A compact proximity‐fed 2.4 GHz monostatic antenna with wide‐band SIC characteristics for in‐band full duplex applications

This article presents a dual polarized, proximity‐fed monostatic patch antenna (single radiator for both transmit and receive modes) with improved interport isolation for 2.4 GHz in‐band full duplex (IBFD) applications. The proximity‐fed radiating patch offers comparatively wider impedance bandwidth for presented design. Very nice self‐interference cancelation (SIC) levels for intended impedance bandwidth have been achieved through differential receive (R_x) mode configuration. The differential R_x mode based on 180° ring hybrid coupler acts as a signal inversion mechanism for effective suppression or cancelation of in‐band self‐interference (SI) that is, the leakage from transmit port. The implemented prototype of proposed antenna achieves ≥87 dB peak isolation for dual polarized IBFD operation. Moreover, the recorded interport isolation for validation model ≥60 dB within 10 dB‐return loss bandwidth of 90 MHz (2.36‐2.45 GHz). The measured radiation characteristics of implemented antenna demonstrate nice gain and low cross‐polarization levels for both transmit (T_x) and receive (R_x) modes. The dimensions of implemented antenna are 70 × 75 × 4.8 mm³. The novelty of this work is wide‐band SIC performance for monostatic antenna configuration with compact structure of presented design.     

A novel compact self‐similar fractal UWB MIMO antenna

A novel compact self‐similar fractal ultra‐wideband (UWB) multiple‐input‐multiple‐output (MIMO) antenna is presented. This fractal geometry is designed by using iterated function system (IFS). Self‐similar fractal geometry is used here to achieve miniaturization and wideband performance. The self‐similarity dimension of proposed fractal geometry is 1.79, which is a fractional dimension. The antenna consists of two novel self‐similar fractal monopole‐antenna elements and their metallic area is minimized by 29.68% at second iteration. A ground stub of T‐shape with vertical slot enhances isolation and impedance bandwidth of proposed MIMO antenna. This antenna has a compact dimension of 24 × 32 mm² and impedance bandwidth (S₁₁ < ?10 dB) of 9.4 GHz ranging from 3.1 to 12.5 GHz with an isolation better than 16 dB. The various diversity performance parameters are also determined. There is good agreement between measured and simulated results, which confirms that the proposed antenna is acceptable for UWB applications.     

On active acceleration control of vibration isolation systems

Active vibration isolation systems (VIS) have been widely used from the space shuttle applications to the ground vehicle suspensions. The main control objective is to achieve the minimum vibrations at the flotor for given vibrations at the stator. With respect to a fundamental limitation of using the PD type flotor acceleration controller, an I (integral) and II (double integral) type flotor acceleration controller is proposed in this paper. By incorporating the feedforward compensation of the umbilical dynamics, the proposed acceleration controller is able to experimentally push down the lowest isolation frequency from 1.4 Hz (when PID control is used) to 0.03 Hz with a sufficiently improved vibration isolation performance up to 10 Hz, with respect to a MIM (Microgravity Vibration Isolation Mount) system tested on the ground. A unique frequency selective filter (FSF) is also proposed, which experimentally suppresses a fixed-frequency umbilical resonant mode at 22.2 Hz with an attenuation of 20 dB.     

Active vibration control of large space flexible slewing truss using cable actuator with input saturation

This paper proposes a composite approach to implementing attitude tracking and active vibration control of a large space flexible truss system. The system dynamic model is based on Hamilton's principle and discretized using the finite difference method. A nonlinear attitude controller for position tracking is developed based on the input‐output linearization of the discretized system, which can effectively improve system performance compared with a traditional proportional‐differential feedback controller. A taut cable actuator scheme is presented to suppress tip vibration because the mechanical model is a large large‐span spatial structure; furthermore, because the cable has the feature of unilateral input saturation constraint, which can provide only a pulling force, a nonlinear quadratic regulator controller is developed by introducing a piecewise nonquadratic cost function to suppress the vibration of the flexible structure. To investigate the factors that influence the damping effects of the cable, the parametrically excited instability of a cable under 2 supports is analyzed. Simulation results illustrate that the proposed attitude controller can implement the task of position tracking, and the vibration suppression control law is shown to be optimal for functional performance with input saturation.     

