Analytical and experimental study of LINC amplifier using unmatched Wilkinson combiners

This work presents an analytical and experimental study of LINC power amplifier where an unmatched Wilkinson combiner is used at the output of two class-B amplifiers. This combiner is called unmatched because of the elimination of the one hundred ohms resistor from its input. This resistor is used to guaranty a good impedance matching between the combiner and the amplifier outputs. An amount of reflection coefficient can be presented at the input of the combiner depending on the signals phase different of the two LINC branches which that may damage the linearity of the amplified signals. Our Analytical study in this paper presents equations for the power efficiency and the signal linearity showing that despite of reflection between the combiner and the amplifiers, very good efficiency and linearity will be obtained. An ADS simulation and experimental work of the LINC system is performed shows an excellent agreement with the analytical study.     

CMOS Outphasing Class-D Amplifier With Chireix Combiner

This letter presents a CMOS outphasing class-D power amplifier (PA) with a Chireix combiner. Two voltage-mode class-D amplifiers used in the outphasing system were designed and implemented with a 0.18-mum CMOS process. By applying the Chireix combiner technique, drain efficiency of the outphasing PA for CDMA signals was improved from 38.6% to 48% while output power was increased from 14.5 to 15.4 dBm with an adjacent channel power ratio of -45 dBc.     

On the average crossing rates in selection diversity

This letter presents new results on the average crossing rate of the combined signal of a selection diversity in Rayleigh fading channels. Exact closed-form expressions are derived for the inphase zero crossing rate, inphase rate of maxima, phase zero crossing rate, and the instantaneous frequency zero crossing rate of the output of the selection combiner. The utility of the new theoretical formulas, validated by Monte Carlo simulations, are briefly discussed as well     

Systematic linearity analysis of RFICs using a two-port lumped-nonlinear-source model

A frequency-domain lumped-nonlinear-source behavioral model is presented. This generalized two-port nonlinear model is used to characterize the linearity of either RF devices or circuits. Similar to two-port ac behavioral models (i.e., using S-, Y-, Z-, or H-parameters), this nonlinear model supports combinations such as shunt, series, and cascade, and thus is suitable for systematic analysis. This model is then applied to analyze the impact of harmonic impedance on the second-order intermodulation and third-order intermodulation of a state-of-the-art SiGe HBTs and circuits. Simple and general linearity expressions are then derived. Harmonic load-pull simulations and measurements are used to demonstrate the usefulness of the proposed analysis technique.     

Analysis of butt coupling in photonic Crystals

We present a detailed analysis of butt coupling from conventional dielectric waveguides into photonic crystal waveguides. Closed-form expressions for the reflection and transmission matrices based on an eigenmode expansion technique are derived and validated by means of simulations. We use them to investigate butt-coupling losses in two kinds of photonic crystal structures: one formed by rods with a higher refractive index than the surrounding medium and the other formed by air holes inserted in a high-refractive-index medium. The origin and difference of coupling losses between the two photonic crystal structures is analyzed and discussed. We show that, although the coupling efficiency is much worse in the former structure, it can be significantly improved by choosing the optimum interface position that minimizes the mode impedance mismatch. Furthermore, the dependence of coupling efficiency on frequency is also analyzed. Finally, we also relate some traditionally used approximate formulas to our rigorous expressions.     

A mathematical characterization and analysis of a feedforward circuit for CDMA applications

Feedforward is known to be one of the best methods for power amplifier linearization due to its superior linearization performance albeit with relatively poor power efficiency. Here we present the derived closed-form expressions, which relate the main channel power and distortion products at the output of a simple feedforward circuitry to the circuit parameters. Consequently, a mathematical handy tool is achieved toward specifying the circuit parameters rapidly for optimum linearity performance and efficiency. The main and error amplifiers used in the feedforward are assumed to have a third-order AM/AM nonlinearity. The derived expressions are verified by simulation. The conditions for the validity of the model choice are highlighted. For the matched and lossless case, a compact relationship is obtained, which clearly demonstrates the tradeoff between nonlinearities of main and error amplifier for a given system linearity and output power. Delay mismatch is also included in the analysis.     

