Steve W. Y. Mung

Novel Active Quasi-Circulator With Phase Compensation Technique

A novel active quasi-circulator using phase compensation technique for wideband isolation is proposed. It is formed by configuring three transistors with a complimenting phase shifter for equalization. It provides wideband frequency operation with sufficient return loss and isolation between ports without the need for passive filters. This compensation technique minimizes the circulators size compared with conventional ferrite circulators and is compatible with monolithic microwave integrated circuit technology. Experimental results show that the proposed quasi-circulator has insertion losses around 0 dB, return losses better than 10 dB at each ports and minimum isolation around 15 dB from 0.8 to 2.2 GHz. Good agreement is obtained between simulation and experimental results.

Active Three-Way Circulator Using Transistor Feedback Network

This letter presents an active three-way circulator with both theoretical analyzes and experimental verifications. The conventional active circulators have their limitations on power handling and noise figure (NF), however, this proposed structure maintains both performances, which is formed by three 2-port transistor feedback networks (TFNs). This TFN is formed by an FET together with a feedback inductor. Experimental results show that this circulator achieves the isolation more than 35 dB, the insertion of around 2 dB, and the return losses better than 10 dB at each port at 1.8 GHz. The output power is linearly proportional to the power operation and the NF is around 5 dB. This compact structure, therefore, is suitable for use in the transmit/receive front end with a sufficient isolation, power handling, and NF for time division duplex operation.

High efficiency power amplifier - Distributed amplifier topology and non-uniform load-pull (NLP) power combining technique

A high efficiency power amplifier (PA) is proposed by using distributed amplifier topology and non-uniform load-pull (NLP) power combining technique. The novel NLP power combining technique is proposed for distributed amplifier (DA) with different stages. This approach allows efficient distributed combining of field-effect transistors (FETs) output power without the use of multi-way power combiners. The proposed distributed amplifier’s topology uses a quarter-wave short-circuit stub or open circuit to replace the drain line lossy dummy load. This topology is able to achieve power equalisation among the FETs at microwave frequencies. This design method ensures optimum loadlines are achieved for all FETs and the efficiency obtained is compared with the conventional single-transistor class-A power amplifier using the same FET type. Distributed amplifier with different stages has different optimum loadline resistance. The optimum characteristic impedance of the drain output transmission line presented here obtains the powermatched condition for all FETs. This NLP power combining technique is demonstrated at 2 GHz with 1-stage, 2-stage and 3-stage distributed amplifiers. Experimental results show that the power-added efficiency (PAE) of these three different distributed amplifiers is greater than 35% at the 1-dB gain compression point. The maximum efficiency is greater than 35% over a bandwidth of 10%. The 3-stage distributed amplifier demonstrates an output power level of 27.4 dBm at the 1-dB gain compression point with power combining efficiency (PCE) around 90%.

A new active quasi-circulator with wideband performance

This work describes a simple active quasi-circulator that gives wideband operation, and differs from previous structures which were limited to a narrow frequency range. Experimental results shows good return loss and isolation within the expected operating frequency range, making it practical to implement.