Band Broadband Research Articles

A Ka-Band Broadband Power Amplifier With Transformer-Based Lossy Magnetically Coupled Resonator Network: Analysis and Design

A <i>Ka</i>-Band Broadband Power Amplifier With Transformer-Based Lossy Magnetically Coupled Resonator Network: Analysis and Design

A Novel Design of G-Band Broadband Low-Gain Fluctuation Slow-Wave Structure With Improved Folded Waveguides

The design method for ultrawideband amplification with low-gain fluctuation is explored for the terahertz folded-waveguide traveling-wave tube (TWT). Although the folded-waveguide circuit has a large cold bandwidth ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 30%), effective amplification with a flat gain characteristic can only be achieved in a limited range due to sharply reduced interaction impedance. The situation further deteriorates in the design of a terahertz TWT where an oversized beam tunnel has to be used to facilitate the transport of the beam. Through careful analysis of the folded-waveguide (FWG) design characteristics, a modification to the geometry of the circuit has been proposed, leading to a significant enhancement in design capability. As a result, the interaction impedance is increased by 26% over a wide operation frequency band in comparison to the normal folded-waveguide circuit. This makes it possible to use the phase velocity tapering technology to increase efficiency and balance the gain at the same time. A design example in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{G}$</tex-math> </inline-formula> -band is presented. The interaction circuit is capable of producing 18-W output power over 30 GHz from 202 to 232 GHz with a gain fluctuation of less than 1.5 dB.

Dual Absorption Broadband Photoacoustic Technique to Eliminate Interference in Gas Mixtures

This article presents a dual-wavelength band broadband photoacoustic spectroscopy (BPAS) technique ideally suited to low-energy broadband sources for industrial and environmental multigas sensing applications. The broad spectral range of the supercontinuum source is used to cover a wide range of absorption bands of various gases. The major limitation in most of the gas sensors with broadband sources is the effect of interference between gases. This article proposes a dual-wavelength technique to eliminate the impact of cross sensitivity among gases. This sensor exhibits a comprehensive concentration measurement from parts per million (ppm) to % levels. The proposed technique showed a ±1.2% error between the calculated and calibrated concentration values. We achieved a minimum detection limit (MDL) of 0.4 and 0.7 ppm for methane (CH4) with an integration time of 142 and 200 s using 2315- and 1650-nm band, respectively, 0.3 and 1.8 ppm of ammonia (NH3) with an integration time of 100 and 48 s using 2315- and 2017-nm band, respectively, and also 2.6 ppm of carbon monoxide (CO) with an integration time of 71 s using the 2315-nm band.

Influence of the Output Window Reflection on the Performance of W-Band Gyrotron Traveling Wave Tubes

Effects of the output window reflection instability on the performance of our designed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${W}$ </tex-math></inline-formula> -band broadband gyrotron traveling wave tube (gyro-TWT) were studied by the simulation and hot test experiments. Strong oscillations and frequency self-modulation (FSM) in the after-cavity interaction (ACI) region were observed in the zero-driven state with a two-layer window and are verified with the beam-wave particle-in-cell simulation. Oscillations and FSM of 80–81.8 GHz and 91.03–94.68 GHz are, respectively, generated from the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">22</sub> and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> modes in the ACI region due to the high window reflection level. By using the “sandwich” and meta-surface windows with low reflection and broad bandwidth, the parasitic ACI oscillations can be effectively suppressed. The maximum saturated output power is improved to 156.8 kW at 94 GHz and is zero-driven stable in our recent hot test experiments.

1.8 µm band broadband hybrid light source employing a combination of a super luminescent diode and thulium-doped fiber amplifier.

We have proposed a broadband hybrid light source that combines a super luminescent diode (SLD) and thulium-doped fiber amplifier (TDFA) and operates in the 1.8 µm band. This light source can improve the characteristics of the output spectrum by amplifying the output light of the SLD with TDFA. In this study, we investigate the dependence of the output spectral characteristics of the hybrid broadband light source on the thulium-doped fiber (TDF) length used in the TDFA as well as the output spectra of three newly developed SLDs of 1660, 1690, and 1730 nm bands. In the evaluation of the output bandwidth, there are various definitions of output bandwidth, but we adopted the bandwidth with power density of over -40dBm/0.1nm. This is because it is possible to evaluate in this band with a dynamic range of "30 dB/0.1 nm" by using a general optical spectrum analyzer. The hybrid light source achieves the bandwidth of 332 nm, from 1579 to 1911 nm, and a high total output power of over 15 dBm. The maximum ripple was less than ∼0.1dB, which is similar to the maximum value of that of the SLD, without any deterioration in the ripple characteristics owing to the hybrid configuration of the SLD and TDFA.

