Mohammad S. Hashmi

An Accurate Calibrate-Able Multiharmonic Active Load–Pull System Based on the Envelope Load–Pull Concept

After calibration, since the systematic imperfections of the envelop load-pull (ELP) components were now fully accounted for, the user is able to rapidly set accurate terminations with full Smith chart coverage. This functionality has been achieved by optimizing the hardware configuration of the envelop load-pull concept. Development of a system whose systematic errors could be described by a magnitude invariant error flow model was critical. As a consequence, a robust calibration mechanism, that is analogous to the one-port error correction of a vector network analyzer, was exploited and comprehensively verified. After calibration, since the systematic imperfections of the ELP components were now fully accounted for, the user is able to set accurately terminations with full Smith chart coverage. Finally, measurements on commercially available transistor devices are presented that verify the rapid nature, accuracy, flexibility, reliability, and ease of calibration of the multiharmonic load-pull system.

Electronic multi-harmonic load-pull system for experimentally driven power amplifier design optimization

This paper presents, for the first time, a multi-harmonic active envelope load-pull system allowing for the robust, high-speed characterization of devices used in modern microwave power amplifiers. Measurements of a commercially available 1W GaAs FET device demonstrate at least an eight-fold improvement in the measurement speed when compared to existing open-loop solutions. The developed active load-pull system, which instantly reacts, via baseband feedback, has the ability to set load impedances that are independent of changing device conditions. Thus it is similar to passive systems, but without the associated loss. This system is shown to be valuable in allowing the utilization of rapid, experimental, measurement driven optimization within the power amplifier design and yield analysis process.

A T-Section Dual-Band Matching Network for Frequency-Dependent Complex Loads Incorporating Coupled Line with DC-Block Property Suitable for Dual-Band Transistor Amplifiers

This paper reports design of a new dual-band T-type impedance transformer also exhibiting DC-blocking feature. The design aims at achieving matching for frequency-dependent complex loads having distinct values at two arbitrary frequencies to Zs (here, 50›). A step-wise analysis on the developed dual-band impedance transformer provides simple closed-form design equations. The design is verifled by simulation in Agilent ADS. For experimental veriflcation a PCB prototype is fabricated using FR-4 material, operating at 1.45GHz and 2.61GHz. A good result is obtained conflrming the theory and simulation.

Highly Reflective Load-Pull

This article presented a review of the most common load-pull approaches adopted in the measurement and characterization of large-periphery microwave transistor devices. Although the quarterwave transformer technique is simple and very cost-effective, it has serious limitations in terms of scalability, thereby necessitating a separate quarterwave transformer for each device and frequency. Furthermore, due to the limited bandwidth of the quarterwave transformer, its usage in harmonic load-pull applications is severely limited.

A Coupled-Line Based L-Section DC-Isolated Dual-Band Real to Real Impedance Transformer and Its Application to a Dual-Band T-Junction Power Divider

This paper presents a dual-band impedance transformer for real source and load impedances that is capable of providing matching at two arbitrary frequencies. There are two possible configurations of the proposed technique, and both the configurations are simple and possess flexibility to cater to wide range of impedance environments. A very useful feature of the design is its inherent ability to provide DC isolation. A prototype, which works at 1 GHz and 2 GHz, fabricated using Rogers RO4350B laminate validates the proposed design with a good match between theoretical and experimental results. In addition, a dual-band T-junction power divider is reported to demonstrate the usefulness of the proposed impedance transformer.

A FLEXIBLE DUAL-INFLECTION POINT RF PREDISTORTION LINEARIZER FOR MICROWAVE POWER AMPLIFIERS

This paper presents a very ∞exible and generic design of a diode-based RF predistortion linearizer that can correct for the dual- in∞ection point type compression characteristics found in the gain proflle of metal semiconductor fleld efiect transistor (MESFET) based and Doherty power ampliflers. It consists of a circuit conflguration that has the head-tail conflguration of Schottky diodes, complemented with a p-intrinsic-n (PIN) diode in parallel, at two ports of a 90 - hybrid coupler for improving the performance of the linearizer. The use of a PIN diode in the linearizer provides it with an extra level of freedom in achieving the desired characteristic. Overall, the linearizer is equipped with three degrees of freedom and hence possesses the capability to achieve output characteristics that can be employed in linearizing various types of power ampliflers. The proposed linearizer has been shown to simultaneously improve the third- and flfth- order intermodulation distortions of a commercial ZHL-4240 gallium arsenide fleld efiect transistor (GaAs FET) based power amplifler over a 10dB power range.

Loop Enhanced Passive Source- and Load-Pull Technique for High Reflection Factor Synthesis

An original source- and load-pull topology based on a passive technique is presented in this paper. The proposed system consists of passive tuners and loop structures. The use of a passive loop structure in cascade with a passive tuner allows for synthesis of reflection coefficients in the order of 0.97 magnitudes at the device under tests access plane. The measurement and characterization results of a 1W GaAs MESFET device show an improvement of 0.9 dB in the gain and 6% in the power-added efficiency when the proposed impedance synthesis techniques are used.

A Dual-Frequency Matching Network for FDCLs Using Dual-Band λ/4-Lines

A new approach to design a dual-band matching network using a dual-band quarter-wave line is presented. The proposed matching network is capable of simultaneously matching frequency- dependent complex loads (FDCLs) having different values at two arbitrary frequencies to a real source impedance, Z0. A very simple step-wise design procedure is discussed for the transformer along with closed-form design equations which are very simple in nature. For experimental verification, two PCB prototypes have been fabricated using FR-4 material, operating at 1 GHz and 2.42 GHz. The measurements results matches well with that obtained from simulation, exhibiting good performance.

Agile harmonic envelope load-pull system enabling reliable and rapid device characterization

This paper presents a robust heterodyne mode of operation for the envelope load-pull system. Extensive performance evaluation and verification demonstrate the reliable, flexible and accurate nature of the system. The new system was compared with the active open-loop load pull, with the new system standing out as having superior performance in terms of measurement throughput, thereby improving the yield and turn-around in the design of power amplifiers. Finally, measurements on commercially available microwave transistor devices show some of the immediate recognized application areas of the developed system.

Active Envelope Load-Pull for Wideband Multi-tone Stimulus Incorporating Delay Compensation

This paper presents, for the first time, a new active load-pull approach capable of supporting wideband multi-tone modulation based on the active envelope load-pull architecture. The new solution utilizes a digital control unit, implemented on a reconfigurable FPGA platform with high-speed signal processing capability, in the feedback loop to track the time varying amplitude and phase envelope of modulated RF communication signals. This novel approach enables a loop delay compensation scheme to be successfully implemented allowing for synchronization of the transmitted and the reflected signals over wide (>5 MHz) bandwidths. Initial, proof of concept, measurements on this active load-pull system have demonstrated that it can provide constant, frequency independent control of load impedances for signal excitations that are relevant for communication systems.