Design and performance analysis of mismatched Doherty amplifiers using an accurate load-pull-based model

An active load-pull-based large-signal modeling approach, suitable for designing and optimizing load modulated amplifiers such as Doherty or linear amplification using nonlinear components based amplifiers, is proposed. A Doherty amplifier was designed by optimizing the dynamic loads seen by the amplifier's transistor using a large-signal load-pull-based behavior model built into computer-aided-design software. Simulation and measurement results showed good agreement, while results obtained using an empirical model of this transistor demonstrated discrepancies. The load-pull-based model was then used to study performance degradation of the Doherty amplifier when load impedance was moved out from the perfect 50 /spl Omega/. It has been shown that the load mismatch can greatly affect the linearity and efficiency performance of the amplifier unless its phase is controlled and kept within a specific range. A load mismatch system level compensator scheme, capable of restituting the linearity loss and maintaining the power-added efficiency close to its maximum range, is proposed.     

短槽混合电路功率合成器的优化设计

本文提出了用负阻非线性网络模型来表征短槽混合电路功率合成器相互注入锁定现象的新思想,该模型比较完整地反映了相互注入锁定中的非线性特性,在导出了功率合成系统的非线性方程之后,给出了达到最大功率合成效率时振荡器工作参数的优化方法。优化结果与实验结果吻合较好。     

Diffraction of plane waves by a resistive strip residing between two impedance half-planes

A uniform asymptotic solution is presented for the diffraction of E_z polarized plane waves by a resistive strip residing between two impedance half-planes. The analysis proceeds from triple integral equations approach which leads to a system of uncoupled modified Wiener-Hopf equations (MWHE). This system is then reduced to two pairs of Fredholm integral equations of the second kind which are solved by successive approximations. Diffracted field expressions are derived up to the third order terms which include the surface wave field effects in a uniform manner.     

Single-Frequency Analysis of Radial and Planar Amplifier Combiner Circuits

A single-frequency analysis of radial and planar amplifier combiner circuits is presented and expresses the dependence of amplifier combiner performance on the scattering parameters of the amplifiers and combiner/divider networks. The analysis results in useful design guidelines to achieve optimum performance for small variations in amplifier parameters and graceful degradation under the condition of amplifier failure. Several examples are presented to verify the accuracy of the derived expressions. The scattering matrices of radial and planar combiner/ divider networks are derived in the Appendix.     

Instantaneous junction temperature evaluation of high-power diodes(thyristors) during current transients

In this paper, an approach to the instantaneous junction temperature evaluation of high-power diodes (thyristors) is presented. The model allows obtaining the instantaneous junction temperature waveform starting from the expressions of the device transient thermal impedance and forward voltage drop. The linearity properties of resistors and capacitors (RCs) networks are used to obtain the thermal system transfer function from the transient thermal impedance curve. Thus, an expression that relates the forward voltage drop to the forward current and the junction temperature is used to “feedback” the influence of the temperature variation on the device forward characteristic. The model is also validated by comparing the results obtained from simulation against the one obtained from surge tests performed on one sample device     

基于天牛须算法的宽带功率合成器设计

为了提高宽带Wilkinson功率合成器的设计效率,基于奇偶模分析法和传输线理论,首先列出Wilkinson合成器的电路参数方程,再导出适应度函数,采用天牛须算法对其优化设计,获得功率合成器的设计参数,并且通过HFSS根据初始参数建立仿真模型验证其可行性。与粒子群算法相比,在本文的适应度函数求解过程中,天牛须算法收敛精度较好,寻优效率较高。最后选取两只X波段4W GaN功率放大器芯片组成功率合成模块,在8.5~11GHz频率范围内,测试结果表明,其饱和输出功率大于6.8W,合成效率优于86%,验证了Wilkinson功率合成器的带宽和高合成效率。     

Accurate design equations for 50-600 GHz GaAs Schottky diodevaractor frequency doublers

To maintain the simplicity of equivalent circuit modeling while dramatically increasing accuracy, a set of analytical design equations are derived for nonlinear circuit analysis of 50-600 GHz Schottky diode varactor frequency doublers. These analytical design equations contain semi-empirical coefficients derived from a high performance Monte Carlo harmonic-balance (MCHB) numerical simulator. Both optimal diode embedding impedances and diode parameters for optimal doubler performance can be calculated. The calculated optimal embedding impedance is that which gives the best doubler efficiency for the given diode parameters, the circuit input power, and the input frequency. Thus, these equations allow for multiplier co-design from both a device and circuit point of view in a relatively simple, efficient and accurate manner     

Unified analysis of EGC diversity over Weibull fading channels

In this paper, the performance analysis based on PDF approach of an L ‐branch equal gain combiner (EGC) over independent and not necessarily identical Weibull fading channels is presented. Several closed‐form approximate expressions are derived in terms of only one Fox H‐function as PDF, cumulative distribution function, and moments of the EGC output Signal‐to‐noise ratio (SNR), outage probability, amount of fading, channel capacity, and the average symbol error rate for various digital modulation schemes. All results are illustrated and verified by simulations using computer algebra systems.     

