hand ⩽13-dB conversion loss over 30 GHz of bandwidth (140-170 GHz). The measured conversion loss includes silicon lens absorption and reflection losses, as well as IF mismatch losses. The applications are in new small aperture (7.5-cm lenses) collision-avoidance radars at 150 GHz     

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.     

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 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.     

Properties of an electromagnetically coupled small antenna with asuperconducting thin-film radiator

This paper describes the structure and properties of a 900-MHz-band small antenna with a superconducting thin-film radiator operated by electromagnetic coupling. The radiation efficiency of the antenna with a λ/38 radiator reached 74% at 79 K. The loss in this antenna comprised mismatching loss and radiator loss caused by the surface resistance of the superconducting thin film. A simulation model with a meander-line radiator and a parallel line is also proposed. This model makes it possible to design a superconducting thin-film radiator which can be fabricated on a dielectric substrate by using the moment method without taking account of the dielectric substrate     

Design and analysis of multiple-beam reflector antennas

Simplified design and analysis equations are presented for multiple-beam reflector antennas based on the Gaussian-beam analysis of the primary and secondary patterns. The derived equations are useful for the quick design and performance analysis in terms of the coverage-area directivity and the inter-beam isolation of multiple-beam antenna systems. Results of the analysis given in this paper agree well with rigorous computations based on physical-optics analysis of the reflector-antenna radiation patterns. Extension of the analysis to multiple-beam lens antennas, and to shaped/contoured-beam antennas, is also presented     

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.     

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.     

A curved spiral antenna above a conducting cylinder

A curved spiral antenna above a finite hollow conducting cylinder is analyzed using the method of moments. The effects of cylinder length 2H and cylinder radius r_cy on the radiation characteristics of the spiral are evaluated. As 2H increases, the cross-polarization component of the radiation field in the broadside direction decreases to a constant value (approximately -18 dB). When 2H is greater than one wavelength (λ₀), the input impedance of the spiral above a cylinder of radius r_cy=0.25 λ₀ is almost constant (250-j20 Ω) with a gain of approximately 7 dB. The spiral above a cylinder of (2H, r_cy)=(2.7 λ₀, 0.25 λ₀) shows a 3-dB axial ratio bandwidth of approximately 23%, which is wider than a flat spiral antenna above a flat ground plane of infinite extent     

Ka-band Dielectric Waveguide Antenna Array for Millimeter Wave Active Imaging System

Ka-band compact dielectric waveguide antenna array for active imaging system is given. Antenna array with WR28 metal waveguide direct feeding is specially designed with small size, high gain, good radiation pattern, easy realization, low insertion loss and low mutual coupling. One practical antenna array for 3-D active imaging system is shown with theoretic analysis and experimental results. The mutual coupling of transmitting and receiving units is less than -30dB, the gain from 26.5GHz to 40GHz is (12-16) dB. The results in this paper provide guidelines for the designing of millimeter wave dielectric waveguide antenna array.     

Dielectric Slab Rotman Lens for Microwave/Millimeter-Wave Applications

A new form of a Rotman lens is proposed for microwave/millimeter-wave applications such as a collision-avoidance radar. The proposed lens can be described as a dielectric slab fed by slot lines. The new form is expected to show lower loss and lower mutual coupling than the conventional Rotman lenses fabricated with conducting plates at millimeter-wave frequency. Taking the field distribution inside the dielectric slab into account, the$ TE_0$mode was chosen to excite the dielectric slab lens. The dielectric Rotman lens consists of a dielectric slab, tapered slot structure, and the transitions between the antipodal slots and microstrip lines for subminiature A connectors. The conventional design equations have been modified for use in designing the dielectric slab Rotman lens with a high dielectric material. A prototype was implemented with nine beam ports and nine array ports. Measurements from 10 to 20 GHz show that mutual coupling can be lowered at higher frequency. The obtained efficiency of the dielectric slab lens system is approximately 30%. The efficiency of the lens is comparable to that of the conducting plate lenses even though there is a spillover loss from the dielectric slab.     

Millimeter-wave integrated-horn antenna. II. Experiment

For pt.I see ibid., vol.39, no.11, p.1575-81 (1991). The impedance and radiation patterns of a dipole-fed horn antenna in a ground plane are experimentally investigated at microwave and millimeter-wave frequencies. The agreement with the full-wave analysis technique presented in part I is good. The results indicate that for a 70° flare-angle horn, horn apertures from 1.0 λ-square to 1.5 λ-square with dipole positions between 0.36 and 0.55 λ yield good radiation patterns with a gain of 10-13 dB a cross-polarization level lower than -20 dB, and resonant dipole impedances between 40 Ω and 120 Ω. It is also found that the impedance measurements can be safely used for 2-D horn arrays, but the radiation patterns differ because of the Floquet modes associated with the array environment. The integrated horn antenna is a high-efficiency antenna suitable for applications in millimeter-wave imaging systems, remote-sensing, and radioastronomy