Sum Mode Research Articles

Radiation Pattern Characteristics of a Wideband Novel Modified Archimedean Spiral Antenna Array Covering DCS/PCS/WLAN and LTE Wireless Communication Bands

Radiation pattern characteristics of an array antenna are presented, which employs a wideband novel modified Archimedean spiral antenna reported in a previous work as the radiating elements. The antenna has no ground plane, hence its radiation patterns are bidirectional as it radiates simultaneously in both directions. The sum-mode and difference-mode excitations of the 2 × 2 array configuration are included. The sum-mode excitation of the 2 × 2 array with dimensions 150 × 150 × 0.8 mm3 covers the frequency bands DCS (1710-1880 MHz), PCS (1850-1990 MHz), WLAN (2.3-2.5 GHz), and LTE Band 7 (2.5-2.6 GHz), all with circularly polarized radiation patterns and gain at broadside angle varying between 5-9 dBic. A prototype antenna was fabricated and experimentally verified for the sum mode for both the impedance matching and radiation pattern characteristics. This antenna can also be used in monopulse radar tracking and transmit/receive communications after cavity backing.

Study of charge-sharing in MEDIPIX3 using a micro-focused synchrotron beam

X-ray photon-counting detectors consisting of a silicon pixel array sensor bump-bonded to a CMOS electronic readout chip offer several advantages over traditional X-ray detection technologies used for synchrotron applications. They offer high frame rate, dynamic range, count rate capability and signal-to-noise ratio. A survey of the requirements for future synchrotron detectors carried out at the Diamond Light Source synchrotron highlighted the needs for detectors with a pixel size of the order of 50μm. Reducing the pixel size leads to an increase of charge-sharing events between adjacent pixels and, therefore, to a degradation of the energy resolution and image quality of the detector. This effect was observed with MEDIPIX2, a photon-counting readout chip with a pixel size of 55μm. The lastest generation of the MEDIPIX family, MEDIPIX3, is designed to overcome this charge-sharing effect in an implemented readout operating mode referred to as Charge Summing Mode. MEDIPIX3 has the same pixel size as MEDIPIX2, but it is implemented in an 8-metal 0.13μm CMOS technology which enables increased functionality per pixel. The present work focuses on the study of the charge-sharing effect when the MEDIPIX3 is operated in Charge Summing Mode compared to the conventional readout mode, referred to as Single Pixel Mode. Tests of a standard silicon photodiode array bump-bonded to MEDIPIX3 were performed in beamline B16 at the Diamond Light Source synchrotron. A monochromatic micro-focused beam of 2.9μm x 2.2μm size at 15keV was used to scan a cluster of nine pixels in order to study the charge collection and X-ray count allocation process for each readout mode, Single Pixel Mode and Charge Summing Mode. The study showed that charge-shared events were eliminated when Medipix3 was operated in Charge Summing Mode.

First CT using Medipix3 and the MARS-CT-3 spectral scanner

The MARS research group has created a new version of their scanner for taking improved spectral CT datasets. This version of the scanner (MARS-CT-3) has taken the first Medipix3 CT images of a phantom. MARS-CT-3 incorporates a new gantry, new x-ray sources and the new MARS readout board, as well as the ability to connect gas lines to the specimen. The new gantry has improved mechanical rigidity and can perform scans faster. Magnification can be controlled by moving the detector and the x-ray source independently. The brighter x-ray source means images can be taken six times faster. Gas lines allow the user to control various environmental factors inside the scanner, such as temperature, or deliver oxygen and anaesthetics, providing the ability to do a full spectroscopic CT scan of a live sedated biological specimen, such as a mouse. The new MARS readout is able to read from all current chips from the Medipix family, has faster image downloading, and the use of up to six Medipix detectors in parallel on the same chip carrier. The use of Medipix3 chips allows for compensation of charge sharing via Charge Summing Mode.