A miniaturized multi‐wideband Quasi‐Yagi MIMO antenna system

A multi‐band directional multiple‐input–multiple‐output (MIMO) antenna system is presented based on a rectangular loop excited Quasi‐Yagi configuration. A 64% reduction in size is obtained using a rectangular meandered element as well as a small ground plane. The proposed two‐element MIMO antenna system covers the Telemetry L‐band and several LTE/WLAN bands. It has a wide measured bandwidth of 689 MHz (1.897–2.586 GHz) in the desired band centered at 2 GHz, and a measured bandwidth of more than 168 MHz across rest of the bands. The MIMO antenna system has a total size of 45 × 120 × 0.76 mm³, with a single element size of 55 × 60 × 0.76 mm³. The non‐desired back‐lobe radiation which is obtained using a small ground plane, is significantly reduced by using a novel defected ground structure (DGS) as compared with the complex techniques present in literature. The proposed DGS provides a high measured front‐to‐back ratio of 14 dB at 2 GHz and 11 dB in other bands. A maximum measured realized gain of 5.8 dBi is obtained in the desired band using a single parasitic director element. The proposed MIMO antenna system has a minimum measured radiation efficiency of 70%, isolation of 12 dB, and envelope correlation coefficient of 0.098 within all bands which ensures very good MIMO performance.     

Design of a two‐level controller for an active suspension system

The paper focuses on a control design for a vehicle suspension system in which a balance between different performance demands is achieved. The starting point of the control design is a full–car model which contains nonlinear components, i.e. the dynamics of the dampers and springs and nonlinear actuator dynamics. In order to handle the high complexity of the problem this paper proposes the design of a two‐level controller of an active suspension system. The required control force is computed by applying a high‐level controller, which is designed using a linear parameter varying (LPV) method. For the control design the model is augmented with weighting functions specified by the performance demands and the uncertainty assumptions. The actuator generating the necessary control force is modelled as a nonlinear system for which a low‐level force‐tracking controller is designed. To obtain the low‐level controller a backstepping method is proposed. As an alternative solution a feedback linearization method is also presented. The operation of the controller is illustrated through simulation examples. Copyright © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

Active vibration isolation in a “smart spring” mount using a repetitive control approach

In a variety of different engineering systems there is a requirement to isolate sensitive equipment from foundation vibration or alternatively, isolate the foundation from machinery vibration. Passive solutions to this problem provide some isolation but performance is significantly degraded in the presence of structural compliance. A recently proposed hybrid active/passive solution known as the “Smart Spring” mounting system specifically addresses this problem of compliance. The work reported here investigates the application of a repetitive control approach to deal with periodic vibration sources in such a mounting system. The industrial potential of the approach has been shown using an experimental facility where isolation results in the region of 50 dB have been achieved.     

Dual‐wideband filtering power divider based on center‐fed three‐line coupled structure

In this article, a dual‐wideband filtering power divider is proposed by using a center‐fed three‐line coupled structure with three open stubs and two isolation resistors. The center‐fed three‐line coupled structure can generate two wide passbands separated by a transmission zero (TZ). The three open stubs can achieve four TZs around the two passbands, which is conducive to the frequency selectivity. Compared with the reported designs, the bandwidth is extended and the performance of isolation, insertion loss and circuit size can reach balance. The proposed design is implemented with size of 0.22 λ_g × 0.39 λ_g (λ_g is the guided wavelength at the center frequency of the lower passband) which exhibits the 3‐dB fractional bandwidths of 56.5%/24.27% and the insertion loss of 0.51/0.68 dB at the center frequency of two passband (f₁/ f₂) of 1.94/4.2 GHz, while the isolation at f₁/f₂ are higher than 22.5/20.1 dB.     

