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Formation control finds broad applications in numerous fields, such as cooperative detection, surveillance, transportation, and disaster rescue. In this article, aiming at hunting a moving target, a two-stage surrounding control algorithm is proposed for linear multiagent systems subject to input saturations. An adaptive distributed observer is developed for each agent to reconstruct the target's position. With the assistance of the algebraic graph theory and low gain feedback technique, distributed controllers are designed to drive the agents to encircle the moving target with a fixed radius and evenly distributed phase angles. Finally, both numerical simulations and experiments are conducted to verify the effectiveness of the proposed control algorithm.

The paper presents a novel method for the improvement in the bandwidths by mode merging of the circularly polarized dielectric resonator antenna (CPDRA). The results of improved axial-ratio bandwidth and impedance bandwidth is compared with the previous work. In this design, 50 $$\Omega$$ terminator diverts current in such a way that adjacent exited modes get merged. Also the upper order modes are merged to the lower order modes and a significant enhancement is achieved in overlapping bandwidth. The proposed CPDRA provides axial ratio bandwidth of 53.78% (axial ratio

In order to further improve the output power of W-band traveling wave tube (TWT), a low gain TWT was proposed as a secondary amplifier. It uses a double staggered grating slow wave structure (DSG-S...

In this note, we investigate the stabilization of discrete-time linear systems with an unknown time-varying delay. Existing literature on the stabilization of time-delay systems require some knowledge, such as an upper bound, of the delay. In this paper, by proposing a switched low-gain feedback control law, we are able to achieve asymptotic stabilization of the system without any knowledge of the delay. In addition, the proposed switched low-gain feedback law also significantly improves the closed-loop system performance in terms of overshoot and convergence speed in comparison with the traditional fixed gain design. Simulation study illustrates the effectiveness of our theoretical results.

The narrow bandwidth and low gain performances of a reflectarray are generally improved at the cost of high design complexity, which is not a good sign for high-frequency operation. A dual resonance asymmetric patch reflectarray antenna with a single layer is proposed in this work for 5G communication at 26 GHz. The asymmetric patch is developed from a square patch by tilting its one vertical side by a carefully optimized inclination angle. A progressive phase range of 650&deg, is acquired by embedding a circular ring slot in the ground plane of the proposed element for gain improvement. A 332-element, center feed reflectarray is designed and tested, where its high cross polarization is suppressed by mirroring the orientation of asymmetric patches on its surface. The asymmetric patch reflectarray offers a 3 dB gain bandwidth of 3 GHz, which is 4.6% wider than the square patch reflectarray. A maximum measured gain of 24.4 dB has been achieved with an additional feature of dual linear polarization. Simple design with wide bandwidth and high-gain of asymmetric patch reflectarray make it suitable to be used in 5G communications at high frequencies.

This paper investigates the stabilization problem of linear systems with distributed infinite input delays. By introducing a stability result on systems with infinite delays, it is shown that a stabilizable linear system with distributed infinite input delays can be globally asymptotically stabilized with low gain controllers as long as the open-loop system is not exponentially unstable. Our result includes constant delay and bounded distributed delay as its special cases. It should be noted that the stabilization problem of systems with distributed infinite input delays, to our best knowledge, has not been considered in existing literatures. Simulation examples are provided to illustrate the effectiveness of our theoretical results.

The coverage control problem for mobile sensor networks with limited communication ranges is addressed in this paper. The goal of the problem is to minimize a coverage cost function which indicates the largest arrival time from the mobile sensor network to the points on a circle. Different input constraints are imposed on the sensors with first-order dynamics due to their different movement capabilities. To deal with this problem, low gain feedback is utilized to develop a distributed coverage control law for each sensor and an upper bound on the low gain is also provided. It is shown that networked mobile sensors can be driven to the configuration minimizing the coverage cost function as long as their communication ranges exceed a threshold and network connectivity of the sensors does not need to be preserved during the coverage task. Finally, a numerical example is given to illustrate the effectiveness of the proposed coverage control law.

