Gain Fluctuations Research Articles

A Shaped-Beam Antenna for Wide-Angle Scanning Phased Array

A phased array usually suffers from severe gain drop when its beam steers in a wide range. In this article, an alleviating technique based on a gain-compensating approach is proposed. Isolated element pattern (IEP) and array factor are jointly considered. When calculating the array factor, mutual couplings between antennas in an array are also included. The IEP is optimized in such a way that the element gain is nearly inversely proportional to the peak gain of the array factor. As a result, the peak gain of the overall array beam can be kept almost the same in a wide scanning range. As an example, a cylindrical dielectric resonator antenna (DRA) array is investigated. In such a design, a dip is introduced to the top of the element pattern so that the top peak in the array factor envelope can be compensated. This idea is demonstrated by using an X-band cylindrical DRA, with its beam shaped by using a loading peripheral metal ring and two top dielectric slabs. This shaped-beam DRA element is used to construct a nine-element H-plane linear phased array. The element and array prototypes were fabricated and measured, and reasonable agreement between the measured and simulated results is observed. The measured 3-dB beamwidths of the DRA element are 172° and 149° in the E- and H-planes, respectively. It is found that the H-plane main beam of the DRA array can scan from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$- \mathrm{72}^{\circ }$ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$+ \mathrm{72}^{\circ }$ </tex-math></inline-formula> with a small gain fluctuation of less than 0.9 dB.

Hidden Markov model based non-fragile sampled-data control design for mode-dependent fuzzy systems with actuator faults

This paper investigates the dissipativity-based asynchronous sampled-data control design for a class of Takagi–Sugeno fuzzy Markovian jump systems along with time delay, gain fluctuations, and actuator failures. To do this, the hidden Markov model is introduced to describe the phenomenon of asynchronization between the controller and the given fuzzy jump systems. Then, a novel mode-dependent Lyapunov–Krasovskii functional is constructed to achieve the stability conditions and expand the maximum sampling period of fuzzy systems. The main purpose of this study is to design the asynchronous non-fragile reliable control with sampled-data information such that the mode-dependent fuzzy system is stochastically stable and possesses the dissipativity performance. For this, a sufficient condition is derived for the proposed system in the form of linear matrix inequalities. Meanwhile, the less conservative results and the desired controller are attained by solving the inequalities. At last, the validity and the superiority of our design technique are demonstrated by numerical examples.

Optical sensor using space-domain active fiber cavity ringdown technique

A novel active fiber cavity ringdown (FCRD) technique using frequency-shifted interferometry (FSI) is proposed for the first time. Using this scheme, external parameters can be monitored in the space domain by measuring the ringdown distance instead of ringdown time. A bidirectional erbium-doped fiber amplifier (Bi-EDFA) is employed to compensate the inherent cavity loss for achieving higher sensitivity. And two band-pass filters are used to reduce the amplified spontaneous emission (ASE) noise of the Bi-EDFA. Compared with the well-known time-domain active FCRD scheme, our proposed method enables us to avoid using pulsed laser needed in time-domain active FCRD, it uses continuous-wave laser to inject into the fiber cavity and stabilize the optical power in the fiber cavity, which can suppress the baseline drift of ringdown signal caused by the gain fluctuations of the EDFA and thus improve the detecting precision. Moreover, this novel method enables us to use differential detection method for further reducing the ASE noise, and thus eliminating the baseline drift of ringdown signal. A magnetic field sensor was developed as a proof-of-concept demonstration. The experimental results demonstrate that the proposed sensor with a sensitivity of 0.01537 (1/km·Gs) was achieved. This is the highest magnetic field sensitivity compared to the time-domain active FLRD method. Due to the reduced ASE noise, the stability of the proposed sensing system was also greatly improved.

Nonfragile Sampled-Data Control of T–S Fuzzy Systems With Time Delay

To reduce the influence of controller uncertainties and lower the computational burden of the system, a novel nonfragile sampled-data control scheme is proposed in this article for the Tagaki–Sugeno fuzzy system with time delay. First, an improved Lyapunov–Krasovskii functional is established with adjusted looped functional, which contains not only the current states, but the delayed states. Then, utilizing the Wirtinger inequality and improved single integral inequality, the new stability criteria are proposed with less conservativeness. By calculating the solution of linear matrix inequalities, the nonfragile controller parameters can be acquired. Furthermore, the sampled-data fuzzy controller leads to a good stable performance for the system, even under the possible gain fluctuations. Finally, three examples are given to verify the effectiveness and superiority of the proposed control scheme.

