Power optimization of high-efficiency microwave MESFET oscillators

Achieving high output power and efficiency in GaAs MESFET oscillators is mainly hampered by the device's parasitics, its static I-V characteristics, and the circuit embedding impedance. In this paper, the derivation of the relationship between oscillator output power and various circuit and device parameters is presented. From these analytical expressions, optimum operating conditions for maximum oscillator output power and efficiency are determined. The analysis method employed here is based upon a quasi-linear approach and an open-loop model of the oscillator. The design procedure is verified by measurements on an experimental circuit, which have demonstrated a dc/radio-frequency conversion efficiency of 54%     

Nonlinear optimization tools for the design of microwave high-conversion gain harmonic self-oscillating mixers

A new optimization method is presented for the design of microwave high-conversion gain harmonic self-oscillating mixers (SOMs). It is based on the control of the harmonic content of the transistor input-voltage waveform of the self-oscillation, through the use of a nonperturbing auxiliary generator and a substitution generator. The combination of the two generators allows obtaining the optimum harmonic content of the transistor-gate voltage waveform for a maximum conversion gain. Two different downconverter circuits have been designed using this method, a second harmonic SOM and a third harmonic SOM, obtaining a high conversion gain. A good agreement between the simulated and experimental results has been found.     

Solution-grown epitaxial InP for high-efficiency circuit-controlled microwave oscillators

High-purity epitaxial InP has been prepared by solution growth with free-donor concentrations of 2×1015 cm?3 and liquid-nitrogen mobility of 49 000 cm2/Vs. The growth technique is described and the electrical properties of the layers are given. The microwave characteristics of diodes made on this material are described, and these, together with experiments on specially constructed diodes, suggest that a circuit-controlled bulk negative-resistance mode can be set up in this material. Devices have been produced which give up to 16% efficiency when operated in coaxial circuits at X band.     

Guidelines for the design of high-efficiency mode avalanche diode oscillators

In this paper, we have developed a set of guidelines for the design of high-efficiency mode avalanche diode oscillators, based on the previously published theory of this mode. An important feature in the development is the "design triangle"--an area in design space which is compatible with the existence of a set of waveforms characterized by efficiencies of up to 60 percent. The particular subregion of the design triangle which is most suitable depends on whether the goal is CW or high-pulsed-power operation. Examination of available data for the highest efficiency oscillators indicates that most of these are likely exhibiting oscillations of the type described and that the quantitative results developed are indeed applicable. In order to achieve extremely high efficiencies, severe circuit demands must be met; doing this systematically is likely to prove quite difficult. Combining the design results with thermal calculations indicates that one may anticipate UHF or L-band single-chip CW power levels of over 20 W with a conventional copper heat sink and considerably more power with a heat sink of type IIA diamond.     

Nonlinear mixed analysis/optimization algorithm for microwave poweramplifier design

A nonlinear mixed analysis/optimization algorithm for the design of microwave power amplifiers is presented. Matching conditions for optimum power and efficiency performance are imposed together with the balancing equations of the nonlinear analysis in a consistent way. The analysis/preoptimization of the power stage requires a computation time comparable to or smaller than a single conventional harmonic balance analysis. The algorithm forms the basis of a design procedure for the fulfilment of design specifications in terms of output power, power-added efficiency, and gain. Comparisons to the results of commercial CAD nonlinear analysis programs are presented     

Nonlinear analysis of microwave FET oscillators using Volterraseries

A novel approach for determining the amplitude and frequency of nonlinear FET oscillators is presented. The nonlinear elements of the active device are modeled by the Volterra series method. The frequency and amplitude of oscillation are then calculated by solving two algebraic equations. Experimental results obtained from a constructed oscillator confirm the validity of the theory, the discrepancy between measured and calculated frequency and amplitude values being less than 10%     

Nonlinear design of multiple-cavity switchable dielectric-resonator oscillators

The application of nonlinear CAD techniques to the design of multiple-cavity dielectric-resonator oscillators is demonstrated. The circuit topology consists of an FET oscillator which can be coupled to one of several dielectric resonators by means of a diode switching network. The circuit is numerically designed as a whole making use of a novel broadband optimisation technique especially devised for autonomous nonlinear circuits. At each fundamental frequency of interest the steady state of oscillation is determined by harmonic-balance analysis and at the same time the oscillator is tuned to the prescribed frequency by changing a parameter of the corresponding resonator. The electrical performance is simultaneously specified at all the fundamentals, and the optimisation is carried out with respect to the circuit parameters of the frequency-invariant part of the network.<>     

Nonlinear analysis tools for the optimized design of harmonic-injection dividers

New nonlinear analysis tools for harmonic-injection dividers are presented based on bifurcation concepts. The advantage of these tools is their application simplicity and efficiency, which has enabled their use for actual circuit design and optimization. The tools allow control over the divided frequency and output power and predict the variation of the synchronization bands versus the circuit element values, which facilitates design correction. They have been extended to the analysis and optimization of phase-locked harmonic-injection dividers, which contain a low-frequency feedback loop. The use of this loop, together with the accuracy of the analysis, has enabled the implementation of novel frequency-division functions, such as the division of variable order, versus a circuit parameter, or the division by fractional order. The output noise of the frequency dividers is analyzed through the conversion-matrix approach, studying the noise variation along the division bands. The new techniques have been applied to the design of a frequency divider by order 4 and 5, with 18-GHz input frequency, and excellent agreement with experimental results has been obtained.     