This paper represents the clinical decision support system for video head impulse test (vHIT) based on fuzzy inference system. It examines the eye and head movement recorded by the eye movement tracking device, calculates the vestibulo-ocular reflex (VOR) gain, and applies fuzzy inference system to output the normality and artifact index of the test result. The position VOR gain and the proportion of covert and overt catch-up saccades (CUS) within the dataset are used as the input of the inference system. In addition, this system yields one more factor, the artifact index, which represents the current interference in the dataset. Data of fifteen vestibular neuritis patients and two of normal subjects were evaluated. The artifact index appears to be very high in the lesion side of vestibular neuritis (VN) patients, indicating highly theoretical contradictions, which are low gain but without CUS, or normal gain with the appearance of CUS. Both intact side and normal subject show high normality and low artifact index, even though the intact side has slightly lower normality and higher artifact index. In conclusion, this is a robust system, which is the first one that takes gain and CUS into account, to output not only the normality of the vHIT dataset, but also the artifacts.

In this study, the authors investigate the semi-global leader-following consensus problem of multi-agent systems in the presence of both position saturation and bounded rate disturbances. Each follower agent is described by a general linear dynamic with actuator position saturation and rate disturbances. Based on low-gain feedback design technique and integral sliding mode, discontinuous and continuous control protocols are developed. It is established that semi-global leader-following consensus can be achieved under the assumptions that the system is asymptotically null controllable with bounded controls and the leader agent has a directed path to every follower agent. Simulations are presented to illustrate the results.

A five-level LLC resonant converter is proposed, which is composed of two three-level (TL) bridge arms, main/auxiliary transformers, resonant elements and a set of rectifier bridge. The DC side and AC side of the two TL bridge arms are parallel connected and serial connected, respectively. With different modulation methods, the converter has three different operation modes with low, medium and high voltage gains. Compared with the traditional TL LLC resonant converter, it has lower switching frequency and higher efficiency at low gain mode. Using the same resonant parameters, it has a higher voltage gain and is more suitable for wide output range. A prototype with 90–220 V output was built. The measured efficiency of the new topology was 1.9% higher than that of the traditional topology at low voltage gain mode, and three gain modes were validated.

Q-switched lasers operating at wavelengths around 2 µm have many applications including materials processing and LIDAR. However, the low gain of the quasi-three-level gain media available at 2 µm can lead to problems with pulse-to-pulse fluctuations in their output, known as jitter. Here we present a methodology for characterising the level of jitter in a Q-switched laser and apply it to a Tm:YAP system. We also look at the causes of jitter and evaluate some methods of reducing it. The methodology developed here will aid in the development and characterisation of Q-switched lasers at any wavelength.

This paper considers adaptive consensus problem on directed graphs of multi-agent systems with unknown control directions. The proposed consensus protocol assumes that each agent receives information about delayed values of state and control signals of respective neighbors. In case of unknown sign of the high-frequency gain of agent dynamics, the proposed algorithm employs Nussbaum-like switching function. The algorithm allows for a designer to select low gain or high gain consensus protocols. Assuming that the underlying graph is strongly connected, it is proved that all agent states converge toward the same value, and the inter-agent coupling parameters are convergent functions. Copyright © 2015John Wiley & Sons, Ltd.

This study addresses the semi-global consensus of linear multi-agent systems with a virtual leader, in which the control input of each agent is subject to periodically intermittent saturating actuator. Depending on multiple Lyapunov stability theorem and applying the algebraic-Riccati-equation-based low-gain feedback technique, the authors can obtain that: when the control width is larger than a fixed value, a connected system with each agent being asymptotically null controllable with bounded controls and marginally stable can guarantee the semi-global consensus of multi-agent systems with a virtual leader. Numerical simulations verify the author's theoretical analysis.

We propose systematic design methods for realization of a given LTI compensator with complex poles using a modulated-demodulated control framework. Applicability of the proposed realization methods is established through simulations performed on an undamped resonant plant compensated by a low gain controller to obtain better noise rejection performance. It is demonstrated how a modulated-demodulated structure may reduce the sampling rate in a hybrid control system. In addition, superior robust performance is achieved against variations in baseband parameters using direct reference injection into the modulated-demodulated control systems compared to the indirect injection approach.