基于神经预测的模糊主动隔振控制技术研究

将基于神经网络预测的模糊控制技术应用于静电悬浮加速度计地面实验装置主动隔振系统。神经网络预测模型可以根据当前时刻控制器与隔振平台的输出,能够对下一时刻隔振平台的运动状态提前作出预测,并将这一状态反馈输入到模糊控制器,能够使模糊控制器提前作出判断对隔振平台进行控制。研究结果表明该算法不仅可以限制控制信号的振荡,而且有利于抑制超调,对0.1Hz以上的低频激扰具有良好的隔振效果。     

A miniature coupled‐line‐based 3‐dB directional coupler using GaAs PHEMT process

A novel complementary‐conducting‐strip (CCS) coupled‐line (CL) design is proposed to achieve compact size by applying two‐dimensional layout and standard gallium‐arsenide (GaAs) thin‐film technology. To obtain high coupling and satisfy the design rules of GaAs process, mixed‐couple mechanism with edge and broadside coupling are also used. A CCS CL‐based Ka‐band 3‐dB directional coupler is fabricated using WIN 0.15‐μm GaAs pseudomorphic high electron mobility transistor technology. Experimental results show that the proposed directional coupler can cover the entire Ka‐band (26–40 GHz) with through and coupling of approximately 3.7 ± 0.25 dB, and isolation of better than 13 dB. In addition, the phase difference between the two output ports is approximately 90° ± 5°. The occupied area of the prototype (without I/O networks) is only 220 × 220 μm². © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:21–26, 2016.     

A low‐profile quad‐port UWB MIMO antenna using defected ground structure with dual notch‐band behavior

A compact (45 × 45 × 1.6 mm³) ultrawide‐band (UWB), multiple‐input multiple‐output (MIMO) design using microstrip line feeding is presented. The proposed design comprises four elliptical monopoles placed orthogonally on a cost‐effective FR‐4 substrate. In order to improve the impedance bandwidth and lessen the return loss of the MIMO antenna, defects in ground plane are created by etching symmetrical square slots and half‐rings. Moreover, a different method (of unsymmetrical H‐shaped slot with C‐shaped slot) was proposed into the patch to introduce dual‐band rejection performance from UWB at center frequency 5.5 GHz (covering lower WLAN as well as upper WLAN) and 7.5 GHz (X band). In addition, a stub is introduced at the edge of each defected ground structure to obtain isolation >–22 dB covering entire performing band from 2 to 16.8 GHz (where, S₁₁ < –10 dB). The proposed design has miniaturized size, very low envelop correlation coefficient less than 0.1, stable gain (2‐4 dBi except for notch bands). Furthermore, various MIMO performance parameters are within their specifications, such as diversity gain (= 10 dB), total active reflection coefficient (<–5 dB, and channel capacity loss (<0.35 bits/s/Hz). The presented design is optimized using the HFSS software, and fabricated design is tested using vector network analyzer. The experimental results are in good agreement with the simulation results.     

A millimeter‐wave CMOS power amplifier design using high‐Q slow‐wave transmission lines

A three‐stage 60‐GHz power amplifier (PA) has been implemented in a 65 nm Complementary Metal Oxide Semiconductor (CMOS) technology. High‐quality‐factor slow‐wave coplanar waveguides (S‐CPW) were used for input, output and inter‐stage matching networks to improve the performance. Being biased for Class‐A operation, the PA exhibits a measured power gain G of 18.3 dB at the working frequency, with a 3‐dB bandwidth of 8.5 GHz. The measured 1‐dB output compression point (OCP_1dB) and the maximum saturated output power P_sat are 12 dBm and 14.2 dBm, respectively, with a DC power consumption of 156 mW under 1.2 V voltage supply. The measured peak power added efficiency PAE is 16%. The die area is 0.52 mm² (875 × 600 μm²) including all the pads, whereas the effective area is only 0.24 mm². In addition, the performance improvement of the PA in terms of G, OCP_1dB, P_sat, PAE and the figure of merit using S‐CPW instead of thin film microstrip have been demonstrated. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:99–109, 2016.     