Design and Measurement of a Broadband Beryllium Oxide Window With High Power Handling Capability

A broadband dielectric window with high power handling capability for gyrotron traveling wave tubes (gyro-TWTs) had been designed based on the step-type impedance transition structure. The manufactured beryllium oxide (BeO) window can achieve a relative bandwidth of 35.3% with a maximum reflection of −20 dB in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${X}$ </tex-math></inline-formula> -band, and the corresponding transmission loss is over −0.1 dB. The resonant spikes caused by engineering factors, including assembly tilt and gap, are investigated and analyzed. Thermal analysis shows that the BeO window can achieve a high average/CW power handling capability of over 232 kW within a wide frequency range. The fabricated input window has been successfully applied in our <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${X}$ </tex-math></inline-formula> -band broadband and high-power gyro-TWT.

Design of L-S band broadband power amplifier using microstip lines

This contribution introduces a novel broadband power amplifier design, operating in the frequency band ranging from 1.5 GHz to 3 GHz which cover the mainstream applications running in L and S bands. Both matching and biasing networks are synthesized by using microstrip transmission lines. In order to provide a wide bandwidth, two broadband matching techniques are deployed for this purpose, the first technique is an approximate transformation of a previously designed lumped elements matching networks into microstrip matching circuits, and the second technique is a binomial multi-sections quarter wave impedance transformer. The proposed work is based on ATF-13786 active device. The simulation results depict a maximum power gain of 16.40 dB with an excellent input and output matching across 1.5 GHz ~ 3 GHz. At 2.2 GHz, the introduced BPA achieves a saturated output power of 16.26 dBm with a PAE of 21.74%, and a 1-dB compression point of 4.5 dBm input power level. The whole circuitry is unconditionally stable over the overall bandwidth. By considering the broadband matching, the proposed design compares positively with the most recently published BPA.

Er3+/Pr3+/Nd3+ tri-doped tellurite glass for ultra-broadband amplification applications

The near-infrared band luminescence from Er3+/Pr3+/Nd3+ tri-doped tellurite glasses were investigated in this work. The tellurite glasses were prepared by melt-quenching method and under the excitation of 488 nm laser, an ultra-broadband emission from 1260 to 1650 nm with FWHM about 256 nm was found to appear owing to the perfect overlapping of emission bands from Er3+, Pr3+ and Nd3+, respectively. Additionally, the studied tellurite glasses possess high glass transition temperature with Tg > 420 °C. The ultra-broadband and flat emission properties as well as good thermal stability indicates that Er3+/Pr3+/Nd3+ tri-doped tellurite glass has great application prospect in near-infrared band broadband fiber amplifiers.

PRINCIPLES OF DEVELOPMENT OF THE TERAHERTZ BAND TELECOMMUNICATION SYSTEM BASED ON THE TECHNOLOGY OF HARMONIC SIGNAL AS THE INFORMATION CARRIER

Physical principles of introduction and reproduction of the information transmitted using the harmonic signal as the information carrier, are analyzed. Based on the performed theoretical calculations confirmed by the results of modeling, there are formed the principles and rules of determining optimal parameters of the ultra-wideband terahertz frequency range communication system on the basis of the technology of electronics using the harmonic signal as the information carrier. The necessity of using the terahertz frequency band while deploying future super high throughput rate telecommunication systems is reasoned. Analysis of the state-of-the-art problem is performed, the direction of research is selected and the mission is set with regards to creation of the terahertz band broadband access telecommunication system with the Gigabit throughput rate within the operating frequencies range of 130…134 GHz. Characteristics of the signal propagation path and defining of the signal losses under the conditions of the terahertz frequency band radio relay system operation are analyzed. On the basis of the analysis performed it is shown that operation of radio relay links in the terahertz band allows practically disregarding the refraction and interference of the electromagnetic waves reflected from the obstacles in the radio signal propagation domain that occurs primarily under the conditions of a dense urban building. The domains of the terahertz band frequencies, which are most of all suitable for use in the radio relay communication lines, are determined. Physical modeling of the super high data rate former is performed on the basis of the multifrequency multiplexing of the OFDM-modulated digital flows, testing at the experimental stand and the optimization aimed at attaining of the maximal throughput capacity of the channel used for transmission of the digital information of the flow are fulfilled in the Ethernet format using the developed software means. The created software and hardware means allowed attaining, for the first time, the general channel data rate of up to 1.2 Gbps at the full duplex. There are developed the block circuit diagram of the system transceiver path – the frequency converters with subharmonic pumping, the heterodyne using a high-stability setting quartz oscillator with the subsequent circuitry of multiplying and amplifying cascades, the bandpass filter using a thin metal plate in the E-plane of the 1.6×0.8 mm waveguide channel, and the horn-lens antenna.

