Substrate Lens Research Articles

A new concept of focusing antennas using plane-parallel fabry-perot cavities with nonuniform mirrors

An original configuration of low-profile directive antennas is presented in V-band. The focusing effect is performed by a plane-parallel Fabry-Perot (FP) resonator illuminated by a printed antenna. Both reflecting mirrors are made of metal strip gratings. The dimensions of the strips and slots of the nonperiodic output mirror are much smaller than the working wavelength; they are computed locally so that this mirror behaves as a spherical equiphase surface. Theoretical and experimental results show that the radiation patterns are symmetric and have low sidelobes. The antenna directivity is controlled by the value of the synthesized radius of curvature, that is to say by the nonperiodic distribution of the metal strips. It typically varies between 15 and 23.5 dB at 60 GHz. This new radiating structure is much more compact than substrate lenses and is compatible with low-cost multilayer technologies at millimeter wave frequencies. This is a possible candidate for user mobile-stations of indoor broadband communication systems.

Radiation efficiency analysis of submillimeter‐wave receivers based on a modified spectral domain integration technique

Reflector backed submillimeter‐wave slot antennas on substrate lenses are promising candidates for novel astronomical applications in integrated receivers for the far infrared region. Using an adjustable reflector, considerable resonance frequency tuning can be achieved, but with the risk of exciting parasitic parallel plate wave modes. Employing a surface/volume integral equation method and advanced spectral domain integration techniques, a complete radiation efficiency analysis of such kind of receivers is performed. Convenient integration path deformations in complex wavenumber planes allow a very fast evaluation of the spectral domain integrals in combination with efficient database and asymptotic extraction techniques. Saddle point and residue calculation techniques are employed to accurately determine the power of each parallel plate mode and the space wave contributions. The simulations reveal an appropriate set of parameters reducing the radiation loss to less than 10 percent for doubleslot and quadratic slot geometries preserving high tuning capability and optimized radiation patterns as well.

Combinatorial investigations of interfacial failure

AbstractConventional measurements of interfacial strength focus on a single variable, whereas many variables couple nontrivially and simultaneously to define this property. We present a combinatorial methodology that allows the effects of multivariable environments on interfacial strength to be investigated in a high‐throughput, parallel, and quantitative manner. This technique is largely based on the theory of Johnson, Kendall, and Roberts that quantifies adhesion through the contact and separation of a spherical lens and flat substrate. For our experiments, we fabricated a combinatorial library consisting of a two‐dimensional array of spherical caps and a complementary substrate. The array of spherical caps was brought into contact and subsequently separated from the substrate, whereas the relative displacement and contact area of the individual lenses were recorded. With gradient library‐fabrication methods, two adhesion‐controlling parameters can be continuously varied along the orthogonal axes of the array. In this manner, each lens quantifies the interfacial strength at a unique point in parameter space. We demonstrate this multilens contact‐adhesion test by measuring the effect of temperature and coating thickness on the self‐adhesion of polystyrene thin films. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 883–891, 2003

Design and characterization of single- and multiple-beam mm-wave circularly 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/spl les/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/spl deg/ 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.

Millimeter-wave proximity-coupled microstrip antenna on an extended hemispherical dielectric lens

A low-cost, high-gain, millimeter-wave antenna is presented. The antenna is composed of a proximity-coupled microstrip patch mounted on the back surface of a substrate lens. The antenna utilizes low dielectric constant, low-cost materials and is therefore suitable to many commercial millimeter-wave systems. A full-wave analysis was developed to analyze the performance of the printed antenna and a prototype was developed for operation at 38 GHz. The impedance bandwidth of the prototype was 8% and the gain was approximately 30 dBi across this frequency span with a front-to-back ratio greater than 60 dB.

Analysis of Electrically Small Slot-Fed Substrate Lens Antennas Using the Physical Optics Hybrid Method

Typical limitations of integrated antennas such as bidirectional radiation, power loss via substrate modes, and broad radiation patterns can be corrected using a substrate lens. In this paper, various slot-fed substrate lens antenna (SLA) configurations are examined, and a novel hybrid physical optics analysis technique, suitable for electrically small geometries, is presented. Based on this method, directivity and reflection loss calculations for elliptical and hyperhemispherical synthesized lenses are carried out. It is found that the conditions for maximum directivity and minimum reflection loss do not coincide, and thus certain performance compromises are necessary. The results are confirmed experimentally.

