Conception of Very Broad Band Amplifiers

A design of broad band FET amplifier circuits is presented in this paper, using a unilateral equivalent circuit of the FET proved by its S parameter measurements : this method consists of decomposing the gain in a product of three transfer functions : one is constant versus frequency and the other two are of second order type. We show that we can obtain a flat gain in a very broad band by simply adjusting four parameters : input tuning, output tuning, generator resistance and load resistance. Numerical results show that with the FET used the load resistance can be taken equal to 50 ¿ and that the generator resistance must be slightly lower than 50 ¿. Under these conditions, we have realized amplifier stages covering the 1.7 GHz - 13 GHz and 6 GHz - 18 GHz bands. By placing stages in parallel between 3 - dB couplers we obtained balanced stages covering the 6 - 12 GHz and 2 - 8 GHz bands with an input-output VSWR lower than 2.