Compact dual‐polarized dipole antenna with high isolation using hybrid balun circuit

In this article, a crossed dipole antenna with compact size (43 × 43 mm²) and high isolation (42 dB) is proposed using a hybrid balun circuit. The hybrid balun consists of a tapered balun and a Marchand balun. The tapered balun transforms the microstrip line into the parallel feeding lines for one pair of dipoles, and the Marchand balun transforms the stripline transmission line into a couple of out‐of‐phase feeding lines for the crossed pair of dipoles. Due to the low coupling between two different baluns, a high isolation of the antenna can be achieved when the crossed dipole antenna is cascaded with the hybrid balun. Moreover, these two baluns can improve impedance matching and therefore further miniaturize the size of the crossed dipole antenna. The impedance matching of two baluns can be controlled and adjusted independently. As a result, the proposed dual‐polarized antenna has the bandwidth of 1.7 to 2.8 GHz for S11 < ?15 dB with compact size and high isolation. The proposed antenna with the hybrid balun circuit are fabricated, and the simulated and measured results meet well.     

Gain enhancement and mutual coupling reduction of multiple‐intput multiple‐output antenna for millimeter‐wave applications using two types of novel metamaterial structures

A method to significantly increase the gain and reduce the mutual coupling of microstrip multiple‐intput multiple‐output (MIMO) antenna based on metamaterial concept is presented. The μ‐negative and ε‐negative features of the proposed modified peace‐logo planar metamaterial (MPLPM) and two‐sided MPLPM (TSMPLPM) structures are calculated. The antenna structure consists of eight MPLPM slabs and two TSMPLPM, which are embedded in azimuth plane of a MIMO antenna vertically. The dimensions of MIMO antenna are 28 × 16 × 6.3 mm³ at 40 GHz. As a result, a compact MIMO antenna is simulated in comparison with primary microstrip structures. The corresponding return‐loss of the antenna is better than 10 dB over 34.5 to 45.5 GHz for Ka‐band applications. Good consent between the measured and simulated result is tacked. The maximum simulated gain of the structure is 15.5 dB at 40 GHz, creating a maximum gain improvement of 11.5 dB in comparison with a MIMO antenna without any metamaterial combinations. The value of the insertion‐loss (isolation) is 33 dB, which has improved by more than 25 dB compared to the conventional sample.     

Self-learning active vibration control of a flexible plate structure with piezoelectric actuator

In this paper, an active vibration control (AVC) incorporating active piezoelectric actuator and self-learning control for a flexible plate structure is presented. The flexible plate system is first modelled and simulated via a finite difference (FD) method. Then, the validity of the obtained model is investigated by comparing the plate natural frequencies predicted by the model with the reported values obtained from literature. After validating the model, a proportional or P-type iterative learning (IL) algorithm combined with a feedback controller is applied to the plate dynamics via the FD simulation platform. The algorithms were then coded in MATLAB to evaluate the performance of the control system. An optimized value of the learning parameter and an appropriate stopping criterion for the IL algorithm were also proposed. Different types of disturbances were employed to excite the plate system at different excitation points and the controller ability to attenuate the vibration of observation point was investigated. The simulation results clearly demonstrate an effective vibration suppression capability that can be achieved using piezoelectric actuator with the incorporated self-learning feedback controller.     

Nonlinear output‐feedback control of torsional vibrations in drilling systems

This paper considers the design of a nonlinear observer‐based output‐feedback controller for oil‐field drill‐string systems aiming to eliminate (torsional) stick–slip oscillations. Such vibrations decrease the performance and reliability of drilling systems and can ultimately lead to system failure. Current industrial controllers regularly fail to eliminate stick–slip vibrations under increasingly challenging operating conditions caused by the tendency towards drilling deeper and inclined wells, where multiple vibrational modes play a role in the occurrence of stick–slip vibrations. As a basis for controller synthesis, a multi‐modal model of the torsional drill‐string dynamics for a real rig is employed, and a bit–rock interaction model with severe velocity‐weakening effect is used. The proposed model‐based controller design methodology consists of a state‐feedback controller and a (nonlinear) observer. Conditions, guaranteeing asymptotic stability of the desired equilibrium, corresponding to nominal drilling operation, are presented. The proposed control strategy has a significant advantage over existing vibration control systems as it can effectively cope with multiple modes of torsional vibration. Case study results using the proposed control strategy show that stick–slip oscillations can indeed be eliminated in realistic drilling scenarios in which industrial controllers fail to do so. Moreover, key robustness aspects of the control system involving the robustness against uncertainties in the bit–rock interaction and changing operational conditions are evidenced. Copyright © 2017 John Wiley & Sons, Ltd.     

