Adam K. Jastrzebski

A tunable all-pass MMIC active phase shifter

This paper describes a novel structure for a monolithic-microwave integrated-circuit active phase shifter based on a bridge all-pass network. The design procedure has been developed, leading to a fixed-frequency circuit with large tunable phase variation, associated to a low-gain ripple, and requiring nearly no design optimization. Simulated results predicted an analog tunable 180/spl deg/ phase variation, at 5-GHz operation frequency. The circuit was implemented using GEC-Marconi pseudomorphic high electron-mobility transistor H40 technology, and measured results validated the proposed design method and circuit structure.

The design of microwave monolithic voltage controlled oscillators

The paper describes a complete design procedure for a monolithic microwave VCO. The procedure includes a computer simulation of the nonlinear active circuit. Practical implementation of the designed circuit and measured results are given.

Compuier-Aided Design of Microwave Integrated Circuits

This paper describes a general computer program for the analysis and design of passive, active and non-linear lumped/distributed circuits. This program is particularly suitable for the analysis of active microwave networks and GaAs integrated circuits.

Characterisation and Modelling of Temperature and Dispersion Effects in Power MESFETs

Currently used modelling approaches fail to predict accurately non-linear dynamic behaviour of power MESFETs when self-heating and dispersion effects are present. A novel non-linear MESFET model and a method of extraction of its parameters are proposed, which take into account these effects. The main measurements required to characterise the device are pulsed I-V characteristics and small-signal S-parameters, performed for a range of ambient temperatures and quiescent bias points. A specialised computer controlled pulsed measurement system has been designed and constructed to perform device characterisation. The method is illustrated on the example of a power MESFET but is equally applicable to HEMTs.

Analysis and sensitivities of noisy networks using nodal approach

An enhancement of nodal noise analysis of electrical networks is presented by computing noise sensitivities with respect to network parameters. The noise figure and spot noise parameters sensitivities of the reduced two-port network are obtained from the partial inversion of the nodal admittance matrix. Analytical formulas are derived to calculate first- and second-order noise sensitivities directly, rather than using a computer-time intensive perturbation method. Expressions for noise sensitivities of cascaded networks are also given. Numerical results for an actively matched amplifier are shown to illustrate the advantages of the proposed technique. >

Non-Linear MESFET Modelling

A new technique for non-linear modelling of MESFETs has been developed based on the extraction of both linear and non-linear model parameters in one optimization step. The technique eliminates various modelling inconsistency problems and can be used for MESFETs with dispersi ve model parameters. The only required device measurements are small-signal S-parameters and DC or RF characteristics. Also an improved MESFET model suitable for CAD programs is proposed. Both the new parameter extraction technique and the model are illustrated on the example of a half-micron monolithic MESFET with frequency dispersion.

The design of waveguide-to-finline taper transitions at millimetre wave frequencies

Traditional techniques for designing the waveguide-to-finline taper transitions are based on the design a suitable impedance transformation profile first, and then the conversion of this profile into a finline contour. These techniques disregard the electrical discontinuities involved in the transition, such as the step model of two finlines with different widths. This introduces a phase error in the design, because the propagating wave in the taper is not a plane wave if the gradient of the finline contour is not zero. The change of the slotline gap causes changes in the impedance and propagation constant of the slotline, and thus alters the phase in the travelling wave. In this paper, it is demonstrated that there are significant effects related to the electrical discontinuities in the taper shape and that a better understanding of the discontinuities is needed. By compensating the taper phase errors, the return loss could be improved.

Optically frequency modulated 6 GHz MMIC oscillator

Optical illumination is used to modulate a 6 GHz GaAs MMIC VCO. Tuning can be achieved by illuminating either the MESFET or the Varactor. The MESFET tuning is caused by photocurrents varying the self-bias condition. Varactor optical tuning results from both a change in the junction capacitance and by external voltages generated by a photocurrent. Although both devices achieved similar D.C. optical tuning levels, tuning via the Varactor was found to be frequency limited. Preference is therefore given to illumination of the MESFET as the optical interface component. The resulting FM modulation bandwidth achieved is sufficient for the transmission of video signals with bandwidths up to 10 MHz.

Parameter extraction technique for nonlinear MESFET models

A nonlinear parameter extraction technique, that gives both rapid convergence and consistency of the derived model is proposed. The computational aspect of the technique is divided into two processes: (1) direct extraction of intrinsic element values by a statistically based routine and (2) optimization of intrinsic and extrinsic element values and/or nonlinear functions simultaneously at all bias points. The nonlinear elements are extracted as some analytical functions of bias and also as bias-dependent values. The results of the modeling of chip and packaged MESFET devices are presented and very good agreements between measurements and calculations are obtained. The technique has already been implemented as an extension to the existing SOPTIM program.<<ETX>>

Pulsed I-V and temperature measurement system for characterisation of microwave FETs

Systems for pulsed I-V characterisation of GaAs devices must meet specific requirements concerning not just accuracy and pulse width but also the way the measurements are performed and the definition of various quantities which need to be measured in order to acquire a full picture of the device behaviour. Over the last few years such a system has been iteratively developed and tested at the University of Kent at Canterbury. In the light of the experience gained, a number of new measuring concepts together with some vital observations are presented, raising doubts about the validity of currently existing interpretations of pulsed characteristics. Also the design of an inexpensive system incorporating the new concepts is briefly described.<<ETX>>