Narrow-band filter for satellite communication systems

Design narrow-band compact filters, based on high-quality waveguide-dielectric resonators with anisotropic materials is the subject of this paper. Filter represents a segment of a rectangular waveguide rotated around the longitudinal axis of the waveguide 90 degrees and containing one or more dielectric inserts that completely fill the resonator along the narrow wall of the waveguide and partially along the wide one. A distinctive feature of the proposed filter is higher slope steepness of the amplitude-frequency characteristic, and high manufacturability in the centimeter range. The designed narrow-band filter satisfies contradictory requirements: it combines narrow bandwidth (≈ 0.1% of center frequency <em>f</em>₀) with low passband insertion loss (≤ 1 dB).

Propagating characteristics of mesospheric gravity waves observed by an OI 557.7 nm airglow all-sky camera at Mt. Bohyun (36.2°N, 128.9°E)

We analyzed all-sky camera images observed at Mt. Bohyun observatory (36.2°N, 128.9°E) for the period of 2017–2019. The image data were acquired with a narrow band filter centered at 557.7 nm for the OI airglow emission at ~96 km altitude. The total of 150 wave events were identified in the images of 144 clear nights. The interquartile ranges of wavelength, phase speed, and periods of the identified waves are 20.5–35.5 km, 27.4–45.0 m/s and 10.8–13.7 min with the median values of 27.8 km, 36.3 m/s and 11.7 min, respectively. The summer and spring bias of propagation directions of northeast- and northward, respectively, can be interpreted as the effect of filtering by the prevailing winds in the lower atmosphere. In winter the subdominant northwestward waves may be observed due to nullified filtering effect by small northward background wind or secondary waves generated in the upper atmosphere. Intrinsic phase speeds and periods of the waves were also derived by using the wind data simultaneously observed by a nearly co-located meteor radar. The nature of vertical propagation was evaluated in each season. The majority of observed waves are found to be freely propagating, and thus can be attributed to wave sources in the lower atmosphere.

CONTROLLED GENERATORS ON SAW FILTERS AND OF SYNTHESIZED NONLINEAR INDUCTANCE

Проведены исследования качественных характеристик однокаскадных частотно-модулированных (ЧМ) генераторов, выполненных на однокаскадном усилителе по схеме с общим коллектором и узкополосным фильтром на поверхностных акустических волнах (ПАВ) при использовании в качестве управителя частоты синтезированной нелинейной индуктивности (СНИ). Получены расчетные соотношения для определения девиации основной частоты, уровня нелинейных искажений для третьей и пятой гармоник и крутизны модуляционной характеристики, которая практически постоянна как при перестройке генератора по частоте, так и изменении уровня модулирующего сигнала. В результате этого в процессе модуляции уровень паразитной амплитудной модуляции не повышается, что обеспечивает высокую частоту спектра формируемого ЧМ радиосигнала. Проведен анализ полученных технических характеристик, который показал, что исследуемый формирователь ЧМ сигнала при управлении напряжением СНИ практически не создает сдвига центральной частоты, который приводит в процессе модуляции к уменьшению стабильности частоты. Установлено, что при девиации основной частоты около 90 кГц коэффициент нелинейных искажений по третьей и пятой гармоникам составляет менее 1 % и 0.1 % соответственно. Это соизмеримо с уровнем нелинейных искажений ЧМ генератора, в котором в качестве управителя частоты используются варакторы с резким законом изменения вольтфарадной характеристики, обеспечивающей минимально возможные нелинейные искажения при модуляции генераторов с помощью варакторов и практически полным отсутствием этих искажений на четных гармониках We investigated qualitative characteristics of the single-stage FM generators made on a single-stage amplifier according to the scheme with a common collector and a narrow-band filter on surface acoustic waves (SAW) using synthesized nonlinear inductance (SNI) as a frequency controller. We obtained the calculated ratios for base frequency deviation, level of nonlinear distortions for third and fifth harmonics and slope of modulation characteristic, which is practically constant both during generator tuning by frequency and change of level of modulating signal. As a result, during modulation, the level of parasitic amplitude modulation does not increase, which provides a high purity of the spectrum of the generated FM radio signal. We carried out an analysis of the obtained technical characteristics, which showed that the FM signal generator under the control of the SNI voltage practically does not create a central frequency shift, which leads to a decrease in frequency stability during modulation. We found that when the main frequency deviates about 90 kHz, the non-linear distortion coefficient for the third and fifth harmonics is less than 1% and 0.1%, respectively. This is comparable to the level of non-linear distortion of the FM generator, in which varactors with a sharp law of changing the voltfarade characteristic are used as a frequency controller, which provides the minimum possible non-linear distortion when modulating generators using varactors and the almost complete absence of these distortions on even harmonics

Ultra-Narrow-Band Filter Based on High Q Factor in Metallic Nanoslit Arrays

Here we propose a novel high Q ultra-narrow-band filter in the optical regime. Multiple high Q resonances are achieved in ultra-thin metallic nanoslit arrays on stacked low index–high index dielectric (LID–HID) substrate. Based on the cooperative effect of suppressed modes and transmission modes, the high spectral resolution of transmission peaks is obtained. The number and Q factor of transmission peaks can be freely manipulated by a simple combination of the stacked LID–HID. It is demonstrated that the linewidths of the transmission peaks can be reduced down to the extreme limit of 1 nm and the Q factor is up to 700 by optimizing the structure parameter of the three-layer LID–HID. The results provide a theoretical basis to design a multi-band nanophotonic device with a high Q factor and have potential applications in the next generation of high-resolution plasmonic biosensing and filtering.

Hydrogen recombination near-infrared line mapping of Centaurus A with IRSF/SIRIUS

Centaurus A (Cen A) is one of the most famous galaxies hosting an active galactic nucleus (AGN), where the interaction between AGN activities and surrounding interstellar and intergalactic media has been investigated. Recent studies reported detections of Hα emission from clouds in the galactic halo toward the northeast and southwest of the nucleus of Cen A, suggesting that AGN jets may have triggered star formation there. We performed near-infrared line mapping of Cen A with the IRSF 1.4 m telescope, using the narrow-band filter tuned for Paβ, from which we find that Paβ emission is not detected significantly from either of the northeast or southwest regions. The upper limit of the Paβ/Hα ratio in the northeast region is compatible with that expected for a typical H ii region, in line with the scenario that AGNs have triggered star formation there. On the other hand, the upper limit of Paβ/Hα in the southwest region is significantly lower than that expected for a typical H ii region. A possible explanation of the low Paβ/Hα ratio in the southwest region is the scattering of Hα and Paβ photons from the center of Cen A by dust grains in the halo clouds. From the upper limit of Paβ/Hα in the southwest region, we obtain constraints on the dust size distribution, which is found to be compatible with those seen in the interstellar medium of our Galaxy.