In-Orbit Performance of the MAXI/SSC onboard the ISS

We report here the in-orbit performance of the CCD camera (MAXI/SSC) onboard the International Space Station (ISS). It was commissioned in 2009 August. This is the first all-sky survey mission employing X-ray CCDs. It consists of 32 CCDs, each of which is 1 inch square. It is a slit camera with a field of view of 1$^\circ\!\!\!.$5 $\times$ 90$^\circ$, and scans the sky as the rotation of the ISS. The CCD on the SSC is cooled down to the working temperature around $-$60$^\circ$C by the combination of a peltier cooler, a loop heat pipe and a radiator. The standard observation mode of the CCD is in a parallel sum mode (64-binning). The CCD functions properly, although it suffers an edge glow when the Sun is near the field of view (FOV), which reduces the observation efficiency of the SSC down to about 30%. The performance of the CCD is continuously monitored both by the Mn-K X-rays and by the Cu-K X-rays. There are many sources detected, not only point sources, but extended sources. Due to the lack of an effective observation time, we need more observation time to obtain an extended emission analysis extraction process.

A modified spectrum reconstruction method for the Charge Summing Mode of Medipix3

Because of its spectral capabilities, the MEDIPIX2 [2] detector has been used to determine the spectrum of an X-ray tube [1]. The measured spectrum is smeared out in the detector due to charge sharing among pixels. Therefore, a deconvolution method has been applied to reconstruct the real spectrum. The Medipix3 [3], as successor of the Medipix2, will be able reduce the influence of charge sharing in real time. Based on simulations, the aim of this paper is to investigate how good one will be able to determine an incoming X-ray spectrum with the Medipix3.

Medipix3: A 64 k pixel detector readout chip working in single photon counting mode with improved spectrometric performance

Medipix3 is a 256×256 channel hybrid pixel detector readout chip working in a single photon counting mode with a new inter-pixel architecture, which aims to improve the energy resolution in pixelated detectors by mitigating the effects of charge sharing between channels. Charges are summed in all 2×2 pixel clusters on the chip and a given hit is allocated locally to the pixel summing circuit with the biggest total charge on an event-by-event basis. Each pixel contains also two 12-bit binary counters with programmable depth and overflow control. The chip is configurable such that either the dimensions of each detector pixel match those of one readout pixel or detector pixels are four times greater in area than the readout pixels. In the latter case, event-by-event summing is still possible between the larger pixels. Each pixel has around 1600 transistors and the analog static power consumption is below 15 μW in the charge summing mode and 9 μW in the single pixel mode. The chip has been built in an 8-metal 0.13 μm CMOS technology. This paper describes the chip from the pixel to the periphery and first electrical results are summarized.

Prediction of background levels for the Wind WAVES instrument and implications for the galactic background radiation

We investigate and predict the observed background levels for the TNR, RAD1, and RAD2 receivers when connected to the X, Y, and Z antennas of the WAVES instrument on the spacecraft Wind. The receivers are connected to either a single antenna, in “SEP” mode, or a combination of antennas, in “SUM” mode. With the TNR receiver in SEP (X) mode, the predicted backgrounds agree to within 20% when modeled using a two component model for the quasi‐thermal plasma noise (QTN). Calibrating the RAD1 in SEP (X) mode observations against TNR allows us to calculate the relative receiver gain GR1 = 1.43 ± 0.18. Using the RAD1 data in SUM (X+Z) mode, the ratio of antenna gains is found to be R = 6.5, in agreement with preflight measurements. Observed differences between the SEP (X) and SUM (X+Z) modes are explained for the first time, and the predicted levels of QTN and galactic background are found to agree to within 20%. RAD2 is also calibrated against RAD1 and TNR, yielding a total gain GR2Gy = 2.5 ± 0.3. Differences between the predicted and observed galactic background spectra are used to estimate the effective antenna lengths for the X and Y antennas, which are found to be between the physical monopole antenna length L and the Hansen (1981) prediction of L. The analyses are consistent with the Novaco and Brown (1978) galactic background model, which decreases much faster than that of Cane (1979). Our model background spectrum is useful for theory‐data comparisons of type II and III bursts.