Experimental study of ultrafast carrier dynamics in polycrystalline ZnTe nanofilm

Zinc telluride, due to its direct band gap and broadband light absorption, has the good application prospects in terahertz devices, solar cells, waveguide devices, and green light emitting diodes. In the photovoltaic field, it is possible to further improve the photoelectron conversion efficiency of multi-junction tandem solar cells by combining zinc telluride with III-V semiconductors. Ultrafast photo-excited carrier dynamics is fundamental to understand photoelectron conversion process of nanofilm solar cells. In this study, the ultrafast energy carrier dynamics of N-doped polycrystalline zinc telluride is investigated by using the femtosecond laser two-color pump-probe method at room temperature. The polycrystalline zinc telluride nanofilm is grown on a 500 μm GaAs (001) substrate via molecular beam epitaxy and doped by using a nitrogen ratio frequency plasma cell. The laser pulses with a central wavelength of 800 nm are divided into pump beam and probe beam by a beam splitter, after which the pump beam passes through a bismuth triborate crystal and its frequency is doubled to 400 nm. The 400 nm pump beam and 800 nm probe beam are focused on the sample collinearly through the same objective lens. Photo-excited carriers will be generated since the excitation photon energy of 400 nm pump beam (3.1 eV) is higher than the band gap of zinc telluride (～ 2.39 eV). The experimental data are analyzed by using the theoretical fitting model which includes energy relaxation processes of electrons and lattice, and the theoretical curves are consistent well with the experimental data. The fitted results show that the three dominated relaxation processes which affect the initial reflectivity recovery are in sub-picosecond time regime. The positive amplitude electron relaxation process is attributed to inter-band carrier cooling and carrier diffusion through electron-photon interactions, and the deduced decay time of this positive amplitude electron relaxation process is about 0.75 ps. The negative amplitude electron relaxation process is characterized as a photo-generated carrier trapping process induced by defects, and the decay time of this process is about 0.61 ps. The lattice heating process is realized through electron-phonon coupling process, and the calculated time constant of the lattice heating is about 0.86 ps.

A high flattening C + L band broadband source based on single pump and the same erbium-doped fiber

In order to realize a high flattening C+L band amplified spontaneous emission (ASE) light output, a broadband source using just one 976nm laser diode (LD) and two stages erbium-doped fibers (EDF) with the same concentration is proposed theoretically and demonstrated experimentally, and the theoretical analysis and experimental verification are presented in details. Firstly, based on the energy level of Er3+, the methods of realizing C+L band ASE output is presented. Then, the system configuration is designed. One 976nm LD is used for pumping, and the pump light, which is divided into two parts by one coupler, is pumped into two EDFs by wavelength division multiplexer (WDM). A fiber loop mirror (FLM) is used to improve working efficiency. Meanwhile, an optical isolator is used to avoid the effect of reflected wavelength from output facet. Finally, based on the mathematical model of the ASE gain, the length of EDF is discussed as well. In the experiment, by optimizing the length of EDF1 and EDF2, a 0.12m EDF1 and 16m EDF2 are adopted. In the end, the flatness of the spectra from 1540nm to 1610nm is ±0.91dB, and the flatness is ±1.65dB during 1520–1610nm without any filter. The high flattening C+L band ASE output is achieved by just one 976nm LD, which can optimize system and reduce the cost as well.

Simple aspects of femtosecond stimulated Raman spectroscopy

Femtosecond stimulated Raman spectroscopy (FSRS), using an overlapping pair of narrow band Raman pump and broadband probe pulses with heterodyne detection along the probe pulse direction, is a new nonlinear spectroscopic technique to record vibrational spectra of even highly fluorescent molecules and to study vibrational dynamics on excited electronic states of molecules, as in photoisomerization. FSRS is described by diagrammatic third-order perturbation theory with wave packet analysis. The phase matching condition gives rise to forty-eight terms for FSRS, but the resonant condition reduces it to just eight terms, which can be depicted by Feynman dual time-line diagrams, or closed time path loop diagrams, or the complementary four-wave mixing energy level diagrams. The eight terms fall into four sets-SRS(I), SRS(II), IRS(I), IRS(II)-where SRS stands for stimulated Raman scattering and IRS stands for inverse Raman scattering. The SRS(I) set can also account for spontaneous Raman scattering, but the remaining SRS(II), IRS(I) and IRS(II) terms are only present in stimulated scattering with the presence of a probe field. The SRS(I) set accounts for the Stokes Raman lines while the IRS(I) term accounts for the anti-Stokes lines, relative to the Raman pump frequency, in the FSRS spectrum. The remaining SRS(II) and IRS(II) terms give rise to broad baselines. Using a harmonic oscillator model, analytic results are obtained for the four-time correlation functions in the third-order polarizations. The issue of high time and high frequency resolution in time-resolved FSRS spectra is discussed. Calculations are made with the theory to compare with experimental results for: (a) resonance FSRS of fluorescent Rhodamine 6G and (b) 2D-FSRS from a coherent vibrational state that has been prepared by an impulsive, off-resonant pump pulse on CDCl3. The calculated results compared well with experimental results, and in the case of 2D-FSRS on CDCl3 there is a dominant cascade effect contributing to the FSRS spectra.

