Active Microwave Circuits Research Articles

Analysis of waveguide inserted by a metallic sheet of arbitrary shape with the method of lines

In this paper, one type of waveguide three-dimension discontinuity, rectangular waveguide inserted by a metallic sheet of arbitray shape with zero thickness, is firstly analysed by using the Method of Lines. This waveguide discontinuity can be regarded as basic unit of microwave and MMW passive components and active circuits. Numerical results are in good agreement with physical meanings and other published data. Numerical results of several characteristics are presented at the end of the paper, including convergent characteristic of which the scattering parameters are depended on the number of discretization lines, dependence of scattering parameters on the size of metallic sheet and frequency response of scattering parameters.

Computer‐aided analysis of nonlinear microwave circuits using frequency‐domain nonlinear analysis techniques: The state of the art

AbstractFrequency‐domain nonlinear analysis techniques for the simulation of active microwave circuits solve the linear and nonlinear network equations entirely in the frequency‐domain. by so doing, they avoid the aliasing problems inherent in piecewise harmonic balance approaches. Consequently, frequency‐domain techniques have extremely wide dynamic range and easily accommodate high order multitone excitation. However, this is at the expense of requiring more restrictive nonlinear device models. There are a large number of frequency‐domain nonlinear analysis techniques but all are based on functional expansions which enable the frequency components of the output spectrum to be calculated directly from the input spectrum. These techniques have been used to analyze many nonlinear circuits and are the only candidates for the hierarchical simulation of nonlinear microwave circuits. This paper first uses frequency‐domain concepts to discuss nonlinear distortion phenomena, then, a review of the frequency‐domain nonlinear analysis literature is made with the aim of presenting the major advances in these techniques.

An MMAC C-band FET feedback power amplifier

A feedback power amplifier using miniaturized microwave active circuit (MMAC) technology was developed for satellite C-band applications. This design demonstrates that a strong negative feedback can be implemented in the microwave frequencies to improve amplifier linearity and output power over a 750 MHz bandwidth. The amplifier provides a third-order intermodulation distortion improvement of 7 to 9 dB across the band at backoff, compared to results obtained using the conventional approach without feedback. The theory, proof-of-concept experiment, design, and MMAC implementation of the feedback amplifier are presented. >

Computer-aided-design techniques based on feedback concepts

Proven feedback theory applied to linear and nonlinear microwave active circuits enables designers to predict true stability margins in amplifiers. H.W. Bode's return ratio can always be defined for transistors, and some applications in analysis and design are clarified by examples. Combined with a semigraphical technique, it shows the influence of feedback on reflection properties of singly terminated transistors. Return ratio is a powerful CAD concept for oscillators. The first known combination with nonlinear simulation using the direct method is both effective and accurate, as demonstrated for a nonlinear VCO. Possible extensions to matching and interstage design and to other nonlinear microwave circuits are noted. The current worldwide drive towards more realistic characterisation and modelling of active and passive components and of circuits will provide data from which more accurate assessments of feedback can be achieved using the return ratio concept

Generalized scattering parameters and their applications

The physical concepts of power waves, exchangeable power, power wave reflection coefficients and generalized scattering parameters are interpreted in this paper. Extensions are made. Several examples for application are cited. It is proved that these tools are very useful when dealing with microwave active circuits, especially those including negative resistances.

Generalised nonlinear theory for one-port microwave active circuits

A nonlinear model characterising two-terminal microwave active circuits under dynamic and steady-state conditions is developed from a generalised circuit approach. The model considers the active circuit as a black box consisting of a one-port passive circuit and a one-port active device. The response of the active and passive circuits to modulated time-dependent signals with slowly varying amplitude and phase is derived. The model takes into consideration the nonlinear dependence of the active-device currents on RF voltage amplitude and frequency; also it considers the effects of nonlinearities of the passive circuit on frequency. This makes the model suitable for applications which employ strongly modulated signals for which Van der Pol's cubic nonlinearity model fails.

Nonlinear modelling applied to one-port microwave active circuits

A recently developed nonlinear model for characterising two-terminal microwave active circuits under dynamic and steady-state conditions has been reduced to a form suitable for numerical calculations. The simplified model retains the nonlinear dependence of the active-device currents on RF voltage and frequency and it also takes into consideration the nonlinearity in frequency of the passive circuit. The model is applied to two hypothetically postulated Impatt-diode oscillators and dynamic solutions are calculated. Furthermore the calculated transients are compared with those obtained for a practical oscillator.

Broad-band circulator models for active microwave circuit analysis

A general method is presented for determining a broad-band equivalent circuit of a lossy, nonideal circulator from the scattering parameters over the frequency range of interest. The equivalent circuit has application to the design and analysis of circulator-coupled circuits such as amplifiers and oscillators. The method is applied to two different circulator forms, in coaxial line and waveguide, to show the close agreement to measured performance that can be attained by the method in practice.

Book Review: Passive and Active Microwave Circuits

Book Review: Passive and Active Microwave Circuits

Passive and Active Microwave Circuits

Passive and Active Microwave Circuits

On the Use of Describing Functions in the Study of Nonlinear Active Microwave Circuits

It is shown that a nonlinear microwave circuit can easily be represented by a feedback model. This formalistic identity with nonlinear control systems suggests that methods and results can be borrowed from nonlinear control theory. The describing function technique, a concept that has been developed to a high degree of sophistication in control theory, is applied to the problem of phase-locking of microwave oscillators. The use of describing functions in the study of nonlinear microwave circuits may give a simple conceptual understanding of locking phenomena, for example, and thereby reduce computational efforts.

New design techniques for active microwave circuits

Two methods of measuring output power as a function of frequency and load impedance of an oscillator or a reflection amplifier are presented. The measurements are made under true large signal conditions. The two methods are applied to an L-band transistor oscillator design. The oscillator data are very close to those expected from the measurements.