Entanglement between collective fields via atomic coherence effects

We explore the quantum entanglement between two collective fields via atomic coherence effects. For three-level atoms in $\mathsf{V}$ configuration driven by two applied fields on two-photon resonance, one coherent superposition of the excited states is not excited, which is the counterpart of coherent population trapping. The coherence-induced depopulation makes two cavity fields in each collection combine into a quantum-beat, i.e., equivalently, the difference mode of the two components decouples from the driven atoms. The two sum modes, when they are arranged in the four-wave mixinglike interactions, can be prepared in Einstein-Podolsky-Rosen entangled state. Correspondingly, any two individual fields from different collective modes are entangled with each other. Furthermore, the effects of thermal reservoir and laser linewidths are discussed, and a generalization is given to the case in which each quantum beat involves more than two modes.

Excitation matching procedure for sub-arrayed monopulse arrays with maximum directivity

In this paper, the maximization of the directivity of compromise difference patterns in subarrayed monopulse linear array antennas with optimum sum mode is addressed by means of a two-stage excitation matching procedure. The knowledge of the independently optimum difference excitations, which provide the maximum directivity, is exploited with an efficient matching technique based on the contiguous partition method. Simple and reliable compromise solutions, characterized by a reduced complexity as well as easier antenna manufacturing, are synthesized to assess the effectiveness of the proposed method also in comparison with state-of-the-art methods devoted to the directivity maximization. This paper is a postprint of a paper submitted to and accepted for publication in Radar, Sonar & Navigation and is subject to Institution of Engineering and Technology Copyright. The copy of record is available at IET Digital Library.

Quantum-beat lasers as bright sources of entangled sub-Poissonian light

We show that a quantum-beat system with incoherent pump or coherent driving produces an entangled sub-shot-noise laser that operates well above threshold. The numerical results and physical analyses are presented using the combination modes of the lasing fields. The relative mode is decoupled from the active medium and thus remains in its vacuum state, while the sum mode operates well above threshold and has sub-shot-noise. The quantum beat and the sum mode intensity noise reduction combine to yield entanglement between two bright beams and sub-Poissonian photon statistics of the respective beams.

Folded Reflectarray를 이용한 고이득 94 GHz 모노펄스 안테나

본 논문은 94GHz를 중심 주파수로 하며, 모노펄스 형식의 추적 레이다 시스템에 사용되는 folded reflectarray 안테나를 제안한다. 추적 레이다는 대부분 목표물로부터 반사되어 돌아온 반사 신호들을 비교하여 목표물을 찾으며, 모노펄스 형식에서는 이러한 신호들의 비교를 동시에 수행한다. 본 논문에서 제안한 모노펄스 형식의 folded reflectarray 안테나는 polarizing grid, reflectarray, 다중 모드 feed horn, 그리고 도파관으로 제작된 comparator로 이루어져 있다. 제작된 안테나는 다중 모드 feed horn과 comparator의 모노펄스 급전부에 의해 sum 모드, azimuth 모드, 그리고 elevation모드, 이렇게 세 개의 방사 패턴 형식을 나타낼 수 있다. 측정 결과, sum 패턴에서는 36dB, azimuth 패턴에서는 33.5dB, 그리고 elevation 패턴에서는 27.2 dB의 이득을 확인할 수 있었다 This paper proposes a high-gain monopulse antenna using the folded reflectarray for a monopulse target-tracking radar systems designed at the center frequency of 94 GHz. In target-tracking radar systems, the angle of arrival of the incoming wave Is determined by comparing the signal received on two or more non-coincident antenna patterns. This is the physical basis of most target-tracking techniques and the comparison is made simultaneously in a monopulse radar systems. In this paper, the antenna consists of polarizing grid, reflectarray, multimode feed horn, and comparator implemented by wavguide. The antenna is able to have three radiation patterns by using the monopulse feed systems assembled by multimode feed horn and comparator. The antenna demonstrates maximum gains 36dB, 33.5dB and 27.2dB at sum mode, azimuth mode, and evevation mode respectively.