SEP performance of coherent MPSK over fading channels in the presence of phase/quadrature error and I-Q gain mismatch

This letter presents a joint approach to the symbol-error probability (SEP) of coherent M-ary phase-shift keying in a situation where the phase error, quadrature error, and in-phase-quadrature (I-Q) gain mismatch problems take place all concurrently over an additive white Gaussian noise and arbitrary fading channel. A set of equations that characterizes the conditional SEP on an instantaneous fading signal-to-noise ratio is derived in the form of the Craig representation.     

高功率非对称泵浦耦合器理论研究

高功率非对称泵浦耦合器是高功率连续光纤激光器的关键无源光器件,它可以将多路泵浦光高效率地耦合进主光纤中,从而为光纤激光器提供所需的泵浦光功率,但已有双波导耦合理论并不能直接应用于该型耦合器的研究。为解决这一问题,在双波导定向耦合器的不完全耦合理论基础上,针对高功率泵浦耦合器非对称的特点,将其耦合系数和光功率方程组做了进一步推导,并进行了数值仿真,研究结果表明:两光纤中的光功率按照一定周期变化,当泵浦光纤的锥角在1~1.5之间时,可以获得97%以上的最佳耦合效率,且与其对应耦合长度的局部变化对耦合效率的影响较小。该研究结果对高功率非对称泵浦耦合器的设计及制作均具有指导意义。     

Moments-based approach to the performance analysis of equal gain diversity in Nakagami-m fading

In this letter, an alternative moments-based approach for the performance analysis of an L-branch predetection equal gain combiner (EGC) over independent or correlated Nakagami-m fading channels is presented. Exact closed-form expressions are derived for the moments of the EGC output signal-to-noise ratio (SNR), while the corresponding moment-generating function (MGF) is accurately approximated with the aid of Pade/spl acute/ approximants theory. Important performance criteria are studied; the average output SNR, which is expressed in closed form both for independent and correlative fading and for arbitrary system parameters, the average symbol-error probability for several coherent, noncoherent, and multilevel modulation schemes, and the outage probability, which are both accurately approximated using the well-known MGF approach. The proposed mathematical analysis is illustrated by various numerical results, and computer simulations have been performed to verify the validity and the accuracy of the theoretical approach.     

基于GaN的大功率高线性固态发射机研制

介绍了一种GaN大功率高线性固态发射机。利用GaN HEMT的高功率特性,结合新型波导魔T低损耗功率合成的特点,在7.9~8.4GHz范围内实现了连续波饱和输出功率大于200W,效率大于20%。此外,应用新型模拟预失真方法提升功放的线性化指标,在额定输出功率下三阶交调指标(IMD3)优于-30dBc,改善功放的线性度11dB。该发射机具有输出功率大,线性度好等优点,整体性能优于国外同类产品。     

线缆仿真器的校准方法研究

针对线缆仿真器的校准,国内还没有相关的校准规范和检定规程,对线缆仿真器的校准就成为迫切需要解决的问题。利用阻抗转换器解决了线缆仿真器和网络分析仪的阻抗不匹配和连接端口不同的问题,使用网络分析仪测试线缆仿真器的插入损耗,通过实验确定了线缆仿真器的插入损耗的校准方法。对数据进行不确定度的评定分析证明了上述校准方法能达到校准线缆仿真器插入损耗的要求,为编制线缆仿真器的校准规范或检定规程解决了技术上的难题。     

Performance Analysis of Rayleigh Fading Channel in the Presence of Co-channel Interference with Multiple Interferers Under Different Adaptation Policies

In this paper, an approach to performance analysis on signal-to-interference ratio operating over Rayleigh fading channels experiencing an arbitrary number of multiple, Rayleigh co-channel interferers is presented. We have presented a general analysis of selection combining, where each branch experiences an arbitrary number of multiple equal power co-channel interference. Useful closed-form expressions are derived for the probability density function and cumulative distribution function at the output of the combiner. Also, outage analysis is performed in order to show the effects of interferers and diversity order. Capacity per unit bandwidth expressions are derived for selection diversity scheme under different adaptation policies.