Robust non-fragile boundary control for non-linear parabolic PDE systems with semi-Markov switching and input quantization

In this paper, the robust boundary control problem for non-linear PDE systems is discussed. Specifically, the PDE under investigation is of parabolic type with semi-Markov jumping signals subject to non-linearities and parameter uncertainties. The main goal of this paper is to devise a non-fragile boundary control law which assures the robust stabilization of the addressed system in spite of gain fluctuations and quantization in its design. In particular, to reduce the burden in the communication medium, the input signals can be quantized before transmitted to the actuator by using logarithmic quantizers. Moreover, by utilizing the Lyapunov stability theory and vector-valued Wirtinger’s inequality, a set of sufficient conditions for robust stabilization of the underlying system is established in the form of linear matrix inequalities (LMIs). Based on the obtained conditions, the existence of the desired controller is confirmed and an explicit form of the controller gains are developed. Eventually, the efficacious of the extracted theoretical results are manifested by virtue of two simulation examples.

Pattern-Reconfigurable Dielectric Resonator Antenna With Endfire Beam-Scanning Feature

A novel pattern-reconfigurable dielectric resonator (DR) antenna with endfire beam-scanning feature is proposed in this letter. The proposed antenna consists of a DR, a switchable director with 10 p-i-n diodes, and a differential feeding structure. The differential-fed DR operating in TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01δ</sub> mode can provide a primary endfire pattern with wide beam. Based on this, a large-coverage beam-scanning performance can be obtained by introducing a switchable director placed in front of the DR. A prototype is fabricated and measured to verify the proposed design. By switching the p-i-n diodes of the switchable director, the proposed antenna enables a near-continuous beam scanning from −48° to +48° in the azimuth plane with a gain fluctuation of less than 0.5 dB. Besides, the 3 dB scanning coverage is up to 164° (from −82° to +82°), which shows good beam-scanning performance.

A broadband bifocal conformal transmitarray antenna with wide scanning angles

AbstractTransmitarray (TA) antenna has great research value based on its unique advantages of low profile, high gain, and flexible performance, especially in the field of spaceborne, airborne, and unmanned aerial vehicles. Unfortunately, traditional TA antennas are usually of flat structures, which lack conformal flexibility and installation simplicity in certain complex application scenarios. In this letter, a broadband bifocal conformal TA antenna is proposed based on a designed concave‐cylindrical‐shaped triple‐layer TA surface with phase modulation capability. The broadband bifocal conformal TA antenna is simulated, fabricated, and measured by assembling the TA surface with a dual‐mode conical horn as a feed antenna. To better demonstrate the beam scanning stability of the bifocal TA antenna, a monofocal TA antenna is designed and simulated as a comparison. Simulation and experimental results confirm that the proposed bifocal conformal TA antenna can achieve a high gain of 24.4 dBi at 30 GHz and a 3‐dB gain bandwidth of 13.3% (27.4–31.3 GHz) under normal incidence. Antenna peak gain fluctuation is less than 1 dB with a maximum beam scanning range of , which is much more stable than that of the monofocal TA antenna (3.6 dB). The proposed design can be a promising candidate in many military and civilian application scenarios.

Networked control systems with probabilistic time-varying delay based on event-triggered non-fragile [formula omitted] control

The non-fragile H∞ problem for networked control systems with probabilistic time-varying delay, stochastic nonlinear, controller gain fluctuation and adaptive event-triggered mechanism is studied. The random interval delay, nonlinear fluctuation and gain fluctuation of the controller all obey a certain uncorrelated Bernoulli distribution white noise sequence. An improved time continuous delay system model for networked control systems is constructed by using input delay method. A two-sided closed-loop Lyapunov–Krasovskii functional is constructed considering the sawtooth structure of artificial time delay, and the asymptotically stable conditions of closed-loop system with little conservatism are obtained. A non-fragile H∞ control strategy based on adaptive event-triggered is proposed and the co-design method for gain matrix of the non-fragile controller and event-triggered matrix is obtained. Finally, the effectiveness of the proposed method is verified by two simulation examples.

