Simulation of noise figure of nonlinear amplifiers using the orthogonalization of the nonlinear model

A simulation procedure of noise figure (NF) of nonlinear amplifiers is developed. NF is defined in terms of the effective signal‐to‐noise ratio (SNR) at the output of a nonlinear amplifier. The effective output SNR when the input consists of a communication signal plus Gaussian noise is evaluated through the identification of the effective output noise and nonlinear distortion power using the orthogonalization of the nonlinear model. The approach is useful for the assessment of noise performance of low‐noise amplifiers in wireless systems. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE 2009.     

Realization of FTA with High Tracking Accuracy in FSO

High tracking accuracy is a prerequisite of reliable space optical communication links and its effective means is the utilization of coarse and fine compound‐axis structure. After an in‐depth study of the active laser tracking mechanism of fine tracking assembly, this paper emphasizes the exploration of these methods enabling the improvement of tracking accuracy under the condition of relative movement and platform vibration. Firstly, switching technique using a single beacon between different divergence angles is put forward to improve the signal to noise ratio (SNR) of the focal spot. Secondly, the high‐frame rate charge‐coupled device is achieved after proposing the pseudo random window readout technique. Thirdly, the unique design of the high resonant frequency of two‐dimensional PZT fast steering mirror (FSM) and sub‐pixel subdivision technique with adaptive control of integral time is used to achieve high accuracy and fast beam pointing. Fourthly, this paper puts forward a digital servol control method with intelligent variable structure. Finally, after building a hardware‐in‐loop simulation platform, the tracking accuracy of 3μrad is concluded according to simulation experimental results.     

Trench‐type deep N‐well dual guard ring for the suppression of substrate noise coupling

This article presents a study on the isolation performance of the trench‐type deep n‐well (DNW) dual guard ring (GR) and its effect on the suppression of the substrate digital noise coupling on a low noise amplifier (LNA) based on measurement and TCAD simulation. The trench‐type DNW dual GR, in which the DNW is formed beneath the ring‐shaped n‐well region only, can be adopted for protecting the noise‐sensitive analog/RF circuits or circuit blocks against the substrate noise. An in‐depth analysis on the performance of the trench‐type DNW was carried out based on both measurement and a heavy use of TCAD. The results show that the trench‐type DNW dual GR exhibits comparable isolation to that of the pocket‐type DNW dual GR at high frequency regime. The effect of various GR dimension parameters and GR bias conditions on the GR isolation performance was also investigated and analyzed. Furthermore, the trench‐type DNW dual GR was applied to a 5.8‐GHz LNA and its effect on the suppression of the substrate digital noise coupling was studied for various digital noise conditions and GR bias schemes. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Wideband filtering power dividers using single‐ and double‐layer periodic spoof surface plasmon polaritons

In this article, four wideband power dividers (two are filtering power dividers) using single‐ and double‐layer periodic spoof surface plasmon polaritons (SSPPs) are proposed. Double‐sided parallel‐strip line is used to realize the wideband and low loss for the double‐layer SSPPs. T‐shaped SSPPs power dividers with large bandwidth, wideband isolation, and low loss using double‐layer SSPPs to single‐layer SSPPs transition are realized. Conventional coplanar waveguide is used as the output ports for the single‐layer SSPPs. Moreover, two new SSPPs power dividers with filtering performance are realized with adding via holes in the double‐layer SSPPs. The theoretical analysis, parametric study, and design procedure for these wideband power dividers are illustrated. In addition, for validity demonstration, four wideband SSPPs power dividers are fabricated in microstrip technology and characterized. Good agreements can be observed between the measured and simulated results, indicating good potential applications in the integrated plasmonic devices.     

电能质量监测装置数字滤波器设计应用研究

利用数字滤波器数据处理速度快、系统工作性能稳定、能获得理想的幅度特性等特点,设计一种应用于某系列高端电能质量监测装置的数字滤波器,通过仿真实验和实际采样信号处理证明,此种数字滤波器可提高监测装置测量信号的信噪比,可达到[2009]《电能质量监测终端技术规范》试行国标A级标准.     

