A 100-MESFET planar grid oscillator

A 100-MESFET oscillator which gives 21 W of CW effective radiated power (ERP) with a 16-dB directivity and a 20% DC-to-RF conversion efficiency at 5 GHz is presented. The oscillator is a planar grid structure periodically loaded with transistors. The grid radiates and the devices combine quasi-optically and lock to each other. The oscillator can also be quasi-optically injection-locked to an external signal. The planar grid structure is very simple. All of the devices share the same bias, and they can be power and frequency tuned with a mirror behind the grid or dielectric slabs in front of it. An equivalent circuit for an infinite grid predicts the mirror frequency tuning. The planar property of the oscillator offers the possibility of a wafer-scale monolithically integrated source. Thousands of active solid-state devices can potentially be integrated in a high-power source for microwave or millimeter-wave applications

Beam Diffraction by a Planar Grid Structure at 93 GHz

The idea of using diode grids for electronic beam steering was introduced by Lam et al [l]. As shown in Figure 1, when an incident beam reflects off the diode grid, the direction of the reflected wave can be controlled by progressively varying the ref1ection phase across the grid. The reflection phase of the diode grid can be controlled by varying the DC bias on the diodes. Later, a monolithic diode grid was fabricated with l600 varactor diodes, and a relative phase shift of 70° at 93 GHz was measured [2]. This work verified the transmission-line theory used to design the grid, but the phase shift was not sufficient to steer the beam, recently, Johansson [3] designed and built a passive planar grating reflector antenna that focused a beam. A rigorous moment-method solution was applied to choose a grating geometry to select the first-order diffracted wave. In this work, using the transmission-line model approach, the goal was to demonstrate that the beam can be steered by building a grid structure without diodes to give a fixed beam shift. In these grids, diodes were replaced by gaps with different sizes to obtain different capacitances needed to steer a beam at 93 GHz. The result show a successful beam shift of 30° with a loss of 2.5 dB

Bar-grid oscillators

Grid oscillators are an attractive way of obtaining high power levels from the solid-state devices, since potentially the output powers of thousands of individual devices can be combined. The active devices do not require an external locking signal, and the power combining is done in free space. Thirty-six transistors were mounted on parallel brass bars, which provide a stable bias and have a low thermal resistance. The output power degraded gradually when the devices failed. The grid gave an effective radiated power of 3 W at 3 GHz. The directivity was 11.3 dB, and the DC-to-RF efficiency was 22%. Modulation capabilities of the grid were demonstrated. An equivalent circuit model for the grid is derived, and comparison with experimental results is shown

A 100-Element MESFET Grid Oscillator

A planar grid oscillator which combines the outputs of 100 devices quasi-optically is presented. The planar configuration is attractive because it is compatible with present-day IC fabrication techniques. In addition, the grid's structure leads to a transmission-line model that can readily be applied to the design of larger grids in the future. This approach is particularly attractive for wafer-scale integration at millimeter wavelengths. The grid oscillates near 5 GHz and can be frequency tuned with mirror spacing from 4.8 GHz to 5.2 GHz. The far-field radiation patterns for the grid are shown. From the pattern, the directivity is calculated to be 16 dB. The ERP is measured to be 25 W. The DC input power is 3 W, and the power radiated from the grid is calculated to be 0.625 W. This gives a DC-to-RF efficiency of 20%

A 100-element planar Schottky diode grid mixer

The authors present a Schottky diode grid mixer suitable for mixing or detecting quasi-optical signals. The mixer is a planar bow-tie grid structure periodically loaded with diodes. A simple transmission line model is used to predict the reflection coefficient of the grid to a normally incident plane wave. The grid mixer power handling and dynamic range scales as the number of devices in the grid. A 10-GHz 100-element grid mixer has shown an improvement in dynamic range of 16.3 to 19.8 dB over an equivalent single-diode mixer. The conversion loss and noise figure of the grid are equal to those of a conventional mixer. The quasi-optical coupling of the input signals makes the grid mixer suitable for millimeter-wave and submillimeter-wave applications by eliminating waveguide sidewall losses and machining difficulties. The planar property of the grid potentially allows thousands of devices to be integrated monolithically

Operational parameter influence on heavy metal removal from metal plating wastewater by electrocoagulation process

Among the different treatment processes available for industrial wastewater treatment, electrocoagulation represents a challenging option due to several features, such as environmental compatibility, inherent safety, energy and cost effectiveness. The effectiveness of electrocoagulation process (ECP) using aluminium and iron electrodes for the removal of heavy metals from industrial wastewater has been investigated, with particular attention to the effects of operating parameters (pH, inter-electrode distance, hydraulic retention time and current density) on removal efficiency. In the first step of the experimental phase, a laboratory-made artificial wastewater containing heavy metals (Cu, Ni and Pb) was adopted in order to identify the optimum conditions that were subsequently applied to treat a metal plating industrial wastewater. Experimental results revealed that under the optimal experimental conditions (actual pH 6.32, current density 0.026 A cm-2), the removal efficiency of heavy metals from artificial wastewater was higher than 95 %

A 6.5 GHz-11.5 GHz source using a grid amplifier with a twist reflector

The authors have constructed and tested an oscillator using a grid amplifier with external feedback from a twist reflector. The twist reflector serves two functions; it changes the output polarization to match the input, and its position sets the feedback phase. This permits a wider tuning range than has been possible with previous grid oscillators. The source could be continuously tuned from 8.2 GHz to 11.0 GHz by moving the twist reflector. By moving the polarizer and mirror in the twist reflector independently, a 1.8-to-1 frequency range from 6.5 GHz to 11.5 GHz was achieved. The peak effective radiated power was 6.3 W at 9.9 GHz

Surface plasmon resonance: a versatile technique for biosensor applications

Surface plasmon resonance (SPR) is a label-free detection method which has emerged during the last two decades as a suitable and reliable platform in clinical analysis for biomolecular interactions. The technique makes it possible to measure interactions in real-time with high sensitivity and without the need of labels. This review article discusses a wide range of applications in optical-based sensors using either surface plasmon resonance (SPR) or surface plasmon resonance imaging (SPRI). Here we summarize the principles, provide examples, and illustrate the utility of SPR and SPRI through example applications from the biomedical, proteomics, genomics and bioengineering fields. In addition, SPR signal amplification strategies and surface functionalization are covered in the review.open1

A 10 GHz Quasi-Optical Grid Amplifier Using Integrated HBT Differential Pairs

We report the fabrication and testing of a 10 GHz grid amplifier utilizing sixteen GaAs chips each containing an HBT differential pair plus integral bias/feedback resistors. The overall amplifier consists of a 4x4 array of unit cells on an RT Duroid™ board having a relative permittivity of 2.2. Each unit cell consists of an emitter-coupled differential pair at the center, an input antenna which extends horizontally in both directions from the two base leads, an output antenna which extends vertically in both directions from the two collector leads, and high inductance bias lines. In operation, the active grid array is placed between a pair of crossed polarizers. The horizontally polarized input wave passes through the input polarizer and couples to the input leads. An amplified current then flows on the vertical leads, which radiate a vertically polarized amplified signal through the output polarizer. The polarizers serve dual functions, providing both input-output isolation as well as independent impedance matching for the input and output ports. The grid thus functions essentially as a free-space beam amplifier. Calculations indicate that output powers of several watts per square centimeter of grid area should be attainable with optimized structures