A Magnetic-Field-Tolerant Low-Noise SiGe Pre-Amplifier and T/R Switch

David Ian Hoult¹, Glen Kolansky¹

The noise figure and gain of GaAs field effect transistors degrade in magnetic fields. A SiGe bipolar transistor is advocated as a replacement giving at 123 MHz a noise figure of 0.6 dB with ~ 20 dB current blocking. Our SiGe pre-amplifier has a noise figure < 1dB from 90 to 200 MHz, a gain of 30 dB, a bandwidth of 73 to 163 MHz and a group delay of 5.4 ns. The accompanying 300 W quarter-wave PIN diode transmit/receive switch has 0.1 dB noise figure, an insertion loss of 1 dB and isolation of ~ 65 dB.