Digital techniques to mitigate feedback impairment and noise of look‐up table digital predistortion

In this article, some new effects of feedback impairment and noise on look‐up table (LUT) digital predistortion (DPD) are presented. Several digital techniques are proposed to mitigate these effects. A smoothing filter (SMF) for LUTs is used to eliminate fluctuations of the transfer function of the overall DPD amplification system. By combining SMF method with iterative average (IA) method, the LUTs iterative process becomes stable and well converged. A postcompensator is established according to the proposed two‐box model for feedback impairment. For the demonstration, both simulation and experiments are carried out based on a Hammerstein‐type PA. Simulation results give some preliminary cognition of these new effects and the effectiveness of proposed techniques. Experimental tests are performed on an S‐band amplifier excited with single‐carrier WCDMA signal. The adjacent channel power ratio (ACPR) at 5‐MHz offset is ?48 dBc after DPD with SMF method and postcompensator. A total of 8 dB extra improvement of ACPR is obtained compared with that with neither SMF nor postcompensator. The result clearly shows that the proposed digital techniques are qualified for LUT DPD system, especially when it suffers significant feedback impairment and noise. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Ultracompact two‐way and four‐way SIW/HMSIW power dividers loaded by complementary split‐ring resonators

In this paper, two ultracompact power dividers based on the substrate integrated waveguide (SIW) and half‐mode SIW (HMSIW) technologies loaded by complementary split‐ring resonators (CSRRs) are presented. The presented structures are designed based on the theory of evanescent mode propagation. To obtain a size reduction, the CSRR unit cells are etched on the metallic surface of the SIW and HMSIW structures. First, a two‐way HMSIW power divider is reported. In this circuit, the concept of HMSIW is utilized aiming at a further size reduction in addition to the size reduction by the CSRR unit cells. Then, a four‐way SIW power divider is designed so that the direct coaxial feed is used for the input port and microstrip transmission lines are used for the output ports. Both two‐way and four‐way SIW/HMSIW power dividers at 5.8 GHz covering WLAN are designed, fabricated, and measured. They respectively have 0.18 × 0.21 λg² and 0.38 × 0.21 λg² total size. A fair agreement between simulated and measured results is achieved. The measured insertion losses are 0.5 ± 0.5 and 0.6 ± 0.5 dB for the two‐way and four‐way SIW/HMSIW power dividers, respectively, in the operating band of interest.     

A W‐band RF‐MEMS switched LNA in a 70 nm mHEMT process

This work presents a monolithic integrated reconfigurable active circuit consisting of a W‐band RF micro‐electro‐mechanical‐systems (MEMS) Dicke switch network and a wideband low‐noise amplifier (LNA) realized in a 70 nm gallium arsenide (GaAs) metamorphic high electron mobility transistor process technology. The RF‐MEMS LNA has a measured gain of 10.2–15.6 dB and 1.3–8.2 dB at 79–96 GHz when the Dicke switch is switched ON and OFF, respectively. Compared with the three‐stage LNA used in this design the measured in‐band noise figure (NF) of MEMS switched LNA is minimum 1.6 dB higher. To the authors’ knowledge, the experimental results represent a first time demonstration of a W‐band MEMS switched LNA monolithic microwave integrated circuit (MMIC) in a GaAs foundry process with a minimum NF of 5 dB. The proposed novel integration of such MEMS switched MMICs can enable more cost‐effective ways to realize high‐performance single‐chip mm‐wave reconfigurable radiometer front‐ends for space and security applications, for example. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:639–646, 2015.     

Application of the envelope‐transient method to the analysis and design of autonomous circuits

The envelope transient enables a very efficient simulation of circuits with two different time scales, such as those that contain modulated signals (for example, amplifier or mixers), where an accurate prediction of intermodulation distortion is needed. The method has also been extended to oscillator analysis, where it requires additional techniques in order to avoid convergence to degenerate mathematical solutions, for which the circuit is not actually oscillating. It allows an efficient analysis of transients in these circuits and an accurate prediction of the phase‐noise spectrum. This article presents an overview of the envelope‐transient method and its most recent applications to the simulation of autonomous circuits, such as free and forced oscillators, frequency dividers, and phase‐locked loops. Using this method, the operation bands of these circuits (which are delimited by qualitative stability changes or bifurcations) can be determined in a straightforward manner. This technique can also be applied to predict intermodulation distortion in self‐oscillating mixers and to simulate the response of synchronized oscillators containing modulated signals. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005.     

An efficient method of designing dual‐ and wide‐band power dividers with arbitrary power division

Capability of microstrip nonuniform transmission lines (MNTLs) for construction of dual‐band and broadband unequal Wilkinson power dividers with arbitrary‐way, arbitrary frequency band operations, and arbitrary power divisions is evaluated. Also, the MNTL transformers are introduced for dual‐band/broadband matching of the unequal output impedances of the MNTL power divider with arbitrary output terminal impedances. The strip width of MNTLs is considered variable and is written as a truncated Fourier series expansion. To show the validity of the design procedure, three experimental MNTL Wilkinson power dividers, which are dual‐band two‐ and three‐way power dividers with different power divisions working at 1 and 3.4 GHz and one broadband equal power divider working from 0.4 to 1.8 GHz, have been designed and fabricated. In the first ones with power division of 1.5, outputs isolation and ports matching of less than ?30 dB are achieved. Next, an extended recombinant structure is presented for achieving three‐way MNTL power dividers with dual‐band operation. The measured isolation between outputs and ports matching are better than 30 dB and measured forward transmissions are between ?4.87 and ?5.45 in two passbands of the divider. Also, for the proposed broadband divider, the measured isolation between the outputs is better than 13 dB in 127% desired bandwidth. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Optimal‐switched extended H∞ filter for nonlinear systems with stochastic uncertainties