The Effects of Neural Gain on Reactive Cognitive Control

Fluctuations in global neural gain, arising from brainstem arousal systems, have been found to shape attention, learning, and decision-making as well as cortical state. Comparatively, little is known about how fluctuations in neural gain affect cognitive control. In the present study, we examined this question using a combination of behavioral methods, pupillometry, and computational modeling. Simulations of a comprehensive model of the Stroop task incorporating task conflict and both proactive and reactive forms of control indicated that increasing global gain led to an overall speeding of reaction times, increased Stroop interference, and decreased Stroop facilitation. Pupil analyses revealed that the pre-trial pupil derivative (i.e., rate of change), a putative non-invasive index of global gain, showed the same diagnostic relationships with the Stroop-task performance of human participants. An analysis of the internal model dynamics suggested that a gain-related increase in task conflict and corresponding (within-trial) increase in reactive control are vital for understanding this pattern of behavioral results. Indeed, a similar connectionist model without this task-conflict-control loop could not account for the results. Our study suggests that spontaneous fluctuations in neural gain can have a significant impact on reactive cognitive control.

Encoding–decoding strategy based resilient state estimation for bias-corrupted stochastic nonlinear systems

This paper is concerned with the resilient state estimation problem for a type of stochastic nonlinear systems, in which the possible dynamical bias is considered that is depicted by a dynamical equation. In pursuit of enhancing the robustness of the propagated data, a binary encoding strategy (BES) is exploited in the binary symmetric channel (BSC). While the random bit errors caused by the channel noise may take place during the propagation of the binary bit string via the memoryless BSC. To characterize the occurrence of the bit errors, a series of Bernoulli distributed random variables is adopted. More specifically, in order to deal with the possible gain fluctuation of the estimator in the execution process, a resilient state estimator is employed. This paper intends to put forward a novel resilient estimation scheme under the BES, which can assure that the estimation error dynamics is exponentially ultimately bounded in mean square. A sufficient criterion is first acquired for the existence of the expected resilient estimator and the estimator parameter is achieved by solving a convex optimization problem. Finally, an illustrative simulation example is provided to verify the validity of the theoretical results.

A phased array design using a novel pattern reconfigurable antenna element

A novel pattern reconfigurable patch antenna is proposed. For the proposed antenna, the surface of the radiation patch is vertical to the ground plane, and it can be considered as a one-dimensional wire antenna. By embedding two positive-intrinsicnegative diodes into the radiating patch, a pair of tilted beams can be generated in the E plane, and they are directed to θ = ± 30°; besides, a side lobe level of less than −15 dB is also obtained. The mechanism of generating the tilted beams is explained. Based on the pattern reconfigurable antenna, a 1 × 8 phased array is designed. Both measured and simulated results demonstrate that the phased array operated at 3.45 GHz can give a gain fluctuation of less than 1 dB when the beam is scanned from −70° to 70°, and a side lobe level of lower than −11 dB is realized in the scanning range from −60° to 60°. Details of antenna structures and array performances are presented.

Multipoint space-domain active fiber cavity ringdown technique for quasi-distributed magnetic field monitoring

A multipoint space-domain active fiber cavity ringdown (FCRD) sensing technique based on frequency-shifted interferometry (FSI) is proposed and investigated for quasi-distributed magnetic field measurements. Multiple FSI-based fiber ringdown cavities (RDCs) are cascaded together to constitute a sensor array, share one continuous-wave optical source and one slow balanced detector, and thus the system is economical and highly sensitive. In each RDC a bidirectional erbium-doped fiber amplifier (Bi-EDFA) is inserted to compensate the inherent cavity loss for achieving higher sensitivity. Compared to the time-domain active FCRD techniques, the amplifier has lower gain fluctuation because the continuous light (instead of pulse light) coupled into the cavity enables more stable optical power, and has lower amplified spontaneous emission noise due to the use of two narrow bandpass filters and differential detection. Magnetic fields in different locations are synchronously resolved in the space domain by measuring the ringdown distances of continuous light, rather than measuring the ringdown times of pulse light in the time domain as in conventional multipoint FCRD techniques. A dual-point active FSI-FCRD magnetic field sensor was experimentally built, and two side-polished fibers coated with magnetic fluid were incorporated inside the fiber cavities as the sensing probes. By applying the external magnetic field from 0 to 230 Gs, the sensitivities of 6.68 × 10−3 and 4.45 × 10−3/(km Gs) were respectively achieved, which are at least one order of magnitude higher than the conventional passive FCRD techniques. After repeated measurements, the obtained ringdown baseline stabilities of the two units were 0.91% and 2.00%, which were much higher than those of time-domain active FCRD sensing systems. Using power budget analysis, the maximum number of identical sensing units can be expected to be 48 over a 25.89-km distance under the nearly same experimental conditions. The proposed multipoint active FCRD sensing scheme has the merits of low cost, high sensitivity, good stability, and strong multiplexing ability, which would find good application prospects at electric grids, national defense, biology, and medicine for monitoring quasi-distributed magnetic field.