This paper investigates the problem of leader-following consensus of a linear multi-agent system on a switching network. The input of each agent is subject to saturation. Low gain feedback based distributed consensus protocols are developed. It is established that, under the assumptions that each agent is asymptotically null controllable with bounded controls and that the network is connected or jointly connected, semi-global leader-following consensus of the multi-agent system can be achieved. Numerical examples are presented to illustrate this result.

In this paper, the on-body propagation performance measured totally wirelessly with 4-mm-thick and 50 $\,\times\,$ 50 mm size textile monopole antennas is presented. At a relatively low operating frequency 867 MHz, with small size, low gain textile antennas mean channel gain values from $-$ 47 to $-$ 56 dB including the antenna performances were recorded in various on-body propagation scenarios. The majority of the recorded links could be well described with the Nakagami distribution.

In this paper, we study the stabilization of linear critically unstable systems subject to input saturation and multiple unknown input delays. We find tight upper bounds for delays which are inversely proportional to the maximal magnitude of open-loop eigenvalues on the imaginary axis. For delays satisfying these upper bounds, linear low-gain state and finite dimensional dynamic measurement feedbacks are constructed to solve the semi-global stabilization problem. The effectiveness of the proposed design is illustrated by an example.

We investigate pulse cleaning behaviors in short-pulse-pumped optical parametric amplifiers (OPA). We theoretically study the contrast enhancement of amplified signal pulse and generated idler pulse, and reveal their dependence on the parametric gain in both the regimes of small signal and saturated amplifications. The signal contrast enhancement is nearly equal to the parametric gain, while the idler contrast is approximately equal to the product of the contrasts of the pump and signal pulses in a low gain OPA and increases with the gain. The effects of group-velocity mismatch and group-velocity dispersion on the contrast enhancement are also investigated. The results presented in this paper are of value for pulse cleaning.

For stabilization of linear systems subject to input saturation, there exist four different approaches of low-gain design all of which are independently proposed in the literature, namely direct eigenstructure assignment, H2 and Hoo algebraic Riccati equation (ARE) based methods, and parametric Lyapunov equation based method. It is shown in Wang et al. [2010b] that for continuous-time linear systems, all these methods are rooted in and can be unified under two fundamental control theories, H2 and Hoo theory. In this paper, we extend such a result to a discrete-time setting. Both the H2 and Hoo ARE based methods are generalized to consider systems where all input channels are not necessarily subject to saturation, and explicit design methods are developed.

We suggest a first-order model to distinguish between nose control (canards) and tail control. We present optimal guidance strategies and demonstrate the superiority of nose control. This simple model enables us to develop simple and robust guidance strategies based on three approaches: unconstrained optimal control, constrained optimal control, and constrained differential games. It turns out that nose control requires low gain and is capable of forcing small miss distance in the presence of a maneuvering target.

International audience; Several solutions of the problem of stabilizing linear systems with bounded control rely on a one-parameter family of low-gain linear control laws u=K(ε)x. This paper presents an online scheduling of the parameter ensuring, in addition to closed-loop stability, the fastest possible transient between two extreme values of ε, chosen for stability and performance, respectively.

A low-gain design for linear discrete-time systems subject to input saturation was recently developed to solve both semi-global stabilization and semi-global output regulation problems. This paper proposes an improvement to the low-gain design and determines controllers with the new design that achieve semi-global output regulation. The improvement is reflected in better utilization of available control capacity and consequently better closed-loop performance.

A measurement system for determining the gain distributions of avalanche photodiodes (APDs) in a low gain range is presented. The system is based on an ultralow-noise charge--sensitive amplifier and detects the output carriers from an APD. The noise of the charge--sensitive amplifier is as low as 4.2 electrons at a sampling rate of 200 Hz. The gain distribution of a commercial Si APD with low average gains are presented, demonstrating the McIntyre theory in the low gain range., 3 pages, 4 figures

The problem of global almost disturbance decoupling problem with stability for nonlinear system is revisited and is shown to be solvable for a class of nonlinear systems whose zero dynamics contains a chain of integrators affected by disturbance. This result complements some recent work on the topic, where unstable zero dynamics is not allowed to be affected by the disturbances.