The extended H_∞ filter (EH_∞F) is a conservative solution with infinite‐horizon robustness for the state estimation problem regarding nonlinear systems with stochastic uncertainties, which leads to excessive costs in terms of filtering optimality and reduces the estimation precision, particularly when uncertainties related to external disturbances and noise appear intermittently. In order to restore the filtering optimality lost due to the conservativeness of the EH_∞F design, we developed an optimal‐switched (OS) filtering mechanism based on the standard EH_∞F to obtain an optimal‐switched extended H_∞ filter (OS‐EH_∞F). The OS mechanism has an error‐tolerant switched (ETS) structure, which switches the filtering mode between optimal and H_∞ robust by setting a switching threshold with redundancy to uncertainties, and a robustness‐optimality cost function (ROCF) is introduced to determine the threshold and optimize the ETS structure online. The ROCF is the weighted sum of the quantified filtering robustness and optimality. When a weight is given, the proposed OS‐EH_∞F can obtain the optimal state estimates while maintaining the filtering robustness at an invariant ratio. A simulation example of space target tracking has demonstrated the superior estimation performance of the OS‐EH_∞F compared with some other typical filters, thereby verifying the effectiveness of using the weight to evaluate the estimation result of the filters.     

Recent advances in microwave active filter design. Part 1: Low‐frequency techniques and noise optimization

This two‐part article presents a representative sample of recent advances in microwave active filter design. In part one, we discuss design techniques based on both analog and digital low‐frequency methods that have been adapted to microwaves. From circuits with analog origins, we present simulated results, with some experimental verification, for a frequency‐dependent negative resistance (FDNR) and active‐inductance MMIC bandpass filters. From circuits with digital origins, we present experimental results for recursive filters, including MMIC bandpass and bandstop structures as well as higher‐order cascaded sections. Part one concludes with a discussion of the noise‐wave formalism and experimental results for active‐recursive and tunable ring‐resonator filters with minimum noise figure. © 2002 Wiley Periodicals, Inc. Int J RF and Microwave CAE 12: 159–176, 2002.     

PDα‐type iterative learning control for fractional‐order linear continuous‐time switched systems

For a class of fractional‐order linear continuous‐time switched systems specified by an arbitrary switching rule, this paper proposes a PD^α‐type fractional‐order iterative learning control algorithm. For systems disturbed by bounded measurement noise, the robustness of PD^α‐type algorithm is first discussed in the iteration domain and the tracking performance is analyzed. Next, a sufficient condition for monotone convergence of the algorithm is studied when external noise is absent. The results of analysis and simulation illustrate the feasibility and effectiveness of the proposed control algorithm.     

A multiband carrier generation architecture for UHF, 2.4 GHz,and 5 GHz ISM applications

Novel multiband carrier generation architecture is proposed that can be applicable for RFID reader, WLAN 802.11a‐b‐g, and ZigBee sensor network, and implemented with 0.18 μm CMOS technology. In the proposed architecture, a quadrature voltage controlled oscillator (QVCO) is implemented by coupling two differential cross‐coupled LC VCOs to generate in‐phase (I) and quadrature (Q) signals operating at one‐thirds of the 5 GHz frequency range. As well, the differential second harmonic signal of the VCO core frequency is generated by mixers, and then converted to I/Q signals via a single‐stage tunable polyphase filter. By single sideband mixing of the I/Q signals of the QVCO and the polyphase filter, a cleaner carrier signal can be generated in the frequency band of 5 GHz. By including extra frequency dividers, the architecture can also be reconfigured to generate UHF band and 2.4 GHz band. The proposed architecture draws about 32 mA including the QVCO core current consumption of 2.8 mA from 1.8 V supply. The measured tuning frequency of the QVCO core ranges from 1.57 to 1.84 GHz. The measured phase noise is ?104.5 dBc/Hz at 1 MHz offset from 4.84 GHz. The chip layout occupies an area of 1.44 × 1.4 mm² on Si substrate, including the DC and RF pads. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.     