The Medipix3 Prototype, a Pixel Readout Chip Working in Single Photon Counting Mode With Improved Spectrometric Performance

A prototype pixel detector readout chip has been developed with a new front-end architecture aimed at eliminating the spectral distortion produced by charge diffusion in highly segmented semiconductor detectors. In the new architecture neighbouring pixels communicate with one another. At the corner of each pixel summing circuits add the total charge deposited in each sub-group of 4 pixels. Arbitration logic assigns a hit to the summing circuit with the highest charge. In the case where incoming X-ray photons produce fluorescence-a particular issue in high-Z materials-the charge deposited by those fluorescent photons will be included in the charge sum provided that the deposition takes place within the volume of the pixels neighbouring the initial impact point. The chip is configurable such that either the dimensions of each detector pixel match those of one readout pixel or detector pixels are 4 times greater in area than the readout pixels. In the latter case event-by-event summing is still possible between the larger pixels. As well as this innovative analog front-end circuit, each pixel contains comparators, logic circuits and two 15-bit counters. When the larger detector pixels are used these counters can be configured to permit multiple thresholds in a pixel providing spectroscopic information. The prototype chip has been designed and manufactured in an 8-metal 0.13 mum CMOS technology. First measurements show an electronic pixel noise of ~ 72 e-rms (Single Pixel Mode) and ~ 140 e-rms (Charge Summing Mode).

Nonlinear coupling of fluctuating drag and lift on cylinders undergoing forced oscillations

Experiments with cylinders undergoing forced oscillations show a coupling between the fluctuating lift and drag forces as a result of nonlinear wave interactions. The fluctuating lift and drag components are computed from the instantaneous pressure around the azimuth of a circular cylinder measured with an array of miniature microphones. Quadratic nonlinear interaction between the von Karman vortex-shedding modes and the forcing field produces sum and difference modes, which appear in the spectrum of the surface pressure signals when the forcing frequency is different from the von Karman vortex-shedding frequency, f 0 . The spatial symmetry of the interacting modes determines whether the combination modes appear in the lift spectrum or the drag spectrum. Furthermore, the spatial symmetry of the modes can be predicted from the symmetries of the two interacting parent modes. Crossflow excitation of the cylinder produces combination modes that appear in the drag spectrum. Consequently, attempts to enhance the fluctuating lift by crossflow excitation will necessarily affect the fluctuating drag through nonlinear interaction.

Characterization of a differential radio-frequency single-electron transistor

We have fabricated and characterized a new type of electrometer that couples two parallel single-electron transistors (SETs) to a radio-frequency tank circuit for use as a differential RF-SET. We demonstrate operation of this device in summing, differential, and single-SET operation modes, and use it to measure a Coulomb staircase from a differential single Cooper-pair box. In differential mode, the device is sensitive to uncorrelated input signals while screening out correlated ones.

SQUEEZING EFFECTS IN THE SUM AND DIFFERENCE OF THE FIELD AMPLITUDE IN THE RAMAN PROCESS

Sum and difference squeezing of the field amplitude are higher-order squeezing effects. These effects are studied in the Raman process under the short-time approximation based on a fully quantum mechanical approach. It is shown that for uncorrelated modes, the normal squeezing in the sum and difference-frequency field depends on the sum and difference squeezing of input field modes respectively, which can generate normal squeezing in the sum and difference-frequency field mode. All the possibilities for obtaining sum and difference squeezing in two modes and its dependence on squeezing of individual field modes are investigated. We have also shown that if the high-frequency mode is in a coherent state and the low-frequency mode is squeezed, the field state will be difference squeezed if the amplitude of the high-frequency mode is large enough; otherwise the state may or may not be difference squeezed. If both modes are squeezed, then the state may or may not be difference squeezed. These higher-order squeezing effects are useful in the production of squeezing in the Raman process.