A well known control system which can reduce the adverse effect of a periodic disturbance with single frequency is the disturbance obsever. However, in many cases of industrial systems disturbance frequency is varied for some frequency range. Therefore, it may be difficult to reduce the adverse effect of the disturbance by the use of the traditional disturbance observer.In this paper, a design method of new disturbance observer which can cope with the frequency variation is proposed. The main idea of this design method is to synthesize the disturbance observer as a gain-scheduled controller. The proposed disturbance observer is constructed as low degree and low gain controller with superior steadystate characteristic. As compared with the traditional disturbance observer and the H∞ controller, the usefulness of the proposed disturbance observer was shown by numerical simulations.

This letter describes the design and performance of a dual band tri-mode receiver front-end compliant with the IEEE 802.11a, b, and g standards. The receiver front-end was built in a 0.18-/spl mu/m CMOS process and achieves a noise figure of 4.7 dB/5.1 dB for the 2.4-GHz/5-GHz bands, respectively. The receiver front-end provides a dual gain mode of 5 dB/30 dB with an IIP3 of -1dBm for the low gain mode. The front-end draws 25 mA/27 mA from a 1.8-V supply for the 2.4-GHz/5-GHz bands, respectively.

This paper is concerned with the design of state feedback controllers in order to achieve an objective called perfect regulation (p.r.). Necessary and sufficient conditions for the existence of state feedback controllers that achieve p.r. are derived for general linear multivariable time-invariant discrete-time systems. More importantly, an explicit eigenstructure assignment procedure by state feedback that achieves p.r. is developed.

We discuss wave-guide Free Electron Laser gain formulae including inhomogeneous broadening and saturation effects. The analysis is not limited to the low gain regime. It is also proven that, after a proper redefinition, most of the “empirical” formulae exploited for the free space case can be utilised to model the wave-guide evolution.

We study the modifications induced on the longitudinal dynamical behaviour of an e-beam circulating in a Storage-Ring (S.R.) and undergoing a FEL interaction. We discuss the low gain amplifier case and, using the Fokker-Planck equation, evaluate the effect of the FEL interaction on the longitudinal damping time, which is shown to be a function of the detuning parameter and of the intensity itself. We develop a self-consistent model of the S.R. FEL dynamics capable of including saturation, induced energy spread and damping time modifications. The model is shown to be particularly useful to investigate the system evolution and the interplay between the various features causing the saturation of the device.

Intercept points are often used to describe the non-linear performance of transceiver stages. This letter introduces an intercept measure. The intercept measure is a performance parameter including both intercept point and gain parameters. Particularly for low gain stages the intercept measure is useful and is better to use than the traditional output intercept point. The intercept measure is very useful as a single non-linear performance parameter. Copyright © 2003 John Wiley & Sons, Ltd.

This paper studies the consensus among identical agents that are at most critically unstable and coupled through networks with uniform constant communication delay. An achievable upper bound of delay tolerance is obtained which explicitly depends on agent dynamics and network topology. The dependence on network topology disappears in the case of undirected networks. For any delay satisfying this upper bound, a controller design methodology without exact knowledge of the network topology is proposed so that the multi-agent consensus in a set of unknown networks can be achieved. Moreover, when the network topology is known, a larger delay tolerance is possible via a topology-dependent consensus controller. The results are illustrated by simulations.

The modification induced in the Optical-Klystron gain by an e-beam with non-negligible energy spread and emittances is analyzed. The analysis is carried out including the inhomogeneous broadening contributions due to the undulators and dispersive parts. The paper deals essentially with the low gain regime, the corrections due to the high gain effects are also discussed.

