소형 3-dB 브랜치 라인 결합기를 이용한 고출력 평형 증폭기 설계

Abstract

The hybrid coupler plays an important role in microwave circuits such as balanced mixers, image-rejection mixers, and balanced amplifier. Among them, the balanced amplifier is used for the mismatched power amplifier. However, the balanced amplifier may still be mismatched at both path of two equal amplifier because the power TR has low input-output impedance.

Besides of it the standard balanced amplifier configuration has the disadvantage requiring a large space owing to the coupler's size. The method of applying arbitrary lumped-distributed impedance transforming couplers to balanced amplifiers significantly reduces the size of over the conventional balanced amplifier with 50 Ω input/output couplers. then, the size of arbitrary lumped-distributed impedance transforming couplers tend to be restricted by the characteristic impedance.

In order to solve the above problem, in this thesis, design graphs were drawn for the reduced size coupler, which was terminated by arbitrary impedances and shorted coupled-line pair. The coupler size was 90 percent smaller than the conventional coupler.

A balanced amplifier was designed using the coupler with shorted coupled-line pair and lumped capacitor. The measured gain is 6 ± 0.2 dB, the input and output VSWR are lower than 1.40.