A variable‐gain constant‐phase dual‐gate amplifier with series feedback

Abstract

This paper presents series feedback used in a variable‐gain constant‐phase dual‐gate amplifier for T / R module applications. The inductive series feedback element shifts the input match of the dual gate FET to an impedance that is much easier to match 50 ohms. This allows the amplifier to have a much broader bandwidth and increased gain while maintaining constant phase in the different gain states. This amplifier was fabricated as a MMIC chip using the ITT MSAG process, and we obtained excellent performance: variable gain range of 13 dB, VSWR better than 2.0:1, phase variation less than ±2°, and gain flatness of ±0.4 dB over the 4.5‐6‐GHz frequency range.