A low-noise MMIC amplifier as a microwave-to-optics link

A low-noise MMIC distributed amplifier was designed to operate as a microwave-to-optics link in certain radar applications. It was designed to have a small signal gain of 12 dB in the frequency band of 3.1 to 3.5 GHz. In addition to the flat gain requirement, good input and output return losses with a noise figure less than 5 dB were to be realized. The amplifier has 50 Ω input and output impedances. Test measurements on the first built prototype show that amplifier has an average small signal gain of 6.2 dB in the band under the bias conditions V
ds
=3.5 V, and V
gs
=0.56 V. Input return loss is −5.47 dB, output return loss is −9.49 dB and the average isolation is −29.51 dB. Noise figure of the amplifier changes between 5.48 and 6.46 dB in the band. A gain ripple of ±0.50 dB is obtained.