Improved diode and circuit procedures for high-efficiency S-band oscillators

Avalanche diodes designed on the basis of recently published guidelines for the high-efficiency mode and a new microstrip circuit were combined to obtain record S-band pulsed oscillator powers. Outputs of up to 325 W from a pair of chips mounted in one package were obtained. The new circuit is characterized by a number of advantages of a practical nature including ruggedness and ease of tuning.     

Experimental analysis of high-efficiency avalanche-resonance pumped oscillators

Silicon avalanche diodes yielded efficiencies of 10, 20 and 45% at the first, second and seventh subharmonic of an essential self-generated pump signal close to the diode's avalanche resonance. Measured large-signal impedances and dynamic characteristics explain the efficiency degradation at higher frequencies and suggest measures for further improvement.     

A circuit mode chart for high-efficiency avalanche diode oscillators

A circuit mode chart for use with TRAPATT diode microwave oscillators is described. The chart relates the diode mean voltage and mean current levels to the parameters of the diode microwave waveforms. It consists of lines drawn in the diode `mean current-mean voltage' plane which define boundaries to an area in which the oscillator can operate. With the exception of a bias load line, these lines originate from consideration of the maximum and minimum values of the diode voltage waveform and from the properties of the two components, the trigger waveform, and the extraction waveform, into which the diode voltage may be resolved. It is shown how the chart takes account of waveform clipping at the breakdown voltage, frequency doubling, triggering, trapping, frequency shifts, an efficiency reduction effect, and the existence of a low-frequency cutoff. It is also shown how a dynamic characteristic, as well as a static breakdown characteristic may be incorporated on the chart.     

High-power high-efficiency operation of read-type IMPATT-diode oscillators

C.W. operation of GaAs Schottky-barrier Read-type IMPATT-diode oscillators is reported. These devices exhibited efficiences from 20 to 24% with output powers of 2 ~ 3 W c.w. in the Ku-band. The best efficiency was 24%, with an output power of 1.8 W c.w., while the maximum output power was 3.2 W c.w., with an efficiency of 20.7% at frequencies near 14 GHz.     

General stabilization techniques for microwave oscillators

A general stabilization technique is proposed to suppress undesired spurious oscillations in microwave oscillators. The purpose is to eliminate these oscillations while maintaining the oscillation frequency and amplitude of the originally-unstable solution. The main advantage of the technique is its wide generality of application, not restricted to low-frequency spurious oscillations. It has been tested on an unstable 18-GHz push-push oscillator that has been manufactured and measured, with very good agreement with the simulation results.     

Large signal design of broadband monolithic microwave frequencydividers and phase-locked oscillators

This paper presents a design method for phaselocked devices such as frequency dividers or injection-locked oscillators. The method requires a full nonlinear analysis of the circuit. This analysis relies upon harmonic balance techniques and is suitable for monolithic circuits simulation. First, a modified formulation of the general harmonic balance equation is proposed which includes the presence of probes. These probes allow us to suppress the degenerated solution of the HB equation in autonomous cases. Moreover, a global stability analysis of phaselocked regimes is carried out. It provides invaluable information on the nonlinear behavior of the device. In particular, synchronization bandwidths as well as power ranges for which the circuit can be synchronized are obtained from the stability loci drawn in the parameter space. All these features have been used to design a broadband monolithic frequency divider, and the simulated and experimental results have been compared with very good accuracy. Therefore, the method proposed is a very useful tool for the design of potentially unstable circuits     

CAD tools for efficient RF/microwave transistor modeling and circuit design

In today’s radiofrequency and microwave communication circuits, there is an ever-increasing demand for higher integration and miniaturization. This trend leads to massive computational tasks during simulation, optimization and statistical analyses, requiring robust modeling tools so that the whole process can be achieved reliably. In this paper, the authors proposed frequency- and time-domain computer-aided design tools that can characterize RF/microwave field effect and heterojunction bipolar transistors and efficiently predict a circuit performance. The proposed tools are demonstrated through examples.     

Optimum Schottky-barrier height for high-efficiency microwave transferred-electron diodes

Optimum Schottky-barrier heights are given to make high-efficiency GaAs and InP tnmferred-electron diodes by injecting electrons directly into the upper valley from cathode contact.     

Design of cavity-stabilised microwave oscillators

A comparison is made between transmission reaction and reflection cavity-stabilised oscillators. Their essential features such as maximum loaded Q factor and tunuble frequency range are shown to differ markedly. Based on these considerations, outlines are given for designing highly stable microwave oscillators.     

Nonlinear device model of microwave power GaN HEMTs for high power-amplifier design

This paper presents a nonlinear equivalent circuit model of microwave power GaN high electron-mobility transistors (HEMTs), amenable for integration into commercial harmonic balance or transient simulators. All the steps taken to extract its parameter set are explained, from the extrinsic linear elements up to the intrinsic nonlinear ones. The predictive model capabilities are illustrated with measured and simulated output power and intermodulation-distortion data of a GaN HEMT. The model is then fully validated in a real application environment by comparing experimental and simulated results of output power, power-added efficiency, and nonlinear distortion obtained from a power amplifier.     

Varactor diode for tuning high-power solid-state microwave oscillators

A novel varactor diode has been developed for tuning high-power microwave solid-state oscillators. The resulting output power against frequency remains much flatter than conventional high-power varactor-tuned oscillators.