A dual-polarized quasi-optical SIS mixer at 550 GHz

In this paper, we describe the design, fabrication, and the performance of a low-noise dual-polarized quasi-optical superconductor-insulator-superconductor (SIS) mixer at 550 GHz. The mixer utilizes a novel cross-slot antenna on a hyperhemispherical substrate lens, two junction tuning circuits, niobium trilayer junctions, and an IF circuit containing a lumped element 180/spl deg/ hybrid. The antenna consists of an orthogonal pair of twin-slot antennas, and has four feed points, two for each polarization. Each feed point is coupled to a two-junction SIS mixer. The 180/spl deg/ IF hybrid is implemented using a lumped element/microstrip circuit located inside the mixer block. Fourier transform spectrometer measurements of the mixer frequency response show good agreement with computer simulations. The measured co-polarized and cross-polarized patterns for both polarizations also agree with the theoretical predictions. The noise performance of the dual-polarized mixer is excellent giving uncorrected receiver noise temperature of better than 115 K (double sideband) at 528 GHz for both the polarizations.

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/spl plusmn/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 /spl les/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.

Analysis of terahertz waveforms measured by photoconductive and electrooptic sampling

Terahertz (THz) waveform measurements by photoconductive (PC) sampling and free-space electrooptic sampling (FS-EOS) are analyzed and quantitatively compared. Our data suggest that a short dipole antenna used in a PC receiver contributes a flat frequency response when used without a substrate lens and a j/spl omega/ response when used with a substrate lens, for the specific THz frequency range and optical system investigated in our experiments. These findings are explained using results from basic antenna theory. Experiments testing our theory for a variety of THz waveforms (obtained by using different THz emitters and simple as well as shaped optical excitation pulses) and for different carrier lifetimes are also presented. Finally, we demonstrate near-field effects in the PC sampling measurements of broad-band THz waveforms and explore the evolution of THz radiation from the near field into the far field.

A 530-GHz balanced mixer

We report on the design and performance of a 530-GHz balanced SIS mixer, the first balanced mixer in this frequency range. This quasi-optical balanced mixer utilizes a cross-slot antenna on a hyperhemispherical substrate lens with eight superconductor-insulator-superconductor (SIS) junctions and a 180/spl deg/ lumped element IF hybrid circuit. The local oscillator (LO) and the radio frequency (RF) signal, orthogonal in polarization to each other, are coupled to the mixer using a wire-grid polarizer. The noise performance of the mixer is excellent, giving an uncorrected receiver noise temperature of 105 K (DSB) at 528 GHz.

Surface characterisation of electro-active thin polymeric film bearings

We report the results of a recent study of tribological properties of electropolymerised thin film bearings. Poly(pyrrole) films of different thickness and incorporating different counter ions have been grown onto gold electrodes on glass lens substrates and tested under a pin-on-disk apparatus. The topography of the films has been studied in order to set up correlation between surface parameters and the tribological functions, which is in turn to identify crucial parameters in the film processes for an optimum surface performance. Based upon this study, roughness distribution parameter, skewness and kurtosis are playing an important role in controlling friction. Film surfaces with positive skewness and high kurtosis values are favourable for low friction bearings.

Integrated modified rectangular loop slot antenna on substrate lenses for millimeter- and submillimeter-wave frequencies mixer applications

A coplanar waveguide (CPW)-fed rectangular-loop slot antenna with built-in tuning and DC-return capabilities on extended hemispherical lenses is examined. The proposed configuration is scalable up to the submillimeter-wave frequencies. For designing and analyzing the impedance characteristics of the proposed antenna, a multilayer method of moments (MoM) solver has been developed based on the mixed potential integral equation (MPIE) formulation. The corresponding patterns through the lens are obtained using geometrical optics and the surface equivalence principle. Three models have been simulated and one of them has been built and tested at 65 GHz. The integrated antenna exhibits tuning capability, rotationally symmetric patterns, high directivity, good Gaussian coupling efficiency, and a reasonable bandwidth. In addition, computed results agree well with measurements and are used to characterize the input impedance and pattern behavior of the antenna.

Optical Dispersion Characteristics of Planar Microlenses

It is essential to know the wavelength dispersion of a planar microlens in order to suitably design optical systems which use such a component. For this purpose, the measurement of focal length over a wide range of the spectrum has been performed. It was clarified that the focal length varies by about 20% from blue (ƛ=0.442 μm) to near-infra red (ƛ=1.55μm) region. The maximum index difference between the lens center and substrate, an important parameter for the characterization of planar microlenses, has been estimated as a function of wavelength using the ray equation. The effect of angled incidence has been discussed.

Gain and noise bandwidth of NbN hot-electron bolometric mixers

We have measured the noise performance and gain bandwidth of 35 Å thin NbN hot-electron mixers integrated with spiral antennas on silicon substrate lenses at 620 GHz. The best double-sideband receiver noise temperature is less than 1300 K with a 3 dB bandwidth of ≈5 GHz. The gain bandwidth is 3.2 GHz. The mixer output noise dominated by thermal fluctuations is 50 K, and the intrinsic conversion gain is about −12 dB. Without mismatch losses and excluding the loss from the beamsplitter, we expect to achieve a receiver noise temperature of less than 700 K.