Archimedean Spiral Slotted Leaky-Wave Antenna

In this work, a novel leaky-wave antenna (LWA) with Archimedean spiral slots is proposed for realizing high radiation efficiency and stable gain performance in both frequency-controlled and fixed-frequency beam-scanning applications. The structural feature of the proposed Archimedean spiral slot privileges LWA with properties of easy impedance matching and high leakage rate, because it avoids the strong reflection from large-size slots that commonly used in LWA design for high leakage rate. The bandwidths of the final designed Ka-band LWA defined by radiation efficiency larger than 90% and 80% are 13% and 25%, respectively, while the bandwidth defined by return loss less than −10 dB is 29%. And the gain fluctuations between different scanned beams are less than 2.4 dBi in the whole broadband. The LWA is further applied in designing a new-type antenna with double-layer substrate-integrated waveguide (SIW) structures, which has four feeding ports at the ends and a coupling plane in the middle interface and can realize the fixed-frequency beam switching between directions of −46°, −36°, 34°, and 45° at 28 GHz through changing the excitation port. The proposed LWAs are potential candidates for applying in future millimeter wave communication systems where multifunction integrated and multifrequency adaptive antennas are required.

Improved Gain Equalization Technique for Q-Band Folded-Waveguide TWT for Potential Application in High-Data-Rate Communication

With demanding applications in high-data-rate communication, a folded-waveguide (FWG) traveling-wave tube (TWT) faces the challenge of gain fluctuation and bandwidth limitation. To flatten gain and extend bandwidth, a novel 3-stage gain equalization technique (GET) is proposed and applied in FWG-TWT in this article. This technique shifts the operating point to a high-frequency range in the middle section. Gain equalization can be implemented by improving gain at high frequency and decreasing gain at low frequency. Furthermore, the GET also has a significant advantage in extending bandwidth. Accordingly, a 3-stage FWG-TWT is realized. Compared with a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> -band FWG-TWT with a uniform slow-wave structure (SWS), the 3-stage FWG-TWT extends the 3-dB bandwidth by more than ~45% and the gain variation less than 0.3 dB in the operating bandwidth, which demonstrates great improvement.

Vertically Polarized 360° Azimuth Scanning Array

In this letter, a vertically polarized 360&#x00B0; azimuth scanning phased array based on a wide beamwidth element is proposed. The proposed array consists of two back-to-back linear arrays. The broadside and endfire scanning modes are combined to realize 360&#x00B0; beam scanning in the azimuth plane (H-plane). A 2 &#x00D7; 8 array working at 3 GHz has been fabricated and measured. The array scans from &#x2212;180&#x00B0; to 180&#x00B0; in the H-plane with the measured peak gain of 10.8 dBi, the measured gain fluctuation less than 2 dB. The total height of the proposed array is 0.32 &#x03BB;, showing its potentials in aircraft-based application.

State quantized sampled-data control design for complex-valued memristive neural networks

In this paper, several resultful control schemes based on data quantization are proposed for complex-valued memristive neural networks (CVMNNs). Firstly, considering the finite communication resources and the interference of failures to the system, a state quantized sampled-data controller (SQSDC) is designed for CVMNNs. Next, taking the interference of gain fluctuations into account, a non-fragile sampled-data control (SDC) law is proposed for CVMNNs in the framework of data quantification. In order to full capture more inner sampling information, a newly Lyapunov-Krasovskii function (LKF) is constructed on the basis of the proposed triple integral inequality. After that, in the framework of taking full advantage of the property of Bessel-Legendre inequality, a time-dependent discontinuous LKF (TDDLKF) is proposed for CVMNNs with SQSDC. Based on the useful LKF, several stability criteria are established. Finally, the numerical simulations are provided to substantiate the validity and less conservatism of the proposed schemes.