Bound mode of an atom laser

Summary form only given. Hope, Savage and Moy have presented a model Hamiltonian for an atom mirror. In conjunction with a Bose-Einstein condensate such a device can model the output coupler for an atom laser. The basic structure of the Hamiltonian is identical to the optical output coupler. A cavity mode at a particular wavevector is coupled to a set of output modes over a range of wavevectors. The difference is that the parameter in the Hamiltonian which would be the frequency in the optical case is the square of the wavevector for atoms. This has the consequence that the cavity mode is only coupled to one of the two superposition (sum and difference) modes of the output. We present a Fano diagonalisation of this output coupler model. The Hamiltonian can be expressed in terms of the diagonal operators together with operators representing a bound mode. This mode appears when the coupling is strong compared to the energy of the cavity mode. Any states of the bound mode represent excitations which will not propagate out of the cavity. We give the criterion for the existence of the mode in the cases where the interaction strengths are real and complex.

Energy transfer in a fluid with a uniform density gradient

Energy transfer via resonance in a stratified fluid with a constant Brunt–Väisälä frequency is studied through the Manley–Rowe relation and direct numerical simulations. The objectives of this study are two-fold. One is to determine if there is a limitation on the lengthscale of small-scale waves to which primary energy can be effectively transferred. The other is to study factors affecting the growth of parametric subharmonic instability. Resonantly interacting modes are classified into three groups: local sum modes, quasi-subharmonic modes and remote parametric subharmonic instability modes (characterized by interaction with very small-scale waves). The latter two involve energy transfer from a primary wave to secondary waves with half the frequency. Most energy transfer is through local sum resonant modes and quasi-subharmonic modes. Energy cannot effectively transfer to higher wavenumber modes since dynamical systems are altered as wavenumbers of excited modes increase. In the remote modes, the solution is sinusoidal with high angular frequency and very small energy capacity. As a consequence, these modes are inactive in energy transfer despite their high energy growth rates. Effects of non-uniform white noise amplitude and primary mode propagation angle on the quasi-subharmonic modes are also investigated. Implications for energy transfer in the ocean are discussed.

A beam-forming technique for leaky-wave antennas

A beam-forming technique for leaky-wave antennas (LWAs) which can switch electronically in three different radiation patterns is developed in this letter. A simple two-terminal feeding microstrip-line LWA works as a radiating element. By varying the phase of the two injection signals from 0 to 180°, the emitting power from the LWA can produce three different radiation modes: the normal mode (one sharp beam), the difference mode (Δ), and the sum mode (Σ). The antenna displays large-bandwidth characteristics, and can be useful near crossroads for collision avoidance or in the radio location of vehicles. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 28: 108–110, 2001.

Lambda quantum-beat laser with another laser cascaded

In this paper we investigate the quantum statistical properties in a cascade laser system with the lower transition being in a quantum-beat configuration. It is shown that a type of three-mode squeezing may be generated. The fluctuations of the intensity difference between the sum-mode from the quantum-beat and the cascade single mode may be reduced below the shot-noise limit. The best achievable noise reduction is up to 50%. Good squeezing occurs when the sum mode and the cascade single mode have normalized intensities much larger than unity and the intensity difference is much smaller than the respective intensity.

Squeezed Cascade Two-Quantum-Beat Lasers

Noise squeezing of intensity difference between the pair of sum modes may be generated in a cascade laser of Λ and V quantum-beats. The best achievable squeezing is up to 50% below the shot noise limit. This new kind of squeezed lasers has potential for quantum communications and precision measurements.