Gain Variation Research Articles

Event‐Triggered Generalized Extended State Observer‐Based Control for Nonlinear Networked Systems Under Gain Variation and Multi‐Channel Attacks

ABSTRACTThis paper investigates the event‐triggered generalized extended state observer‐based estimation issue for a class of nonlinear networked control systems with unmodeled dynamics, external disturbances and multi‐channel attacks. In order to resist different forms of attack threats on multiple communication channels from sensors to the observer, Markov chain is introduced to describe the stochastic switching or jumping behavior between different attack modes. Considering the limited network resources, the measured outputs are transmitted to the observer only when the triggering conditions are met. Moreover, the parameters modeled by the Bernoulli process are adopted to help analyze potential random gain variations of the generalized extended state observer. By employing Lyapunov stability theory and stochastic systems analysis, sufficient conditions are derived to ensure that the augmented system is exponentially bounded in mean square, and the expected observer gains are further determined through linear matrix inequalities. Finally, a numerical example and a simulation related to the RLC series circuit system are conducted, illustrating the proposed method's effectiveness.

Single-Input Multiple-Output (SIMO) Cascode Low-Noise Amplifier with Switchable Degeneration Inductor for Carrier Aggregation.

This paper presents a single-input multiple-output (SIMO) cascode low-noise amplifier with inductive degeneration for inter- and intra-band carrier aggregation. The proposed low-noise amplifier has two output ports for flexible operation in carrier aggregation combinations for band 30 and band 7. However, during inter- and intra-band operation, gain variation occurs depending on the output mode. To compensate for this, a switching circuit is proposed to adjust the degeneration inductor, optimizing gain performance for both modes. The switching operation can minimize the control for the dynamic range in the receiver system to support carrier aggregation. The designed low-noise amplifier was fabricated using a 65 nm CMOS process, occupying an area of 2.1 mm2. In inter-band operation, the small-signal gain was measured by 18.9 dB for band 30 and 18.6 dB for band 7, with the noise figures of 1.03 dB and 1.07 dB, respectively. For intra-band operation, the small-signal gain was 17.3 dB and 17.2 dB, with the noise figures of 1.3 dB and 1.41 dB. The IIP3 values were measured by -7.6 dBm and -6.7 dBm for inter-band, and -6.3 dBm and -6.2 dBm for intra-band. Power consumption was 8.04 mW and 7.68 mW in inter-band, and 17.04 mW and 17.64 mW in intra-band depending on the output configuration.

A Compact V-Band Temperature Compensation Low-Noise Amplifier in a 130 nm SiGe BiCMOS Process.

This paper presents a compact V-band low-noise amplifier (LNA) featuring temperature compensation, implemented in a 130 nm SiGe BiCMOS process. A negative temperature coefficient bias circuit generates an adaptive current for temperature compensation, enhancing the LNA's temperature robustness. A T-type inductive network is employed to establish two dominant poles at different frequencies, significantly broadening the amplifier's bandwidth. Over the wide temperature range of -55 °C to 85 °C, the LNA prototype exhibits a gain variation of less than 1.5 dB at test frequencies from 40 GHz to 65 GHz, corresponding to a temperature coefficient of 0.01 dB/°C. At -55 °C, 25 °C, and 85 °C, the measured peak gains are 25.5 dB, 25 dB, and 24.4 dB, respectively, with minimum noise figures (NF) of 3.0 dB, 3.5 dB, and 4.2 dB, and DC power consumptions of 22.3 mW, 27.6 mW, and 34.4 mW. Moreover, the total silicon area of the LNA chip is 0.37 mm2, including all test pads, while the core area is only 0.09 mm2.

Simulation studies of charging-up effect for single GEMs

Many experiments revealed a charging-up effect inside the Gas Electron Multipliers (GEMs) holes, resulting in variation of GEM effective gain. Charge accumulation on the insulator surface inside the GEM hole (charge process) is involved in the present simulation models. With only the charge process in the simulation, a longer and larger gain stability of GEM was observed while comparing the charging-up curves to references, even distinct in the relatively high conductivity of GEM insulator. This observation indicates that charge transportation within the GEM insulator (discharge process) is non-negligible; the charging-up stability depends on the dynamic balance of the charge and discharge process. Therefore, a discharge model is induced and expressed by a piecewise function based on the presence of a simulation framework. Charging-up curves are compared for single GEMs with two different structures under different gain values and input flux; the trend from simulation with the discharge process is consistent with those from references. Although the deviation of simulated charging-up curves is observed at the region started to be stable, indicating improvements in the discharge formulation, it can still predict the trend of stability and values of GEM effective gain. This study improves the present simulation model of the charging-up effect for single GEMs and provides a reference for other charging-up models.