We show that longitudinal and transverse mode correction to the FEL low gain formula can be expressed by means of higher order derivatives of the complex spontaneous emission function. The analysis is then extended to the high gain regime.

A neon 633 nm laser with an unstable cavity was made to lase in the negative unstable region. The characteristic parameters were measured. The loss calculated by using both the geometric approach and the diffraction integral is higher than the gain of the gas mixture, it contradicts the experimental results. If the radial dependence of the gain is taken into account then the calculated loss fits the experimental results satisfactorily.

This paper presents an analysis of the slow-peaking phenomenon, a pitfall of low-gain designs that imposes basic limitations to large regions of attraction in nonlinear control systems. The phenomenon is best understood on a chain of integrators perturbed by a vector field up(x, u) that satisfies p(x, 0)=0. Peaking may cause a loss of global controllability unless severe growth restrictions are imposed on p(x, u). These growth restrictions are expressed as a higher order condition with respect to a particular weighted dilation related to the peaking exponents of the nominal system. When this higher order condition is satisfied, an explicit control law is derived that achieves global asymptotic stability of x=0. This stabilization result is extended to more general cascade nonlinear systems in which the perturbation p(x, /spl upsi/)/spl upsi/, /spl upsi/=(/spl xi/, u)/sup T/, contains the state /spl xi/ and the control u of a stabilizable subsystem /spl xi//spl dot/=a(/spl xi/, u). As an illustration, a control law is derived that achieves global stabilization of the frictionless ball-and-beam model.

A new derivation of the fundamental mode equations describing the resonance condition for low gain distributed feedback fiber lasers is presented. This derivation is a refinement of that given in a previous publication by the author, but dispenses with a number of unnecessary restrictions and makes the general context of the result more transparent

This paper presents the design of an ultralow power receiver front-end designed for a wireless sensor network (WSN) in a 0.18 μm CMOS process. The author designs two front-ends working in the saturation region and the subthreshold region respectively. The front-ends contain a two-stage cross-coupling cascaded common-gate (CG) LNA and a quadrature Gilbert IQ mixer. The measured conversion gain is variable with high gain at 24 dB and low gain at 7 dB for the saturation one, and high gain at 22 dB and low gain at 5 dB for the subthreshold one. The noise figure (NF) at high gain mode is 5.1 dB and 6.3 dB for each. The input 1 dB compression point (IP1dB) at low gain mode is about −6 dBm and −3 dBm for each. The front-ends consume about 2.1 mA current from 1.8 V power supply for the saturation one and 1.3 mA current for the subthreshold one. The measured results show that, comparing with the power consumption saving, it is worth making sacrifices on the performance for using the subthreshold technology.

A new technique is proposed to compensate for the loop gain degradation in correlated level shifting. The technique allows the use of a simple single-stage opamp with low gain to realise high effective loop gain. The effect of gain variations on the performance of the proposed correlated level shifting technique is discussed.

We present a simple, easily tunable cavity configuration which, by means of two low-loss frequency selectors, is capable of forcing low-gain oscillators to reliably operate in single mode. Its application for tunable (up to 20 nm), 100% single-mode operation of a Q -switched, low gain ( G =2), Nd-phosphate glass laser is discussed.

A type of ring antenna has been studied for applications on satellite in sub-orbital as well as in orbital flight, in view of realizing a small sized structure and a low gain. Admittance properties and radiation patterns are given together with indications for a proper designing of the antenna.

The paper describes the design of a Fresnel zone plate suitable for use as an antenna in the centimetric or lower wavelength range. It has been shown that such antennas can be fabricated by using either metal or dielectric rings. Its properties have been analysed by employing the simple methods of electromagnetic diffraction. Experimental results are reported showing close agreement with the theory. A theory has been presented explaining the working of the dielectric ring zone plate. The investigation leads to the conclusion that both the metal and dielectric zone plates are useful as low gain antennas.

Strategies are presented for the optimum design of FIR switched-capacitor decimators using low-gain amplifiers. It is illustrated that one such new design improves the amplitude response of an existing circuit when the DC gain of the amplifiers is as low as 100.