Branko Bukvic

Simple Design of a Class-J Amplifier With Predetermined Efficiency

We present theoretical background of a Class-J power amplifier (PA), with infinite number of harmonic components in the output voltage, explicitly deriving novel simple formulas which govern the amplifier efficiency. We also derive a novel design curve which governs the optimal PA parameters for a predetermined (high) efficiency. The presented theory is applied in a design and fabrication of a 1.5 GHz high-gain GaN HEMT PA. Measured drain efficiencies of the PA at 1 and 2 dB compression points are 55.2% and 70%, respectively. The maximum drain efficiency is higher than 85% at the saturated output power of 40 dBm. Measured (small signal)

Reconfigurable RF power amplifiers for wireless transmitters

S

Comparison of approximate and full-wave electromagnetic numerical modeling of microstrip matching networks

- parameters, output power, gain, and drain efficiency of the PA compare extremely well with full-wave and circuit-based cosimulations.

Circuit-based versus full-wave modelling of active microwave circuits

In this paper, a reconfigurable input matching network (IMN) is used to obtain reconfigurable RF power amplifier (RPA). An Input Matching Network is realized as simple T-section, where reconfigurability is achieved by switch in shunt transmission line. An optical switch (OS) and a PIN diode are used separately, and results are presented for both cases. When an OS or a PIN diode switch is ON, RPA operates at 1.9 GHz, otherwise RPA operates at 2.2 GHz. An Output Matching Network (OMN) is realized as wideband circuit. A Crees CGH21240 AWR Microwave Office (MWO) model of wideband transistor is used for RPAs. The S-parameters and power added efficiency (PAE) of about 50% and 35% at 1.9 GHz and 2.2 GHz, respectively, for both types of RPAs are presented.

Graphene-based waveguide resonators for submillimeter-wave applications

We consider several planar microstrip circuit elements, often appearing as parts of microwave matching networks, as well as discrete chip components with associated pads. We analyze all considered elements and components using a circuit-based solver and full-wave electromagnetic solvers and compare the analysis results with measurements on manufactured prototypes, discussing the obtained differences and giving specific recipes for good modeling practices using different methods.

A magnetically biased graphene based CPW switch for microwave applications

ABSTRACT Modern full-wave computational tools enable rigorous simulations of linear parts of complex microwave circuits within minutes, taking into account all physical electromagnetic (EM) phenomena. Non-linear components and other discrete elements of the hybrid microwave circuit are then easily added within the circuit simulator. This combined full-wave and circuit-based analysis is a must in the final stages of the circuit design, although initial designs and optimisations are still faster and more comfortably done completely in the circuit-based environment, which offers real-time solutions at the expense of accuracy. However, due to insufficient information and general lack of specific case studies, practitioners still struggle when choosing an appropriate analysis method, or a component model, because different choices lead to different solutions, often with uncertain accuracy and unexplained discrepancies arising between the simulations and measurements. We here design a reconfigurable power amplifier, as a case study, using both circuit-based solver and a full-wave EM solver. We compare numerical simulations with measurements on the manufactured prototypes, discussing the obtained differences, pointing out the importance of measured parameters de-embedding, appropriate modelling of discrete components and giving specific recipes for good modelling practices.

Compensation of nonlinear distortion in RF power amplifiers by injection for LTE applications

Utilization of graphene covered waveguide inserts to form tunable waveguide resonators is theoretically explained and rigorously investigated by means of full-wave numerical electromagnetic simulations. Instead of using graphene-based switching elements, the concept we propose incorporates graphene sheets as parts of a resonator. Electrostatic tuning of the graphene surface conductivity leads to changes in the electromagnetic field boundary conditions at the resonator edges and surfaces, thus producing an effect similar to varying the electrical length of a resonator. The presented outline of the theoretical background serves to give phenomenological insight into the resonator behavior, but it can also be used to develop customized software tools for design and optimization of graphene-based resonators and filters. Due to the linear dependence of the imaginary part of the graphene surface impedance on frequency, the proposed concept was expected to become effective for frequencies above 100 GHz, which is confirmed by the numerical simulations. A frequency range from 100 GHz up to 1100 GHz, where the rectangular waveguides are used, is considered. Simple, all-graphene-based resonators are analyzed first, to assess the achievable tunability and to check the performance throughout the considered frequency range. Graphene–metal combined waveguide resonators are proposed in order to preserve the excellent quality factors typical for the type of waveguide discontinuities used. Dependence of resonator properties on key design parameters is studied in detail. Dependence of resonator properties throughout the frequency range of interest is studied using eight different waveguide sections appropriate for different frequency intervals. Proposed resonators are aimed at applications in the submillimeter-wave spectral region, serving as the compact tunable components for the design of bandpass filters and other devices.

Reconfigurable matching networks for wireless transmitters

This paper presents a coplanar waveguide (CPW) transmission line with added graphene patches in order to obtain switching properties. To toggle the switch state, magnetic biasing of graphene is used. The switch is simulated and results show that it can be operable at microwave frequencies.

Characterization of nonlinearities in a class-J power amplifier

A linerization technique for reducing the third-order intermodulation products that uses simultaneous injection of the second harmonics at the amplifier input and output has been investigated in this paper. This technique was considered in theory and by simulation. The amplifier with the second harmonics components were designed and simulated using Agilent Design System (ADS) program. The linearization has been accomplished by adjusting the amplitudes and phases of the second harmonics on the optimal values. The analysis and results included in this paper relate to the case when an OFDM signal is at the amplifier input.

Reconfigurable and tunable efficient power amplifiers for transmitters in telecommunication devices

In this paper a reconfigurable input matching network (IMN) for power amplifiers (PA) is designed and simulated. An IMN is realized as T-section, where reconfigurability is achieved by switch element (PIN diode switch). When PIN diode switch is ON the PA operates at 3.45 GHz. In PIN diode switch OFF state the PA operates at 3.75 GHz. The S-parameters and power added efficiency (PAE), of about 45% and 50% at 3.45 GHz and 3.75 GHz respectively, are presented.