Simple 1-mm receivers with fixed tuned double sideband SIS mixer and wideband InP MMIC amplifier

We report on attempts to broaden the IF bandwidth of the BIMA 1mm SIS receivers by cascading fixed tuned double-sideband (DSB) SIS mixers and wideband MMIC IF amplifiers. To obtain the flattest receiver gain across the IF band we tested three schemes for keeping the mixer and amplifier as electrically close as possible. In Receiver I, we connected separate mixer and MMIC modules by a 1" stainless steel SMA elbow. In Receiver II, we integrated mixer and MMIC into a modified BIMA mixer module. In Receiver III, we devised a thermally split block where mixer and MMIC can be maintained at different temperatures in the same module. The best average receiver noise we achieved by combining SIS mixer and MMIC amplifier is 45 -50 K DSB for ν_(LO) = 215 - 240 GHz and below 80 K DSB for ν_(LO) = 205 - 270 GHz. The receiver noise can be made reasonably flat over the CARMA IF band (ν_(IF) = 1 - 5 GHz). Noise temperatures for all three receivers are comparable to or better than those obtained with the BIMA receiver

Synergic photocatalytic effect between TiO2 and a fluorinated transparent ionomeric material in the oxidation of hydrosoluble pollutants in turbid suspensions

The crystal violet (CV) dye has been chosen to study the photooxidation activity of titanium dioxide immobilized into a transparent fluoropolymeric matrix toward organic pollutants. The photoactive matrix was directly coated on the UV source by applying a TiO2 containing fluorinated ionomeric dispersion and a perfluorinated transparent amorphous polymer in an appropriate sequence. The photocatalytic activity of the multilayered coating towards the hydrosoluble organic CV dye was evaluated in transparent solution and in highly turbid suspension. The turbidity was obtained by dispersing insoluble microparticles of calcium sulfate in the polluted aqueous solution. The photoabatement rates obtained in transparent and in turbid conditions were 0.0918 min-1 and 0.0300 min-1, respectively. The TiO2 nanoparticle dispersed in the fluorinated matrix revealed a higher photocatalytic activity than simple dispersed TiO2 in both transparent as well as turbid conditions. The immobilization of the catalyst in a stable fluorinated matrix avoided the TiO2 separation and prevented catalyst losses. The synergism in the activity between the TiO2-based photocatalyst and the fluorinated matrix was particularly evident at low pollutant concentrations

Advanced Techniques for VNA Characterization of Millimetre-Wave Orthomode Transducers (OMTs)

We report on advanced techniques for the characterization of millimeter-wave orthomode transducers (OMTs). These techniques include standard mm-wave frequency-domain VNA (Vector Network Analyser) measurement and time-domain methods, which can be applied to remove the effects of the waveguide transitions necessary to access the OMT ports and excite the desired modes. First, we present the main parameters of the OMT by defining its general S-matrix and discuss the different methods that allow characterizing the insertion loss, the reflection, the cross-polarization and the isolation of the device. Advantages and disadvantages of each method are presented and compared between them. We provide a list of waveguide components necessary in the various OMT test setups (adapters, loads, quarter-wave and longer waveguide sections, feed-horn, etc.). Different OMT configurations, with distinct orientation of the waveguide input and outputs are discussed. Alternative characterization methods of the OMT parameters are presented and the associated setups discussed. Although the presented techniques refer to the characterization of a specific configuration of a W-band (3 mm wavelength) OMT, the described method can be applied to other OMT configurations and frequency ranges (from microwave to THz frequencies), therefore having a general validity

Double Ridged 180° Hybrid Power Divider With Integrated Band Pass Filter

We describe the design, construction and performance of a 180 hybrid power divider with integrated band pass filter for L-band (1.3–1.8 GHz). The hybrid is based on a cavity and two novel broadband coaxial-to-double ridged waveguide transitions. The design was optimized using a commercial 3-D electromagnetic simulator. The device was tested at room and cryogenic temperature. At the physical temperature of 77Kthe measured input reflection was less than -17 dB, the maximum deviation from the ideal -3dB coupling and 180° phase difference were respectively +/- 0.25 dB and +/- 0.9°. The experimental results are in good agreement with simulation

A waveguide cavity 180° hybrid coupler with coaxial ports

We describe the design, construction, and performance of a 180° hybrid coupler for the frequency band 1.3-1.8 GHz (L-band). The hybrid utilizes a WR650 rectangular waveguide cavity and has three 50 Ω, coaxial ports. The signals are coupled in and out of the cavity through broadband coaxial probes attached to 7/16-type connectors. The measured performances are in excellent agreement with the electromagnetic simulations. © 2009 Wiley Periodicals, Inc

The effect of oxygen in the photocatalytic oxidation pathways of perfluorooctanoic acid

The influence of oxygen in the photocatalytic oxidation of perfluorooctanoic acid (PFOA) promoted by a commercial nano-sized titanium dioxide was studied by testing the reaction in different conditions: static air, oxygen flux, nitrogen flux and pre-saturated nitrogen flux. The reaction was monitored by Total Organic Carbon (TOC) analysis and Ionic Chromatography (IC). Shorter chain perfluorocarboxylic acids (PFCAs; C-n, n = 1-7) intermediate degradation products were quantitatively determined by High-Performance Liquid Chromatography combined with Mass Spectrometry (HPLC-MS) analysis. The presence of shorter chain PFCAs in solution was also monitored by F-19 NMR. The experimental findings are in agreement with two major oxidative pathways: C-n -> Cn-1 photo-redox and beta-scissions routes mediated by COF2 elimination. Depending on the experimental conditions, the mutually operating mechanisms could be unbalanced up to the complete predominance of one pathway over the other. In particular, the existence of the beta-scissions route with COF2 elimination was corroborated by the isolation and characterization of carbonyl difluoride, a predicted fluorinated decomposition by-product

A simple K-band waveguide-to-microstrip probe transition

We describe the design, construction, and test of a simple K-band waveguide-to-microstrip transition based on a radial-shaped probe patterned on a quartz substrate. From 16 to 28 GHz, the measured reflection coefficient at the coaxial SMA input, used for test purposes of the adapter, was less than -14 dB, and the dissipative loss was about 0.30 dB. The estimated loss of the waveguide to microstrip transition only, with coaxial connector effects removed, is of about 0.08 dB

A New Monitor and Control Power Supply PCB for Biasing LNAs of Large Radio Telescopes Receivers

The biasing of low noise amplifiers (LNA) is of paramount importance for the receivers of large radio telescopes. High stability, optimal trade-off between gain and noise figure, remote control, and mitigation of the radio frequency interferences (RFIs) are all desirable features in the choice of the electronic board devoted to power supply the LNAs. In this paper, we propose the design and characterization of a multilayer printed circuit board (PCB), named GAIA, able to meet all the aforementioned requirements. The GAIA board is a 3-Unit, four-layer, rack-mountable, programmable PCB for the remote biasing of the LNAs, with monitor and control capabilities, specifically designed to operate in the receivers of the 64-m diameter Sardinia Radio Telescope (SRT). We describe the architecture, layout, and measurements of the GAIA board. Our results show that the GAIA power supply provides high stability of the output bias voltages and, in comparison with the old analogic biasing board used so far in the SRT receivers, it shows comparable or better frequency stability, other than a remarkable mitigation of the RFIs