A 28 GHz balun‐first LNA with db‐linear 32 db gain range for 5 G applications

AbstractThis letter presents a 28 GHz balun‐first low noise amplifier (LNA) featuring a wide dB‐linear variable gain range. The architecture of LNA includes three‐stage cascode amplifiers. An integrated balun at the input stage provides RF ESD protection and converts a single‐ended signal to a differential one (S‐to‐D). A transformer‐based dual‐resonant matching network is designed and analyzed to achieve wideband performance. To realize a continuous dB‐linear variable gain range and consistent input/output matching, gain control is implemented in the second stage using a 5‐bit digital‐to‐analog converter (DAC) for a 32 dB gain range. The DAC can generate a nonlinear analog voltage to control the gate of the common‐gate transistor in the second cascode stage, inversely compensating for the nonlinear gain variations of the cascode amplifier. The LNA is fabricated in 65‐nm CMOS process with a core size of 0.154 mm². Measurement results exhibit a maximum gain of 33.5 dB and a minimum noise figure (NF) of 3.65 dB with a 3‐dB bandwidth of 23–29.5 GHz. The measured variable gain range is approximately 32 dB across 32 different gain states, with a linear gain step of ~1 dB per state and an IP1dB ranging from −6.5 dBm to −35.25 dBm. The power consumption is 35.4–48 mW from a 1.2 V supply voltage.

423 Comparative post-weaning performance characteristics of four breeds of rabbit in hot humid climate of Nigeria

Abstract Rabbits are one of the most popular livestock breeds raised for their meat, fur, and companionship. Rabbit meat is fast gaining prominence as a healthier meat compared with beef, mutton, pork and chevon, which are mostly consumed in Nigeria. This study investigated breed differences in mortality, survival rates and post-weaning growth rate of rabbits reared under inimical environmental conditions. The animals were fed commercially compounded feed with 18% crude protein and 2300Kcal metabolizable energy with intermittent feeding of Panicum sp and Tridax sp. The study area, located at latitude 6.5867° N and longitude 3.9700° E, had an average daily temperature of 35°C and relative humidity of 64%, which negatively impacted the adaptation, survival rates and growth performance of the rabbits. A total of 48 weaner rabbits 8 wk of age, comprising 12 each (9 does and 3 bucks) of Checkered, Chestnut, Dutch and Hyla breeds were reared for 10 wk post-weaning. Mortality was recorded across the breeds and the body weights (BW) of the rabbits were also recorded on a weekly basis for the entire 10-wk period. The study evaluated survival rates across breeds and sex and BW gain. Statistical analyses were conducted using the Minitab software for Chi Squared test of independence for counts and descriptive statistics and general linear model analysis of variance for bodyweight gain. The statistical model describing the analysis was Yijk = µ + αi + (α:β)ij + eijk where αi is the ith fixed effect of breed and βj is the jth fixed effect of sex. The model accounted for 67.03% variation in total weight gain. Further mean separation was done using the Tukey’s multiple comparison procedure. Mortality rates across breeds on the average was 56.25%, with Checkered, Chestnut, Dutch and Hyla respectively recording 66.67%, 41.67%, 50.00% and 66.67% mortality, respectively. Mortality rate across sexes was 63.89% for does and 33.33% for bucks; however, mortality rates were independent (P > 0.05) of both breed and sex with a Chi-Squared value of 2.285 and 3.41, respectively, despite the numerical differences in mortality rates across breeds and sexes. Average total BW gain during the study period across the breeds and within breeds is as presented in Table 1. The nesting of sex within breed revealed that the only significant (P > 0.05) difference was noticed between the Hyla buck and Chestnut doe, while other means were not statistically different (P > 0.05). The Chestnut breed with the least BW gain adapted well in the environment with greatest survival rate, while the Hyla breed had the greatest BW gain and least survival rate throughout the study. This study indicated a negative relationship between survival rates and BW gain, that lighter breeds of rabbit tend to have greater survival rates than the heavier breeds.