An efficient combination of digital predistortion and OFDM clipping for power amplifiers

This article presents a strategy for enhancing efficiency in power amplifiers (PAs) by combining digital predistortion (DPD) linearization and clipping strategies for orthogonal frequency division multiplexing signals in a WiMAX scenario. On the one hand, by reducing the peak‐to‐average power ratio of multicarrier signals using the well‐known clipping technique, it is possible to perform a more efficient PA amplification. On the other hand, nonlinear and linear distortion introduced by the PA operating close to saturation is compensated by the baseband adaptive DPD linearizer. The DPD has to counteract not only the PA nonlinear behavior, but also its dynamics. A test‐bench implementing a WiMAX transmitter was deployed to evaluate the possibilities for enhancing power efficiency while fulfilling the demanded linearity requirements. Experimental results showing the power efficiency and linearity enhancement achieved by the proposed strategy are provided. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.     

Noise‐margin analysis of a‐Si:H digital circuits

Abstract— The noise margin is one of the fundamental metrics in evaluating the viability and robustness of digital circuits. An analytical model of amorphous‐silicon digital‐circuit noise margin was developed, including the effects of circuit aging. The threshold voltage of a‐Si:H transistors increases over time with electrical stress, degrading the performance and eventually leading to circuit wear‐out. Since static and dynamic inverters are the basic digital‐circuit design elements, they are the basis for this analysis. The analytical model is verified with experimental measurements. The lifetime of dynamic a‐Si:H digital circuits is found to exceed the lifetime for static a‐Si:H circuits by a factor of 2–3. Although the lifetimes are relatively short (～10⁵ sec) and under continuous electrical stress, they are sufficient for low‐duty‐cycle applications.     

Balanced power dividers with improved bandwidth using folded lines

Two novel wideband balanced‐to‐unbalanced power dividers based on transmission lines and coupled lines are proposed in this article. Multifunction can be realized without cascading single devices with common mode suppression. The desired power divider configurations can be obtained using the even/odd‐mode characteristic impedance of the coupled lines and characteristic impedance of the transmission lines. A resistor in the middle of two single‐ended ports is used to realize isolation between output ports. Two prototypes of wideband balanced‐to‐unbalanced power dividers operating at 2.3 GHz with differential‐mode bandwidths of 79.6 and 134.1% are designed and fabricated. The theoretical and measured results are in good agreement and show good in‐band performances.     

A broadband coplanar waveguide to rectangular waveguide power divider using a slot

In this article, a broadband coplanar waveguide (CPW) to rectangular waveguide power divider using the dipole slot is proposed. The power divider consists of an input CPW port and two output rectangular waveguide ports. The CPW to rectangular waveguide power divider using the dipole slot has a return loss larger than 15 dB and an insertion loss equal to 3.08–3.27 dB in the whole X‐band (8.2–12.4 GHz). Furthermore, to broaden the bandwidth, the dipole slot is replaced by the bow‐tie slot. The CPW to rectangular waveguide power divider using the bow‐tie slot yields a return loss larger than 16 dB and an insertion loss equal to 3.05–3.29 dB from 8 to 13 GHz, which exceeds the X‐band. To verify our design, power dividers that use the dipole slot or the bow‐tie slot are fabricated and measured. The measurement results of both power dividers are in good agreement with the simulation results. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Event‐triggered fault detection for switched systems with time‐varying sojourn probabilities

In this paper, a codesign strategy of an event‐triggered scheme and a fault detection filter (FDF) is developed for the networked switched systems with delayed measurements. A novel switching rule is proposed to better describe the switching behavior in a real system, under which the probability staying in each subsystem is time varying and results in a piecewise continuous system dynamics. An event‐triggered strategy based on the relative error with respect to the delayed measurement signal is established to reduce the communication burden. Our attention is concentrated on the construction of an event‐triggered fault detection technique for the proposed switched system with delayed measurements. Combining the stochastic analysis techniques and the average dwell time (ADT) method, a sufficient condition is obtained to guarantee the finite‐time boundedness of the generated residual system, the sensitivity of the residual signal to faults, and the disturbance attenuation of the switched system to external disturbances. Based on the established condition, a codesign strategy is developed to get the event‐triggered threshold and the FDF gain. Finally, two simulation results verify the effectiveness of the proposed design method.     

A novel broadband magnetoelectric antenna

A broadband antenna based on magnetoelectric dipole is proposed. The proposed antenna is composed of a bowtie‐shaped electric dipole and an elliptical ring antenna that works as a magnetic dipole. For a broadband performance, a microstrip‐to‐coplanar stripline transition balun is used to excite the antenna. All of them are printed on the same plane perpendicular to the ground. To validate the design, prototypes of the proposed antenna have been fabricated and measured. The measurement results show that the antenna has a wide impedance bandwidth of 66.7% (2.45–4.90 GHz) for voltage standing wave ratio (VSWR) less than 2 and a gain of 6.0–7.3 dBi over the operating frequency band. Meanwhile a high front‐to back ratio better than 16 dB over the operating frequency is achieved. The agreements between the simulation and measurement results indicate that the proposed antenna is suitable for wireless communication systems and phased array systems. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:213–218, 2015.