A compact UWB‐MIMO with dual grounded CRR for isolation improvement

In this article, a compact half‐hexagonal ultra‐wide band multiple‐input‐multiple‐output (MIMO) antenna is presented. The key feature of the antenna is its novel isolation improvement technique which includes grounded stub along with dual grounded circular ring resonator. The antenna contains two counter facing half‐hexagonal monopoles having hybrid isolation circuit. The antenna has a compact size of 20 × 34 mm², with operating frequency band of 3‐11 GHz where port isolation is better than 20 dB in most of the band. The MIMO performance is ensured by calculating envelop correlation coefficient and mean effective gain ratio for isotropic, indoor, and outdoor environment. The performance of the antenna with multilayer printed circuit board having large dual ground plane and device housing is also studied. Results show that the proposed MIMO antenna is a good candidate for handheld devices for wireless personal‐area networks application.     

Six-degree-of-freedom active vibration isolation using a stewart platform mechanism

Intelligent Automation, Inc. has performed a study of a six-degree-of-freedom (dof) active vibration isolation system based on a Stewart platform mechanism to be used for precision control of a wide range of space-based structures as well as earth-based systems. This article presents part of the study results, which includes a new Terfenol-D actuator design and analysis, a design of a Stewart platform as a vibration isolation device, and robust adaptive filter algorithms for active vibration control. Prototype hardware of a six-dof active vibration isolation system has been implemented and tested. About 30 dB of vibration attenuation is achieved in real-time experiments.     

Optimal fractional order PIλDμ controller for stabilization of cart‐inverted pendulum system: Experimental results

The cart‐inverted pendulum is a non‐minimum phase system having right half s‐plane pole and zero in close vicinity to each other. Linear time invariant (LTI) classical controllers cannot achieve satisfactory loop robustness for such systems. Therefore, in the present work the fractional order PI^λD^μ (FOPID) controller is addressed for robust stabilization of the system, since fractional order controller design allows more degrees of freedom compared to its integer order counterparts by virtue of its two parameters λ and μ. The controller parameters are tuned by three evolutionary optimization techniques. In order to select the controller parameters optimally, a novel non‐linear fitness function using integral time square error (ITSE), settling‐time, and rise time is proposed here. The control algorithm is implemented successfully in real‐time. Moreover, stability analysis of the system compensated with a fractional order controller is presented using Riemann surface. Robustness of the physical cart‐inverted pendulum system towards multiplicative gain variations and plant parameter variations is verified. In this regard, it is shown that the fractional order controller provides satisfactory robust performance in both simulation and real‐time system.     

Ten switched‐beams with 2 × 2 series‐fed 2.4 GHz array antenna and a simple beam‐switching network

This article presents a 2 × 2 series fed 2.4 GHz patch antenna array having multiple beam switching capabilities by using two simple 3 dB/90° couplers to achieve required amplitude and phase excitations for array elements with reduced complexity, cost and size. The beam switching performance with consistent gain and low side lobe levels (SLL) is achieved by exciting the array elements from orthogonally placed thin quarter‐wave (λ_g/4) feeds. The implemented array is capable to generate ten (10) switched‐beams in 2‐D space when series fed elements are excited from respective ports through 3 dB quadrature couplers. The dual polarized characteristics of presented array provide intrinsic interport isolation between perpendicularly placed ports through polarization diversity to achieve independent beam switching capabilities for intended directions. The implemented antenna array on 1.575 mm thick low loss (tan δ = 0.003) NH9450 substrate with ε_r = 4.5 ± 0.10 provides 10 dB return loss impedance bandwidth of more than 50 MHz. The measured beam switching loss is around 0.8 dB for beams switched at θ = ±20°, Ф = 0°, 90°, and 45° with average peak gain of 9.5 dBi and SLL ≤ ?10 dB in all cases. The novelty of this work is the capability of generating ten dual polarized switched‐beams by using only two 3 dB/90° couplers as beam controllers.