Effect of inorganic compound size on the relative gain of polymer-based optical waveguide amplifiers

Polymer based waveguide amplifiers are the key devices to improve the performance of integrated communication systems. However, due to their comparatively low relative gain, their widespread practical application has been limited. In polymer based optical waveguide amplifiers, the size of inorganic compounds in the composite gain media has a significant impact on the gain performance of the amplifier. Up to now, there has been limited research on the size influence of inorganic compound on the gain variation in organic polymer based optical waveguide amplifiers. In this study, a series of NaLu0.8-xYxF4: Yb, Er-PMMA composite polymer were used as gain media to prepare organic waveguide amplifiers working in the C-band (1530–1565 nm). The size of NaLu0.8-xYxF4: Yb, Er compounds varies between 20 nm and 150 nm. In the polymer based optical waveguide amplifiers, variations in the size of the inorganic NaLu0.8-xYxF4:Yb,Er compound affects not only the C-band emission intensity but also the relative gain. When the size of the inorganic compound is 65 nm, the composite gain media exhibits the maximum emission peak intensity at 1550 nm and the corresponding device achieves a maximum relative gain of 19.3 dB/cm. Our results show that the size of inorganic compounds affects the variation of luminescence intensity and ultimately the gain of waveguide amplifiers. The gain of future polymer optical waveguide amplifiers can be improved by this method.

Low-gainer diet-induced obese microbiota transplanted mice exhibit increased fighting.

Weight gain variation is a great challenge in diet-induced obesity studies since low-gainer animals are of limited experimental value. The inbred C57BL/6 (B6) mice are frequently used models due to their genetic homogeneity and susceptibility to diet-induced obesity (DIO). The aim of this study is to investigate if the gut microbiota (GM) influences the fraction of low weight gainers in DIO studies. A total of 100 male B6 mice (donor population) were fed a high-fat diet for 14 weeks and divided into the study groups high gainer (HG) and low gainer (LG) based on their weight gain. Subsequently, fecal matter transplantation (FMT) was done on germ-free B6 mice with GM from HG and LG donors (FMT population). LG (13.35 ± 2.5 g) and HG (25.52 ± 2.0 g) animals were identified by the weight gain from week 1 to week 12. Interestingly, the start weight of the LG (20.36 ± 1.4 g) and HG (21.59 ± 0.7 g) groups differed significantly. Transplanting LG or HG fecal matter to germ-free mice resulted in significant differences in weight gain between HG and LG, as well as differences in serum leptin levels and epididymal fat pad weight. A clear LG-specific GM composition could not be distinguished by 16S rRNA gene amplicon sequencing. Surprisingly, significantly more fighting was recorded in LG groups of both donor populations and when transplanted to germ-free mice. The HG and LG phenotypes could be transferred to germ-free mice. The increased fighting in the LG group in both studies suggests not only that the tendency to fight can be transferred by FMT in these mice, but also that fighting should be prevented in DIO studies to minimize the number of LG animals.

Spatial Nonuniformity of Photoresponse in SiC UV Avalanche Photodiodes Operating in Linear and Geiger Mode

Silicon Carbide's intrinsic material properties, along with the availability of low-defect density, 6" substrates, make it an attractive material system for visible-blind ultraviolet (UV) detectors. Avalanche photodiodes (APDs) made from SiC have been shown to operate both as linear mode detectors with high gain (>10⁷) and as single-photon avalanche detectors (SPADs) with competitive photon detection efficiency. However, reported spatial non-uniformities in photoresponse of these devices will reduce sensitivity [1,2].In this paper, we examine the impact of device geometry, epitaxial variations, and crystal anisotropy on the spatial uniformity of photoresponse in SiC APDs. Photoresponse maps are generated using a fast 285 nm pulsed LED source that is tightly focused to a ~10 µm spot. Response maps are measured for devices with different geometries fabricated on the same chip in both linear-mode and Geiger-mode. Measurements on standard pin diodes will be presented, along with separate absorption, charge, and multiplication (SACM) structures.Experimental results indicate that all devices exhibit localized regions of high photoresponse at gain > 1000 and that the spreading of the photoresponse is highly directional. Finger diodes with 120 μm x 30 μm mesas exhibit good response uniformity with a variation < 30% across the device. In contrast, diodes with 60 and 90 μm square-shaped mesas exhibit similar uniform response spreading along one edge that is bounded by the size of the mesa, but a >10x drop in relative response over ~30-40 μm in the orthogonal direction which is much shorter than the extent of the mesa. Devices with 100 μm circular mesas exhibit somewhat similar results to the square diodes, but with the presence of multiple hot spots in response.Experimental results are analyzed through 3D numerical modeling of devices which accounts for the effects of doping and thickness variations across the substrate as well as the anisotropy of impact ionization. Modeling indicates that small variations in the thickness in the drift regions of a diode can yield meaningful variations in avalanche gain across the mesa. The impact of anisotropic impact ionization will be considered using full-band 3D Monte Carlo calculations. X. Bai, H.-D. Liu, D. C. McIntosh and J. C. Campbell, "High-Detectivity and High-Single-Photon-Detection-Efficiency 4H-SiC Avalanche Photodiodes," IEEE J. Quantum Electron. 45 300-303 (2009). DOI: 10.1109/JQE.2009.2013093.L. Su et al, "Recent progress of SiC UV single photon counting avalanche photodiodes," J. Semicond. 40 121802 (2019). DOI: 10.1088/1674-4926/40/12/121802. Figure 1

