Ricardo Finger

A Sideband-separating Receiver with a Calibrated Digital If-Hybrid Spectrometer for the Millimeter Band

Due to its advantages over other configurations, sideband-separating receivers are usually preferred for radio astronomy, particularly in the presence of high atmospheric noise. However, even with all the advances that have been made in recent years in the field of receiver technology, one of the most important figures of merit for this kind of receiver, the sideband rejection ratio, is still relatively low and typically around 10 to 20 dB. This is because keeping low amplitude and phase imbalances over large RF and IF bands is extremely difficult. In order to overcome this problem, it has been suggested that by introducing a digital back-end that mimics the performance of an IF-hybrid, such imbalances can be calibrated out. Until now, this has been demonstrated only at very low RF frequencies (below 4 GHz). Here, for the first time, we demonstrate that this technique can be applied at higher frequencies. We have implemented a sideband-separating receiver with a calibrated digital IF-hybrid spectrometer for the 3 mm band, and have demonstrated that, even in the presence of large imbalances of individual components, sideband ratios above 35 dB can be obtained in the entire RF band.

A calibrated digital sideband separating spectrometer for radio astronomy applications

Dual sideband (2SB) receivers are well suited for the spectral observation of complex astronomical signals over a wide frequency range. They are extensively used in radio astronomy, their main advantages being to avoid spectral confusion and to diminish effective system temperature by a factor 2 with respect to double sideband (DSB) receivers. Using available millimeter-wave analog technology, wideband 2SB receivers generally obtain sideband rejection ratios (SRR) of 10–15 dB, insufficient for a number of astronomical applications. We report here the design and implementation of an FPGA-based sideband separating FFT spectrometer. A 4 GHz analog front end was built to test the design and measure sideband rejection. The setup uses a 2SB front end architecture, except that the mixer outputs are directly digitized before the IF hybrid, using two 8 bit ADCs sampling at 1 GSPS. The IF hybrid is implemented on the FPGA together with a set of calibration vectors that, properly chosen, compensate for the analog front end amplitude and phase imbalances. The calibrated receiver exhibits a sideband rejection ratio in excess of 40 dB for the entire 2 GHz RF bandwidth.

Effect of parasitic capacitances on impedance measurements in microsensors structures: a numerical study

The use of solid electrolyte cells to detect specific gases is widely applied in the electronic control systems. Ionic conduction in this type of sensors is normally studied through impedance spectroscopy, since the data obtained with this technique provide valuable information about the electrical properties of the solid electrolyte and electrode behavior. This work addresses the influence of inter-electrode capacitance on the impedance characterization of small structures. Parasitic capacitance was determined by solving Laplace equation and integrating the potential over a Gauss surface including the electrode. Computer simulations of electrode impedance behavior of a solid cell were carried out using a well-known electronic simulator. It is concluded that parasitic capacitances introduce a small distortion on the high-frequency portions of Nyquist plot that are important when miniaturized sensor are electrically characterized.

The diffuse molecular component in the nuclear bulge of the Milky Way

Context: The bulk of the Molecular gas in the Central Molecular Zone (CMZ) of the Galactic center region shows warm kinetic temperatures, ranging from

Effects of cryostat infrared filters on the performance of ALMA band 1 (35–52 GHz) receiver optics

>20

Ultra-pure digital sideband separation at sub-millimeter wavelengths

K in the coldest and densest regions (n

The Atacama Large Millimeter/sub-millimeter Array band-1 receiver

\sim 10^{4-5}

Development of band-1 receiver cartridge for Atacama Large Millimeter/submillimeter Array (ALMA)

cm

New capabilities for the Southern 1.2m mm-Wave Telescope

^{-3}

Dust?Gas Scaling Relations and OH Abundance in the Galactic ISM

) up to more than 100 K for densities of about n