Quasienergy band engineering and broadband dynamic localization in photonic lattices with long-range interaction

Polychromatic dynamic localization in tight-binding lattices with long-range interaction is theoretically proposed and experimentally demonstrated in curved-waveguide photonic lattices. Efficient suppression of discrete diffraction over the whole white-light spectral region ($450\ensuremath{-}750$ nm) has been demonstrated in femtosecond-laser-written triangular-waveguide lattices with first- and second-order coupling.

Ka Band Broadband Fourth Harmonic Image Rejection Mixer

This paper presents the design and implementation of Ka band broadband hybrid integrated image rejection mixer with a fourth harmonic mixer as unit mixer. Detailed design and analysis have been carried out. The mixer was fabricated by hybrid microwave integrated circuit (HMIC) process based on the thin film ceramic substrate which can reduce the cost compared to monolithic microwave integrated circuit (MMIC). The measured results showed conversion loss less than 11.2 dB and image rejection ratio (IRR) more than 20 dB in 4 GHz RF bandwidth. It can also play the role of up-converter from the test data.

Synthesis of TLM-Based UWB Planar Monopole Impedance Bandwidth

A simple formula based on transmission line modeling (TLM) is proposed to determine the impedance bandwidth upper frequency limit for a staircase-profile planar monopole antenna. After a brief description of TLM analogy for planar monopoles, the formula is derived from a theoretical exposition. Accordingly, four prototypes are designed, implemented and measured in such a way that they are required to cover direct sequence ultrawideband (DS-UWB) first band (up to 4.85 GHz), UWB (up to 10.6 GHz) and possible future broadband systems (e.g., up to 15 and 21.4 GHz). The formula predicts this limit with a maximum error of 7.4% in the prototypes studied. The height of the antennas is chosen so that they help to filter WLAN 5 GHz band on the H-plane. This condition determines the lower impedance bandwidth limit (1.3 GHz for all of them). The resulting improvement on antenna system transfer functions (ASTF) is also discussed.

Instabilities driven by higher-order modes in a radio frequency system with a passive higher-harmonic cavity

The effect of a higher-order mode upon longitudinal beam stability in an electron storage ring is modeled analytically and with simulations. Narrow band parasitic modes and broadband impedance are considered for the Aladdin and MAX-II electron storage rings. The simulations confirm that a passive harmonic cavity strongly suppresses parasitic coupled-bunch instabilities, in agreement with the analytic model. In the long-bunch regime where the bunch length exceeds the vacuum pipe radius, analytic modeling and simulations indicate that a harmonic cavity also suppresses the microwave instability. In the short-bunch regime where the bunch length is smaller than the vacuum pipe radius, analytic modeling and simulations indicate that tuning in a harmonic cavity may worsen the microwave instability.

STS地震計による広帯域・広ダイナミックレンジ地震観測

Since late 1986, we have been operating a three-component set of STS seismometers (STS-1) at Inuyama Observatory, Nagoya University, Japan. This is a preliminary report of the two years observation. The STS-1 seismometer equips with three component BRB (BRoadband Band) outputs and three component LP (Long Period) outputs. The lowpass filtered LP outputs are digitized and recorded continuously at a sampling interval of 10s in a dynamic range of about 120dB. These continuous data have been used so far to determine seismic moment or centroid moment tensor of large Japanese earthquakes. The BRB output is recorded on an event recordering system, where the BRB and LP outputs after an eight-pole analog anti-aliased filtering are digitized and recorded for 50 minutes at sampling intervals of 0.1 and 0.4s, respectively. The dynamic range of this system is limited at present by the A/D converter to about 90dB. The triggered BRB data have been used so far to determine the source time functions of large Japanese earthquakes, which suggest the occurrence of backswing of fault motion. To maintain the horizontal component instruments in a stable condition, a care must be taken for variation of atmospheric pressure. The results of the analyses indicate a unique importance of nearby observation of large earthquakes by broadband, wide dynamic range and high precision seismometers such as the STS instruments.