H-plane gap-RGW horn antenna with very low side lobe level

This paper presents and applies a new concept of gap-RGW to develop a new configuration for RGW H-plane horn antennas. The proposed antenna is fully metallic and can generate a very low side-lobe level along with a flat gain response over a reasonable bandwidth, which is one of the advantages of this antenna. A prototype of the presented structure is designed and fabricated which provides the impedance bandwidth (S11 < − 10 dB) of about 25% with SLL < − 20 dB and 2 dB gain variation over the operating bandwidth.

Relative intensity noise management and thermal/shot noise control for high speed ultra high bandwidth fiber reach transmission performance

Abstract This work has clarified the relative intensity noise management and thermal/shot noise control for high speed ultra high bandwidth fiber reach transmission performance. Total link losses variations are clarified against ambient temperature and relative refractive index difference variations at 1,550 nm wavelength, 20 km fiber link length, and 45 % fluoride dopant ratio inside the fiber material cable. Besides the total link losses variations are demonstrated versus fiber link length and relative refractive index difference variations at 1,550 nm wavelength, room temperature, and 45 % fluoride dopant ratio inside the fiber material cable. Required optical signal per noise ratio (OSNR), electronic signal to noise ratio (SNR), and optimum gain variations are measured and analyzed versus the fiber link length and relative refractive index difference variations at 1,550 nm wavelength, room temperature, and 45 % fluoride dopant ratio inside the fiber material cable.

Theoretical proposal for a broadband on-chip multistage quantum amplifier

A broadband on-chip multistage quantum amplifier (MQA) for reading out multiple superconducting qubits is proposed. The bandwidth of quantum amplifier is enhanced by concatenating amplifiers with modular nonreciprocal elements, which are superconducting isolators and circulators based on tunable inductor bridge. The circuit model of MQA is built and simulated. The variation of bandwidth, gain and gain-bandwidth product (GBP) of MQA with the number of stages and bandpass of the constitutive amplifiers are simulated. It is revealed that the bandwidth can be as large as ∼3.2 GHz with a gain of 20 dB at 4–8 GHz frequency range. For a 4-stage MQA composed of four quantum amplifiers with 20 dB gain and 0.3 GHz BW-pass, the bandwidth is 2.14 GHz at 20 dB gain, which is quite cost-efficient. Due to its non-reciprocity, MQA can effectively prevent signals from reflecting to quantum processors. In addition, MQA breaks the limitation of GBP and is easy to integrate with superconducting circuits. The MQA would play a crucial role in the high-fidelity readout of multiple qubits in large-scale superconducting quantum computers.

High-gain mmWave shorted rectangular ring antenna with complementary segmented-cavity backed structure

An efficient gain-enhancement technique for millimeter wave (mmWave) planar patch antennas (PPAs) using a novel slot-loaded and segmented-cavity backed structure is newly proposed in this study. By incorporating a main radiator with a rectangular slot and employing a muli-layered segemented-cavity, the proposed antenna design significantly increases antenna gain beyond conventional approaches. Unlike traditional patch antennas or those with shorting pin structures, our gain-enhanced PPA utilizes the rectangular slot to electrically expand the radiation aperture, while the addition of substrate integrated pillars acorss multiple segmented ground layers markedly improves antenna directivity. The strategric use of a segmented cavity not only facilitates flexible impedance matching but also ensures consistent performance within the n257 band, accompanied by minimal gain variation. To verify the gain enhancement from the conventional patch, the proposed antenna was fabricated with a size of 1.03 λ0 × 1.03 λ0 × 0.1 λ0 at 28 GHz. The measured 10-dB impedance bandwidth was 12.14 % with a maximum measured gain of the 11.28 dBi at 28 GHz. Compared to the measured gain of the conventional PPA with the same size, the gain was 39.6 % higher, which represents the highest gain per total antenna volume observed for a single PPA in the mmWave spectrum for high-gain applications, to the best of our knowledge.