ALPSS: A millimetre-wave aperture-coupled patch antenna on a substrate lens

The feasibility of millimetre-wave (MM-wave) aperture-coupled patch antennas, printed at the back surface of substrate-lenses is demonstrated and the corresponding radiation characteristics are investigated. A specific realisation of such an air-lens-patch-slot-strip (ALPSS) antenna on a low-permittivity /spl epsiv//sub r/=4.0 extended hemispherical lens substrate is theoretically and experimentally characterised at 70 GHz. It is demonstrated that the ALPSS antenna exhibits clean, axially symmetric patterns of low cross-polarisation (26 dB), a directivity of 30.4 dB and the 3 dB pattern full-beamwidth remains within 6/spl deg/-5/spl deg/ between 60-80 GHz. In addition, a very-high front-to-back (F/B) ratio, of the order of 50 dB is measured at 70 GHz, despite the absence of a backing ground-plane. The ALPSS antenna is well suited for low-cost broadband point-to-point communications and collision avoidance applications.

Quasi-optical log-periodic antenna SIS mixers for the 100 GHz band

We designed and tested a quasi-optical SIS mixer that incorporates a substrate lens for the 100 GHz band. The mixer uses a planar self-complementary log-periodic antenna with an integrated tuning circuit. The antenna has a frequency independent impedance of around over several octaves. The tuning circuit consists of two SIS junctions connected in parallel through a superconducting stripline inductor for tuning out the junction capacitances and a impedance transformer for matching the junction resistance to the antenna impedance. The SIS junctions are and have an area of and a current density of . The IF output from the mixer is brought out in a balanced way at each edge of the antenna, and is coupled to a cooled low-noise amplifier through a balun transformer by using a hybrid coupler. A double-sideband receiver noise temperature less than 130 K was measured from 85 to 110 GHz. The best noise temperature was 90 K at 101 GHz, which is the same as for waveguide receivers.

New Cases of Crystalline Deposits on Intraocular Lenses Not Related to Any Specific Viscoelastic

My colleagues and I recently reported 11 cases of crystalline deposits on intraocular lenses associated with one viscoelastic.1Soon after that report, additional cases were brought to my attention. We have since surveyed the ophthalmologists in the Rocky Mountain area. With 175 responses, we now have 11 additional cases since our initial report. All 11 cases were associated with three different viscoelastics (not only the viscoelastic originally reported). One case of crystalline deposition was associated with a membrane on an intraocular lens that was peeled off the surface of the lens in a gelatinous substrate. These crystalline deposits have calcium as their major component, which would appear to be unrelated to the viscoelastic used. With 22 cases now documented, obviously, crystallization can occur more frequently than previously suggested. After 18 months, some of our original cases persisted with decreased vision without resolution where the crystals are sequestered against the

A uniplanar 90-GHz Schottky-diode millimeter-wave receiver

A 90 GHz Schottky-diode receiver based on a double slot antenna fed by a coplanar-waveguide (CPW) transmission line is presented. The double slot antenna is placed on an extended hemispherical high-resistivity silicon substrate lens. The uniplanar receiver results in a 9.3/spl plusmn/0.3 dB measured SSB conversion loss at 88-90 GHz including antenna and IF circuit losses and a 1-dB loss due to the use of a nonoptimal matching cap layer at the silicon lens-air interface. The calculated conversion loss agrees very well with the RF measurements. The uniplanar double-slot antenna receiver is very small, less than 1.1/spl times/4 mm including the RF/IF filter, and is compatible with monolithic two- and three-terminal devices on GaAs substrates. The application areas are in millimeter-wave receivers for automotive systems, communication systems, and radiometric linear imaging arrays.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A planar quasi-optical mixer using a folded-slot antenna

A quasioptical mixer using only planar structures such as coplanar-waveguide and slotline is presented. The mixer, which can be scaled for millimeter-wave applications and placed on a substrate lens, uses orthogonal modes in a folded-slot antenna to achieve intrinsic RF/LO isolation without BF filtering or subharmonic pumping. The folded-slot balanced mixer was fabricated on RT/Duriod and obtained a minimum isotropic conversion loss of 1.2 dB at 11.6 GHz. Numerical integration of full two-dimensional antenna patterns yielded an antenna directivity of 7 dB, corresponding to a single side-band (SSB) mixer conversion loss of 8.2 dB. The mixer demonstrated -18 dB RF/IF isolation and -30 dB LO/IF isolation. >

20-GHz power combining slot-oscillator array

A four-element power-combining array of quasioptical slot oscillators has been constructed at 20 GHz. The array is placed on a dielectric substrate lens to increase the directivity and the effective isotropic radiated power (EIRP). The array delivers a total power output of 68 mW with an effective isotropic radiated power of 4.4 W. The DC to RF efficiency of the array is 12%. The substrate lens approach provides a planar design that eliminates substrate mode problems and, therefore, is easily scaled to millimeter-wave frequencies. >