A novel low‐cost beam‐controlling antenna based on digital coding metasurface

In this paper, a novel beam-controlling antenna based on a single-layer digital coding metasurface (DCMS) is presented. A transmission-type DCMS is placed in the near-field of the source antenna to form a low-profile structure with the height of 0.15λ0 in total. These DCMS elements have two kinds of particles with different transmissivity responses to y-polarized wave, corresponding to two basic digital element 0 and 1 respectively. By designing the coding sequences on DCMS carefully, the radiating mode can be dynamically and real-time controlled. The proposed antenna has multi-function that can realize wide-angle beam-scanning and wide-to-narrow beam switching simultaneously. The scanning angle ranges from −85° to +85° in H-plane with the gain fluctuation less than 2dBi. The simulation results are verified by experiments. This type of antenna can be applied in a variety of wireless communication systems with the outstanding advantages of low-profile, low-cost, and multi-function.

A 45° Polarized Wideband and Wide-Coverage Patch Antenna Array for Millimeter-Wave Communication

A 45° polarized millimeter-wave (mmWave) patch antenna and arrays with wide impedance and gain bandwidth are proposed in this article. The compact antenna consists of stacked patches, one substrate integrated waveguide (SIW) back cavity, one SIW square cavity, and a feeding line. The patches and the SIW back cavity rotate 45° with respect to the SIW square cavity. For the antenna, the −10 dB impedance bandwidth is from 22.31 to 29.65 GHz, and the peak gain is greater than 5 dBi in the bandwidth from 22 to 30.5 GHz. Based on the proposed antenna, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times16$ </tex-math></inline-formula> linear array is designed, fabricated, and measured. According to the experimental results, all antenna elements can realize the −10 dB impedance bandwidth from 21.7 to 27 GHz. Within 3 dB gain fluctuation, the scanning coverage of the linear array can achieve 116° in the frequency band from 22 to 26 GHz and 110° at 27 GHz. Then, an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times 8$ </tex-math></inline-formula> planar array with wide bandwidth and wide scanning coverage is proposed. The reflection coefficient can achieve less than −10 dB from 21.82 to 27.22 GHz. The main beam of the radiation pattern can be widely spatially scanned. In the bandwidth from 22 to 26 GHz, the scanning coverage within 3 dB gain fluctuation can achieve 107°. Also, at 27 GHz, the coverage can achieve 90°. Due to the outstanding performance, reliable multilayer printed circuit board (PCB) fabrication technology, and easy integration with circuits, the proposed antenna and arrays are good candidates for the fifth-generation (5G) mmWave communication systems, satellite communication systems, and so on.

A linear wide‐angle scanning phased array based on pattern reconfigurable elements

AbstractA wide‐angle scanning phased array based on pattern reconfigurable elements is proposed. There are seven metallic cylinders arranged on both sides of each unit separately to improve the isolation. The design of metallic cavities instead of a ground plate and cooperating with cylinders ingeniously solved the inconvenience of DC bias supply, significantly reducing the size of the antenna element and the entire system, and also the coupling between elements. The 3 dB beamwidth of the joint pattern generated by the pattern reconfigurable technology covers 217° in H‐plane at 5GHz. The phased array can scan from −75° to 75° in H‐plane, with gain fluctuation within 1 dB. The phased array processes a high‐aperture efficiency of 75.76%. The measured results of the phased array prototype agree with the simulation.

Dynamic polarization-insensitive BOTDA in direct-detection OFDM with CNN-based BFS extraction.

We propose a dynamic polarization-insensitive Brillouin optical time domain analyzer (D/PI-BOTDA) with orthogonal frequency division multiplexing (OFDM) based on intensity-modulated direct-detection (IM-DD). A polarization-division-multiplexed (PDM) pump signal enables polarization diversity of the stimulated Brillouin scattering while a multi-frequency OFDM probe signal realizes dynamic sensing with single-shot transmission. We experimentally demonstrated distributed temperature sensing along a total 940-meter fiber with a temperature sensing coefficient of 1.2°C/MHz. The experimental results indicated a remarkable suppression of Brillouin gain fluctuation up to 4.38 times compared to the case without polarization diversity. To facilitate the Brillouin frequency shift (BFS) extraction process, we also implement a CNN-based BFS extraction method with SE-Res2Net block. The adopted algorithm achieves a higher accuracy than conventional curve fitting method, with a 10-time enhancement in the time efficiency.