A novel programmable gain control low noise amplifier (PGCLNA) design for automatic gain control loop in BLE applications

Bluetooth low energy (BLE) is a widely used short-range communication protocol and BLE receivers frequently encounter transient high-power RF (radio frequency) signals from antennas, leading to receiver saturation. To address this issue, this work proposes a 2.4 GHz programmable gain control low-noise amplifier (PGCLNA), which is a key element in an automatic gain control (AGC) system for BLE receiver applications. The proposed PGCLNA achieves discrete levels of gain using the g m -boosting technique by splitting the negative feedback. The proposed circuit is simulated in UMC 180 nm technology and the maximum gain achieved is 41.4 dB, with a step decrease of 15 dB in discrete levels. The gain variations do not degrade the performance of S11, which is always less than -16 dB. The noise figure (NF) is always minimum of 5.5 dB and in high gain mode, the minimum value of NF is 1.82 dB. The third-order intercept point (IIP3) is −7.621 dBm in the best circumstances and always remains above −10.69 dBm. These results are achieved by utilising 5.4 mW power at 1.8 V of supply voltage. The circuit occupies an area of 732 μm × 771 μm. The proposed PGCLNA design offers a solution to accommodate a wide range of input signals in BLE receivers, excellent gain control, low noise and robust performance characteristics, making it an essential component in an AGC system for BLE receiver applications.

Analysis of Diffracted Mode Outcoupling in the Context of Amplified Spontaneous Emission of Organic Thin Films.

The existence of amplified spontaneous emission (ASE) is a fundamental principle of laser dyes. ASE indicates the spectral variation of the optical gain of a laser dye. Analyzing the spectral distribution of ASE is important for designing lasers. We demonstrate ASE investigations on planar waveguides made of a (co-)polymer. Similar to organic DFB (distributed feedback) lasers, a line grating allows a partial decoupling of the guided radiation. This decoupled radiation is detected as an indicator of the guided radiation. The diffraction of the radiation is utilized to perform a spectrally selective investigation of the ASE by spatially splitting it. This analysis method reduces the influence of isotropic photoluminescence and allows ASE to be analyzed across its entire spectrum. We were able to observe ASE in F8BT over a range from λASE,min = 530 nm to λASE,max = 570 nm and determine ASE threshold power densities lower than EASE< 2.57 μJ/cm2. The study of the power density of the ASE threshold is performed spectrally selectively.

Widening Multi‐Beam Scan Angle of Conventional Waveguide Lens Antennas by Increasing Focal Points for Multi‐Feed Excitations

AbstractThis paper presents an alternative approach to improve the achievable beam scan angle of a traditional multi‐beam waveguide lens antenna. Due to the focusing mechanism by manipulating the geometrical curvatures of the waveguide lens, the angular scan range is limited in the conventional waveguide lens design using dual‐focal points of excitations because the geometrical curvatures of the waveguide lens only provide two design freedoms. To overcome this limitation, a solution of treating the waveguide lens as a transmit array consisting of non‐identical elements is proposed so that each element of the antenna array can be well calibrated to improve the maximum scan angular range, where a third focus point of excitation can be created by adding another design freedom from the differentiation between non‐identical elements. Each element of this new transmitting array can be well calibrated with the help of a mathematical expression to improve the maximum angular scan range. Numerical simulations show that the proposed antenna architecture exhibits better radiation characteristics than the traditional waveguide lens antenna. Radiation characteristics are studied and compared for both types of lens antennas to validate the design concept. The proposed triple‐focal point provides a higher gain than the traditional lens antenna with fewer antenna elements. The gains of the beams at ±10°, ±20°, ±30°, and ±40° are found to be 27.78, 26.94, 26.19, and 24.04 dBi, respectively. From the comparison, it is seen that the variation in gain by the proposed triple‐focal array design is more stable than the conventional dual‐focal point design.

Genome-wide identification and phylogenetic analysis of the tetraspanin gene family in lepidopteran insects and expression profiling analysis in Helicoverpa armigera.

The tetraspanin gene family encodes cell-surface proteins that span the membrane 4 times and play critical roles in a wide range of biological processes across numerous organisms. Recent findings highlight the involvement of a tetraspanin of the lepidopteran pest Helicoverpa armigera in resistance to Bacillus thuringiensis Cry insecticidal proteins, which are extensively used in transgenic crops. Thus, a better understanding of lepidopteran tetraspanins is urgently needed. In the current study, genome scanning in 10 lepidopteran species identified a total of 283 sequences encoding potential tetraspanins. Based on conserved cysteine patterns in the large extracellular loop and their phylogenetic relationships, these tetraspanins were classified into 8 subfamilies (TspA to TspH). Six ancestral introns were identified within lepidopteran tetraspanin genes. Tetraspanins in TspA, TspB, TspC, and TspD subfamilies exhibit highly similar gene organization, while tetraspanins in the remaining 4 subfamilies exhibited variation in intron loss and/or gain during evolution. Analysis of chromosomal distribution revealed a lepidopteran-specific cluster of 10 to 11 tetraspanins, likely formed by tandem duplication events. Selective pressure analysis indicated negative selection across all orthologous groups, with ω values ranging between 0.004 and 0.362. However, positive selection was identified at 18 sites within TspB5, TspC5, TspE3, and TspF10. Furthermore, spatiotemporal expression analysis of H. armigera tetraspanins demonstrated variable expression levels across different developmental stages and tissues, suggesting diverse functions of tetraspanin members in this globally important insect pest. Our findings establish a solid foundation for subsequent functional investigations of tetraspanins in lepidopteran species.

Quantifying and mitigating recorder-induced variability in ecological acoustic indices

Due to the complexity of soundscapes, Ecological Acoustic Indices (EAI) are frequently used as metrics to summarize ecologically meaningful information from audio recordings. Recent technological advances have allowed the rapid development of many audio recording devices with significant hardware/firmware variations among brands, whose effects in calculating EAI have not yet been determined. In this work, we show how recordings of the same landscape with different devices effectively hinder reproducibility and produce contradictory results. To address these issues, we propose a preprocessing pipeline to reduce EAI variability resulting from different hardware without altering the target information in the audio. To this end, we tested eight EAI commonly used in soundscape analyses. We targeted three common cases of variability caused by recorder characteristics: sampling frequency, microphone gain variation, and frequency response. We quantified the difference in the probability density functions of each index among recorders according to the Kullback-Leibler divergence. As a result, our approach reduced up to 75% variations among recorders from different brands (AudioMoth and SongMeter) and identified the conditions in which these devices are comparable. In conclusion, we demonstrated that different devices effectively affect EAI and show how these variations can be mitigated.

Gain variations as induced by the diffuse night sky background: the ASTRI-Horn experience

ASTRI-Horn is the prototype of the nine telescopes that form the ASTRI Mini-Array, under construction at the Teide Observatory in Tenerife (Spain), devoted to observe the sky in the 1–200 TeV energy band. It adopts an innovative optical design based on a dual-mirror Schwarzschild-Couder configuration, and the camera, composed by a matrix of monolithic multipixel silicon photomultipliers (SiPMs) is managed by ad-hoc tailored front-end electronics based on a peak-detector operation mode. During the Crab Nebula campaign in 2018–2019, ASTRI-Horn was affected by gain variations induced by high levels of night sky background. This paper reports the work performed to detect and quantify the effects of these gain variations in shower images. The analysis requested the use of simultaneous observations of the night sky background flux in the wavelength band 300–650 nm performed with the auxiliary instrument UVscope, a calibrated multi-anode photomultiplier working in single counting mode. As results, a maximum gain reduction of 15% was observed, in agreement with the value previously computed from the variance of the night sky background level in each image. This ASTRI-Horn gain reduction was caused by current limitation of the voltage supply. The analysis presented in this paper provides a method to evaluate possible variations in the nominal response of SiPMs when scientific observations are performed in the presence of high night sky background as in moon conditions.

RCS-reduced patch antenna with wide frequency tuning range based on absorbing metasurface

A frequency-tunable patch antenna with reduced radar cross section (RCS) based on absorbing metamaterial is proposed. By controlling the external voltage of the varactor diodes, the working frequency of the patch can be adjusted. Through an investigation of the composite structure of the patch and absorbing metamaterial, RCS reduction is achieved over the entire wide tunable frequency range of the antenna. Measured results illustrate that the proposed patch antenna can dynamically operate in the range from 2.28 to 3.6 GHz with a gain variation of 7.1–8.7 dBi. Meanwhile, the RCS can be reduced by at least 7 dB and up to 20 dB in a fractional bandwidth of 44.9% of the antenna under a normal incidence. In comparison to conventional RCS-reduced antennas, the proposed one features a broader frequency tuning range and has potential value in wideband radar systems under complex electromagnetic interference environments.